fix(replication): resume partial chunk reads on EOF instead of re-downloading (#8607)

* fix(replication): resume partial chunk reads on EOF instead of re-downloading

When replicating chunks and the source connection drops mid-transfer,
accumulate the bytes already received and retry with a Range header
to fetch only the remaining bytes. This avoids re-downloading
potentially large chunks from scratch on each retry, reducing load
on busy source servers and speeding up recovery.

* test(replication): add tests for downloadWithRange including gzip partial reads

Tests cover:
- No offset (no Range header sent)
- With offset (Range header verified)
- Content-Disposition filename extraction
- Partial read + resume: server drops connection mid-transfer, client
  resumes with Range from the offset of received bytes
- Gzip partial read + resume: first response is gzip-encoded (Go auto-
  decompresses), connection drops, resume request gets decompressed data
  (Go doesn't add Accept-Encoding when Range is set, so the server
  decompresses), combined bytes match original

* fix(replication): address PR review comments

- Consolidate downloadWithRange into DownloadFile with optional offset
  parameter (variadic), eliminating code duplication (DRY)
- Validate HTTP response status: require 206 + correct Content-Range
  when offset > 0, reject when server ignores Range header
- Use if/else for fullData assignment for clarity
- Add test for rejected Range (server returns 200 instead of 206)

* refactor(replication): remove unused ReplicationSource interface

The interface was never referenced and its signature didn't match
the actual FilerSource.ReadPart method.

---------

Co-authored-by: Copilot <copilot@github.com>

weed/replication/sink/filersink/fetch_write.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net/http"
 	"os"
 	"path/filepath"
 	"strings"
@@ -241,17 +242,44 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 	}
 
 	eofBackoff := time.Duration(0)
+	var partialData []byte
+	var savedFilename string
+	var savedHeader http.Header
+	var savedSourceUrl string
 	retryName := fmt.Sprintf("replicate chunk %s", sourceChunk.GetFileIdString())
 	err = util.RetryUntil(retryName, func() error {
-		filename, header, resp, readErr := fs.filerSource.ReadPart(sourceChunk.GetFileIdString())
+		filename, header, resp, readErr := fs.filerSource.ReadPart(sourceChunk.GetFileIdString(), int64(len(partialData)))
 		if readErr != nil {
 			return fmt.Errorf("read part %s: %w", sourceChunk.GetFileIdString(), readErr)
 		}
 		defer util_http.CloseResponse(resp)
 
-		sourceUrl := ""
+		// Save metadata from first successful response
-		if resp.Request != nil && resp.Request.URL != nil {
+		if len(partialData) == 0 {
-			sourceUrl = resp.Request.URL.String()
+			savedFilename = filename
+			savedHeader = header
+			if resp.Request != nil && resp.Request.URL != nil {
+				savedSourceUrl = resp.Request.URL.String()
+			}
+		}
+
+		// Read the response body
+		data, readBodyErr := io.ReadAll(resp.Body)
+		if readBodyErr != nil {
+			// Keep whatever bytes we received before the error
+			partialData = append(partialData, data...)
+			return fmt.Errorf("read body: %w", readBodyErr)
+		}
+
+		// Combine with previously accumulated partial data
+		var fullData []byte
+		if len(partialData) > 0 {
+			fullData = append(partialData, data...)
+			glog.V(0).Infof("resumed reading %s, got %d + %d = %d bytes",
+				sourceChunk.GetFileIdString(), len(partialData), len(data), len(fullData))
+			partialData = nil
+		} else {
+			fullData = data
 		}
 
