XML API overview

This document gives an overview of the Cloud Storage XML API and is intended for software developers. It assumes that you are familiar with RESTful services and web programming and that you are comfortable creating applications that operate through HTTP requests. If this does not describe you, consider one of the following alternatives:

• If you are just starting out with Cloud Storage, you should first try either the Cloud Console Quickstart or the gsutil Quickstart. These tutorials demonstrate the basics of using Cloud Storage without the need to use the API directly.

• If you work in certain programming languages, you can use the Cloud Storage Client Libraries.

• If you are a mobile or web app developer, you can use the Firebase SDKs for Cloud Storage.

• If you are not a software developer and want to store your personal data in the cloud and share it with others, you can use Google Drive.

Overview

The Cloud Storage XML API is a RESTful interface that lets you manage Cloud Storage data in a programmatic way. As a RESTful API, it relies on method information and scoping information to define the operations to perform:

• Method information

  You specify the method information with standard HTTP methods, such as DELETE, GET, HEAD, and PUT.

• Scoping information

  You specify the scoping information with a publicly-accessible endpoint (URI) and various scoping parameters. For the XML API, the primary scoping parameters are the bucket and object names. You can further scope your operations by using HTTP headers and query string parameters.

You use HTTP methods to perform operations on the resource you specify in the scope. For a list of operations available in the XML API, see XML API Request Methods.

Access to Cloud Storage through the XML API is useful when you are using tools and libraries that must work across different storage providers, or when you are migrating from another storage provider to Cloud Storage. In the latter case, you only need to make a few simple changes to your existing tools and libraries to begin sending requests to Cloud Storage. For more information about migrating to Cloud Storage, see Migrating from Amazon S3 to Google Cloud Storage.

Requests

Note: We recommend that you use HTTPS when reading or writing data to Cloud Storage so that your data is encrypted during transfer. Cloud Storage automatically encrypts your data before it is written to disk. For more information, see Encryption.

The Cloud Storage XML API provides a web interface for making HTTP requests and handling HTTP responses. Each request implements a standard HTTP method. Along with these methods, you can use various HTTP request headers.

Authentication

All requests to Cloud Storage must be authenticated, with the exception of requests made to anonymously accessible objects or buckets. For detailed information about how you set the Authorization headers for Cloud Storage requests, see Authentication.

Endpoints

Important: If you intend to serve content through a browser, note that the XML API serves content from the same origin as the request endpoint. If you need to serve content from a unique origin, consider using the JSON API or Authenticated browser downloads.

Most Cloud Storage XML API requests use the following URI for accessing buckets and objects:

storage.googleapis.com

You can scope this further by adding a bucket and object to the URI. The resulting URL can take two forms:

BUCKET_NAME.storage.googleapis.com/OBJECT_NAME
storage.googleapis.com/BUCKET_NAME/OBJECT_NAME

You can use the Cloud Storage URI with unsecured requests (HTTP) and secured requests (HTTPS) that use secure sockets layer (SSL) encryption.

For additional endpoints, such as dedicated upload and download endpoints for the XML API, see Request Endpoints.

Headers and query string parameters

The Cloud Storage XML API supports HTTP/1.1 request headers. It also supports several extension (custom) request headers, which have an x-goog- prefix. Request header requirements vary depending on the kind of request you're making. Some frequently used request headers include:

Request Header	Description	Usage
Authorization	The authentication string for requests.	Required for all authenticated requests.
Content-Length	The size of the request body (excluding headers) in bytes.	Required for all PUT and POST requests, except chunked transfers.
Content-Type	The MIME type of the request body, such as application/xml or text/html.	Recommended for requests that contain an entity body.
Date	The date and time of the request.	Required for all requests.
Host	The URI for the request.	Required for all requests.
x-goog-project-id	The ID of the project you want to use.	Required for creating buckets or listing buckets except when you are using the XML API for interoperability, such as for compatibility with Amazon S3. For more information, see Migrating from Amazon S3 to Google Cloud Storage.

The Cloud Storage XML API also supports a variety of query string parameters, which you can use to scope your requests. Append query string parameters to the HTTP path portion of the request with the following syntax:

PATH_TO_OBJECT/?PARAMETER=VALUE&PARAMETER=VALUE...

For a complete list of XML API headers and query string parameters, see HTTP headers and query string parameters.

Example request

A typical authenticated Cloud Storage request is shown in the following example. This request retrieves a list of objects that are stored in a bucket named travel-maps. The request limits the list of objects to only those objects that have the prefix /europe/france.

GET /?prefix=/europe/france/ HTTP/1.1
Host: travel-maps.storage.googleapis.com
Date: Wed, 17 Feb 2010 15:31:56 -0800
Content-Length: 0
Authorization: Bearer ya29.AHES6ZRVmB7fkLtd1XTmq6mo0S1wqZZi3-Lh_s-6Uw7p8vtgSwg

Responses

The Cloud Storage XML API returns standard HTTP/1.1 response headers and several extension (custom) response headers. The response headers vary according to the operation you perform. Some frequently used response headers include:

Response Header	Description
Cache-Control	The cache control setting for the response.
Content-Length	The size of the response body (excluding headers) in bytes.
Content-Type	The MIME type of the response body, such as application/xml or text/html.
Date	The date and time of the response.
ETag	An HTTP 1.1 entity tag, which you can use to determine

whether an object has changed.

Responses can also include a status code. Cloud Storage uses the standard HTTP/1.1 status codes. An error response includes an XML document in the response body, which contains information about the error conditions. For a list of status codes used by the XML API, see HTTP Status and Error Codes.

A typical Cloud Storage response is shown in the following example. This example is a response to a request for listing a bucket's contents. The bucket name is travel-maps and the request is scoped so that only objects with the prefix /europe/france/ are returned in the list.

HTTP/1.1 200 OK
Content-Length: 4061
Content-Type: application/xml
Date: Wed, 17 Feb 2010 23:31:57 GMT
Cache-Control: private, max-age=0

<?xml version='1.0' encoding='utf-8'?>
<ListBucketResult xmlns='http://doc.storage.googleapis.com/2010-03-01'>
  <Name>travel-maps</Name>
  <Prefix>/europe/france/</Prefix>
  <Marker></Marker>
  <IsTruncated>false</IsTruncated>
  <Contents>
    <Key>europe/france/cannes.jpg</Key>
    <LastModified>2010-02-17T22:11:12.487Z</LastModified>
    <ETag>"53fc311c15eda0a031809982ccf92aac"</ETag>
    <Size>5061631</Size>
    <StorageClass>STANDARD</StorageClass>
    <Owner>
      <ID>84fac329bceSAMPLE777d5d22b8SAMPLE77d85ac2SAMPLE2dfcf7c4adf34da46</ID>
      <DisplayName></DisplayName>
    </Owner>
  </Contents>
  <Contents>
    <Key>europe/france/paris.jpg</Key>
    <LastModified>2010-02-17T22:09:57.457Z</LastModified>
    <ETag>"53fc311c15eda0a031809982ccf92aac"</ETag>
    <Size>5061631</Size>
    <StorageClass>STANDARD</StorageClass>
    <Owner>
      <ID>84fac329bceSAMPLE777d5d22b8SAMPLE77d85ac2SAMPLE2dfcf7c4adf34da46</ID>
      <DisplayName></DisplayName>
    </Owner>
  </Contents>
</ListBucketResult>