What’s the difference between a POST and a PUT HTTP REQUEST?

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They both seem to be sending data to the server inside the body, so what makes them different?

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HTTP PUT:

PUT puts a file or resource at a specific URI, and exactly at that URI. If there’s already a file or resource at that URI, PUT replaces that file or resource. If there is no file or resource there, PUT creates one. PUT is idempotent, but paradoxically PUT responses are not cacheable.

HTTP 1.1 RFC location for PUT

HTTP POST:

POST sends data to a specific URI and expects the resource at that URI to handle the request. The web server at this point can determine what to do with the data in the context of the specified resource. The POST method is not idempotent, however POST responses are cacheable so long as the server sets the appropriate Cache-Control and Expires headers.

The official HTTP RFC specifies POST to be:

  • Annotation of existing resources;
  • Posting a message to a bulletin board, newsgroup, mailing list,
    or similar group of articles;
  • 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.

HTTP 1.1 RFC location for POST

Difference between POST and PUT:

The RFC itself explains the core difference:

The fundamental difference between the
POST and PUT requests is reflected in
the different meaning of the
Request-URI. The URI in a POST request
identifies the resource that will
handle the enclosed entity. That
resource might be a data-accepting
process, a gateway to some other
protocol, or a separate entity that
accepts annotations. In contrast, the
URI in a PUT request identifies the
entity enclosed with the request —
the user agent knows what URI is
intended and the server MUST NOT
attempt to apply the request to some
other resource. If the server desires
that the request be applied to a
different URI, it MUST send a 301 (Moved Permanently) response; the user agent MAY then make
its own decision regarding whether or not to redirect the request.

Additionally, and a bit more concisely, RFC 7231 Section 4.3.4 PUT states (emphasis added),

4.3.4. PUT

The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation
enclosed in the request message payload.

Using the right method, unrelated aside:

One benefit of REST ROA vs SOAP is that when using HTTP REST ROA, it encourages the proper usage of the HTTP verbs/methods. So for example you would only use PUT when you want to create a resource at that exact location. And you would never use GET to create or modify a resource.

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