lib/fetch/asmfs.cpp

// Copyright 2016 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#define __NEED_struct_iovec
#include "syscall_arch.h"
#include <ctype.h>
#include <emscripten/emscripten.h>
#include <emscripten/fetch.h>
#include <emscripten/threading.h>
#include <libc/fcntl.h>
#include <math.h>
#include <string.h>
#include <sys/stat.h>
#include <time.h>

// Uncomment the following and clear the cache with emcc --clear-cache to rebuild this file to
// enable internal debugging. #define ASMFS_DEBUG

extern "C" {

// http://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers
#define MAX_PATHNAME_LENGTH 2000

#define INODE_TYPE uint32_t
#define INODE_FILE 1
#define INODE_DIR 2

struct inode {
  char name[NAME_MAX + 1]; // NAME_MAX actual bytes + one byte for null termination.
  inode* parent;           // ID of the parent node
  inode* sibling; // ID of a sibling node (these form a singular linked list that specifies the
                  // content under a directory)
  inode* child;   // ID of the first child node in a chain of children (the root of a linked list of
                  // inodes)
  uint32_t uid;   // User ID of the owner
  uint32_t gid;   // Group ID of the owning group
  uint32_t mode;  // r/w/x modes
  time_t ctime;   // Time when the inode was last modified
  time_t mtime;   // Time when the content was last modified
  time_t atime;   // Time when the content was last accessed
  size_t size;    // Size of the file in bytes
  size_t capacity; // Amount of bytes allocated to pointer data
  uint8_t* data;   // The actual file contents.

  INODE_TYPE type;

  emscripten_fetch_t* fetch;

  // Specifies a remote server address where this inode can be located.
  char* remoteurl;
};

#define EM_FILEDESCRIPTOR_MAGIC 0x64666d65U // 'emfd'
struct FileDescriptor {
  uint32_t magic;
  ssize_t file_pos;
  uint32_t mode;
  uint32_t flags;

  inode* node;
};

static inode* create_inode(INODE_TYPE type, int mode) {
  inode* i = (inode*)malloc(sizeof(inode));
  memset(i, 0, sizeof(inode));
  i->ctime = i->mtime = i->atime = time(0);
  i->type = type;
  i->mode = mode;
  return i;
}

// The current working directory of the application process.
static inode* cwd_inode = 0;

static inode* filesystem_root() {
  static inode* root_node = create_inode(INODE_DIR, 0777);
  return root_node;
}

static inode* get_cwd() {
  if (!cwd_inode)
    cwd_inode = filesystem_root();
  return cwd_inode;
}

static void set_cwd(inode* node) { cwd_inode = node; }

static void inode_abspath(inode* node, char* dst, int dstLen) {
  if (!node) {
    assert(dstLen >= (int)strlen("(null)") + 1);
    strcpy(dst, "(null)");
    return;
  }
  if (node == filesystem_root()) {
    assert(dstLen >= (int)strlen("/") + 1);
    strcpy(dst, "/");
    return;
  }
#define MAX_DIRECTORY_DEPTH 512
  inode* stack[MAX_DIRECTORY_DEPTH];
  int depth = 0;
  while (node->parent && depth < MAX_DIRECTORY_DEPTH) {
    stack[depth++] = node;
    node = node->parent;
  }
  char* dstEnd = dst + dstLen;
  *dstEnd-- = '\0';
  while (depth > 0 && dst < dstEnd) {
    if (dst < dstEnd)
      *dst++ = '/';
    --depth;
    int len = strlen(stack[depth]->name);
    if (len > dstEnd - dst)
      len = dstEnd - dst;
    strncpy(dst, stack[depth]->name, len);
    dst += len;
  }
}

// Deletes the given inode. Ignores (orphans) any children there might be
static void delete_inode(inode* node) {
  if (!node)
    return;
  if (node == filesystem_root())
    return; // As special case, do not allow deleting the filesystem root directory
#ifdef ASMFS_DEBUG
  EM_ASM(err('delete_inode: ' + UTF8ToString($0)), node->name);
#endif
  if (node->fetch)
    emscripten_fetch_close(node->fetch);
  free(node->remoteurl);
  free(node);
}

// Deletes the given inode and its subtree
static void delete_inode_tree(inode* node) {
  if (!node)
    return;
#ifdef ASMFS_DEBUG
  EM_ASM(err('delete_inode_tree: ' + UTF8ToString($0)), node->name);
#endif
  inode* child = node->child;
  while (child) {
    inode* sibling = child->sibling;
    delete_inode_tree(child->child);
    delete_inode(child);
    child = sibling;
  }
  if (node !=
      filesystem_root()) // As special case, do not allow deleting the filesystem root directory
  {
    delete_inode(node);
  } else {
    // For filesystem root, just make sure all children are gone.
    node->child = 0;
  }
}

// Makes node the child of parent.
static void link_inode(inode* node, inode* parent) {
  char parentName[PATH_MAX];
  inode_abspath(parent, parentName, PATH_MAX);
#ifdef ASMFS_DEBUG
  EM_ASM(err('link_inode: node "' + UTF8ToString($0) + '" to parent "' + UTF8ToString($1) + '".'),
    node->name, parentName);
#endif
  // When linking a node, it can't be part of the filesystem tree (but it can have children of its
  // own)
  assert(!node->parent);
  assert(!node->sibling);

  // The inode pointed by 'node' is not yet part of the filesystem, so it's not shared memory and
  // only this thread is accessing it. Therefore setting the node's parent here is not yet racy, do
  // that operation first.
  node->parent = parent;

  // This node is to become the first child of the parent, and the old first child of the parent
  // should become the sibling of this node, i.e.
  //  1) node->sibling = parent->child;
  //  2) parent->child = node;
  // However these two operations need to occur atomically in order to be coherent. To ensure that,
  // run the two operations in a CAS loop, which is possible because the first operation is not racy
  // until the node is 'published' to the filesystem tree by the compare_exchange operation.
  do {
    __atomic_load(
      &parent->child, &node->sibling, __ATOMIC_SEQ_CST); // node->sibling <- parent->child
  } while (
    !__atomic_compare_exchange(&parent->child, &node->sibling, &node, false, __ATOMIC_SEQ_CST,
      __ATOMIC_SEQ_CST)); // parent->child <- node if it had not raced to change value in between
}

// Traverse back in sibling linked list, or 0 if no such node exist.
static inode* find_predecessor_sibling(inode* node, inode* parent) {
  inode* child = parent->child;
  if (child == node)
    return 0;
  while (child && child->sibling != node)
    child = child->sibling;
  if (!child->sibling)
    return 0;
  return child;
}

static void unlink_inode(inode* node) {
#ifdef ASMFS_DEBUG
  EM_ASM(
    err('unlink_inode: node ' + UTF8ToString($0) + ' from its parent ' + UTF8ToString($1) + '.'),
    node->name, node->parent->name);
#endif
  inode* parent = node->parent;
  if (!parent)
    return;
  node->parent = 0;

  if (parent->child == node) {
    parent->child = node->sibling;
  } else {
    inode* predecessor = find_predecessor_sibling(node, parent);
    if (predecessor)
      predecessor->sibling = node->sibling;
  }
  node->parent = node->sibling = 0;
}

// Compares two strings for equality until a '\0' or a '/' is hit. Returns 0 if the strings differ,
// or a pointer to the beginning of the next directory component name of s1 if the strings are
// equal.
static const char* path_cmp(const char* s1, const char* s2, bool* is_directory) {
  *is_directory = true;
  while (*s1 == *s2) {
    if (*s1 == '/')
      return s1 + 1;
    if (*s1 == '\0') {
      *is_directory = false;
      return s1;
    }
    ++s1;
    ++s2;
  }
  if (*s1 == '/' && *s2 == '\0')
    return s1 + 1;
  if (*s1 == '\0' && *s2 == '/')
    return s1;
  return 0;
}

#define NIBBLE_TO_CHAR(x) ("0123456789abcdef"[(x)])
static void uriEncode(char* dst, int dstLengthBytes, const char* src) {
  char* end =
    dst + dstLengthBytes - 4; // Use last 4 bytes of dst as a guard area to avoid overflow below.
  while (*src && dst < end) {
    if (isalnum(*src) || *src == '-' || *src == '_' || *src == '.' || *src == '~')
      *dst++ = *src;
    else if (*src == '/')
      *dst++ = *src; // NB. forward slashes should generally be uriencoded, but for file path
                     // purposes, we want to keep them intact.
    else
      *dst++ = '%', *dst++ = NIBBLE_TO_CHAR(*src >> 4),
      *dst++ = NIBBLE_TO_CHAR(*src & 15); // This charater needs uriencoding.
    ++src;
  }
  *dst = '\0';
}

// Copies string 'path' to 'dst', but stops on the first forward slash '/' character.
// Returns number of bytes written, excluding null terminator
static int strcpy_inodename(char* dst, const char* path) {
  char* d = dst;
  while (*path && *path != '/')
    *dst++ = *path++;
  *dst = '\0';
  return dst - d;
}

// Copies src to dst, writes at most maxBytesToWrite out. Always null terminates dst. Returns the
// number of characters written, excluding null terminator.
static int strcpy_safe(char* dst, const char* src, int maxBytesToWrite) {
  char* dst_start = dst;
  char* dst_end = dst + maxBytesToWrite - 1;
  while (dst < dst_end && *src)
    *dst++ = *src++;
  *dst = '\0';
  return dst - dst_start;
}

// Returns a pointer to the basename part of the string, i.e. the string after the last occurrence
// of a forward slash character
static const char* basename_part(const char* path) {
  const char* s = path;
  while (*path) {
    if (*path == '/')
      s = path + 1;
    ++path;
  }
  return s;
}

static inode* create_directory_hierarchy_for_file(
  inode* root, const char* path_to_file, unsigned int mode) {
  assert(root);
  if (!root)
    return 0;