 		currentFileId, uploadResult, uploadErr, _ := uploader.UploadWithRetry(
@@ -266,20 +294,20 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 				Path:        path,
 			},
 			&operation.UploadOption{
-				Filename:          filename,
+				Filename:          savedFilename,
 				Cipher:            false,
-				IsInputCompressed: "gzip" == header.Get("Content-Encoding"),
+				IsInputCompressed: "gzip" == savedHeader.Get("Content-Encoding"),
-				MimeType:          header.Get("Content-Type"),
+				MimeType:          savedHeader.Get("Content-Type"),
 				PairMap:           nil,
 				RetryForever:      false,
-				SourceUrl:         sourceUrl,
+				SourceUrl:         savedSourceUrl,
 			},
 			func(host, fileId string) string {
 				fileUrl := fs.buildUploadUrl(host, fileId)
-				glog.V(4).Infof("replicating %s to %s header:%+v", filename, fileUrl, header)
+				glog.V(4).Infof("replicating %s to %s header:%+v", savedFilename, fileUrl, savedHeader)
 				return fileUrl
 			},
-			resp.Body,
+			util.NewBytesReader(fullData),
 		)
 		if uploadErr != nil {
 			return fmt.Errorf("upload data: %w", uploadErr)
@@ -291,17 +319,18 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 		eofBackoff = 0
 		fileId = currentFileId
 		return nil
-	}, func(uploadErr error) (shouldContinue bool) {
+	}, func(retryErr error) (shouldContinue bool) {
 		if fs.hasSourceNewerVersion(path, sourceMtime) {
-			glog.V(1).Infof("skip retrying stale source %s for %s: %v", sourceChunk.GetFileIdString(), path, uploadErr)
+			glog.V(1).Infof("skip retrying stale source %s for %s: %v", sourceChunk.GetFileIdString(), path, retryErr)
 			return false
 		}
-		if isEofError(uploadErr) {
+		if isEofError(retryErr) {
 			eofBackoff = nextEofBackoff(eofBackoff)
-			glog.V(0).Infof("source connection interrupted while replicating %s for %s, backing off %v: %v", sourceChunk.GetFileIdString(), path, eofBackoff, uploadErr)
+			glog.V(0).Infof("source connection interrupted while replicating %s for %s (%d bytes received so far), backing off %v: %v",
+				sourceChunk.GetFileIdString(), path, len(partialData), eofBackoff, retryErr)
 			time.Sleep(eofBackoff)
 		} else {
-			glog.V(0).Infof("replicate %s for %s: %v", sourceChunk.GetFileIdString(), path, uploadErr)
+			glog.V(0).Infof("replicate %s for %s: %v", sourceChunk.GetFileIdString(), path, retryErr)
 		}
 		return true
 	})

weed/replication/source/filer_source.go

@@ -3,7 +3,6 @@ package source
 import (
 	"context"
 	"fmt"
-	"io"
 	"net/http"
 	"strings"
 
@@ -18,10 +17,6 @@ import (
 	util_http "github.com/seaweedfs/seaweedfs/weed/util/http"
 )
 
-type ReplicationSource interface {
-	ReadPart(part string) io.ReadCloser
-}
-
 type FilerSource struct {
 	grpcAddress    string
 	grpcDialOption grpc.DialOption
@@ -104,14 +99,14 @@ func (fs *FilerSource) LookupFileId(ctx context.Context, part string) (fileUrls
 	return
 }
 
-func (fs *FilerSource) ReadPart(fileId string) (filename string, header http.Header, resp *http.Response, err error) {
+func (fs *FilerSource) ReadPart(fileId string, offset int64) (filename string, header http.Header, resp *http.Response, err error) {
 
 	if fs.proxyByFiler {
-		filename, header, resp, err = util_http.DownloadFile("http://"+fs.address+"/?proxyChunkId="+fileId, "")
+		filename, header, resp, err = util_http.DownloadFile("http://"+fs.address+"/?proxyChunkId="+fileId, "", offset)
 		if err != nil {
-			glog.V(0).Infof("read part %s via filer proxy %s: %v", fileId, fs.address, err)
+			glog.V(0).Infof("read part %s via filer proxy %s offset %d: %v", fileId, fs.address, offset, err)
 		} else {
-			glog.V(4).Infof("read part %s via filer proxy %s content-length:%s", fileId, fs.address, header.Get("Content-Length"))
+			glog.V(4).Infof("read part %s via filer proxy %s offset %d content-length:%s", fileId, fs.address, offset, header.Get("Content-Length"))
 		}
 		return
 	}
@@ -122,11 +117,11 @@ func (fs *FilerSource) ReadPart(fileId string) (filename string, header http.Hea
 	}
 
