Updated comments on LZ4F_getFrameInfo()

2 files changed, 8 insertions, 4 deletions

diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 5683eee..5f69c95 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -918,10 +918,10 @@ LZ4F_errorCode_t LZ4F_getFrameInfo(LZ4F_decompressionContext_t decompressionCont
 
     if (dctxPtr->dStage == dstage_getHeader)
     {
-        LZ4F_errorCode_t errorCode = LZ4F_decodeHeader(dctxPtr, srcBuffer, *srcSizePtr);
-        if (LZ4F_isError(errorCode)) return errorCode;
-        *srcSizePtr = errorCode;   /* nb Bytes consumed */
-        *frameInfoPtr = dctxPtr->frameInfo;
+        size_t frameHeaderSize = LZ4F_decodeHeader(dctxPtr, srcBuffer, *srcSizePtr);
+        if (LZ4F_isError(frameHeaderSize)) return frameHeaderSize;
+        *srcSizePtr = frameHeaderSize;   /* nb Bytes consumed */
+        *frameInfoPtr = dctxPtr->frameInfo;   /* copy into */
         dctxPtr->srcExpect = NULL;
         return 4;   /* nextSrcSizeHint : 4 == block header size */
     }
diff --git a/lib/lz4frame.h b/lib/lz4frame.h
index 01a756a..9d12c7d 100644
--- a/lib/lz4frame.h
+++ b/lib/lz4frame.h
@@ -214,8 +214,12 @@ size_t LZ4F_getFrameInfo(LZ4F_decompressionContext_t dctx,
  * This function decodes frame header information, such as blockSize.
  * It is optional : you could start by calling directly LZ4F_decompress() instead.
  * The objective is to extract header information without starting decompression, typically for allocation purposes.
+ * The function will work only if srcBuffer points at the beginning of the frame,
+ * and *srcSizePtr is large enough to decode the whole header (typically, between 7 & 15 bytes).
+ * The result is copied into an LZ4F_frameInfo_t structure, which is pointed by frameInfoPtr, and must be already allocated.
  * LZ4F_getFrameInfo() can also be used *after* starting decompression, on a valid LZ4F_decompressionContext_t.
  * The number of bytes read from srcBuffer will be provided within *srcSizePtr (necessarily <= original value).
+ * It is basically the frame header size.
  * You are expected to resume decompression from where it stopped (srcBuffer + *srcSizePtr)
  * The function result is an hint of how many srcSize bytes LZ4F_decompress() expects for next call,
  *                        or an error code which can be tested using LZ4F_isError().