  // Traverse . and ..
  while (path_to_file[0] == '.') {
    if (path_to_file[1] == '/')
      path_to_file += 2; // Skip over redundant "./././././" blocks
    else if (path_to_file[1] == '\0')
      path_to_file += 1;
    else if (path_to_file[1] == '.' &&
             (path_to_file[2] == '/' ||
               path_to_file[2] == '\0')) // Go up to parent directories with ".."
    {
      root = root->parent;
      if (!root)
        return 0;
      assert(
        root->type == INODE_DIR); // Anything that is a parent should automatically be a directory.
      path_to_file += (path_to_file[2] == '/') ? 3 : 2;
    } else
      break;
  }
  if (path_to_file[0] == '\0')
    return 0;

  inode* node = root->child;
  while (node) {
    bool is_directory = false;
    const char* child_path = path_cmp(path_to_file, node->name, &is_directory);
#ifdef ASMFS_DEBUG
    EM_ASM_INT({err('path_cmp ' + UTF8ToString($0) + ', ' + UTF8ToString($1) + ', ' +
                    UTF8ToString($2) + ' .')},
      path_to_file, node->name, child_path);
#endif
    if (child_path) {
      if (is_directory && node->type != INODE_DIR)
        return 0; // "A component used as a directory in pathname is not, in fact, a directory"

      // The directory name matches.
      path_to_file = child_path;

      // Traverse . and ..
      while (path_to_file[0] == '.') {
        if (path_to_file[1] == '/')
          path_to_file += 2; // Skip over redundant "./././././" blocks
        else if (path_to_file[1] == '\0')
          path_to_file += 1;
        else if (path_to_file[1] == '.' &&
                 (path_to_file[2] == '/' ||
                   path_to_file[2] == '\0')) // Go up to parent directories with ".."
        {
          node = node->parent;
          if (!node)
            return 0;
          assert(node->type ==
                 INODE_DIR); // Anything that is a parent should automatically be a directory.
          path_to_file += (path_to_file[2] == '/') ? 3 : 2;
        } else
          break;
      }
      if (path_to_file[0] == '\0')
        return node;
      if (path_to_file[0] == '/' && path_to_file[1] == '\0' /* && node is a directory*/)
        return node;
      root = node;
      node = node->child;
    } else {
      node = node->sibling;
    }
  }
  const char* basename_pos = basename_part(path_to_file);
#ifdef ASMFS_DEBUG
  EM_ASM(err('path_to_file ' + UTF8ToString($0) + ' .'), path_to_file);
  EM_ASM(err('basename_pos ' + UTF8ToString($0) + ' .'), basename_pos);
#endif
  while (*path_to_file && path_to_file < basename_pos) {
    node = create_inode(INODE_DIR, mode);
    path_to_file += strcpy_inodename(node->name, path_to_file) + 1;
    link_inode(node, root);
#ifdef ASMFS_DEBUG
    EM_ASM(out('create_directory_hierarchy_for_file: created directory ' + UTF8ToString($0) +
               ' under parent ' + UTF8ToString($1) + '.'),
      node->name, node->parent->name);
#endif
    root = node;
  }
  return root;
}

#define RETURN_NODE_AND_ERRNO(node, errno)                                                         \
  do {                                                                                             \
    *out_errno = (errno);                                                                          \
    return (node);                                                                                 \
  } while (0)

// Given a pathname to a file/directory, finds the inode of the directory that would contain the
// file/directory, or 0 if the intermediate path doesn't exist. Note that the file/directory pointed
// to by path does not need to exist, only its parent does.
static inode* find_parent_inode(inode* root, const char* path, int* out_errno) {
  char rootName[PATH_MAX];
  inode_abspath(root, rootName, PATH_MAX);
#ifdef ASMFS_DEBUG
  EM_ASM(err('find_parent_inode(root="' + UTF8ToString($0) + '", path="' + UTF8ToString($1) + '")'),
    rootName, path);
#endif

  assert(out_errno); // Passing in error is mandatory.

  if (!root)
    RETURN_NODE_AND_ERRNO(0, ENOENT);
  if (!path)
    RETURN_NODE_AND_ERRNO(0, ENOENT);

  // Traverse . and ..
  while (path[0] == '.') {
    if (path[1] == '/')
      path += 2; // Skip over redundant "./././././" blocks
    else if (path[1] == '\0')
      path += 1;
    else if (path[1] == '.' &&
             (path[2] == '/' || path[2] == '\0')) // Go up to parent directories with ".."
    {
      root = root->parent;
      if (!root)
        RETURN_NODE_AND_ERRNO(0, ENOENT);
      assert(
        root->type == INODE_DIR); // Anything that is a parent should automatically be a directory.
      path += (path[2] == '/') ? 3 : 2;
    } else
      break;
  }
  if (path[0] == '\0')
    RETURN_NODE_AND_ERRNO(0, ENOENT);
  if (path[0] == '/' && path[1] == '\0')
    RETURN_NODE_AND_ERRNO(0, ENOENT);
  if (root->type != INODE_DIR)
    RETURN_NODE_AND_ERRNO(
      0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"

  // TODO: RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in translating pathname");
  // TODO: RETURN_ERRNO(EACCES, "one of the directories in the path prefix of pathname did not allow
  // search permission");

  const char* basename = basename_part(path);
  if (path == basename)
    RETURN_NODE_AND_ERRNO(root, 0);
  inode* node = root->child;
  while (node) {
    bool is_directory = false;
    const char* child_path = path_cmp(path, node->name, &is_directory);
    if (child_path) {
      if (is_directory && node->type != INODE_DIR)
        RETURN_NODE_AND_ERRNO(
          0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"

      // The directory name matches.
      path = child_path;

      // Traverse . and ..
      while (path[0] == '.') {
        if (path[1] == '/')
          path += 2; // Skip over redundant "./././././" blocks
        else if (path[1] == '\0')
          path += 1;
        else if (path[1] == '.' &&
                 (path[2] == '/' || path[2] == '\0')) // Go up to parent directories with ".."
        {
          node = node->parent;
          if (!node)
            RETURN_NODE_AND_ERRNO(0, ENOENT);
          assert(node->type ==
                 INODE_DIR); // Anything that is a parent should automatically be a directory.
          path += (path[2] == '/') ? 3 : 2;
        } else
          break;
      }

      if (path >= basename)
        RETURN_NODE_AND_ERRNO(node, 0);
      if (!*path)
        RETURN_NODE_AND_ERRNO(0, ENOENT);
      node = node->child;
      if (node->type != INODE_DIR)
        RETURN_NODE_AND_ERRNO(
          0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"
    } else {
      node = node->sibling;
    }
  }
  RETURN_NODE_AND_ERRNO(
    0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"
}

// Given a root inode of the filesystem and a path relative to it, e.g.
// "some/directory/dir_or_file", returns the inode that corresponds to "dir_or_file", or 0 if it
// doesn't exist. If the parameter out_closest_parent is specified, the closest (grand)parent node
// will be returned.
static inode* find_inode(inode* root, const char* path, int* out_errno) {
  char rootName[PATH_MAX];
  inode_abspath(root, rootName, PATH_MAX);
#ifdef ASMFS_DEBUG
  EM_ASM(err('find_inode(root="' + UTF8ToString($0) + '", path="' + UTF8ToString($1) + '")'),
    rootName, path);
#endif

  assert(out_errno); // Passing in error is mandatory.

  if (!root)
    RETURN_NODE_AND_ERRNO(0, ENOENT);

  // TODO: RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in translating pathname");
  // TODO: RETURN_ERRNO(EACCES, "one of the directories in the path prefix of pathname did not allow
  // search permission");

  // special-case finding empty string path "", "." or "/" returns the root searched in.
  if (root->type != INODE_DIR)
    RETURN_NODE_AND_ERRNO(
      0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"
  if (!path)
    RETURN_NODE_AND_ERRNO(root, 0);

  // Traverse . and ..
  while (path[0] == '.') {
    if (path[1] == '/')
      path += 2; // Skip over redundant "./././././" blocks
    else if (path[1] == '\0')
      path += 1;
    else if (path[1] == '.' &&
             (path[2] == '/' || path[2] == '\0')) // Go up to parent directories with ".."
    {
      root = root->parent;
      if (!root)
        RETURN_NODE_AND_ERRNO(0, ENOENT);
      assert(
        root->type == INODE_DIR); // Anything that is a parent should automatically be a directory.
      path += (path[2] == '/') ? 3 : 2;
    } else
      break;
  }
  if (path[0] == '\0')
    RETURN_NODE_AND_ERRNO(root, 0);

  inode* node = root->child;
  while (node) {
    bool is_directory = false;
    const char* child_path = path_cmp(path, node->name, &is_directory);
    if (child_path) {
      if (is_directory && node->type != INODE_DIR)
        RETURN_NODE_AND_ERRNO(
          0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"

      // The directory name matches.
      path = child_path;

      // Traverse . and ..
      while (path[0] == '.') {
        if (path[1] == '/')
          path += 2; // Skip over redundant "./././././" blocks
        else if (path[1] == '\0')
          path += 1;
        else if (path[1] == '.' &&
                 (path[2] == '/' || path[2] == '\0')) // Go up to parent directories with ".."
        {
          node = node->parent;
          if (!node)
            RETURN_NODE_AND_ERRNO(0, ENOENT);
          assert(node->type ==
                 INODE_DIR); // Anything that is a parent should automatically be a directory.
          path += (path[2] == '/') ? 3 : 2;
        } else
          break;
      }

      // If we arrived to the end of the search, this is the node we were looking for.
      if (path[0] == '\0')
        RETURN_NODE_AND_ERRNO(node, 0);
      if (path[0] == '/' && node->type != INODE_DIR)
        RETURN_NODE_AND_ERRNO(
          0, ENOTDIR); // "A component used as a directory in pathname is not, in fact, a directory"
      if (path[0] == '/' && path[1] == '\0')
        RETURN_NODE_AND_ERRNO(node, 0);
      node = node->child;
    } else {
      node = node->sibling;
    }
  }
  RETURN_NODE_AND_ERRNO(0, ENOENT);
}

