lz4frame: correct start and size after flush

when the block mode changes a flush is executed, to prevent
mixing compressed and uncompressed data.
Prior to this commit dstStart, dstPtr, dstCapacity
where not updated to include the offset from bytesWritten.
For inputs > blockSize this meant the flushed data was
overwritten.

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 251521e..f32ed1d 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -886,7 +886,7 @@ static size_t LZ4F_compressUpdateImpl(LZ4F_cctx* cctxPtr,
     size_t const blockSize = cctxPtr->maxBlockSize;
     const BYTE* srcPtr = (const BYTE*)srcBuffer;
     const BYTE* const srcEnd = srcPtr + srcSize;
-    BYTE* const dstStart = (BYTE*)dstBuffer;
+    BYTE* dstStart = (BYTE*)dstBuffer;
     BYTE* dstPtr = dstStart;
     LZ4F_lastBlockStatus lastBlockCompressed = notDone;
     compressFunc_t const compress = LZ4F_selectCompression(cctxPtr->prefs.frameInfo.blockMode, cctxPtr->prefs.compressionLevel);
@@ -896,6 +896,9 @@ static size_t LZ4F_compressUpdateImpl(LZ4F_cctx* cctxPtr,
     /* flush currently written block, to continue with new block compression */
     if (cctxPtr->blockCompression != blockCompression) {
       bytesWritten = LZ4F_flush(cctxPtr, dstBuffer, dstCapacity, compressOptionsPtr);
+      dstStart = (BYTE*)dstBuffer + bytesWritten;
+      dstPtr = dstStart;
+      dstCapacity -= bytesWritten;
       cctxPtr->blockCompression = blockCompression;
     }