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).

weed/s3api/s3api_object_handlers_put_error_test.go

@@ -0,0 +1,51 @@
+package s3api
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/operation"
+	"github.com/seaweedfs/seaweedfs/weed/s3api/s3err"
+)
+
+func TestMapChunkedUploadErrorToS3Error(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want s3err.ErrorCode
+	}{
+		{
+			// A truncated body (client abort or reverse-proxy timeout) reaches
+			// putToFiler tagged exactly like UploadReaderInChunks reports it.
+			name: "truncated source read maps to IncompleteBody",
+			err:  fmt.Errorf("%w: read chunk at offset %d (got %d bytes): %w", operation.ErrTruncatedBody, 0, 8056500, io.ErrUnexpectedEOF),
+			want: s3err.ErrIncompleteBody,
+		},
+		{
+			// A volume-server upload dropping mid-write is a server fault, not a
+			// client truncation, even though it also carries io.ErrUnexpectedEOF.
+			name: "volume upload unexpected EOF maps to InternalError",
+			err:  fmt.Errorf("upload chunk: %w", io.ErrUnexpectedEOF),
+			want: s3err.ErrInternalError,
+		},
+		{
+			name: "payload checksum mismatch maps to InvalidDigest",
+			err:  errors.New(s3err.ErrMsgPayloadChecksumMismatch),
+			want: s3err.ErrInvalidDigest,
+		},
+		{
+			name: "other errors map to InternalError",
+			err:  errors.New("assign volume: no free volumes"),
+			want: s3err.ErrInternalError,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := mapChunkedUploadErrorToS3Error(tt.err); got != tt.want {
+				t.Errorf("mapChunkedUploadErrorToS3Error(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}