// Same as above, but the root node is deduced from 'path'. (either absolute if path starts with
// "/", or relative)
static inode* find_inode(const char* path, int* out_errno) {
  inode* root;
  if (path[0] == '/')
    root = filesystem_root(), ++path;
  else
    root = get_cwd();
  return find_inode(root, path, out_errno);
}

void emscripten_asmfs_set_remote_url(const char* filename, const char* remoteUrl) {
  int err;
  inode* node = find_inode(filename, &err);
  if (!node)
    return;
  free(node->remoteurl);
  node->remoteurl = strdup(remoteUrl);
}

void emscripten_asmfs_set_file_data(const char* filename, char* data, size_t size) {
  int err;
  inode* node = find_inode(filename, &err);
  if (!node) {
    free(data);
    return;
  }
  free(node->data);
  node->data = (uint8_t*)data;
  node->size = node->capacity = size;
}

char* find_last_occurrence(char* str, char ch) {
  char* o = 0;
  while (*str) {
    if (*str == ch)
      o = str;
    ++str;
  }
  return o;
}

// Given a filename outputs the remote URL address that file can be located in.
void emscripten_asmfs_remote_url(const char* filename, char* outRemoteUrl, int maxBytesToWrite) {
  if (maxBytesToWrite <= 0 || !outRemoteUrl)
    return;
  *outRemoteUrl = '\0';
  if (maxBytesToWrite == 1)
    return;

  char trailing_path[PATH_MAX + 1] = {};
  char full_path[PATH_MAX + 1] = {};
  char full_path_temp[PATH_MAX + 1] = {};
  strcpy(full_path, filename);

  int err;
  inode* node = find_inode(full_path, &err);
  while (!node) {
    char* s = find_last_occurrence(full_path, '/');
    if (!s) {
      node = filesystem_root();
      strcpy(full_path_temp, trailing_path);
      strcpy(trailing_path, full_path);
      if (full_path_temp[0] != '\0') {
        strcat(trailing_path, "/");
        strcat(trailing_path, full_path_temp);
      }
      break;
    }
    *s = '\0';
    node = find_inode(full_path, &err);

    strcpy(full_path_temp, trailing_path);
    strcpy(trailing_path, filename + (s - full_path));
    if (full_path_temp[0] != '\0') {
      strcat(trailing_path, "/");
      strcat(trailing_path, full_path_temp);
    }
  }

  char uriEncodedPathName[3 * PATH_MAX + 4];
  full_path[0] = full_path[PATH_MAX] = full_path_temp[0] = full_path_temp[PATH_MAX] = '\0';

  while (node) {
    if (node->remoteurl && node->remoteurl[0] != '\0') {
      int nWritten = strcpy_safe(outRemoteUrl, node->remoteurl, maxBytesToWrite);
      if (maxBytesToWrite - nWritten > 1 && outRemoteUrl[nWritten - 1] != '/' &&
          full_path[0] != '/') {
        outRemoteUrl[nWritten++] = '/';
        outRemoteUrl[nWritten] = '\0';
      }
      strcat(full_path + strlen(full_path), trailing_path);
      uriEncode(uriEncodedPathName, 3 * PATH_MAX + 4, full_path);
      strcpy_safe(outRemoteUrl + nWritten,
        (outRemoteUrl[nWritten - 1] == '/' && uriEncodedPathName[0] == '/')
          ? (uriEncodedPathName + 1)
          : uriEncodedPathName,
        maxBytesToWrite - nWritten);
      return;
    }

    strcpy_safe(full_path_temp, full_path, PATH_MAX);
    int nWritten = strcpy_safe(full_path, node->name, PATH_MAX);
    if (full_path_temp[0] != '\0') {
      full_path[nWritten++] = '/';
      full_path[nWritten] = '\0';
      strcpy_safe(full_path + nWritten, full_path_temp, PATH_MAX - nWritten);
    }

    node = node->parent;
  }
  strcat(full_path + strlen(full_path), trailing_path);
  uriEncode(uriEncodedPathName, 3 * PATH_MAX + 4, full_path);
  strcpy_safe(outRemoteUrl, uriEncodedPathName, maxBytesToWrite);
}

// Debug function that dumps out the filesystem tree to console.
void emscripten_dump_fs_tree(inode* root, char* path) {
  char str[256];
  sprintf(str, "%s:", path);
  EM_ASM(out(UTF8ToString($0)), str);

  // Print out:
  // file mode | number of links | owner name | group name | file size in bytes | file last modified
  // time | path name which aligns with "ls -AFTRl" on console
  inode* child = root->child;
  uint64_t totalSize = 0;
  while (child) {
    sprintf(str, "%c%c%c%c%c%c%c%c%c%c  %d user%u group%u %lu Jan 1 1970 %s%c",
      child->type == INODE_DIR ? 'd' : '-', (child->mode & S_IRUSR) ? 'r' : '-',
      (child->mode & S_IWUSR) ? 'w' : '-', (child->mode & S_IXUSR) ? 'x' : '-',
      (child->mode & S_IRGRP) ? 'r' : '-', (child->mode & S_IWGRP) ? 'w' : '-',
      (child->mode & S_IXGRP) ? 'x' : '-', (child->mode & S_IROTH) ? 'r' : '-',
      (child->mode & S_IWOTH) ? 'w' : '-', (child->mode & S_IXOTH) ? 'x' : '-',
      1, // number of links to this file
      child->uid, child->gid,
      child->size ? child->size : (child->fetch ? (int)child->fetch->numBytes : 0), child->name,
      child->type == INODE_DIR ? '/' : ' ');
    EM_ASM(out(UTF8ToString($0)), str);

    totalSize += child->size;
    child = child->sibling;
  }

  sprintf(str, "total %llu bytes\n", totalSize);
  EM_ASM(out(UTF8ToString($0)), str);

  child = root->child;
  char* path_end = path + strlen(path);
  while (child) {
    if (child->type == INODE_DIR) {
      strcpy(path_end, child->name);
      strcat(path_end, "/");
      emscripten_dump_fs_tree(child, path);
    }
    child = child->sibling;
  }
}

void emscripten_asmfs_dump() {
  EM_ASM({err('emscripten_asmfs_dump()')});
  char path[PATH_MAX] = "/";
  emscripten_dump_fs_tree(filesystem_root(), path);
}

void emscripten_asmfs_discard_tree(const char* path) {
#ifdef ASMFS_DEBUG
  emscripten_asmfs_dump();
  EM_ASM(err('emscripten_asmfs_discard_tree: ' + UTF8ToString($0)), path);
#endif
  int err;
  inode* node = find_inode(path, &err);
  if (node && !err) {
    unlink_inode(node);
    delete_inode_tree(node);
  }
#ifdef ASMFS_DEBUG
  else
    EM_ASM(err('emscripten_asmfs_discard_tree failed, error ' + $0), err);
  emscripten_asmfs_dump();
#endif
}

#ifdef ASMFS_DEBUG
#define RETURN_ERRNO(errno, error_reason)                                                          \
  do {                                                                                             \
    EM_ASM(err(UTF8ToString($0) + '() returned errno ' + #errno + '(' + $1 + '): ' +               \
               error_reason + '!'),                                                                \
      __FUNCTION__, errno);                                                                        \
    return -errno;                                                                                 \
  } while (0)
#else
#define RETURN_ERRNO(errno, error_reason)                                                          \
  do {                                                                                             \
    return -(errno);                                                                               \
  } while (0)
#endif

static char stdout_buffer[4096] = {};
static int stdout_buffer_end = 0;
static char stderr_buffer[4096] = {};
static int stderr_buffer_end = 0;

static void print_stream(void* bytes, int numBytes, bool stdout) {
  char* buffer = stdout ? stdout_buffer : stderr_buffer;
  int& buffer_end = stdout ? stdout_buffer_end : stderr_buffer_end;

  memcpy(buffer + buffer_end, bytes, numBytes);
  buffer_end += numBytes;
  int new_buffer_start = 0;
  for (int i = 0; i < buffer_end; ++i) {
    if (buffer[i] == '\n') {
      buffer[i] = 0;
      EM_ASM_INT({out(UTF8ToString($0))}, buffer + new_buffer_start);
      new_buffer_start = i + 1;
    }
  }
  size_t new_buffer_size = buffer_end - new_buffer_start;
  memmove(buffer, buffer + new_buffer_start, new_buffer_size);
  buffer_end = new_buffer_size;
}

long __syscall3(int which, ...) // read
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  void* buf = va_arg(vl, void*);
  size_t count = va_arg(vl, size_t);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(
    err('read(fd=' + $0 + ', buf=0x' + ($1).toString(16) + ', count=' + $2 + ')'), fd, buf, count);
#endif

  iovec io = {buf, count};
  return __syscall145(145 /*readv*/, fd, &io, 1);
}

long __syscall4(int which, ...) // write
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  void* buf = va_arg(vl, void*);
  size_t count = va_arg(vl, size_t);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(
    err('write(fd=' + $0 + ', buf=0x' + ($1).toString(16) + ', count=' + $2 + ')'), fd, buf, count);
#endif

  iovec io = {buf, count};
  return __syscall146(146 /*writev*/, fd, &io, 1);
}

// TODO: Make thread-local storage.
static emscripten_asmfs_open_t __emscripten_asmfs_file_open_behavior_mode =
  EMSCRIPTEN_ASMFS_OPEN_REMOTE_DISCOVER;

void emscripten_asmfs_set_file_open_behavior(emscripten_asmfs_open_t behavior) {
  __emscripten_asmfs_file_open_behavior_mode = behavior;
}

emscripten_asmfs_open_t emscripten_asmfs_get_file_open_behavior() {
  return __emscripten_asmfs_file_open_behavior_mode;
}

