Add transcoding/validation to Writer::RawValue()

Fix #1152

include/rapidjson/writer.h

diff --git a/include/rapidjson/writer.h b/include/rapidjson/writer.h
index e610ebb..a978891 100644
--- a/include/rapidjson/writer.h
+++ b/include/rapidjson/writer.h
@@ -460,9 +460,14 @@
 
     bool WriteRawValue(const Ch* json, size_t length) {
         PutReserve(*os_, length);
-        for (size_t i = 0; i < length; i++) {
-            RAPIDJSON_ASSERT(json[i] != '\0');
-            PutUnsafe(*os_, json[i]);
+        GenericStringStream<SourceEncoding> is(json);
+        while (RAPIDJSON_LIKELY(is.Tell() < length)) {
+            const Ch c = is.Peek();
+            RAPIDJSON_ASSERT(c != '\0');
+            if (RAPIDJSON_UNLIKELY(!(writeFlags & kWriteValidateEncodingFlag ? 
+                Transcoder<SourceEncoding, TargetEncoding>::Validate(is, *os_) :
+                Transcoder<SourceEncoding, TargetEncoding>::TranscodeUnsafe(is, *os_))))
+                return false;
         }
         return true;
     }

test/unittest/writertest.cpp

diff --git a/test/unittest/writertest.cpp b/test/unittest/writertest.cpp
index b190c6c..232b03d 100644
--- a/test/unittest/writertest.cpp
+++ b/test/unittest/writertest.cpp
@@ -538,6 +538,43 @@
     EXPECT_STREQ("{\"a\":1,\"raw\":[\"Hello\\nWorld\", 123.456]}", buffer.GetString());
 }
 
+TEST(Write, RawValue_Issue1152) {
+    {
+        GenericStringBuffer<UTF32<> > sb;
+        Writer<GenericStringBuffer<UTF32<> >, UTF8<>, UTF32<> > writer(sb);
+        writer.RawValue("null", 4, kNullType);
+        EXPECT_TRUE(writer.IsComplete());
+        const unsigned *out = sb.GetString();
+        EXPECT_EQ(static_cast<unsigned>('n'), out[0]);
+        EXPECT_EQ(static_cast<unsigned>('u'), out[1]);
+        EXPECT_EQ(static_cast<unsigned>('l'), out[2]);
+        EXPECT_EQ(static_cast<unsigned>('l'), out[3]);
+        EXPECT_EQ(static_cast<unsigned>(0  ), out[4]);
+    }
+
+    {
+        GenericStringBuffer<UTF8<> > sb;
+        Writer<GenericStringBuffer<UTF8<> >, UTF16<>, UTF8<> > writer(sb);
+        writer.RawValue(L"null", 4, kNullType);
+        EXPECT_TRUE(writer.IsComplete());
+        EXPECT_STREQ("null", sb.GetString());
+    }
+
+    {
+        // Fail in transcoding
+        GenericStringBuffer<UTF16<> > buffer;
+        Writer<GenericStringBuffer<UTF16<> >, UTF8<>, UTF16<> > writer(buffer);
+        EXPECT_FALSE(writer.RawValue("\"\xfe\"", 3, kStringType));
+    }
+
+    {
+        // Fail in encoding validation
+        StringBuffer buffer;
+        Writer<StringBuffer, UTF8<>, UTF8<>, CrtAllocator, kWriteValidateEncodingFlag> writer(buffer);
+        EXPECT_FALSE(writer.RawValue("\"\xfe\"", 3, kStringType));
+    }
+}
+
 #if RAPIDJSON_HAS_CXX11_RVALUE_REFS
 static Writer<StringBuffer> WriterGen(StringBuffer &target) {
     Writer<StringBuffer> writer(target);