Uploads an object to a bucket by using an HTML form.
Usage notes
To upload an object to a bucket by using an HTML form, you must have the
oss:PutObject
permission. For more information, see Common examples of RAM policies.The size of the object that is uploaded by calling the PostObject operation cannot exceed 5 GB.
To initiate a PostObject request to a bucket, you must have write permissions on the bucket. If the access control list (ACL) of the bucket to which you want to initiate a PostObject request is public-read-write, you do not need to sign the PostObject request. Otherwise, Object Storage Service (OSS) verifies the signature information contained in the request.
Unlike the PutObject operation, the PostObject operation calculates the signature based on the AccessKey secret and policy form field. The calculated signature string is used as the value of the Signature form field. OSS checks this value to verify the validity of the signature.
The URL of the submitted form is the domain name of the bucket. You do not need to specify the object that you want to upload to the bucket in the URL. The request line is in the format of
POST / HTTP/1.1
instead ofPOST /ObjectName HTTP/1.1
.OSS does not check the signature information that is contained in headers or URLs in PostObject requests.
Versioning
If you initiate a PostObject request to a versioning-enabled bucket, OSS generates a unique version ID for the uploaded object and returns the version ID as the value of the x-oss-version-id header in the response.
If you initiate a PostObject request to a versioning-suspended bucket, OSS generates a version ID of null for the uploaded object and returns the version ID as the value of the x-oss-version-id header in the response. An object can have only one version whose ID is null.
Request syntax
POST / HTTP/1.1
Host: BucketName.oss-cn-hangzhou.aliyuncs.com
User-Agent: browser_data
Content-Length: ContentLength
Content-Type: multipart/form-data; boundary=9431149156168
--9431149156168
Content-Disposition: form-data; name="key"
key
--9431149156168
Content-Disposition: form-data; name="success_action_redirect"
success_redirect
--9431149156168
Content-Disposition: form-data; name="Content-Disposition"
attachment;filename=oss_download.jpg
--9431149156168
Content-Disposition: form-data; name="x-oss-meta-uuid"
myuuid
--9431149156168
Content-Disposition: form-data; name="x-oss-meta-tag"
mytag
--9431149156168
Content-Disposition: form-data; name="OSSAccessKeyId"
access-key-id
--9431149156168
Content-Disposition: form-data; name="policy"
encoded_policy
--9431149156168
Content-Disposition: form-data; name="Signature"
signature
--9431149156168
Content-Disposition: form-data; name="file"; filename="MyFilename.jpg"
Content-Type: image/jpeg
file_content
--9431149156168
Content-Disposition: form-data; name="submit"
Upload to OSS
--9431149156168--
Request headers
The message body of a PostObject request is encoded in the multipart/form-data format. In the PostObject operation, the parameters are passed as form fields in the request message body, whereas the parameters are passed as HTTP request headers in the PutObject operation.
You cannot add tags to objects by passing the x-oss-tagging request header during the PostObject operation. You can call the PutObjectTagging operation to add tags to objects after the PostObject operation is complete.
Header | Type | Required | Description |
Content-Type | String | No | The type of the object that you want to upload and the encoding format of the web page. Browsers determine how to read and encode the object based on the value of the header. The form submitted in the PostObject operation must be encoded in the In this format, boundary is a boundary string that is randomly generated by the form. You do not need to specify a boundary string. If you use an OSS SDK to create a form, the SDK also generates a random boundary string. |
x-oss-object-acl | String | No | The ACL of the object that you want to upload. If you specify x-oss-object-acl in the request header and the form field, the ACL that is specified in the form field takes precedence over the ACL that is specified in the request header. Valid values:
For more information about ACLs, see Object ACL. |
For more information about the common request headers contained in PostObject requests, such as Host and Date, see Common HTTP headers.
Request elements
The last form field must be file. No particular order is required for other form fields.
The key of a form field cannot exceed 8 KB, and the value of a form field cannot exceed 2 MB.
