From 0a5c22b57e179a60d49cca93871a070f1c816cf0 Mon Sep 17 00:00:00 2001
From: Chris Lu <chrislusf@users.noreply.github.com>
Date: Mon, 20 Apr 2026 21:26:34 -0700
Subject: [PATCH] chore(upload): log offset/bytes-read context on chunk
 ReadFrom errors (#9169)
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chore(upload): add offset/bytes-read context to chunk ReadFrom errors

Wrap io.ErrUnexpectedEOF (and siblings) from bytesBuffer.ReadFrom so
the log shows "read chunk at offset N (got M bytes): ..." instead of
a bare "unexpected EOF". The context distinguishes a client disconnect
before any data arrived (offset=0, got=0) from a mid-stream truncation
(offset>0, got<chunkSize) — diagnosing #9149 in the wild.

Verified at this stage that expectedDataSize is already threaded
correctly from upload_chunked.go (actual ReadFrom bytes) through
s3api assignFunc → filer AssignVolume → master PickForWrite.
No behavioral change to what the master receives.
---
 weed/operation/upload_chunked.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/weed/operation/upload_chunked.go b/weed/operation/upload_chunked.go
index 57109b149..cfcb07634 100644
--- a/weed/operation/upload_chunked.go
+++ b/weed/operation/upload_chunked.go
@@ -99,12 +99,16 @@ uploadLoop:
 		// Read one chunk
 		dataSize, err := bytesBuffer.ReadFrom(limitedReader)
 		if err != nil {
-			glog.V(2).Infof("UploadReaderInChunks: read error at offset %d: %v", chunkOffset, err)
+			// Attach offset + bytes-read to distinguish client disconnect
+			// before any data (offset=0,got=0) from mid-stream truncation.
+			// A bare io.ErrUnexpectedEOF is not actionable on its own (see #9149).
+			wrapped := fmt.Errorf("read chunk at offset %d (got %d bytes): %w", chunkOffset, dataSize, err)
+			glog.V(2).Infof("UploadReaderInChunks: %v", wrapped)
 			chunkBufferPool.Put(bytesBuffer)
 			<-bytesBufferLimitChan
 			uploadErrLock.Lock()
 			if uploadErr == nil {
-				uploadErr = err
+				uploadErr = wrapped
 			}
 			uploadErrLock.Unlock()
 			break