 	for _, fileUrl := range fileUrls {
-		filename, header, resp, err = util_http.DownloadFile(fileUrl, "")
+		filename, header, resp, err = util_http.DownloadFile(fileUrl, "", offset)
 		if err != nil {
-			glog.V(0).Infof("fail to read part %s from %s: %v", fileId, fileUrl, err)
+			glog.V(0).Infof("fail to read part %s from %s offset %d: %v", fileId, fileUrl, offset, err)
 		} else {
-			glog.V(4).Infof("read part %s from %s content-length:%s", fileId, fileUrl, header.Get("Content-Length"))
+			glog.V(4).Infof("read part %s from %s offset %d content-length:%s", fileId, fileUrl, offset, header.Get("Content-Length"))
 			break
 		}
 	}

weed/replication/source/filer_source_test.go

@@ -0,0 +1,284 @@
+package source
+
+import (
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"sync/atomic"
+	"testing"
+
+	util_http "github.com/seaweedfs/seaweedfs/weed/util/http"
+)
+
+func TestMain(m *testing.M) {
+	util_http.InitGlobalHttpClient()
+	os.Exit(m.Run())
+}
+
+func TestDownloadFile_NoOffset(t *testing.T) {
+	testData := []byte("0123456789abcdefghij")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Header.Get("Range") != "" {
+			t.Error("Range header should not be set when offset is 0")
+		}
+		w.Header().Set("Content-Type", "application/octet-stream")
+		w.Write(testData)
+	}))
+	defer server.Close()
+
+	_, _, resp, err := util_http.DownloadFile(server.URL, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(data, testData) {
+		t.Fatalf("expected %q, got %q", testData, data)
+	}
+}
+
+func TestDownloadFile_WithOffset(t *testing.T) {
+	testData := []byte("0123456789abcdefghij")
+
+	var receivedRange string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		receivedRange = r.Header.Get("Range")
+		var offset int
+		fmt.Sscanf(receivedRange, "bytes=%d-", &offset)
+		w.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", offset, len(testData)-1, len(testData)))
+		w.WriteHeader(http.StatusPartialContent)
+		w.Write(testData[offset:])
+	}))
+	defer server.Close()
+
+	_, _, resp, err := util_http.DownloadFile(server.URL, "", 10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+
+	if receivedRange != "bytes=10-" {
+		t.Fatalf("expected Range header %q, got %q", "bytes=10-", receivedRange)
+	}
+	if resp.StatusCode != http.StatusPartialContent {
+		t.Fatalf("expected status 206, got %d", resp.StatusCode)
+	}
+
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(data, testData[10:]) {
+		t.Fatalf("expected %q, got %q", testData[10:], data)
+	}
+}
+
+func TestDownloadFile_RejectsIgnoredRange(t *testing.T) {
+	// Server ignores Range header and returns 200 OK with full body
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("full body"))
+	}))
+	defer server.Close()
+
+	_, _, _, err := util_http.DownloadFile(server.URL, "", 100)
+	if err == nil {
+		t.Fatal("expected error when server ignores Range and returns 200")
+	}
+}
+
+func TestDownloadFile_ContentDisposition(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Disposition", `attachment; filename="test.txt"`)
+		w.Write([]byte("data"))
+	}))
+	defer server.Close()
+
+	filename, _, resp, err := util_http.DownloadFile(server.URL, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+
+	if filename != "test.txt" {
+		t.Fatalf("expected filename %q, got %q", "test.txt", filename)
+	}
+}
+
+// TestDownloadFile_PartialReadThenResume simulates a connection drop
+// after partial data, then resumes from the offset. Verifies the combined
+// data matches the original.
+func TestDownloadFile_PartialReadThenResume(t *testing.T) {
+	testData := bytes.Repeat([]byte("abcdefghij"), 100) // 1000 bytes
+	dropAfter := 500
+
+	var requestNum atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		n := requestNum.Add(1)
+		rangeHeader := r.Header.Get("Range")
+
+		if n == 1 && rangeHeader == "" {
+			// First request: write partial data then kill the connection
+			hj, ok := w.(http.Hijacker)
+			if !ok {
+				t.Error("server doesn't support hijacking")
+				return
+			}
+			conn, buf, _ := hj.Hijack()
+			fmt.Fprintf(buf, "HTTP/1.1 200 OK\r\n")
+			fmt.Fprintf(buf, "Content-Length: %d\r\n", len(testData))
+			fmt.Fprintf(buf, "Content-Type: application/octet-stream\r\n")
+			fmt.Fprintf(buf, "\r\n")
+			buf.Write(testData[:dropAfter])
+			buf.Flush()
+			conn.Close()
+			return
+		}
+
+		// Resume request with Range
+		var offset int
+		fmt.Sscanf(rangeHeader, "bytes=%d-", &offset)
+		w.Header().Set("Content-Range",
+			fmt.Sprintf("bytes %d-%d/%d", offset, len(testData)-1, len(testData)))
+		w.WriteHeader(http.StatusPartialContent)
+		w.Write(testData[offset:])
+	}))