Element | Type | Required | Description |
Cache-Control | String | No | The caching behavior of the web page when the object is downloaded. For more information, see RFC 2616. This element is empty by default. |
Content-Disposition | String | No | The name of the object when the object is downloaded. For more information, see RFC 2616. This element is empty by default. |
Content-Encoding | String | No | The content encoding format of the object when the object is downloaded. For more information, see RFC 2616. This element is empty by default. |
Expires | String | No | The time when the cached data expires. For more information, see RFC 2616. This element is empty by default. |
OSSAccessKeyId | String | Conditional | The AccessKey ID of the account that owns the bucket. This element is empty by default. Condition: This form field is required if the bucket ACL is not public-read-write or the policy or Signature form field is specified in the request. |
policy | String | Conditional | The validity of the form fields in the request. A request that does not contain the policy form field is considered as an anonymous request and can be used only to access buckets whose ACLs are public-read-write. This element is empty by default. Condition: This form field is required if the bucket ACL is not public-read-write or the OSSAccessKeyId or Signature form field is specified in the request. Important The form and the policy form field must be UTF-8-encoded. The policy form field must also be Base64-encoded. |
Signature | String | Conditional | The signature information that is calculated based on the AccessKey secret and the policy form field. OSS checks the signature information to verify the validity of the PostObject request. For more information, see PostObject. This element is empty by default. Condition: This form field is required if the bucket ACL is not public-read-write or the OSSAccessKeyId or policy form field is specified in the request. Note Form fields are not case-sensitive, but their values are case-sensitive. |
x-oss-server-side-encryption-key-id | String | No | The ID of the customer master key (CMK) that is managed by Key Management Service (KMS). You can configure this element only when x-oss-server-side-encryption is set to KMS. |
x-oss-content-type | String | No | You can add the x-oss-content-type form field to the message body of a PostObject request to specify the content type of the object that you want to upload. The content type specified by the x-oss-content-type form field takes precedence over the content type specified by the file form field that is automatically generated by browsers. The content types are prioritized in the following order: x-oss-content-type form field > Content-Type specified in the file form field that is automatically generated by browsers. This element is empty by default. |
x-oss-forbid-overwrite | String | No | Specifies whether the PostObject operation overwrites the existing object that has the same name. When versioning is enabled or suspended for the bucket to which you want to upload the object, x-oss-forbid-overwrite does not take effect. In this case, the object that is uploaded by calling the PostObject operation overwrites the existing object that has the same name.
If you specify x-oss-forbid-overwrite, the queries per second (QPS) performance of OSS may be degraded. If you want to use x-oss-forbid-overwrite to perform a large number of operations (QPS greater than 1,000), contact technical support. |
x-oss-object-acl | String | No | The ACL of the object that you want to upload. You can specify the ACL of the object that you want to upload in the request header and the form field. If you specify x-oss-object-acl in the request header and the form field, the ACL that is specified in the form field takes precedence over the ACL that is specified in the request header. Valid values:
For more information about ACLs, see Object ACL. |
x-oss-storage-class | String | No | The storage class of the object that you want to upload. If you specify this form field when you upload an object, the storage class of the uploaded object is the specified value regardless of the storage class of the bucket to which the object is uploaded. For example, if you set x-oss-storage-class to Standard when you upload an object to an Infrequent Access (IA) bucket, the object is stored as a Standard object. Valid values:
For more information about storage classes, see Overview. |
key | String | Yes | The name of the object that you want to upload. You do not need to encode the object name. If the object name contains a path such as This element is empty by default. |
success_action_redirect | String | No | The URL to which the client is redirected after the object is uploaded. If this form field is not specified, the returned result is specified by success_action_status. If the upload fails, OSS returns an error code, and the client is not redirected to a URL. This element is empty by default. |
success_action_status | String | No | The HTTP status code that is returned to the client when the success_action_redirect form field is not specified and the object is uploaded. Valid values: 200, 201, and 204 (default).
|
x-oss-meta-* | String | No | The user metadata that you specify for the object. This element is empty by default. If the request contains a form field that contains the x-oss-meta- prefix, the form field is considered as the user metadata of the object. Example: Note An object can have multiple form fields whose names contain the x-oss-meta- prefix. However, the total size of all user metadata of the object cannot exceed 8 KB. |
x-oss-security-token | String | No | The security token for temporary access authorization. If you obtain temporary access credentials from Security Token Service (STS) and use the temporary access credentials for the request, you must set this form field to the security token and set OSSAccessKeyId to the value of the AccessKey ID in the temporary access credentials. You can calculate the signature for a request that uses a temporary AccessKey ID in the same manner that you calculate the signature for a request that uses an AccessKey ID. This element is empty by default. For more information, see Use temporary credentials provided by STS to access OSS in OSS Developer Guide. You can call the AssumeRole operation or use STS SDKs for various programming languages to obtain temporary access credentials. For more information, see STS SDK overview. |
file | String | Yes | The file or text content. You do not need to encode the content. Browsers automatically add the Content-Type form field based on the file type and overwrite the content type specified in the Content-Type header. You can upload only one object in a PostObject request. This element is empty by default. Important The last form field must be file. |
Response headers
Header | Type | Description |
x-oss-server-side-encryption | String | If x-oss-server-side-encryption is specified in the request, the response contains this header to indicate the algorithm that is used to encrypt the object on the server side. |
For more information about the common response headers contained in the response to a PostObject request, see Common HTTP headers.
