:How to handle common errors when the PostObject operation is called

Overview

This article describes the common errors that occur when the PostObject operation is called and their solutions.

Description

If an error occurs when you call the PostObject operation, make sure that the parameters are correctly configured. For more information, see PostObject. If the error persists, see the following content:

• PostObject common errors
• PostObject FAQ
• PostObject examples
• PostObject introduction

PostObject common errors

PostObject FAQ

Content-Disposition: form-data; name="key"
{key}
--9431149156168

Content-Disposition: form-data; name="file"; filename="images.png"
Content-Type: image/png
{file-content}
--9431149156168

Content-Disposition: form-data; name="file"; filename="images.png"
Content-Type: image/png
{file-content}
--9431149156168

POST / HTTP/1.1
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:1.9.2.6)
Content-Type: multipart/form-data; boundary=9431149156168
Content-MD5: tdqHe4hT/TuKb7Y4by+nJg==
Host: mingdi-hz.oss-cn-hangzhou.aliyuncs.com
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-alive
Content-Length: 5246
--9431149156168

Content-Disposition: form-data; name="Signature"
5L0+KaeugxYygfqWLJLoy0ehOmA=
--9431149156168
Content-Disposition: form-data; name="x-oss-security-token"
{Token}
--9431149156168

Content-Disposition: form-data; name="callback"
eyJjYWxsYmFja0JvZHlUeXBlIjogImFwcGxpY2F0aW9uL3gtd3d3LWZvcm0tdXJsZW5jb2RlZCIsICJjYWxsYmFja0JvZHkiOiAiZmlsZW5hbWU9JHtvYmplY3R9JnNpemU9JHtzaXplfSZtaW1lVHlwZT0ke21pbWVUeXBlfSIsICJjYWxsYmFja1VybCI6ICJodHRwOi8vb3NzLWRlbW8uYWxpeXVuY3MuY29tOjIzNDUwIn0=
--9431149156168

Content-Disposition: form-data; name="x:var1"
{var1-value}
--9431149156168

Content-Disposition: form-data; name="file"; filename="images.png"
Content-Type: image/png
Content-Transfer-Encoding: base64
{file-content}
--9431149156168

Content-Disposition: form-data; name="x-oss-meta-uuid"
{uuid}
--9431149156168
Content-Disposition: form-data; name="x-oss-meta-tag"
{tag}
--9431149156168

{
    "expiration": "2018-01-01T12:00:00.000Z",
    "conditions": [
        ["eq", "[$Bucket]", "md-hz"],
        ["starts-with", "[$Key]", "md/conf/"],
        ["content-length-range", 0, 104857600]
    ]
}

PostObject examples

PostObject form field format

• Take note of the following content when you send a PostObject request:
  • The header of the request must contain Content-Type: multipart/form-data; boundary={boundary}.
  • The request header and body are separated by \r\n--{boundary}.
  • The following code shows the form field format:

    Content-Disposition: form-data;
            name="{key}"\r\n\r\n{value}\r\n--{boundary}

  • The names of form fields are case-sensitive, such as Policy, Key, file, OSSAccessKeyId, OSSAccessKeySecret, and Content-Disposition.
    

    Note: The file form field must be the last form field.

    When the access control list (ACL) of a bucket is public-read-write, you do not have to specify the form fields OSSAccessKeyId, policy, or Signature. If one of OSSAccessKeyId, policy, and Signature is specified, the other two form fields must be specified no matter whether the ACL of the bucket is public read/write.
• The following code shows an example on a PostObject request:

  POST / HTTP/1.1
  User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:1.9.2.6)
  Content-Type: multipart/form-data; boundary=9431149156168
  Host: mingdi-hz.oss-cn-hangzhou.aliyuncs.com
  Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
  Connection: keep-alive
  Content-Length: 5052
  --9431149156168
  Content-Disposition: form-data; name="key"
  test-key
  --9431149156168
  Content-Disposition: form-data; name="Content-Disposition"
  attachment;filename=D:\img\1.png
  --9431149156168
  Content-Disposition: form-data; name="OSSAccessKeyId"
  2NeL********j2

  Note:
  

  • In the preceding sample request, \r\n shows a new line, which is a line feed. This applies to the following sample requests.
  • The preceding sample request is incomplete. For the complete sample request, see PostObject.

