POST Object

Uploads objects by using HTML forms. For tips on uploading to Google Cloud Storage, see best practices.

Query string parameters

This request does not include query string parameters.

Form fields

Field Description Required
acl The predefined ACL that you want to apply to the object that is being uploaded. If you do not specify this field the bucket's default ACL is applied. No
bucket The name of the bucket that you want to upload to. Alternatively, you can include the bucket name in the key field or in the URI (for example, storage.googleapis.com/<bucket>). No
Cache-Control The cache control for the object. You can only set cache control for an object that is accessible to all users. For instance, an object's ACL must be public-read or public-read-write to be able to set the cache-control. No
Content-Disposition Specifies how the object data should be transmitted. For example, a Content-Disposition value of inline means that the object should be displayed immediately. No
Content-Encoding The compression algorithm for the object, such as gzip. No
Content-Length Specifies that uploaded files can only be between a certain size range in bytes. You can specify this condition using the following syntax: ["content-length-range", <min_range>, <max_range>]. No
Content-Type The MIME type of the file you are uploading via the form. If you do not specify a content type, the Cloud Storage system defaults to [`application/octet-stream`](https://tools.ietf.org/html/rfc2046#section-4.5.1) when it serves the content. No
Expires An ISO8601 timestamp that specifies the date and time before an object is considered stale by the browser. No
file The file you are uploading. Must be the last field in the form. You can upload only one object per request. Yes
GoogleAccessId The Cloud Storage email form of the client ID, as described in the section on Signed URLs. Only if you specify a policy
key The name of the object that you are uploading. If you specify the object name without the bucket name, you must append the bucket name to the URI (for example, storage.googleapis.com/<bucket>). If you specify the bucket name and object name (for example, bucket/object), you must specify only the URI (for example, storage.googleapis.com). You can also use the ${filename} variable if a user is providing a file name. Also, if you are using a bucket name that is a CNAME redirect, be sure that the bucket name is specified only once in your request. Yes
policy

The security policy that describes what can and cannot be uploaded in the form. The policy document must be Base64 encoded. See the policy document section for more information.

*If you do not provide a security policy, requests are considered to be anonymous and will only work with buckets that have granted WRITE or FULL_CONTROL permission to anonymous users.

No*
signature The signature of the Base64-encoded policy document you are including in the request. Your signature must be signed with the secret key associated with the GoogleAccessID you specified. (This is the email form of the client ID, as described in the section on Signed URLs). Only if you specify a policy
success_action_redirect A URL that users are redirected to when an upload is successful. If you do not provide a URL, Cloud Storage responds with the status code that you specified in success_action_status. No
success_action_status The status code that you want Cloud Storage to respond with when an upload is successful. The default is 204, but you can change this to 200 or 201. If you choose 200 or 204, Cloud Storage returns an empty document with those status codes. If you choose 201, Cloud Storage returns an XML document with the elements that are described in Response Body Elements. Note: The Adobe Flash player might not handle responses with an empty document body. You should use status code 201 if this is the case. No
x-goog-meta-* A field for custom metadata. You can use this to specify any additional metadata that is not provided by the other form fields. For example, x-goog-meta-reviewer: jane or x-goog-meta-project-manager: john is custom metadata. No

Response body elements

The following response body elements are returned in an XML document only if you set success_action_redirect to 201.

Element Description
Bucket Bucket in which the object was stored.
ETag HTTP 1.1 entity tag for the object.
Key The object's name.
Location The URI for the object.

Usage and examples

The form must be UTF-8 encoded. You can specify form encoding in the form's HTML head tag or by using the Content-Type request header.

Your form tag must specify the following three items:

  • An action.

    The action attribute specifies the bucket that you want the form to upload an object to.

  • A method.

    The method attribute specifies the method that you are using to submit the form. It must be post.

  • An enclosure type.

    The enctype attribute specifies the enclosure type you are using and must always be multipart/form-data.

Policy Document

A policy document defines what a user (with or without a Google account) can upload with a form POST, and provides authorization to ensure that the form can upload files into the target bucket. You can use policy documents to allow visitors to a website to upload files to Google Cloud Storage. You do not need to include a policy document in a form if your form uploads files to a bucket that grants anonymous users WRITE permission. For more information about configuring access to buckets and objects in Cloud Storage, see Access Control.

A policy document is constructed in JavaScript Object Notation (JSON) and contains the following sections:

Entry Description
expiration The expiration time of the policy document. An expired policy document will cause the HTML form to break. This must be in ISO8601 format.
conditions An array of conditions that every upload must satisfy.

The conditions section must include a condition statement for every field in your HTML form except the GoogleAccessId (the email form of the client ID, as described in the section on Signed URLs), signature, file, and policy fields. It is possible to express three types of conditions in your conditions section:

  • Exact Matching

    Performs exact matching for a field. The value of the input field's value must match the specified expected value. You can specify this condition using either of the following syntax styles:

    {"<field>" : "<value>"}
    ["eq", "$<field>", "<value>"]

    All valid policy document fields specified in the table below can use exact matching.

  • Starts With

    If a value of a field must start with a certain value, you can use the starts-with condition. You can specify this condition using the following syntax:

    ["starts-with", "$<field>", "<value>"]

    All valid policy document fields specified in the table below can use the starts-with condition.

