POST

The HTTP POST method sends data to the server. The type of the body of the request is indicated by the Content-Type header.

The difference between PUT and POST is that PUT is idempotent: calling it once or several times successively has the same effect (that is no side effect), where successive identical POST may have additional effects, like passing an order several times.

A POST request is typically sent via an HTML form and results in a change on the server. In this case, the content type is selected by putting the adequate string in the enctype attribute of the <form> element or the formenctype attribute of the <input> or <button> elements:

  • application/x-www-form-urlencoded: the keys and values are encoded in key-value tuples separated by '&', with a '=' between the key and the value. Non-alphanumeric characters in both keys and values are percent encoded (en-US): this is the reason why this type is not suitable to use with binary data (use multipart/form-data instead)
  • multipart/form-data: each value is sent as a block of data ("body part"), with a user agent-defined delimiter ("boundary") separating each part. The keys are given in the Content-Disposition header of each part.
  • text/plain

When the POST request is sent via a method other than an HTML form — like via an XMLHttpRequest — the body can take any type. As described in the HTTP 1.1 specification, POST is designed to allow a uniform method to cover the following functions:

  • Annotation of existing resources
  • Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;
  • Adding a new user through a signup modal;
  • Providing a block of data, such as the result of submitting a form, to a data-handling process;
  • Extending a database through an append operation.
Request has body Yes
Successful response has body Yes
Safe (en-US) No
Idempotent (en-US) No
Cacheable Only if freshness information is included
Allowed in HTML forms Yes

格式

POST /test

範例

使用 application/x-www-form-urlencoded 內容類型的簡易表單:

POST /test HTTP/1.1
Host: foo.example
Content-Type: application/x-www-form-urlencoded
Content-Length: 27

field1=value1&field2=value2

使用 multipart/form-data 內容類型的表單:

POST /test HTTP/1.1
Host: foo.example
Content-Type: multipart/form-data;boundary="boundary"

--boundary
Content-Disposition: form-data; name="field1"

value1
--boundary
Content-Disposition: form-data; name="field2"; filename="example.txt"

value2
--boundary--

規範

規範 標題
RFC 7231, section 4.3.3: POST Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
RFC 2046, section 5.1.1: Common Syntax Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types

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