Response elements
Header | Type | Description |
PostResponse | Container | The container in which the result of the PostObject request is stored. Child nodes: Bucket, ETag, Key, and Location |
Bucket | String | The name of the bucket. Parent nodes: PostResponse |
ETag | String | The entity tag (ETag) that is created when the object is uploaded. If an object is created by calling the PostObject operation, the ETag value is not the MD5 hash of the object content but a unique value calculated based on a specific rule. The ETag value of an object can be used to check whether the object content is modified. Parent nodes: PostResponse |
Location | String | The URL that is used to access the uploaded object. Parent nodes: PostResponse |
Examples
Sample requests
POST / HTTP/1.1 Host: oss-example.oss-cn-hangzhou.aliyuncs.com Content-Length: 344606 Content-Type: multipart/form-data; boundary=9431149156168 --9431149156168 Content-Disposition: form-data; name="key" /user/a/objectName.txt --9431149156168 Content-Disposition: form-data; name="success_action_status" 200 --9431149156168 Content-Disposition: form-data; name="Content-Disposition" content_disposition --9431149156168 Content-Disposition: form-data; name="x-oss-meta-uuid" uuid --9431149156168 Content-Disposition: form-data; name="x-oss-meta-tag" metadata --9431149156168 Content-Disposition: form-data; name="OSSAccessKeyId" 44CF9590006BF252**** --9431149156168 Content-Disposition: form-data; name="policy" eyJleHBpcmF0aW9uIjoiMjAxMy0xMi0wMVQxMjowMDowMFoiLCJjb25kaXRpb25zIjpbWyJjb250ZW50LWxlbmd0aC1yYW5nZSIsIDAsIDEwNDg1NzYwXSx7ImJ1Y2tldCI6ImFoYWhhIn0sIHsiQSI6ICJhIn0seyJrZXkiOiAiQUJDIn1dfQ== --9431149156168 Content-Disposition: form-data; name="Signature" kZoYNv66bsmc10+dcGKw5x2P**** --9431149156168 Content-Disposition: form-data; name="file"; filename="MyFilename.txt" Content-Type: text/plain abcdefg --9431149156168 Content-Disposition: form-data; name="submit" Upload to OSS --9431149156168--
Sample success responses
HTTP/1.1 200 OK x-oss-request-id: 61d2042d-1b68-6708-5906-33d81921362e Date: Fri, 24 Feb 2014 06:03:28 GMT ETag: "5B3C1A2E053D763E1B002CC607C5****" Connection: keep-alive Content-Length: 0 Server: AliyunOSS
Error codes
Error code | HTTP status code | Description |
FieldItemTooLong | 400 | The size of the form field key exceeds 8 KB or the size of the form field value exceeds 2 MB. |
InvalidArgument | 400 | One of the OSSAccessKeyId, policy, and Signature form fields is specified but the other two form fields are not specified in the request regardless of whether the ACL of the bucket is public-read-write. |
InvalidDigest | 400 | The Content-MD5 value that is calculated by OSS based on the request body is different from the Content-MD5 value that is specified in the request header. |
EntityTooLarge | 400 | The total size of the PostObject request body exceeds 5 GB. |
InvalidEncryptionAlgorithmError | 400 | The x-oss-server-side-encryption header is set to a value other than AES256 or KMS. The x-oss-server-side-encryption header can be set only to AES256 or KMS. |
IncorrectNumberOfFilesInPOSTRequest | 400 | The number of objects in the PostObject request is invalid. A PostObject request can contain only one file form field. |
FileAlreadyExists | 409 | The request contains the x-oss-forbid-overwrite=true element but an object that has the same name already exists. |
KmsServiceNotEnabled | 403 | The x-oss-server-side-encryption header is set to KMS but KMS is not activated in advance. |
FileImmutable | 409 | The data that you want to delete or modify is protected by a retention policy. |
Appendix: Policy
The policy form field in a PostObject request is used to verify the validity of the request. The value of the policy form field is a JSON string that is encoded in UTF-8 and Base64. This value specifies the conditions that must be matched for a PostObject request. The policy form field is optional when you upload an object to a bucket whose ACL is public-read-write. However, we recommend that you specify this form field to limit PostObject requests.
Example:
{
"expiration": "2014-12-01T12:00:00.000Z",
"conditions": [
{"bucket": "johnsmith" },
["content-length-range", 1, 10],
["eq", "$success_action_status", "201"],
["starts-with", "$key", "user/eric/"],
["in", "$content-type", ["image/jpg", "image/png"]],
["not-in", "$cache-control", ["no-cache"]]
]
}
The policy form field must contain the expiration and conditions parameters.
expiration
The expiration parameter specifies the expiration time of the request. The time must follow the ISO 8601 standard and must be in GMT. For example,
2014-12-01T12:00:00.000Z
indicates that the PostObject request must be sent before 12:00 on December 1, 2014.conditions
The conditions parameter is a list that specifies the valid values of the form fields in the PostObject request.