// Returns true if the given file can be synchronously read by the main browser thread.
static bool emscripten_asmfs_file_is_synchronously_accessible(inode* node) {
  return node->data // If file was created from memory without XHR, e.g. via fopen("foo.txt", "w"),
                    // it will have node->data ptr backing.
         ||
         (node->fetch && node->fetch->data); // If the file was downloaded, it will be backed here.
}

static long open(const char* pathname, int flags, int mode) {
#ifdef ASMFS_DEBUG
  EM_ASM(err('open(pathname="' + UTF8ToString($0) + '", flags=0x' + ($1).toString(16) + ', mode=0' +
             ($2).toString(8) + ')'),
    pathname, flags, mode);
#endif

  int accessMode = (flags & O_ACCMODE);

  if ((flags & O_ASYNC))
    RETURN_ERRNO(ENOTSUP, "TODO: Opening files with O_ASYNC flag is not supported in ASMFS");
  if ((flags & O_DIRECT))
    RETURN_ERRNO(ENOTSUP, "TODO: O_DIRECT flag is not supported in ASMFS");
  if ((flags & O_DSYNC))
    RETURN_ERRNO(ENOTSUP, "TODO: O_DSYNC flag is not supported in ASMFS");

  // Spec says that the result of O_EXCL without O_CREAT is undefined.
  // We could enforce it as an error condition, as follows:
  //	if ((flags & O_EXCL) && !(flags & O_CREAT)) RETURN_ERRNO(EINVAL, "open() with O_EXCL flag
  //needs to always be paired with O_CREAT");
  // However existing earlier unit tests in Emscripten expect that O_EXCL is simply ignored when
  // O_CREAT was not passed. So do that for now.
  if ((flags & O_EXCL) && !(flags & O_CREAT)) {
#ifdef ASMFS_DEBUG
    EM_ASM(err('warning: open(pathname="' + UTF8ToString($0) + '", flags=0x' + ($1).toString(16) +
               ', mode=0' + ($2).toString(8) +
               ': flag O_EXCL should always be paired with O_CREAT. Ignoring O_EXCL)'),
      pathname, flags, mode);
#endif
    flags &= ~O_EXCL;
  }

  if ((flags & (O_NONBLOCK | O_NDELAY)))
    RETURN_ERRNO(
      ENOTSUP, "TODO: Opening files with O_NONBLOCK or O_NDELAY flags is not supported in ASMFS");
  if ((flags & O_PATH))
    RETURN_ERRNO(ENOTSUP, "TODO: Opening files with O_PATH flag is not supported in ASMFS");
  if ((flags & O_SYNC))
    RETURN_ERRNO(ENOTSUP, "TODO: Opening files with O_SYNC flag is not supported in ASMFS");

  // The flags:O_CLOEXEC flag is ignored, doesn't have meaning for Emscripten

  // TODO: the flags:O_DIRECT flag seems like a great way to let applications explicitly control
  // XHR/IndexedDB read/write buffering behavior?

  // The flags:O_LARGEFILE flag is ignored, we should always be largefile-compatible

  // TODO: The flags:O_NOATIME is ignored, file access times have not been implemented yet
  // The flags O_NOCTTY, O_NOFOLLOW

  if ((flags & O_TMPFILE)) {
    if (accessMode != O_WRONLY && accessMode != O_RDWR)
      RETURN_ERRNO(
        EINVAL, "O_TMPFILE was specified in flags, but neither O_WRONLY nor O_RDWR was specified");
    else
      RETURN_ERRNO(
        EOPNOTSUPP, "TODO: The filesystem containing pathname does not support O_TMPFILE");
  }

  // TODO: if (too_many_files_open) RETURN_ERRNO(EMFILE, "The per-process limit on the number of
  // open file descriptors has been reached, see getrlimit(RLIMIT_NOFILE)");

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  // Find if this file exists already in the filesystem?
  inode* root = (pathname[0] == '/') ? filesystem_root() : get_cwd();
  const char* relpath = (pathname[0] == '/') ? pathname + 1 : pathname;

  int err;
  inode* node = find_inode(root, relpath, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "Search permission is denied for one of the directories in the path prefix of pathname");
  if (err && err != ENOENT)
    RETURN_ERRNO(err, "find_inode() error");
  if (node) {
    if ((flags & O_DIRECTORY) && node->type != INODE_DIR)
      RETURN_ERRNO(ENOTDIR, "O_DIRECTORY was specified and pathname was not a directory");
    if (!(node->mode & 0444))
      RETURN_ERRNO(EACCES, "The requested access to the file is not allowed");
    if ((flags & O_CREAT) && (flags & O_EXCL))
      RETURN_ERRNO(EEXIST, "pathname already exists and O_CREAT and O_EXCL were used");
    if (node->type == INODE_DIR && accessMode != O_RDONLY)
      RETURN_ERRNO(EISDIR, "pathname refers to a directory and the access requested involved "
                           "writing (that is, O_WRONLY or O_RDWR is set)");
    if (node->type == INODE_DIR && (flags & O_TRUNC))
      RETURN_ERRNO(EISDIR,
        "pathname refers to a directory and the access flags specified invalid flag O_TRUNC");

    // A current download exists to the file? Then wait for it to complete.
    if (node->fetch) {
      // On the main thread, the fetch must have already completed before we come here. If not, we
      // cannot stop to wait for it to finish, and must return a failure (file not found)
      if (emscripten_is_main_browser_thread()) {
        if (emscripten_fetch_wait(node->fetch, 0) != EMSCRIPTEN_RESULT_SUCCESS) {
          RETURN_ERRNO(ENOENT, "Attempted to open a file that is still downloading on the main "
                               "browser thread. Could not block to wait! (try preloading the file "
                               "to the filesystem before application start)");
        }
      } else {
        // On worker threads, we can pause to wait for the fetch.
        emscripten_fetch_wait(node->fetch, INFINITY);
      }
    }
  }

  if ((flags & O_CREAT) && ((flags & O_TRUNC) || (flags & O_EXCL))) {
    // Create a new empty file or truncate existing one.
    if (node) {
      if (node->fetch)
        emscripten_fetch_close(node->fetch);
      node->fetch = 0;
      node->size = 0;
    } else if ((flags & O_CREAT)) {
      inode* directory = create_directory_hierarchy_for_file(root, relpath, mode);
      node = create_inode((flags & O_DIRECTORY) ? INODE_DIR : INODE_FILE, mode);
      strcpy(node->name, basename_part(pathname));
      link_inode(node, directory);
    }
  } else if (!node || (node->type == INODE_FILE && !node->fetch && !node->data)) {
    emscripten_fetch_t* fetch = 0;
    if (!(flags & O_DIRECTORY) && accessMode != O_WRONLY) // Opening a file for reading?
    {
      // If there's no inode entry, check if we're not even interested in downloading the file?
      if (!node &&
          __emscripten_asmfs_file_open_behavior_mode != EMSCRIPTEN_ASMFS_OPEN_REMOTE_DISCOVER) {
        RETURN_ERRNO(
          ENOENT, "O_CREAT is not set, the named file does not exist in local filesystem and "
                  "EMSCRIPTEN_ASMFS_OPEN_REMOTE_DISCOVER is not specified");
      }

      // Report an error if there is an inode entry, but file data is not synchronously available
      // and it should have been.
      if (node && !node->data &&
          __emscripten_asmfs_file_open_behavior_mode == EMSCRIPTEN_ASMFS_OPEN_MEMORY) {
        RETURN_ERRNO(
          ENOENT, "O_CREAT is not set, the named file exists, but file data is not synchronously "
                  "available in memory (EMSCRIPTEN_ASMFS_OPEN_MEMORY specified)");
      }

      if (emscripten_is_main_browser_thread() &&
          (!node || !emscripten_asmfs_file_is_synchronously_accessible(node))) {
        RETURN_ERRNO(ENOENT,
          "O_CREAT is not set, the named file exists, but file data is not synchronously available "
          "in memory, and file open is attempted on the main thread which cannot synchronously "
          "open files! (try preloading the file to the filesystem before application start)");
      }

      // Kick off the file download, either from IndexedDB or via an XHR.
      emscripten_fetch_attr_t attr;
      emscripten_fetch_attr_init(&attr);
      strcpy(attr.requestMethod, "GET");
      attr.attributes = EMSCRIPTEN_FETCH_APPEND | EMSCRIPTEN_FETCH_LOAD_TO_MEMORY |
                        EMSCRIPTEN_FETCH_WAITABLE | EMSCRIPTEN_FETCH_PERSIST_FILE;
      // If asked to only do a read from IndexedDB, don't perform an XHR.
      if (__emscripten_asmfs_file_open_behavior_mode == EMSCRIPTEN_ASMFS_OPEN_INDEXEDDB) {
        attr.attributes |= EMSCRIPTEN_FETCH_NO_DOWNLOAD;
      }
      char
        path[3 * PATH_MAX + 4]; // times 3 because uri-encoding can expand the filename at most 3x.
      emscripten_asmfs_remote_url(pathname, path, 3 * PATH_MAX + 4);
      fetch = emscripten_fetch(&attr, path);