  • Content Length Range

    Specifies that uploaded files can only be between a certain size range in bytes. You can specify this condition using the following syntax:

    ["content-length-range", <min_range>, <max_range>]

You can express the following fields in the conditions section, using exact matching, content-length-range or starts- with conditions:

Element Description
acl ACL values for the object from possible predefined ACLs.
bucket The bucket that will hold the object.
cache-control Cache-control for the object.
content-disposition Specifies how the object data should be transmitted.
content-encoding The compression algorithm for the object.
content-length The byte length of the request body.
content-type The MIME type of the file that is being uploaded.
expires An ISO8601 timestamp that specifies the data and time before an object is considered stale by the browser.
key The name of the object you are uploading.
success_action_redirect The URL the user's client is redirected to when the upload is successful.
success_action_status The status code that you want Cloud Storage to respond with when an upload is successful.
x-goog-meta-* An extension header that can be used to store additional metadata that is not provided by the other fields.

The following is an example of a typical policy document:

{"expiration": "2010-06-16T11:11:11Z",
 "conditions": [
  ["starts-with", "$key", "" ],
  {"acl": "bucket-owner-read" },
  {"bucket": "travel-maps"},
  {"success_action_redirect": "http://www.example.com/success_notification.html" },
  ["eq", "$Content-Type", "image/jpeg" ],
  ["content-length-range", 0, 1000000]
  ]
}

The previous policy document defines the following conditions:

  • The form expires on June 16, 2010 at 11:11:11 UTC.
  • The file name can start with any valid character. To specify this, you use the starts-with condition modifier and the empty string ("").
  • The bucket-owner-read ACL is applied to the file.
  • If the upload is successful, the user is redirected to http://www.example.com/success_notification.html.
  • The form allows only images to be uploaded.
  • A user cannot upload a file larger than 1 MB.

If you are including a policy document in your form, you must include a signature in the signature form field. The following procedure shows you how to create the signature:

  1. Create a policy document for your form and make sure it is UTF-8 encoded.
  2. Encode the policy document as a Base64 representation.
  3. Sign your policy document using RSA with SHA-256 using the secret key provided to you in the Google Cloud Platform Console. If you are using interoperable access keys, sign instead using SHA-1.
  4. Encode the message digest as a Base64 representation.

The following pseudocode combines the steps above to create your signature:

Policy = Base-64-Encoding-Of(PolicyDocument)
MessageDigest = SHA256withRSA(SecretKey, Policy)
Signature = Base64-Encoding-Of(MessageDigest)

Below is the Python implementation of the code to create your signature. In the code, key.pem is your service account PKCS12 key converted into PKCS1 (PEM) format.

from base64 import b64encode
from M2Crypto import EVP
def Sign(pem_key, message):
    assert pem_key
    key = EVP.load_key_string(pem_key)
    key.reset_context(md='sha256')
    key.sign_init()
    key.sign_update(str(message))
    return key.sign_final()

SecretKey = open('key.pem', 'r').read()
Policy = b64encode(open('policy.txt', 'r').read())
Signature = b64encode(Sign(SecretKey, Policy))
print Policy
print
print Signature

The following is an example HTML using the policy document above:

<form action="http://travel-maps.storage.googleapis.com" method="post" enctype="multipart/form-data">
<input type="text" name="key" value="">
<input type="hidden" name="bucket" value="travel-maps">
<input type="hidden" name="Content-Type" value="image/jpeg">
<input type="hidden" name="GoogleAccessId" value="1234567890123@developer.gserviceaccount.com">
<input type="hidden" name="acl" value="bucket-owner-read">
<input type="hidden" name="success_action_redirect" value="http://www.example.com/success_notification.html">
<input type="hidden" name="policy" value="eyJleHBpcmF0aW9uIjogIjIwMTAtMDYtMTZUMTE6MTE6MTFaIiwNCiAiY29uZGl0aW9ucyI6IFsNCiAgWyJzdGFydHMtd2l0aCIsICJrZXkiLCAiIiBdLA0KICB7ImFjbCI6ICJidWNrZXQtb3duZXItcmVhZCIgfSwNCiAgeyJidWNrZXQiOiAidHJhdmVsLW1hcHMifSwNCiAgeyJzdWNjZXNzX2FjdGlvbl9yZWRpcmVjdCI6ICJodHRwOi8vd3d3LmV4YW1wbGUuY29tL3N1Y2Nlc3Nfbm90aWZpY2F0aW9uLmh0bWwiIH0sDQogIFsiZXEiLCAiQ29udGVudC1UeXBlIiwgImltYWdlL2pwZWciIF0sDQogIFsiY29udGVudC1sZW5ndGgtcmFuZ2UiLCAwLCAxMDAwMDAwXQ0KICBdDQp9">
<input type="hidden" name="signature" value="BSAMPLEaASAMPLE6SAMPLE+SAMPPLEqSAMPLEPSAMPLE+SAMPLEgSAMPLEzCPlgWREeF7oPGowkeKk7J4WApzkzxERdOQmAdrvshKSzUHg8Jqp1lw9tbiJfE2ExdOOIoJVmGLoDeAGnfzCd4fTsWcLbal9sFpqXsQI8IQi1493mw=">

<input name="file" type="file">
<input type="submit" value="Upload">
</form>

As a best practice you should use the Expect: 100-continue header with POST requests. This allows you to verify that the server will handle the request before you send the object. If you receive a status code 100 Continue you should proceed with the request. If you receive a status code 417 Expectation Failed then you should not send the object.

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