fix(needle): use discovered file content type (#9851)

Problem: Multipart uploads where the first part was a form field and a later part contained the file used the first part's Content-Type for the file metadata.

Root cause: After finding a later part with a filename, parseUpload copied data and MD5 from part2 but read Content-Type from the original part variable.

Fix: Read Content-Type from the discovered file part.

Reproduction: go test ./weed/storage/needle -run TestParseUploadUsesDiscoveredFilePartContentType -count=1 failed before the fix because the parsed MIME type was text/plain instead of application/x-seaweed-test.

Validation: go test ./weed/storage/needle -run TestParseUploadUsesDiscoveredFilePartContentType -count=1; go test ./weed/storage/needle -count=1; git diff --check; git diff --cached --check

weed/storage/needle/needle_parse_upload.go

@@ -208,7 +208,7 @@ func parseUpload(r *http.Request, sizeLimit int64, pu *ParsedUpload) (e error) {
 				// update
 				pu.Data = pu.bytesBuffer.Bytes()
 				pu.FileName = util.CleanWindowsPathBase(fName)
-				contentType = part.Header.Get("Content-Type")
+				contentType = part2.Header.Get("Content-Type")
 				pu.ContentMd5 = part2.Header.Get("Content-MD5")
 				part = part2
 				break

weed/storage/needle/needle_parse_upload_stream_test.go

@@ -76,6 +76,50 @@ func TestParseUpload_GzipStreamCount(t *testing.T) {
 	}
 }
 
+func TestParseUploadUsesDiscoveredFilePartContentType(t *testing.T) {
+	var body bytes.Buffer
+	mw := multipart.NewWriter(&body)
+
+	fieldHeader := make(textproto.MIMEHeader)
+	fieldHeader.Set("Content-Disposition", `form-data; name="description"`)
+	fieldHeader.Set("Content-Type", "text/plain")
+	field, err := mw.CreatePart(fieldHeader)
+	if err != nil {
+		t.Fatalf("create field part: %v", err)
+	}
+	if _, err := field.Write([]byte("metadata")); err != nil {
+		t.Fatalf("write field part: %v", err)
+	}
+
+	fileHeader := make(textproto.MIMEHeader)
+	fileHeader.Set("Content-Disposition", `form-data; name="file"; filename="file.dat"`)
+	fileHeader.Set("Content-Type", "application/x-seaweed-test")
+	filePart, err := mw.CreatePart(fileHeader)
+	if err != nil {
+		t.Fatalf("create file part: %v", err)
+	}
+	if _, err := filePart.Write([]byte("payload")); err != nil {
+		t.Fatalf("write file part: %v", err)
+	}
+	if err := mw.Close(); err != nil {
+		t.Fatalf("close multipart writer: %v", err)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/upload", bytes.NewReader(body.Bytes()))
+	req.Header.Set("Content-Type", mw.FormDataContentType())
+
+	pu, err := ParseUpload(req, 1024, &bytes.Buffer{})
+	if err != nil {
+		t.Fatalf("ParseUpload: %v", err)
+	}
+	if pu.FileName != "file.dat" {
+		t.Fatalf("FileName = %q, want file.dat", pu.FileName)
+	}
+	if pu.MimeType != "application/x-seaweed-test" {
+		t.Fatalf("MimeType = %q, want application/x-seaweed-test", pu.MimeType)
+	}
+}
+
 func gzipBytes(t *testing.T, in []byte) []byte {
 	t.Helper()
 	var buf bytes.Buffer