      // Synchronously wait for the fetch to complete.
      // NOTE: Theoretically could postpone blocking until the first read to the file, but the issue
      // there is that we wouldn't be able to return ENOENT below if the file did not exist on the
      // server, which could be harmful for some applications. Also fread()/fseek() very often
      // immediately follows fopen(), so the win would not be too great anyways.
      emscripten_fetch_wait(fetch, INFINITY);

      if (!(flags & O_CREAT) && (fetch->status != 200 || fetch->totalBytes == 0)) {
        emscripten_fetch_close(fetch);
        RETURN_ERRNO(ENOENT, "O_CREAT is not set and the named file does not exist (attempted "
                             "emscripten_fetch() XHR to download)");
      }
    }

    if (node) {
      // If we had an existing inode entry, just associate the entry with the newly fetched data.
      if (node->type == INODE_FILE)
        node->fetch = fetch;
    } else if ((flags &
                 O_CREAT) // If the filesystem entry did not exist, but we have a create flag, ...
               || (!node && fetch)) // ... or if it did not exist in our fs, but it could be found
                                    // via fetch(), ...
    {
      // ... add it as a new entry to the fs.
      inode* directory = create_directory_hierarchy_for_file(root, relpath, mode);
      node = create_inode((flags & O_DIRECTORY) ? INODE_DIR : INODE_FILE, mode);
      strcpy(node->name, basename_part(pathname));
      node->fetch = fetch;
      link_inode(node, directory);
    } else {
      if (fetch)
        emscripten_fetch_close(fetch);
      RETURN_ERRNO(ENOENT, "O_CREAT is not set and the named file does not exist");
    }
    node->size = fetch ? node->fetch->totalBytes : 0;
  }

  FileDescriptor* desc = (FileDescriptor*)malloc(sizeof(FileDescriptor));
  desc->magic = EM_FILEDESCRIPTOR_MAGIC;
  desc->node = node;
  desc->file_pos = ((flags & O_APPEND) && node->fetch) ? node->fetch->totalBytes : 0;
  desc->mode = mode;
  desc->flags = flags;

  // TODO: The file descriptor needs to be a small number, man page:
  // "a small, nonnegative integer for use in subsequent system calls
  // (read(2), write(2), lseek(2), fcntl(2), etc.).  The file descriptor
  // returned by a successful call will be the lowest-numbered file
  // descriptor not currently open for the process."
  return (long)desc;
}

long __syscall5(int which, ...) // open
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  int flags = va_arg(vl, int);
  int mode = va_arg(vl, int);
  va_end(vl);

  return open(pathname, flags, mode);
}

static long close(int fd) {
#ifdef ASMFS_DEBUG
  EM_ASM(err('close(fd=' + $0 + ')'), fd);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  if (desc->node && desc->node->fetch) {
    if (!emscripten_is_main_browser_thread()) {
      // TODO: This should not be necessary, but do it for now for consistency (test this out)
      emscripten_fetch_wait(desc->node->fetch, INFINITY);
    }

    // TODO: What to do to a XHRed/IndexedDB-backed unmodified file in memory when closing the file?
    //       free() or keep in memory?
    //       If user intends to reopen the file later (possibly often?), it is faster to keep the
    //       file in memory. (but it will consume more memory) If running on the main thread, the
    //       file cannot be loaded back synchronously if we let go of it, so things would break if
    //       the file is attempted to be loaded up again afterwards. Currently use a heuristic that
    //       if a file is closed on the main browser thread, do not free its backing storage. This
    //       can work for many
    //		 cases, but some kind of custom API might be best to add in the future? (e.g.
    //emscripten_fclose_and_retain() vs emscripten_fclose_and_free()?)
    if (!emscripten_is_main_browser_thread()) {
      emscripten_fetch_close(desc->node->fetch);
      desc->node->fetch = 0;
    }
  }
  desc->magic = 0;
  free(desc);
  return 0;
}

void emscripten_asmfs_populate(const char* pathname, int mode) {
  emscripten_asmfs_open_t prevBehavior = emscripten_asmfs_get_file_open_behavior();
  emscripten_asmfs_set_file_open_behavior(EMSCRIPTEN_ASMFS_OPEN_MEMORY);
  int fd = open(pathname, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC, mode);
  if (fd > 0) {
    close(fd);
  }
  emscripten_asmfs_set_file_open_behavior(prevBehavior);
}

EMSCRIPTEN_RESULT emscripten_asmfs_preload_file(
  const char* url, const char* pathname, int mode, emscripten_fetch_attr_t* options) {
  if (!options) {
#ifdef ASMFS_DEBUG
    EM_ASM(err('emscripten_asmfs_preload_file: options not specified!'));
#endif
    return EMSCRIPTEN_RESULT_INVALID_PARAM;
  }

  if (!pathname) {
#ifdef ASMFS_DEBUG
    EM_ASM(err('emscripten_asmfs_preload_file: pathname not specified!'));
#endif
    return EMSCRIPTEN_RESULT_INVALID_PARAM;
  }

  // Find if this file exists already in the filesystem?
  inode* root = (pathname[0] == '/') ? filesystem_root() : get_cwd();
  const char* relpath = (pathname[0] == '/') ? pathname + 1 : pathname;

  int err;
  inode* node = find_inode(root, relpath, &err);
  // Filesystem traversal error?
  if (err && err != ENOENT) {
#ifdef ASMFS_DEBUG
    EM_ASM(err('emscripten_asmfs_preload_file: find_inode error ' + $0 + '!'), err);
#endif
    return EMSCRIPTEN_RESULT_INVALID_TARGET;
  }

  if (node && emscripten_asmfs_file_is_synchronously_accessible(node)) {
    // The file already exists, and its contents have already been preloaded - immediately fire the
    // success callback
    if (options->onsuccess)
      options->onsuccess(0);
    return EMSCRIPTEN_RESULT_SUCCESS;
  }

  // Kick off the file download, either from IndexedDB or via an XHR.
  emscripten_fetch_attr_t attr;
  memcpy(&attr, options, sizeof(emscripten_fetch_attr_t));
  if (strlen(attr.requestMethod) == 0)
    strcpy(attr.requestMethod, "GET");
  // In order for the file data to be synchronously accessible to the main browser thread, must load
  // it directly to memory.
  attr.attributes |= EMSCRIPTEN_FETCH_LOAD_TO_MEMORY;
  // The following attributes cannot be present for preloading.
#ifdef ASMFS_DEBUG
  if ((attr.attributes & (EMSCRIPTEN_FETCH_SYNCHRONOUS | EMSCRIPTEN_FETCH_STREAM_DATA |
                           EMSCRIPTEN_FETCH_WAITABLE)) != 0)
    EM_ASM(err(
      'emscripten_asmfs_preload_file: cannot specify EMSCRIPTEN_FETCH_SYNCHRONOUS, EMSCRIPTEN_FETCH_STREAM_DATA or EMSCRIPTEN_FETCH_WAITABLE flags when preloading!'));
#endif
  attr.attributes &=
    ~(EMSCRIPTEN_FETCH_SYNCHRONOUS | EMSCRIPTEN_FETCH_STREAM_DATA | EMSCRIPTEN_FETCH_WAITABLE);
  // Default to EMSCRIPTEN_FETCH_APPEND if not specified.
  if (!(attr.attributes & (EMSCRIPTEN_FETCH_APPEND | EMSCRIPTEN_FETCH_REPLACE)))
    attr.attributes |= EMSCRIPTEN_FETCH_APPEND;

  emscripten_fetch_t* fetch;
  if (url)
    fetch = emscripten_fetch(&attr, url);
  else {
    char remoteUrl[3 * PATH_MAX +
                   4]; // times 3 because uri-encoding can expand the filename at most 3x.
    emscripten_asmfs_remote_url(pathname, remoteUrl, 3 * PATH_MAX + 4);
    fetch = emscripten_fetch(&attr, remoteUrl);
  }

  if (!node) {
    inode* directory = create_directory_hierarchy_for_file(root, relpath, mode);
    node = create_inode(INODE_FILE, mode);
    strcpy(node->name, basename_part(pathname));
    link_inode(node, directory);
  }
  node->fetch = fetch;

  return EMSCRIPTEN_RESULT_SUCCESS;
}

long __syscall6(int which, ...) // close
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  va_end(vl);

  return close(fd);
}

long __syscall9(int which, ...) // link
{
  va_list vl;
  va_start(vl, which);
  const char* oldpath = va_arg(vl, const char*);
  const char* newpath = va_arg(vl, const char*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('link(oldpath="' + UTF8ToString($0) + '", newpath="' + UTF8ToString($1) + '")'),
    oldpath, newpath);
#endif
  ((void)oldpath);
  ((void)newpath);

  RETURN_ERRNO(ENOTSUP, "TODO: link() is a stub and not yet implemented in ASMFS");
}

long __syscall10(int which, ...) // unlink
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('unlink(pathname="' + UTF8ToString($0) + '")'), pathname);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  int err;
  inode* node = find_inode(pathname, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in translating pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "One of the directories in the path prefix of pathname did not allow search permission");
  if (err == ENOENT)
    RETURN_ERRNO(ENOENT, "A component in pathname does not exist or is a dangling symbolic link");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");

  if (!node)
    RETURN_ERRNO(ENOENT, "file does not exist");

  inode* parent = node->parent;

  if (parent && !(parent->mode & 0222))
    RETURN_ERRNO(EACCES, "Write access to the directory containing pathname is not allowed for the "
                         "process's effective UID");

  // TODO: RETURN_ERRNO(EPERM, "The directory containing pathname has the sticky bit (S_ISVTX) set
  // and the process's effective user ID is neither the user ID of the file to be deleted nor that
  // of the directory containing it, and the process is not privileged");
  // TODO: RETURN_ERRNO(EROFS, "pathname refers to a file on a read-only filesystem");

  if (!(node->mode & 0222)) {
    if (node->type == INODE_DIR)
      RETURN_ERRNO(
        EISDIR, "directory deletion not permitted"); // Linux quirk: Return EISDIR error for not
                                                     // having permission to delete a directory.
    else
      RETURN_ERRNO(EPERM, "file deletion not permitted"); // but return EPERM error for no
                                                          // permission to delete a file.
  }

  if (node->child)
    RETURN_ERRNO(EISDIR, "directory is not empty"); // Linux quirk: Return EISDIR error if not being
                                                    // able to delete a nonempty directory.

