fix(tvix/nar-bridge): chunk blobs

Instead of creating one big BlobChunk containing all data, and creating
way too large proto messages, chunk blobs up to a reasonable (1MiB)
chunk size, and send them to the server like that.

Change-Id: Ia45a53956a6d7c0599cc59ac516ba37e9fb1b30e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9357
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/nar-bridge/pkg/reader/reader.go

@@ -41,7 +41,7 @@ func New(r io.Reader) *Reader {
 func (r *Reader) Import(
 	ctx context.Context,
 	// callback function called with each regular file content
-	fileCb func(fileReader io.Reader) error,
+	blobCb func(fileReader io.Reader) error,
 	// callback function called with each finalized directory node
 	directoryCb func(directory *storev1pb.Directory) error,
 ) (*storev1pb.PathInfo, error) {
@@ -219,9 +219,9 @@ func (r *Reader) Import(
 				// wrap reader with a reader calculating the blake3 hash
 				fileReader := NewHasher(narReader, blake3.New(32, nil))
 
-				err := fileCb(fileReader)
+				err := blobCb(fileReader)
 				if err != nil {
-					return nil, fmt.Errorf("failure from fileCb: %w", err)
+					return nil, fmt.Errorf("failure from blobCb: %w", err)
 				}
 
 				// drive the file reader to the end, in case the CB function doesn't read

tvix/nar-bridge/pkg/server/blob_upload.go

@@ -1,47 +1,70 @@
 package server
 
 import (
-	storev1pb "code.tvl.fyi/tvix/store/protos"
+	"bufio"
 	"context"
 	"encoding/base64"
+	"errors"
 	"fmt"
-	log "github.com/sirupsen/logrus"
 	"io"
+
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+	log "github.com/sirupsen/logrus"
 )
 
-// this returns a callback function that can be used as fileCb
-// for the reader.Import function call
+// the size of individual BlobChunk we send when uploading to BlobService.
+const chunkSize = 1024 * 1024
+
+// this produces a callback function that can be used as blobCb for the
+// reader.Import function call
 func genBlobServiceWriteCb(ctx context.Context, blobServiceClient storev1pb.BlobServiceClient) func(io.Reader) error {
-	return func(fileReader io.Reader) error {
-		// Read from fileReader into a buffer.
-		// We currently buffer all contents and send them to blobServiceClient at once,
-		// but that's about to change.
-		contents, err := io.ReadAll(fileReader)
-		if err != nil {
-			return fmt.Errorf("unable to read all contents from file reader: %w", err)
-		}
-
-		log := log.WithField("blob_size", len(contents))
-
-		log.Infof("about to upload blob")
+	return func(blobReader io.Reader) error {
+		// Ensure the blobReader is buffered to at least the chunk size.
+		blobReader = bufio.NewReaderSize(blobReader, chunkSize)
 
 		putter, err := blobServiceClient.Put(ctx)
 		if err != nil {
 			// return error to the importer
 			return fmt.Errorf("error from blob service: %w", err)
 		}
-		err = putter.Send(&storev1pb.BlobChunk{
-			Data: contents,
-		})
-		if err != nil {
-			return fmt.Errorf("putting blob chunk: %w", err)
+
+		blobSize := 0
+		chunk := make([]byte, chunkSize)
+
+		for {
+			n, err := blobReader.Read(chunk)
+			if err != nil && !errors.Is(err, io.EOF) {
+				return fmt.Errorf("unable to read from blobreader: %w", err)
+			}
+
+			if n != 0 {
+				log.WithField("chunk_size", n).Debug("sending chunk")
+				blobSize += n
+
+				// send the blob chunk to the server. The err is only valid in the inner scope
+				if err := putter.Send(&storev1pb.BlobChunk{
+					Data: chunk[:n],
+				}); err != nil {
+					return fmt.Errorf("sending blob chunk: %w", err)
+				}
+			}
+
+			// if our read from blobReader returned an EOF, we're done reading
+			if errors.Is(err, io.EOF) {
+				break
+			}
+
 		}
+
 		resp, err := putter.CloseAndRecv()
 		if err != nil {
 			return fmt.Errorf("close blob putter: %w", err)
 		}
 
-		log.WithField("digest", base64.StdEncoding.EncodeToString(resp.GetDigest())).Info("uploaded blob")
+		log.WithFields(log.Fields{
+			"blob_digest": base64.StdEncoding.EncodeToString(resp.GetDigest()),
+			"blob_size":   blobSize,
+		}).Info("uploaded blob")
 
 		return nil
 	}