+	defer server.Close()
+
+	// First read — should get partial data + error
+	_, _, resp1, err := util_http.DownloadFile(server.URL, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	partialData, readErr := io.ReadAll(resp1.Body)
+	resp1.Body.Close()
+	if readErr == nil {
+		t.Fatal("expected error from truncated response")
+	}
+	if len(partialData) == 0 {
+		t.Fatal("expected some partial data")
+	}
+	if !bytes.Equal(partialData, testData[:len(partialData)]) {
+		t.Fatal("partial data doesn't match beginning of original")
+	}
+
+	// Resume from where we left off
+	_, _, resp2, err := util_http.DownloadFile(server.URL, "", int64(len(partialData)))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp2.Body.Close()
+	remainingData, readErr := io.ReadAll(resp2.Body)
+	if readErr != nil {
+		t.Fatalf("unexpected error on resume: %v", readErr)
+	}
+
+	// Combined data must match original
+	fullData := append(partialData, remainingData...)
+	if !bytes.Equal(fullData, testData) {
+		t.Fatalf("combined data mismatch: got %d bytes, want %d", len(fullData), len(testData))
+	}
+}
+
+// TestDownloadFile_GzipPartialReadThenResume verifies the tricky case
+// where the first response is gzip-encoded (and Go's HTTP client auto-
+// decompresses it), but the resume request gets uncompressed data (because
+// Go doesn't add Accept-Encoding when Range is set). The combined
+// decompressed bytes must still match the original.
+func TestDownloadFile_GzipPartialReadThenResume(t *testing.T) {
+	testData := bytes.Repeat([]byte("hello world gzip test "), 100) // ~2200 bytes
+
+	// Pre-compress
+	var compressed bytes.Buffer
+	gz := gzip.NewWriter(&compressed)
+	gz.Write(testData)
+	gz.Close()
+	compressedData := compressed.Bytes()
+	dropAfter := len(compressedData) / 2
+
+	var requestNum atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		n := requestNum.Add(1)
+		rangeHeader := r.Header.Get("Range")
+		acceptsGzip := r.Header.Get("Accept-Encoding") != ""
+
+		if n == 1 && acceptsGzip && rangeHeader == "" {
+			// First request: serve gzip-encoded response, drop mid-stream.
+			// Go's HTTP client auto-added Accept-Encoding: gzip (no Range),
+			// so it will auto-decompress and strip the Content-Encoding header.
+			hj, ok := w.(http.Hijacker)
+			if !ok {
+				t.Error("server doesn't support hijacking")
+				return
+			}
+			conn, buf, _ := hj.Hijack()
+			fmt.Fprintf(buf, "HTTP/1.1 200 OK\r\n")
+			fmt.Fprintf(buf, "Content-Encoding: gzip\r\n")
+			fmt.Fprintf(buf, "Content-Length: %d\r\n", len(compressedData))
+			fmt.Fprintf(buf, "Content-Type: application/octet-stream\r\n")
+			fmt.Fprintf(buf, "\r\n")
+			buf.Write(compressedData[:dropAfter])
+			buf.Flush()
+			conn.Close()
+			return
+		}
+
+		// Resume request: Range is set, Go did NOT add Accept-Encoding,
+		// so we serve decompressed data from the requested offset —
+		// mimicking what the volume server does when the client doesn't
+		// advertise gzip support.
+		var offset int
+		fmt.Sscanf(rangeHeader, "bytes=%d-", &offset)
+		remaining := testData[offset:]
+		w.Header().Set("Content-Range",
+			fmt.Sprintf("bytes %d-%d/%d", offset, len(testData)-1, len(testData)))
+		w.Header().Set("Content-Type", "application/octet-stream")
+		w.WriteHeader(http.StatusPartialContent)
+		w.Write(remaining)
+	}))
+	defer server.Close()
+
+	// First read: Go auto-decompresses; truncated stream → error + partial data
+	_, _, resp1, err := util_http.DownloadFile(server.URL, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	partialData, readErr := io.ReadAll(resp1.Body)
+	resp1.Body.Close()
+	if readErr == nil {
+		t.Fatal("expected error from truncated gzip response")
+	}
+	if len(partialData) == 0 {
+		t.Fatal("expected some decompressed partial data")
+	}
+	// Partial decompressed data must match the beginning of the original
+	if !bytes.Equal(partialData, testData[:len(partialData)]) {
+		t.Fatalf("partial decompressed data doesn't match original (got %d bytes)", len(partialData))
+	}
+
+	// Resume: offset is in the *decompressed* domain.
+	// The server (like the volume server) decompresses and serves from that offset.
+	_, _, resp2, err := util_http.DownloadFile(server.URL, "", int64(len(partialData)))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp2.Body.Close()
+	remainingData, readErr := io.ReadAll(resp2.Body)
+	if readErr != nil {
+		t.Fatalf("unexpected error on resume: %v", readErr)
+	}
+
+	fullData := append(partialData, remainingData...)
+	if !bytes.Equal(fullData, testData) {
+		t.Fatalf("combined data mismatch: got %d bytes, want %d", len(fullData), len(testData))
+	}
+}