  unlink_inode(node);      // Detach this from parent
  delete_inode_tree(node); // And delete the whole subtree

  return 0;
}

long __syscall12(int which, ...) // chdir
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('chdir(pathname="' + UTF8ToString($0) + '")'), pathname);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  int err;
  inode* node = find_inode(pathname, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving path");
  if (err == EACCES)
    RETURN_ERRNO(EACCES, "Search permission is denied for one of the components of path");
  if (err == ENOENT)
    RETURN_ERRNO(
      ENOENT, "Directory component in pathname does not exist or is a dangling symbolic link");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");
  if (!node)
    RETURN_ERRNO(ENOENT, "The directory specified in path does not exist");
  if (node->type != INODE_DIR)
    RETURN_ERRNO(ENOTDIR, "Path is not a directory");

  set_cwd(node);
  return 0;
}

long __syscall14(int which, ...) // mknod
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  mode_t mode = va_arg(vl, mode_t);
  int dev = va_arg(vl, int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('mknod(pathname="' + UTF8ToString($0) + '", mode=0' + ($1).toString(8) + ', dev=' +
             $2 + ')'),
    pathname, mode, dev);
#endif
  (void)pathname;
  (void)mode;
  (void)dev;

  RETURN_ERRNO(ENOTSUP, "TODO: mknod() is a stub and not yet implemented in ASMFS");
}

long __syscall15(int which, ...) // chmod
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  int mode = va_arg(vl, int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('chmod(pathname="' + UTF8ToString($0) + '", mode=0' + ($1).toString(8) + ')'),
    pathname, mode);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  int err;
  inode* node = find_inode(pathname, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES, "Search permission is denied on a component of the path prefix");
  if (err == ENOENT)
    RETURN_ERRNO(
      ENOENT, "Directory component in pathname does not exist or is a dangling symbolic link");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");
  if (!node)
    RETURN_ERRNO(ENOENT, "The file does not exist");

  // TODO: if (not allowed) RETURN_ERRNO(EPERM, "The effective UID does not match the owner of the
  // file");
  // TODO: read-only filesystems: if (fs is read-only) RETURN_ERRNO(EROFS, "The named file resides
  // on a read-only filesystem");

  node->mode = mode;
  return 0;
}

long __syscall33(int which, ...) // access
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  int mode = va_arg(vl, int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('access(pathname="' + UTF8ToString($0) + '", mode=0' + ($1).toString(8) + ')'),
    pathname, mode);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  if ((mode & F_OK) && (mode & (R_OK | W_OK | X_OK)))
    RETURN_ERRNO(EINVAL, "mode was incorrectly specified");

  int err;
  inode* node = find_inode(pathname, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "Search permission is denied for one of the directories in the path prefix of pathname");
  if (err == ENOENT)
    RETURN_ERRNO(ENOENT, "A component of pathname does not exist or is a dangling symbolic link");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");
  if (!node)
    RETURN_ERRNO(ENOENT, "Pathname does not exist");

  // Just testing if a file exists?
  if ((mode & F_OK))
    return 0;

  // TODO: RETURN_ERRNO(EROFS, "Write permission was requested for a file on a read-only
  // filesystem");

  if ((mode & R_OK) && !(node->mode & 0444))
    RETURN_ERRNO(EACCES, "Read access would be denied to the file");
  if ((mode & W_OK) && !(node->mode & 0222))
    RETURN_ERRNO(EACCES, "Write access would be denied to the file");
  if ((mode & X_OK) && !(node->mode & 0111))
    RETURN_ERRNO(EACCES, "Execute access would be denied to the file");

  return 0;
}

long __syscall36(int which, ...) // sync
{
#ifdef ASMFS_DEBUG
  EM_ASM(err('sync()'));
#endif
  ((void)which);

  // Spec mandates that "sync() is always successful".
  return 0;
}

// TODO: syscall38,  int rename(const char *oldpath, const char *newpath);

long emscripten_asmfs_mkdir(const char* pathname, mode_t mode) {
#ifdef ASMFS_DEBUG
  EM_ASM(err('mkdir(pathname="' + UTF8ToString($0) + '", mode=0' + ($1).toString(8) + ')'),
    pathname, mode);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  inode* root = (pathname[0] == '/') ? filesystem_root() : get_cwd();
  const char* relpath = (pathname[0] == '/') ? pathname + 1 : pathname;
  int err;
  inode* parent_dir = find_parent_inode(root, relpath, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES, "One of the directories in pathname did not allow search permission");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");
  if (!parent_dir)
    RETURN_ERRNO(
      ENOENT, "A directory component in pathname does not exist or is a dangling symbolic link");

  // TODO: if (component of path wasn't actually a directory) RETURN_ERRNO(ENOTDIR, "A component
  // used as a directory in pathname is not, in fact, a directory");

  inode* existing = find_inode(parent_dir, basename_part(pathname), &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES, "One of the directories in pathname did not allow search permission");
  if (err && err != ENOENT)
    RETURN_ERRNO(err, "find_inode() error");
  if (existing)
    RETURN_ERRNO(EEXIST, "pathname already exists (not necessarily as a directory)");
  if (!(parent_dir->mode & 0222))
    RETURN_ERRNO(EACCES, "The parent directory does not allow write permission to the process");

  // TODO: read-only filesystems: if (fs is read-only) RETURN_ERRNO(EROFS, "Pathname refers to a
  // file on a read-only filesystem");

  inode* directory = create_inode(INODE_DIR, mode);
  strcpy(directory->name, basename_part(pathname));
  link_inode(directory, parent_dir);
  return 0;
}

void emscripten_asmfs_unload_data(const char* pathname) {
  int err;
  inode* node = find_inode(pathname, &err);
  if (!node)
    return;

  free(node->data);
  node->data = 0;
  node->size = node->capacity = 0;
}

uint64_t emscripten_asmfs_compute_memory_usage_at_node(inode* node) {
  if (!node)
    return 0;
  uint64_t sz = sizeof(inode);
  if (node->data)
    sz += node->capacity > node->size ? node->capacity : node->size;
  if (node->fetch && node->fetch->data)
    sz += node->fetch->numBytes;
  return sz + emscripten_asmfs_compute_memory_usage_at_node(node->child) +
         emscripten_asmfs_compute_memory_usage_at_node(node->sibling);
}

uint64_t emscripten_asmfs_compute_memory_usage() {
  return emscripten_asmfs_compute_memory_usage_at_node(filesystem_root());
}

long __syscall39(int which, ...) // mkdir
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  mode_t mode = va_arg(vl, mode_t);
  va_end(vl);

  return emscripten_asmfs_mkdir(pathname, mode);
}

long __syscall40(int which, ...) // rmdir
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('rmdir(pathname="' + UTF8ToString($0) + '")'), pathname);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  if (!strcmp(pathname, ".") || (len >= 2 && !strcmp(pathname + len - 2, "/.")))
    RETURN_ERRNO(EINVAL, "pathname has . as last component");
  if (!strcmp(pathname, "..") || (len >= 3 && !strcmp(pathname + len - 3, "/..")))
    RETURN_ERRNO(ENOTEMPTY, "pathname has .. as its final component");

  int err;
  inode* node = find_inode(pathname, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(
      ENOTDIR, "A component used as a directory in pathname is not, in fact, a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links were encountered in resolving pathname");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "one of the directories in the path prefix of pathname did not allow search permission");
  if (err == ENOENT)
    RETURN_ERRNO(
      ENOENT, "A directory component in pathname does not exist or is a dangling symbolic link");
  if (err)
    RETURN_ERRNO(err, "find_inode() error");
  if (!node)
    RETURN_ERRNO(ENOENT, "directory does not exist");
  if (node == filesystem_root() || node == get_cwd())
    RETURN_ERRNO(EBUSY, "pathname is currently in use by the system or some process that prevents "
                        "its removal (pathname is currently used as a mount point or is the root "
                        "directory of the calling process)");
  if (node->parent && !(node->parent->mode & 0222))
    RETURN_ERRNO(EACCES, "Write access to the directory containing pathname was not allowed");
  if (node->type != INODE_DIR)
    RETURN_ERRNO(ENOTDIR, "pathname is not a directory");
  if (node->child)
    RETURN_ERRNO(ENOTEMPTY, "pathname contains entries other than . and ..");

  // TODO: RETURN_ERRNO(EPERM, "The directory containing pathname has the sticky bit (S_ISVTX) set
  // and the process's effective user ID is neither the user ID of the file to be deleted nor that
  // of the directory containing it, and the process is not privileged");
  // TODO: RETURN_ERRNO(EROFS, "pathname refers to a directory on a read-only filesystem");

  unlink_inode(node);

  return 0;
}

long __syscall41(int which, ...) // dup
{
  va_list vl;
  va_start(vl, which);
  unsigned int fd = va_arg(vl, unsigned int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('dup(fd=' + $0 + ')'), fd);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  inode* node = desc->node;
  if (!node)
    RETURN_ERRNO(-1, "ASMFS internal error: file descriptor points to a nonexisting file");

  // TODO: RETURN_ERRNO(EMFILE, "The per-process limit on the number of open file descriptors has
  // been reached (see RLIMIT_NOFILE)");

  RETURN_ERRNO(ENOTSUP, "TODO: dup() is a stub and not yet implemented in ASMFS");
}

// TODO: syscall42: int pipe(int pipefd[2]);

long __syscall54(int which, ...) // ioctl/sysctl
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  int request = va_arg(vl, int);
  char* argp = va_arg(vl, char*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('ioctl(fd=' + $0 + ', request=' + $1 + ', argp=0x' + $2 + ')'), fd, request, argp);
#endif
  (void)fd;
  (void)request;
  (void)argp;

  RETURN_ERRNO(ENOTSUP, "TODO: ioctl() is a stub and not yet implemented in ASMFS");
}

// TODO: syscall60: mode_t umask(mode_t mask);
// TODO: syscall63: dup2
// TODO: syscall83: symlink
// TODO: syscall85: readlink
// TODO: syscall91: munmap
// TODO: syscall94: fchmod
// TODO: syscall102: socketcall

long __syscall118(int which, ...) // fsync
{
  va_list vl;
  va_start(vl, which);
  unsigned int fd = va_arg(vl, unsigned int);
  va_end(vl);

