Move uploader reader to its own goroutine

backend/media/uploader.go

@@ -30,7 +30,7 @@ type readResult struct {
 
 const (
 	targetPartSizeBytes = 5 * 1024 * 1024 // 5MB
-	bufferOverflowSize  = 16_384          // 16Kb
+	readBufferSizeBytes = 32_768          // 32Kb
 )
 
 func newMultipartUploader(s3Client S3Client) *multipartUploader {
@@ -64,7 +64,13 @@ func (u *multipartUploader) Upload(ctx context.Context, r io.Reader, bucket, key
 			UploadId: output.UploadId,
 		}
 
-		_, abortErr := u.s3.AbortMultipartUpload(ctx, &input)
+		// if the context was cancelled, just use the background context.
+		ctxToUse := ctx
+		if ctxToUse.Err() != nil {
+			ctxToUse = context.Background()
+		}
+
+		_, abortErr := u.s3.AbortMultipartUpload(ctxToUse, &input)
 		if abortErr != nil {
 			log.Printf("error aborting upload: %v", abortErr)
 		} else {
@@ -108,51 +114,32 @@ func (u *multipartUploader) Upload(ctx context.Context, r io.Reader, bucket, key
 
 	wgDone := make(chan struct{})
 	var wg sync.WaitGroup
-	wg.Add(1) // done when the reader returns EOF
+	wg.Add(1) // done when the reader goroutine returns
 	go func() {
 		wg.Wait()
 		wgDone <- struct{}{}
 	}()
 
-	readChan := make(chan readResult)
-	buf := make([]byte, 32_768)
-	go func() {
-		for {
-			var rr readResult
-			rr.n, rr.err = r.Read(buf)
-			readChan <- rr
+	readChan := make(chan error, 1)
 
-			if rr.err != nil {
+	go func() {
+		defer wg.Done()
+
+		var closing bool
+		currPart := bytes.NewBuffer(make([]byte, 0, targetPartSizeBytes+readBufferSizeBytes))
+		partNum := int32(1)
+		buf := make([]byte, readBufferSizeBytes)
+
+		for {
+			n, readErr := r.Read(buf)
+			if readErr == io.EOF {
+				closing = true
+			} else if readErr != nil {
+				readChan <- readErr
 				return
 			}
-		}
-	}()
 
-	var closing bool
-	currPart := bytes.NewBuffer(make([]byte, 0, targetPartSizeBytes+bufferOverflowSize))
-	partNum := int32(1)
-	results := make([]uploadResult, 0, 64)
-
-outer:
-	for {
-		select {
-		case uploadResult := <-uploadResultChan:
-			results = append(results, uploadResult)
-		case uploadErr := <-uploadErrorChan:
-			return 0, fmt.Errorf("error while uploading part: %v", uploadErr)
-		case <-wgDone:
-			break outer
-		case <-ctx.Done():
-			return 0, ctx.Err()
-		case readResult := <-readChan:
-			if readResult.err == io.EOF {
-				wg.Done()
-				closing = true
-			} else if readResult.err != nil {
-				return 0, fmt.Errorf("reader error: %v", readResult.err)
-			}
-
-			_, _ = currPart.Write(buf[:readResult.n])
+			_, _ = currPart.Write(buf[:n])
 			if closing || currPart.Len() >= targetPartSizeBytes {
 				part := make([]byte, currPart.Len())
 				copy(part, currPart.Bytes())
@@ -162,6 +149,30 @@ outer:
 				go uploadPart(&wg, part, partNum)
 				partNum++
 			}
+
+			if closing {
+				return
+			}
+		}
+	}()
+
+	results := make([]uploadResult, 0, 64)
+
+outer:
+	for {
+		select {
+		case readErr := <-readChan:
+			if readErr != io.EOF {
+				return 0, fmt.Errorf("reader error: %v", readErr)
+			}
+		case uploadResult := <-uploadResultChan:
+			results = append(results, uploadResult)
+		case uploadErr := <-uploadErrorChan:
+			return 0, fmt.Errorf("error while uploading part: %v", uploadErr)
+		case <-ctx.Done():
+			return 0, ctx.Err()
+		case <-wgDone:
+			break outer
 		}
 	}