The following table describes the conditions that can be configured in the policy field.
Parameter
Description
Matching mode
bucket
The name of the bucket.
bucket
content-length-range
The minimum and maximum sizes of the object that you want to upload. Unit: bytes.
content-length-range
Cache-Control, Content-Type, Content-Disposition, Content-Encoding, Expires
HTTP request headers.
ImportantTo prevent malicious modifications to the Content-Type header during form upload, we recommend that you specify the Content-Type header in the policy form field. You can use one of the following methods to specify the Content-Type header:
Add the x-oss-content-type element to the message body of a PostObject request to specify the Content-Type header. Example:
Content-Type: image/jpeg
. For more information about the values of the Content-Type header supported by OSS, see How do I configure the Content-Type header?Use the file form field to specify Content-Type. Example:
Content-Type: image/png
. For more information about the values of the Content-Type header supported by OSS, see How do I configure the Content-Type header?
The content type specified by the x-oss-content-type form field takes precedence over the content type specified by the file form field.
eq, starts-with, in, and not-in
key
The name of the object.
eq, starts-with, in, and not-in
success_action_redirect
The URL to which the client is redirected after the object is uploaded.
eq, starts-with, in, and not-in
success_action_status
The HTTP status code to return after the object is uploaded if success_action_redirect is not specified.
eq, starts-with, in, and not-in
x-oss-meta-*
The user metadata of the object that you want to upload.
NoteThe policy field specifies the form fields that must be contained in the PostObject request. If you specify ["eq", "$x-oss-meta-biedb", "biedb-test001"], you must add the key form field x-oss-meta-biedb whose value is biedb-test001 to the form field. Otherwise, the Invalid according to Policy: Policy Condition failed: ["eq", "$x-oss-meta-biedb", "biedb-test001"] error is reported.
eq, starts-with, in, and not-in
If the PostObject request contains additional form fields, OSS adds these form fields to the conditions of the policy and checks their validity.
Condition matching modes
Matching mode
Description
content-length-range
The size of the object that you want to upload must be within the range of supported object sizes. For example, if the supported object size is 1 to 10 bytes, the condition must be ["content-length-range", 1, 10].
eq
The value of a form field must be exactly the same as the value that is specified in the conditions. For example, if the value of the key form field is in the format of {"key":"a"}, the condition must be ["eq", "$key", "a"].
starts-with
The value of a form field must start with the specified prefix. For example, if the value of the key form field starts with user/user1, the condition must be ["starts-with", "$key", "user/user1"].
in
The elements that you want to include in the verification must be specified in the in condition string. For example, if you want to verify whether JPG and PNG images can be uploaded in a PostObject request, the condition must be ["in", "$content-type", ["image/jpg", "image/png"]].
not-in
The elements that you want to exclude from the PostObject request must be specified in the not-in condition string. For example, if you want to specify an object caching behavior and exclude no-cache, the condition must be ["not-in", "$cache-control", ["no-cache"]].
In the policy form field of a PostObject request, the dollar sign ($) indicates a variable. To describe the dollar sign ($), you must use the following escape character: \$. The following table describes the escape characters used in the JSON string of the policy form field in a PostObject request.
Escape character | Description |
\/ | Forward slash |
\\ | Backslash |
\" | Double quotation marks |
\$ | Dollar sign |
\b | Space |
\f | Form feed |
\n | New line |
\r | Carriage return |
\t | Horizontal tab |
\uxxxx | Unicode character |
Appendix: Signature
To verify a PostObject request, you must include the policy and Signature form fields in the HTML form. The policy form field specifies the values that are supported in the request.
You can perform the following steps to calculate the value of the Signature form field:
Create a UTF-8-encoded policy.
Encode the policy in Base64. The result is the value of the policy form field, and the value is used as the string to be signed.
Use the AccessKey secret to sign the string in the following format:
Signature = base64(hmac-sha1(base64(policy), AccessKeySecret))
.
FAQ
What do I do if the Your proposed upload exceeds the maximum allowed size. error message is returned?
Cause: The size of the uploaded object is out of the size range specified for the content-length-range parameter.
Solution: Add the content-length-range parameter to specify the minimum and maximum sizes of the uploaded object. Unit: bytes. For example, if the size of the object that you want to upload is 1 GB, you can set the content-length-range parameter to ["content-length-range", 1, 1073741824].
References
For more information about how to transfer data from a web client to OSS by using form upload, see Add signatures on the client by using JavaScript and upload data to OSS.
For more information about the common errors of and solutions to the PostObject operation, see PostObject.