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  inode* node = desc->node;
  if (!node)
    RETURN_ERRNO(-1, "ASMFS internal error: file descriptor points to a non-file");

  return 0;
}

// TODO: syscall133: fchdir

long __syscall140(int which, ...) // llseek
{
  va_list vl;
  va_start(vl, which);
  unsigned int fd = va_arg(vl, unsigned int);
  unsigned long offset_high = va_arg(vl, unsigned long);
  unsigned long offset_low = va_arg(vl, unsigned long);
  off_t* result = va_arg(vl, off_t*);
  unsigned int whence = va_arg(vl, unsigned int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('llseek(fd=' + $0 + ', offset_high=' + $1 + ', offset_low=' + $2 + ', result=0x' +
             ($3).toString(16) + ', whence=' + $4 + ')'),
    fd, offset_high, offset_low, result, whence);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  if (desc->node->fetch) {
    if (emscripten_is_main_browser_thread()) {
      if (emscripten_fetch_wait(desc->node->fetch, 0) != EMSCRIPTEN_RESULT_SUCCESS) {
        RETURN_ERRNO(ENOENT, "Attempted to seek a file that is still downloading on the main "
                             "browser thread. Could not block to wait! (try preloading the file to "
                             "the filesystem before application start)");
      }
    } else
      emscripten_fetch_wait(desc->node->fetch, INFINITY);
  }

  // TODO: The following does not work, for some reason seek is getting called with 32-bit signed
  // offsets?
  //	int64_t offset = (int64_t)(((uint64_t)offset_high << 32) | (uint64_t)offset_low);
  int64_t offset = (int64_t)(int32_t)offset_low;
  int64_t newPos;
  switch (whence) {
    case SEEK_SET:
      newPos = offset;
      break;
    case SEEK_CUR:
      newPos = desc->file_pos + offset;
      break;
    case SEEK_END:
      newPos = (desc->node->fetch ? desc->node->fetch->numBytes : desc->node->size) + offset;
      break;
    case 3 /*SEEK_DATA*/:
      RETURN_ERRNO(EINVAL, "whence is invalid (sparse files, whence=SEEK_DATA, is not supported");
    case 4 /*SEEK_HOLE*/:
      RETURN_ERRNO(EINVAL, "whence is invalid (sparse files, whence=SEEK_HOLE, is not supported");
    default:
      RETURN_ERRNO(EINVAL, "whence is invalid");
  }
  if (newPos < 0)
    RETURN_ERRNO(EINVAL, "The resulting file offset would be negative");
  if (newPos > 0x7FFFFFFFLL)
    RETURN_ERRNO(EOVERFLOW, "The resulting file offset cannot be represented in an off_t");

  desc->file_pos = newPos;

  if (result)
    *result = desc->file_pos;
  return 0;
}

// TODO: syscall144 msync

long __syscall145(int which, ...) // readv
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  const iovec* iov = va_arg(vl, const iovec*);
  int iovcnt = va_arg(vl, int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('readv(fd=' + $0 + ', iov=0x' + ($1).toString(16) + ', iovcnt=' + $2 + ')'), fd, iov,
    iovcnt);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  inode* node = desc->node;
  if (!node)
    RETURN_ERRNO(-1, "ASMFS internal error: file descriptor points to a non-file");
  if (node->type == INODE_DIR)
    RETURN_ERRNO(EISDIR, "fd refers to a directory");
  if (node->type != INODE_FILE /* TODO: && node->type != socket */)
    RETURN_ERRNO(EINVAL, "fd is attached to an object which is unsuitable for reading");

  // TODO: if (node->type == INODE_FILE && desc has O_NONBLOCK && read would block)
  // RETURN_ERRNO(EAGAIN, "The file descriptor fd refers to a file other than a socket and has been
  // marked nonblocking (O_NONBLOCK), and the read would block");
  // TODO: if (node->type == socket && desc has O_NONBLOCK && read would block)
  // RETURN_ERRNO(EWOULDBLOCK, "The file descriptor fd refers to a socket and has been marked
  // nonblocking (O_NONBLOCK), and the read would block");

  if (node->fetch) {
    if (emscripten_is_main_browser_thread()) {
      if (emscripten_fetch_wait(node->fetch, 0) != EMSCRIPTEN_RESULT_SUCCESS) {
        RETURN_ERRNO(ENOENT, "Attempted to read a file that is still downloading on the main "
                             "browser thread. Could not block to wait! (try preloading the file to "
                             "the filesystem before application start)");
      }
    } else
      emscripten_fetch_wait(node->fetch, INFINITY);
  }

  if (node->size > 0 && !node->data && (!node->fetch || !node->fetch->data))
    RETURN_ERRNO(-1, "ASMFS internal error: no file data available");
  if (iovcnt < 0)
    RETURN_ERRNO(EINVAL, "The vector count, iovcnt, is less than zero");

  ssize_t total_read_amount = 0;
  for (int i = 0; i < iovcnt; ++i) {
    ssize_t n = total_read_amount + iov[i].iov_len;
    if (n < total_read_amount)
      RETURN_ERRNO(EINVAL, "The sum of the iov_len values overflows an ssize_t value");
    if (!iov[i].iov_base && iov[i].iov_len > 0)
      RETURN_ERRNO(
        EINVAL, "iov_len specifies a positive length buffer but iov_base is a null pointer");
    total_read_amount = n;
  }

  size_t offset = desc->file_pos;
  uint8_t* data = node->data ? node->data : (node->fetch ? (uint8_t*)node->fetch->data : 0);
  size_t size = node->data ? node->size : (node->fetch ? node->fetch->numBytes : 0);
  for (int i = 0; i < iovcnt; ++i) {
    ssize_t dataLeft = size - offset;
    if (dataLeft <= 0)
      break;
    size_t bytesToCopy = (size_t)dataLeft < iov[i].iov_len ? dataLeft : iov[i].iov_len;
    memcpy(iov[i].iov_base, &data[offset], bytesToCopy);
#ifdef ASMFS_DEBUG
    EM_ASM(err('readv requested to read ' + $0 + ', read  ' + $1 + ' bytes from offset ' + $2 +
               ', new offset: ' + $3 + ' (file size: ' + $4 + ')'),
      (int)iov[i].iov_len, (int)bytesToCopy, (int)offset, (int)(offset + bytesToCopy), (int)size);
#endif
    offset += bytesToCopy;
  }
  ssize_t numRead = offset - desc->file_pos;
  desc->file_pos = offset;
  return numRead;
}

long __syscall146(int which, ...) // writev
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  const iovec* iov = va_arg(vl, const iovec*);
  int iovcnt = va_arg(vl, int);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('writev(fd=' + $0 + ', iov=0x' + ($1).toString(16) + ', iovcnt=' + $2 + ')'), fd, iov,
    iovcnt);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (fd != 1 /*stdout*/ &&
      fd != 2 /*stderr*/) // TODO: Resolve the hardcoding of stdin,stdout & stderr
  {
    if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
      RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");
  }

  if (iovcnt < 0)
    RETURN_ERRNO(EINVAL, "The vector count, iovcnt, is less than zero");

  ssize_t total_write_amount = 0;
  for (int i = 0; i < iovcnt; ++i) {
    ssize_t n = total_write_amount + iov[i].iov_len;
    if (n < total_write_amount)
      RETURN_ERRNO(EINVAL, "The sum of the iov_len values overflows an ssize_t value");
    if (!iov[i].iov_base && iov[i].iov_len > 0)
      RETURN_ERRNO(
        EINVAL, "iov_len specifies a positive length buffer but iov_base is a null pointer");
    total_write_amount = n;
  }

  if (fd == 1 /*stdout*/ || fd == 2 /*stderr*/) {
    ssize_t bytesWritten = 0;
    for (int i = 0; i < iovcnt; ++i) {
      print_stream(iov[i].iov_base, iov[i].iov_len, fd == 1);
      bytesWritten += iov[i].iov_len;
    }
    return bytesWritten;
  } else {
    // Enlarge the file in memory to fit space for the new data
    size_t newSize = desc->file_pos + total_write_amount;
    inode* node = desc->node;
    if (node->capacity < newSize) {
      size_t newCapacity =
        (newSize > (size_t)(node->capacity * 1.25)
            ? newSize
            : (size_t)(
                node->capacity * 1.25)); // Geometric increases in size for amortized O(1) behavior
      uint8_t* newData = (uint8_t*)realloc(node->data, newCapacity);
      if (!newData) {
        newData = (uint8_t*)malloc(newCapacity);
        memcpy(newData, node->data, node->size);
        // TODO: init gaps with zeroes.
        free(node->data);
      }
      node->data = newData;
      node->size = newSize;
      node->capacity = newCapacity;
    }

    for (int i = 0; i < iovcnt; ++i) {
      memcpy((uint8_t*)node->data + desc->file_pos, iov[i].iov_base, iov[i].iov_len);
      desc->file_pos += iov[i].iov_len;
    }
  }
  return total_write_amount;
}

