From e95805bce43d7212449a9805fe5a9d73b573fc28 Mon Sep 17 00:00:00 2001
From: mo <michael.oliver_@outlook.com>
Date: Sun, 18 Oct 2026 19:58:11 +0100
Subject: [PATCH] fix: correct WAV RIFF length and padding (#1032)

* fix: correct WAV RIFF length and padding

Include the PCM payload in the RIFF chunk size and pad odd-length data chunks. Add regression coverage for empty, odd, even and larger payloads.

* chore: add comment explaning the wav padding byte

---------

Co-authored-by: Jan Laupetin <jan@laupetin.net>
---
 src/ObjWriting/Sound/WavWriter.cpp           |  9 ++++-
 test/ObjWritingTests/Sound/WavWriterTest.cpp | 40 ++++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 test/ObjWritingTests/Sound/WavWriterTest.cpp

diff --git a/src/ObjWriting/Sound/WavWriter.cpp b/src/ObjWriting/Sound/WavWriter.cpp
index 2d8bfe84..f788ad49 100644
--- a/src/ObjWriting/Sound/WavWriter.cpp
+++ b/src/ObjWriting/Sound/WavWriter.cpp
@@ -7,8 +7,8 @@ WavWriter::WavWriter(std::ostream& stream)
 
 void WavWriter::WritePcmHeader(const WavMetaData& metaData, const size_t dataLen) const
 {
-    constexpr auto riffMasterChunkSize = static_cast<uint32_t>(sizeof(WAV_CHUNK_ID_RIFF) + sizeof(uint32_t) + sizeof(WAV_WAVE_ID) + sizeof(WavChunkHeader)
-                                                               + sizeof(WavFormatChunkPcm) + sizeof(WavChunkHeader) + sizeof(uint32_t));
+    const auto riffMasterChunkSize =
+        static_cast<uint32_t>(sizeof(WAV_WAVE_ID) + sizeof(WavChunkHeader) + sizeof(WavFormatChunkPcm) + sizeof(WavChunkHeader) + dataLen + (dataLen & 1u));
 
     m_stream.write(reinterpret_cast<const char*>(&WAV_CHUNK_ID_RIFF), sizeof(WAV_CHUNK_ID_RIFF));
     m_stream.write(reinterpret_cast<const char*>(&riffMasterChunkSize), sizeof(riffMasterChunkSize));
@@ -34,4 +34,9 @@ void WavWriter::WritePcmHeader(const WavMetaData& metaData, const size_t dataLen
 void WavWriter::WritePcmData(const void* data, const size_t dataLen) const
 {
     m_stream.write(static_cast<const char*>(data), static_cast<std::streamsize>(dataLen));
+
+    // > The data is always padded to the nearest WORD boundary.
+    // https://learn.microsoft.com/en-us/windows/win32/xaudio2/resource-interchange-file-format--riff-#chunks
+    if (dataLen & 1u)
+        m_stream.put('\0');
 }
diff --git a/test/ObjWritingTests/Sound/WavWriterTest.cpp b/test/ObjWritingTests/Sound/WavWriterTest.cpp
new file mode 100644
index 00000000..5b1ed62e
--- /dev/null
+++ b/test/ObjWritingTests/Sound/WavWriterTest.cpp
@@ -0,0 +1,40 @@
+#include "Sound/WavWriter.h"
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/generators/catch_generators.hpp>
+#include <cstring>
+#include <sstream>
+#include <string>
+
+TEST_CASE("WavWriter: RIFF contains the complete PCM payload and alignment padding", "[sound][wav]")
+{
+    const auto size = GENERATE(0uz, 1uz, 2uz, 31uz, 2048uz);
+    const std::string samples(size, static_cast<char>(0x81));
+    std::ostringstream output(std::ios::binary);
+    const WavWriter writer(output);
+    writer.WritePcmHeader({1, 22050, 8}, samples.size());
+    writer.WritePcmData(samples.data(), samples.size());
+    const auto bytes = output.str();
+    REQUIRE(bytes.size() >= sizeof(WavHeader));
+    WavHeader header{};
+    std::memcpy(&header, bytes.data(), sizeof(header));
+    CHECK(header.chunkIdRiff == WAV_CHUNK_ID_RIFF);
+    CHECK(header.chunkIdSize == bytes.size() - 8u);
+    CHECK(header.format == WAV_WAVE_ID);
+    CHECK(header.chunkHeader.chunkID == WAV_CHUNK_ID_FMT);
+    CHECK(header.chunkHeader.chunkSize == sizeof(WavFormatChunkPcm));
+    CHECK(header.formatChunk.wFormatTag == WavFormat::PCM);
+    CHECK(header.formatChunk.nChannels == 1u);
+    CHECK(header.formatChunk.nSamplesPerSec == 22050u);
+    CHECK(header.formatChunk.nAvgBytesPerSec == 22050u);
+    CHECK(header.formatChunk.nBlockAlign == 1u);
+    CHECK(header.formatChunk.wBitsPerSample == 8u);
+    CHECK(header.subChunkHeader.chunkID == WAV_CHUNK_ID_DATA);
+    REQUIRE(header.subChunkHeader.chunkSize == samples.size());
+    CHECK(bytes.substr(sizeof(header), samples.size()) == samples);
+    CHECK(bytes.size() % 2u == 0u);
+    if (samples.size() & 1u)
+        CHECK(bytes.back() == '\0');
+    else
+        CHECK(bytes.size() == sizeof(header) + samples.size());
+}