• For more information about the PostObject request, refer to the sample code used by OSS SDKs for the following programming languages:
  • C#
  • Java
  • JS

PostObject policy format

• The Policy form field of a PostObject request is used to verify the validity of the request and declares the conditions that the request must meet. The following content is the conditions:
  • UTF-8 JSON text must be encoded with Base64 before the text is passed into the policy form field.
  • The policy must contain expiration and conditions. Conditions must contain at least one item.
• The following code shows an example of the policy before the policy is encoded with Base64. expiration specifies the expiration time of the request, which in GMT and follows the ISO 8601 standard. For example, 2018-01-01T12:00:00.000Z specifies that the request must be sent before 12:00:00 January 1, 2018.

  {
      "expiration": "2018-01-01T12:00:00.000Z",
      "conditions": [
          ["content-length-range", 0, 104857600]
      ]
  }

• The following table describes the conditions that the POST policy supports.
  

  Condition	Description	Example
  Bucket	The name of the bucket to which the object is uploaded. Exact match is supported.	{"bucket": "johnsmith" } or ["eq", "$bucket", "johnsmith"]
  Key	The name of the uploaded object. Exact match and prefix match are supported.	["starts-with", "$key", "user/etc/"]
  content-length-range	The maximum and minimum allowed sizes of the uploaded object.	["content-length-range", 0, 104857600]
  x-oss-meta-*	The specified object metadata. Exact match and prefix match are supported.	["starts-with", "$x-oss-meta-prop", "prop-"]
  success_action_redirect	The redirection URL after a successful upload. Exact match and prefix match are supported.	["starts-with", "$success_action_redirect", "http://www.aliyun.com"]
  success_action_status	The returned status code after a successful upload if success_action_redirect is not specified. Exact match and prefix match are supported.	["eq", "$success_action_status", "204"]
  Cache-Control, Content-Type, Content-Disposition, Content-Encoding, and Expires	The HTTP headers passed as form fields. Exact match and prefix match are supported.	["eq", "$Content-Encoding", "ZLIB"]

• The Post policy supports the following escape characters. Escape characters begin with a backslash (\) .
  

  Escape character	Description
  \/	Slash
  \	Backslash
  \"	Double quotation mark
  \$	Dollar sign
  \b	Blank
  \f	Form feed
  \n	Line feed
  \r	Enter
  \t	Horizontal tab
  \uxxxx	Unicode character

• For more information about PostPolicy, see Post Policy.

PostObject signature

• For a POST request to be verified, the request must include the AccessKeyID, policy, and signature form fields. To calculate a signature, perform the following steps:
  
  • Create a policy encoded with UTF-8.
  • Encode the policy with base64. The result is the value to be populated into the policy form field. This value is used as the string-to-sign.
  • Sign the string by using AccessKeySecret. Specifically, hash the string by using hmac-sha1 and then encode the hashed string with Base64. The signature method is the same as that for Header Signature. Example:
    

    Signature = base64(hmac-sha1(AccessKeySecret, base64(policy)))

    Specify the calculated signature in the Signature form field. Example:
    

    Content-Disposition: form-data; name="Signature"
    {signature}
    --9431149156168

• If you have questions, see the sample code:
  • C#
  • Java
  • JS

PostObject introduction

You can call the PostObject operation to upload an object to a specified bucket by using an HTML form. The message body of a PostObject request is encoded in the multipart/form-data format. In PostObject operations, parameters are passed as form fields in the request message body, whereas parameters are passed as HTTP request headers in PutObject operations. For more information, see RFC 2388. A PostObject message consists of a header and a body. The request header and the body are separated by \r\n--{boundary}. The body consists of a series of form fields in the following format:

Content-Disposition: form-data; name="{key}"\r\n\r\n{value}\r\n--{boundary}

Common headers include Host, User-Agent, Content-Length, Content-Type, and Content-MD5 . Form fields include key, OSSAccessKeyId, Signature, Content-Disposition, object meta (x-oss-meta-*), x-oss-security-token, other HTTP headers (Cache-Control/Content-Type/Cache-Control/Content-Type/Content-Disposition/Content-Encoding/Expires/Content-Encoding/Expires), and file. The last form field must be file. For more information, see PostObject.

References

• PostObject
• C# Post Demo
• Java Post Demo
• JavaScript Post Demo

Application scope

• OSS