// TODO: syscall148: fdatasync
// TODO: syscall168: poll

// TODO: syscall180: pread64
// TODO: syscall181: pwrite64

long __syscall183(int which, ...) // getcwd
{
  va_list vl;
  va_start(vl, which);
  char* buf = va_arg(vl, char*);
  size_t size = va_arg(vl, size_t);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('getcwd(buf=0x' + $0 + ', size= ' + $1 + ')'), buf, size);
#endif

  if (!buf && size > 0)
    RETURN_ERRNO(EFAULT, "buf points to a bad address");
  if (buf && size == 0)
    RETURN_ERRNO(EINVAL, "The size argument is zero and buf is not a null pointer");

  inode* cwd = get_cwd();
  if (!cwd)
    RETURN_ERRNO(-1, "ASMFS internal error: no current working directory?!");
  // TODO: RETURN_ERRNO(ENOENT, "The current working directory has been unlinked");
  // TODO: RETURN_ERRNO(EACCES, "Permission to read or search a component of the filename was
  // denied");
  inode_abspath(cwd, buf, size);
  if (strlen(buf) >= size - 1)
    RETURN_ERRNO(ERANGE, "The size argument is less than the length of the absolute pathname of "
                         "the working directory, including the terminating null byte.  You need to "
                         "allocate a bigger array and try again");

  return 0;
}

// TODO: syscall192: mmap2
// TODO: syscall193: truncate64
// TODO: syscall194: ftruncate64

static long __stat64(inode* node, struct stat* buf) {
  buf->st_dev =
    1; // ID of device containing file: Hardcode 1 for now, no meaning at the moment for Emscripten.
  buf->st_ino = (ino_t)node; // TODO: This needs to be an inode ID number proper.
  buf->st_mode = node->mode;
  switch (node->type) {
    case INODE_DIR:
      buf->st_mode |= S_IFDIR;
      break;
    case INODE_FILE:
      buf->st_mode |= S_IFREG;
      break; // Regular file
             /* TODO:
             case socket: buf->st_mode |= S_IFSOCK; break;
             case symlink: buf->st_mode |= S_IFLNK; break;
             case block device: buf->st_mode |= S_IFBLK; break;
             case character device: buf->st_mode |= S_IFCHR; break;
             case FIFO: buf->st_mode |= S_IFIFO; break;
             */
  }
  buf->st_nlink = 1; // The number of hard links. TODO: Use this for real when links are supported.
  buf->st_uid = node->uid;
  buf->st_gid = node->gid;
  buf->st_rdev = 1; // Device ID (if special file) No meaning right now for Emscripten.
  buf->st_size = node->fetch ? node->fetch->totalBytes : 0;
  if (node->size > (size_t)buf->st_size)
    buf->st_size = node->size;
  buf->st_blocks =
    (buf->st_size + 511) / 512; // The syscall docs state this is hardcoded to # of 512 byte blocks.
  buf->st_blksize = 1024 * 1024; // Specifies the preferred blocksize for efficient disk I/O.
  buf->st_atim.tv_sec = node->atime;
  buf->st_mtim.tv_sec = node->mtime;
  buf->st_ctim.tv_sec = node->ctime;
  return 0;
}

long __syscall195(int which, ...) // SYS_stat64
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  struct stat* buf = va_arg(vl, struct stat*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('SYS_stat64(pathname="' + UTF8ToString($0) + '", buf=0x' + ($1).toString(16) + ')'),
    pathname, buf);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  // Find if this file exists already in the filesystem?
  inode* root = (pathname[0] == '/') ? filesystem_root() : get_cwd();
  const char* relpath = (pathname[0] == '/') ? pathname + 1 : pathname;

  int err;
  inode* node = find_inode(root, relpath, &err);

  if (!node && (err == ENOENT || err == ENOTDIR)) {
    // Populate the file from the CDN to the filesystem if it didn't yet exist.
    long fd = open(pathname, O_RDONLY, 0777);
    if (fd)
      close(fd);
    node = find_inode(root, relpath, &err);
  }

  if (err == ENOTDIR)
    RETURN_ERRNO(ENOTDIR, "A component of the path prefix of pathname is not a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links encountered while traversing the path");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "Search permission is denied for one of the directories in the path prefix of pathname");
  if (err && err != ENOENT)
    RETURN_ERRNO(err, "find_inode() error");
  if (err == ENOENT || !node)
    RETURN_ERRNO(ENOENT, "A component of pathname does not exist");

  return __stat64(node, buf);
}

long __syscall196(int which, ...) // SYS_lstat64
{
  va_list vl;
  va_start(vl, which);
  const char* pathname = va_arg(vl, const char*);
  struct stat* buf = va_arg(vl, struct stat*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(err('SYS_lstat64(pathname="' + UTF8ToString($0) + '", buf=0x' + ($1).toString(16) + ')'),
    pathname, buf);
#endif

  int len = strlen(pathname);
  if (len > MAX_PATHNAME_LENGTH)
    RETURN_ERRNO(ENAMETOOLONG, "pathname was too long");
  if (len == 0)
    RETURN_ERRNO(ENOENT, "pathname is empty");

  // Find if this file exists already in the filesystem?
  inode* root = (pathname[0] == '/') ? filesystem_root() : get_cwd();
  const char* relpath = (pathname[0] == '/') ? pathname + 1 : pathname;

  // TODO: When symbolic links are implemented, make this return info about the symlink itself and
  // not the file it points to.
  int err;
  inode* node = find_inode(root, relpath, &err);
  if (err == ENOTDIR)
    RETURN_ERRNO(ENOTDIR, "A component of the path prefix of pathname is not a directory");
  if (err == ELOOP)
    RETURN_ERRNO(ELOOP, "Too many symbolic links encountered while traversing the path");
  if (err == EACCES)
    RETURN_ERRNO(EACCES,
      "Search permission is denied for one of the directories in the path prefix of pathname");
  if (err && err != ENOENT)
    RETURN_ERRNO(err, "find_inode() error");
  if (err == ENOENT || !node)
    RETURN_ERRNO(ENOENT, "A component of pathname does not exist");

  return __stat64(node, buf);
}

long __syscall197(int which, ...) // SYS_fstat64
{
  va_list vl;
  va_start(vl, which);
  int fd = va_arg(vl, int);
  struct stat* buf = va_arg(vl, struct stat*);
  va_end(vl);
#ifdef ASMFS_DEBUG
  EM_ASM(
    err('SYS_fstat64(fd="' + UTF8ToString($0) + '", buf=0x' + ($1).toString(16) + ')'), fd, buf);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "fd isn't a valid open file descriptor");

  inode* node = desc->node;
  if (!node)
    RETURN_ERRNO(ENOENT, "A component of pathname does not exist");

  return __stat64(node, buf);
}

// TODO: syscall198: lchown
// TODO: syscall207: fchown32
// TODO: syscall212: chown32

long __syscall220(int which, ...) // getdents64 (get directory entries 64-bit)
{
  va_list vl;
  va_start(vl, which);
  unsigned int fd = va_arg(vl, unsigned int);
  dirent* de = va_arg(vl, dirent*);
  unsigned int count = va_arg(vl, unsigned int);
  va_end(vl);
  unsigned int dirents_size =
    count /
    sizeof(dirent); // The number of dirent structures that can fit into the provided buffer.
  dirent* de_end = de + dirents_size;
#ifdef ASMFS_DEBUG
  EM_ASM(err('getdents64(fd=' + $0 + ', de=0x' + ($1).toString(16) + ', count=' + $2 + ')'), fd, de,
    count);
#endif

  FileDescriptor* desc = (FileDescriptor*)fd;
  if (!desc || desc->magic != EM_FILEDESCRIPTOR_MAGIC)
    RETURN_ERRNO(EBADF, "Invalid file descriptor fd");

  inode* node = desc->node;
  if (!node)
    RETURN_ERRNO(ENOENT, "No such directory");
  if (dirents_size == 0)
    RETURN_ERRNO(EINVAL, "Result buffer is too small");
  if (node->type != INODE_DIR)
    RETURN_ERRNO(ENOTDIR, "File descriptor does not refer to a directory");

  inode* dotdot =
    node->parent ? node->parent : node; // In "/", the directory ".." refers to itself.

  ssize_t orig_file_pos = desc->file_pos;
  ssize_t file_pos = 0;
  // There are always two hardcoded directories "." and ".."
  if (de >= de_end)
    return desc->file_pos - orig_file_pos;
  if (desc->file_pos <= file_pos) {
    de->d_ino = (ino_t)node; // TODO: Create inode numbers instead of using pointers
    de->d_off = file_pos + sizeof(dirent);
    de->d_reclen = sizeof(dirent);
    de->d_type = DT_DIR;
    strcpy(de->d_name, ".");
    ++de;
    desc->file_pos += sizeof(dirent);
  }
  file_pos += sizeof(dirent);

  if (de >= de_end)
    return desc->file_pos - orig_file_pos;
  if (desc->file_pos <= file_pos) {
    de->d_ino = (ino_t)dotdot; // TODO: Create inode numbers instead of using pointers
    de->d_off = file_pos + sizeof(dirent);
    de->d_reclen = sizeof(dirent);
    de->d_type = DT_DIR;
    strcpy(de->d_name, "..");
    ++de;
    desc->file_pos += sizeof(dirent);
  }
  file_pos += sizeof(dirent);

  node = node->child;
  while (node && de < de_end) {
    if (desc->file_pos <= file_pos) {
      de->d_ino = (ino_t)node; // TODO: Create inode numbers instead of using pointers
      de->d_off = file_pos + sizeof(dirent);
      de->d_reclen = sizeof(dirent);
      de->d_type = (node->type == INODE_DIR) ? DT_DIR : DT_REG /*Regular file*/;
      de->d_name[255] = 0;
      strncpy(de->d_name, node->name, 255);
      ++de;
      desc->file_pos += sizeof(dirent);
    }
    node = node->sibling;
    file_pos += sizeof(dirent);
  }

  return desc->file_pos - orig_file_pos;
}

// TODO: syscall221: fcntl64
// TODO: syscall268: statfs64
// TODO: syscall269: fstatfs64
// TODO: syscall295: openat
// TODO: syscall296: mkdirat
// TODO: syscall297: mknodat
// TODO: syscall298: fchownat
// TODO: syscall300: fstatat64
// TODO: syscall301: unlinkat
// TODO: syscall302: renameat
// TODO: syscall303: linkat
// TODO: syscall304: symlinkat
// TODO: syscall305: readlinkat
// TODO: syscall306: fchmodat
// TODO: syscall307: faccessat
// TODO: syscall320: utimensat
// TODO: syscall324: fallocate
// TODO: syscall330: dup3
// TODO: syscall331: pipe2
// TODO: syscall333: preadv
// TODO: syscall334: pwritev

} // ~extern "C"