s3: return IncompleteBody instead of 500 for truncated PUT bodies (#10186)

* s3: add IncompleteBody error code

* operation: tag a truncated source read as ErrTruncatedBody

The chunked uploader wraps both source-read failures and volume-upload failures,
and a mid-write volume server drop also carries io.ErrUnexpectedEOF. Tag only the
source read so callers can tell a truncated input apart from a server-side fault.

* s3: return IncompleteBody for a truncated PUT body

A client abort or reverse-proxy timeout truncates the request body mid-upload.
putToFiler mapped every streaming-upload failure to InternalError (500), which a
reverse proxy relays as a 502. Classify a source-read truncation as IncompleteBody
(400) so the response matches AWS and passes through. All S3 write paths share
putToFiler, so they all benefit.

weed/s3api/s3api_object_handlers_put.go

@@ -545,10 +545,7 @@ func (s3a *S3ApiServer) putToFiler(r *http.Request, filePath string, dataReader
 			s3a.deleteOrphanedChunks(chunkResult.FileChunks)
 		}
 
-		if strings.Contains(err.Error(), s3err.ErrMsgPayloadChecksumMismatch) {
-			return "", s3err.ErrInvalidDigest, SSEResponseMetadata{}
-		}
-		return "", s3err.ErrInternalError, SSEResponseMetadata{}
+		return "", mapChunkedUploadErrorToS3Error(err), SSEResponseMetadata{}
 	}
 
 	// Step 3: Calculate MD5 hash and add SSE metadata to chunks
@@ -1170,6 +1167,22 @@ func filerErrorToS3Error(err error) s3err.ErrorCode {
 	}
 }
 
+// mapChunkedUploadErrorToS3Error classifies a failed streaming upload. A truncated
+// request body (client abort or reverse-proxy timeout) is a request error, so report
+// IncompleteBody (400) rather than a 500 a reverse proxy would relay as a confusing
+// 502. Only the source read is tagged, so a volume-server upload fault still maps to
+// InternalError.
+func mapChunkedUploadErrorToS3Error(err error) s3err.ErrorCode {
+	switch {
+	case strings.Contains(err.Error(), s3err.ErrMsgPayloadChecksumMismatch):
+		return s3err.ErrInvalidDigest
+	case errors.Is(err, operation.ErrTruncatedBody):
+		return s3err.ErrIncompleteBody
+	default:
+		return s3err.ErrInternalError
+	}
+}
+
 // setObjectOwnerFromRequest sets the object owner metadata based on the bucket ownership policy.
 // When BucketOwnerEnforced (the modern AWS default), the bucket owner owns all objects.
 // Otherwise, the uploader's account ID is used (ObjectWriter mode).