chore(gensupport): add idempotency header (#1916)

This header will allow GCS object uploads to be idempotent by
default. For other products, it will have no effect.


---------

Co-authored-by: Noah Dietz <noahdietz@users.noreply.github.com>

internal/gensupport/resumable.go

@@ -43,8 +43,8 @@ type ResumableUpload struct {
 	// retries should happen.
 	ChunkRetryDeadline time.Duration
 
-	// Track current request invocation ID and attempt count for retry metric
-	// headers.
+	// Track current request invocation ID and attempt count for retry metrics
+	// and idempotency headers.
 	invocationID string
 	attempts     int
 }
@@ -81,10 +81,15 @@ func (rx *ResumableUpload) doUploadRequest(ctx context.Context, data io.Reader,
 	req.Header.Set("Content-Type", rx.MediaType)
 	req.Header.Set("User-Agent", rx.UserAgent)
 
+	// TODO(b/274504690): Consider dropping gccl-invocation-id key since it
+	// duplicates the X-Goog-Gcs-Idempotency-Token header (added in v0.115.0).
 	baseXGoogHeader := "gl-go/" + GoVersion() + " gdcl/" + internal.Version
 	invocationHeader := fmt.Sprintf("gccl-invocation-id/%s gccl-attempt-count/%d", rx.invocationID, rx.attempts)
 	req.Header.Set("X-Goog-Api-Client", strings.Join([]string{baseXGoogHeader, invocationHeader}, " "))
 
+	// Set idempotency token header which is used by GCS uploads.
+	req.Header.Set("X-Goog-Gcs-Idempotency-Token", rx.invocationID)
+
 	// Google's upload endpoint uses status code 308 for a
 	// different purpose than the "308 Permanent Redirect"
 	// since-standardized in RFC 7238. Because of the conflict in

internal/gensupport/send.go

@@ -138,9 +138,14 @@ func sendAndRetry(ctx context.Context, client *http.Client, req *http.Request, r
 			}
 			return resp, ctx.Err()
 		}
+
+		// Set retry metrics and idempotency headers for GCS.
+		// TODO(b/274504690): Consider dropping gccl-invocation-id key since it
+		// duplicates the X-Goog-Gcs-Idempotency-Token header (added in v0.115.0).
 		invocationHeader := fmt.Sprintf("gccl-invocation-id/%s gccl-attempt-count/%d", invocationID, attempts)
 		xGoogHeader := strings.Join([]string{invocationHeader, baseXGoogHeader}, " ")
 		req.Header.Set("X-Goog-Api-Client", xGoogHeader)
+		req.Header.Set("X-Goog-Gcs-Idempotency-Token", invocationID)
 
 		resp, err = client.Do(req.WithContext(ctx))