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)
 	})

docs/content/googlecloudstorage.md

@@ -215,6 +215,24 @@ This remote supports `--fast-list` which allows you to use fewer
 transactions in exchange for more memory. See the [rclone
 docs](/docs/#fast-list) for more details.
 
+### Custom upload headers ###
+
+You can set custom upload headers with the `--header-upload`
+flag. Google Cloud Storage supports the headers as described in the
+[working with metadata documentation](https://cloud.google.com/storage/docs/gsutil/addlhelp/WorkingWithObjectMetadata)
+
+- Cache-Control
+- Content-Disposition
+- Content-Encoding
+- Content-Language
+- Content-Type
+- X-Goog-Meta-
+
+Eg `--header-upload "Content-Type text/potato"`
+
+Note that the last of these is for setting custom metadata in the form
+`--header-upload "x-goog-meta-key: value"`
+
 ### Modified time ###
 
 Google google cloud storage stores md5sums natively and rclone stores