gcs: fix --header-upload - #59

Before this code we were settig the headers on the PUT request. However this isn't where GCS needs them.

After this fix we set the headers in the object upload request itself.

This means that we only support a limited range of headers

- Cache-Control
- Content-Disposition
- Content-Encoding
- Content-Language
- Content-Type
- X-Goog-Meta-

Note for the last of those are for setting custom metadata in the form
"X-Goog-Meta-Key: value".

backend/googlecloudstorage/googlecloudstorage.go

@@ -1066,13 +1066,39 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		ContentType: fs.MimeType(ctx, src),
 		Metadata:    metadataFromModTime(modTime),
 	}
+	// Apply upload options
+	for _, option := range options {
+		key, value := option.Header()
+		lowerKey := strings.ToLower(key)
+		switch lowerKey {
+		case "":
+			// ignore
+		case "cache-control":
+			object.CacheControl = value
+		case "content-disposition":
+			object.ContentDisposition = value
+		case "content-encoding":
+			object.ContentEncoding = value
+		case "content-language":
+			object.ContentLanguage = value
+		case "content-type":
+			object.ContentType = value
+		default:
+			const googMetaPrefix = "x-goog-meta-"
+			if strings.HasPrefix(lowerKey, googMetaPrefix) {
+				metaKey := lowerKey[len(googMetaPrefix):]
+				object.Metadata[metaKey] = value
+			} else {
+				fs.Errorf(o, "Don't know how to set key %q on upload", key)
+			}
+		}
+	}
 	var newObject *storage.Object
 	err = o.fs.pacer.CallNoRetry(func() (bool, error) {
 		insertObject := o.fs.svc.Objects.Insert(bucket, &object).Media(in, googleapi.ContentType("")).Name(object.Name)
 		if !o.fs.opt.BucketPolicyOnly {
 			insertObject.PredefinedAcl(o.fs.opt.ObjectACL)
 		}
-		fs.OpenOptionAddHTTPHeaders(insertObject.Header(), options)
 		newObject, err = insertObject.Context(ctx).Do()
 		return shouldRetry(err)
 	})