From 6fa58db6ab2bb0a4f7af466bf282e5e81a7c0f82 Mon Sep 17 00:00:00 2001
From: niksis02 <sisnikoyan@gmail.com>
Date: Fri, 25 Apr 2025 19:06:57 +0400
Subject: [PATCH] fix: fixes the signed chunk encoding reader stashing.

Fixes #1238

The signed chunk reader stashes the header bytes if it can't fully parse the chunk header. On the next `io.Reader` call, the stash is combined with the new buffer data to attempt parsing the header again. The stashing logic was broken due to the premature removal of the first two header bytes (`\r\n`). As a result, the stash was incomplete, leading to parsing issues on subsequent calls.

These changes fix the stashing logic and correct the buffer offset calculation in `parseChunkHeaderBytes`.
---
 s3api/utils/signed-chunk-reader.go | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/s3api/utils/signed-chunk-reader.go b/s3api/utils/signed-chunk-reader.go
index 7a3b201..c0079ac 100644
--- a/s3api/utils/signed-chunk-reader.go
+++ b/s3api/utils/signed-chunk-reader.go
@@ -233,7 +233,7 @@ func (cr *ChunkReader) parseAndRemoveChunkInfo(p []byte) (int, error) {
 		}
 	}
 
-	chunkSize, sig, bufOffset, err := cr.parseChunkHeaderBytes(p[:n], &n)
+	chunkSize, sig, bufOffset, err := cr.parseChunkHeaderBytes(p[:n])
 	if err == errskipHeader {
 		cr.chunkDataLeft = 0
 		return 0, nil
@@ -322,7 +322,7 @@ const (
 // This returns the chunk payload size, signature, data start offset, and
 // error if any. See the AWS documentation for the chunk header format. The
 // header[0] byte is expected to be the first byte of the chunk size here.
-func (cr *ChunkReader) parseChunkHeaderBytes(header []byte, l *int) (int64, string, int, error) {
+func (cr *ChunkReader) parseChunkHeaderBytes(header []byte) (int64, string, int, error) {
 	stashLen := len(cr.stash)
 	if stashLen > maxHeaderSize {
 		return 0, "", 0, errInvalidChunkFormat
@@ -339,14 +339,11 @@ func (cr *ChunkReader) parseChunkHeaderBytes(header []byte, l *int) (int64, stri
 
 	// After the first chunk each chunk header should start
 	// with "\n\r\n"
-	if !cr.isFirstHeader && stashLen == 0 {
+	if !cr.isFirstHeader {
 		err := readAndSkip(rdr, '\r', '\n')
 		if err != nil {
 			return cr.handleRdrErr(err, header)
 		}
-
-		copy(header, header[2:])
-		*l = *l - 2
 	}
 
 	// read and parse the chunk size
@@ -435,10 +432,19 @@ func (cr *ChunkReader) parseChunkHeaderBytes(header []byte, l *int) (int64, stri
 		return cr.handleRdrErr(err, header)
 	}
 
-	ind := bytes.Index(header, []byte{'\r', '\n'})
+	// find the index of chunk ending: '\r\n'
+	// skip the first 2 bytes as it is the starting '\r\n'
+	// the first chunk doesn't contain the starting '\r\n', but
+	// anyway, trimming the first 2 bytes doesn't pollute the logic.
+	ind := bytes.Index(header[2:], []byte{'\r', '\n'})
 	cr.isFirstHeader = false
 
-	return chunkSize, sig, ind + len(chunkHdrDelim) - stashLen, nil
+	// the offset is the found index + 4 - the stash length
+	// where:
+	// ind is the index of '\r\n'
+	// 4 specifies the trimmed 2 bytes plus 2 to shift the index at the end of '\r\n'
+	offset := ind + 4 - stashLen
+	return chunkSize, sig, offset, nil
 }
 
 // Stashes the header in cr.stash and returns "errskipHeader"