weed/util/http/http_global_client_util.go

@@ -201,7 +201,7 @@ func GetUrlStream(url string, values url.Values, readFn func(io.Reader) error) e
 	return readFn(r.Body)
 }
 
-func DownloadFile(fileUrl string, jwt string) (filename string, header http.Header, resp *http.Response, e error) {
+func DownloadFile(fileUrl string, jwt string, offset ...int64) (filename string, header http.Header, resp *http.Response, e error) {
 	req, err := http.NewRequest(http.MethodGet, fileUrl, nil)
 	if err != nil {
 		return "", nil, nil, err
@@ -209,10 +209,29 @@ func DownloadFile(fileUrl string, jwt string) (filename string, header http.Head
 
 	maybeAddAuth(req, jwt)
 
+	var rangeOffset int64
+	if len(offset) > 0 {
+		rangeOffset = offset[0]
+	}
+	if rangeOffset > 0 {
+		req.Header.Set("Range", fmt.Sprintf("bytes=%d-", rangeOffset))
+	}
+
 	response, err := GetGlobalHttpClient().Do(req)
 	if err != nil {
 		return "", nil, nil, err
 	}
+
+	if rangeOffset > 0 {
+		expected := fmt.Sprintf("bytes %d-", rangeOffset)
+		if response.StatusCode != http.StatusPartialContent ||
+			!strings.HasPrefix(response.Header.Get("Content-Range"), expected) {
+			CloseResponse(response)
+			return "", nil, nil, fmt.Errorf("range request %q to %s returned %s with Content-Range %q",
+				req.Header.Get("Range"), fileUrl, response.Status, response.Header.Get("Content-Range"))
+		}
+	}
+
 	header = response.Header
 	contentDisposition := response.Header["Content-Disposition"]
 	if len(contentDisposition) > 0 {