HTTP Methods

Last Updated :

REST APIs enable you to develop all kinds of web applications having all possible CRUD (create, retrieve, update, delete) operations.

REST guidelines suggest using a specific HTTP method on a particular type of call made to the server (though technically it is possible to violate this guideline, yet it is highly discouraged).

Use the below-given information to find a suitable HTTP method for the action performed by API.

Table of Contents

HTTP GET
HTTP POST
HTTP PUT
HTTP DELETE
HTTP PATCH
Summary
Glossary

1. HTTP GET

Use GET requests to retrieve resource representation/information only – and not modify it in any way. As GET requests do not change the resource’s state, these are said to be safe methods.

Additionally, GET APIs should be idempotent. Making multiple identical requests must produce the same result every time until another API (POST or PUT) has changed the state of the resource on the server.

If the Request-URI refers to a data-producing process, it is the produced data that shall be returned as the entity in the response and not the source text of the process, unless that text happens to be the output of the process.

1.1. GET API Response Codes

  • For any given HTTP GET API, if the resource is found on the server, then it must return HTTP response code 200 (OK) – along with the response body, which is usually either XML or JSON content (due to their platform-independent nature).
  • In case the resource is NOT found on the server then API must return HTTP response code 404 (NOT FOUND).
  • Similarly, if it is determined that the GET request itself is not correctly formed then the server will return the HTTP response code 400 (BAD REQUEST).

1.2. Example URIs

HTTP GET http://www.appdomain.com/users
HTTP GET http://www.appdomain.com/users?size=20&page=5
HTTP GET http://www.appdomain.com/users/123
HTTP GET http://www.appdomain.com/users/123/address

2. HTTP POST

Use POST APIs to create new subordinate resources, e.g., a file is subordinate to a directory containing it or a row is subordinate to a database table.

When talking strictly about REST, POST methods are used to create a new resource into the collection of resources.

Responses to this method are not cacheable unless the response includes appropriate Cache-Control or Expires header fields.

Please note that POST is neither safe nor idempotent, and invoking two identical POST requests will result in two different resources containing the same information (except resource ids).

2.1. POST API Response Codes

  • Ideally, if a resource has been created on the origin server, the response SHOULD be HTTP response code 201 (Created) and contain an entity that describes the status of the request and refers to the new resource, and a Location header.
  • Many times, the action performed by the POST method might not result in a resource that can be identified by a URI. In this case, either HTTP response code 200 (OK) or 204 (No Content) is the appropriate response status.

2.2. Example URIs

HTTP POST http://www.appdomain.com/users
HTTP POST http://www.appdomain.com/users/123/accounts

3. HTTP PUT

Use PUT APIs primarily to update an existing resource (if the resource does not exist, then API may decide to create a new resource or not).

If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries SHOULD be treated as stale. Responses to PUT method are not cacheable.

3.1. PUT API Response Codes

  • If a new resource has been created by the PUT API, the origin server MUST inform the user agent via the HTTP response code 201 (Created) response.
  • If an existing resource is modified, either the 200 (OK) or 204 (No Content) response codes SHOULD be sent to indicate successful completion of the request.

3.2. Example URIs

HTTP PUT http://www.appdomain.com/users/123
HTTP PUT http://www.appdomain.com/users/123/accounts/456

The difference between the POST and PUT APIs can be observed in request URIs. POST requests are made on resource collections, whereas PUT requests are made on a single resource.

4. HTTP DELETE

As the name applies, DELETE APIs delete the resources (identified by the Request-URI).

DELETE operations are idempotent. If you DELETE a resource, it’s removed from the collection of resources.

Some may argue that it makes the DELETE method non-idempotent. It’s a matter of discussion and personal opinion.

If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries SHOULD be treated as stale. Responses to this method are not cacheable.

4.1. DELETE API Response Codes

  • A successful response of DELETE requests SHOULD be an HTTP response code 200 (OK) if the response includes an entity describing the status.
  • The status should be 202 (Accepted) if the action has been queued.
  • The status should be 204 (No Content) if the action has been performed but the response does not include an entity.
  • Repeatedly calling DELETE API on that resource will not change the outcome – however, calling DELETE on a resource a second time will return a 404 (NOT FOUND) since it was already removed.

4.2. Example URIs

HTTP DELETE http://www.appdomain.com/users/123
HTTP DELETE http://www.appdomain.com/users/123/accounts/456

5. HTTP PATCH

HTTP PATCH requests are to make a partial update on a resource.

If you see PUT requests modify a resource entity too. So to make it more precise – the PATCH method is the correct choice for partially updating an existing resource, and you should only use PUT if you’re replacing a resource in its entirety.

Please note that there are some challenges if you decide to use PATCH APIs in your application:

Support for PATCH in browsers, servers, and web application frameworks is not universal. IE8, PHP, Tomcat, Django, and lots of other software have missing or broken support for it.

Request payload of a PATCH request is not straightforward as it is for a PUT request. e.g.

HTTP GET /users/1

produces below response:

{ "id": 1, "username": "admin", "email": "[email protected]"}

A sample patch request to update the email will be like this:

HTTP PATCH /users/1
[{ "op": "replace", "path": "/email", "value": "[email protected]" }]

There may be the following possible operations are per the HTTP specification.

[
 { "op": "test",  "path": "/a/b/c",  "value": "foo"  },
 { "op": "remove",  "path": "/a/b/c"  },
 { "op": "add",  "path": "/a/b/c",  "value": [ "foo", "bar" ] },
 { "op": "replace", "path": "/a/b/c",  "value": 42 },
 { "op": "move",  "from": "/a/b/c",  "path": "/a/b/d" },
 { "op": "copy", "from": "/a/b/d",  "path": "/a/b/e" }
 ]

The PATCH method is not a replacement for the POST or PUT methods. It applies a delta (diff) rather than replacing the entire resource.

6. Summary of HTTP Methods

The below table summarises the use of HTTP methods discussed above.

HTTP Method
CRUD
Collection Resource (e.g. /users)
Single Resouce (e.g. /users/123)
POST
Create
201 (Created), ‘Location’ header with link to /users/{id} containing new ID
Avoid using POST on a single resource
GET
Read
200 (OK), list of users. Use pagination, sorting, and filtering to navigate big lists
200 (OK), single user. 404 (Not Found), if ID not found or invalid
PUT
Update/Replace
405 (Method not allowed), unless you want to update every resource in the entire collection of resource
200 (OK) or 204 (No Content). Use 404 (Not Found), if ID is not found or invalid
PATCH
Partial Update/Modify
405 (Method not allowed), unless you want to modify the collection itself
200 (OK) or 204 (No Content). Use 404 (Not Found), if ID is not found or invalid
DELETE
Delete
405 (Method not allowed), unless you want to delete the whole collection — use with caution
200 (OK). 404 (Not Found), if ID not found or invalid

7. Glossary

7.1. Safe Methods

Request methods are considered safe if their defined semantics are essentially read-only. The client does not request, and does not expect, any state change on the origin server as a result of applying a safe method to a target resource.

The GET, HEAD, OPTIONS, and TRACE methods are considered safe methods. As per HTTP specification, the GET and HEAD methods should be used only for retrieval of resource representations – and they do not update/delete the resource on the server.

The purpose of distinguishing between safe and unsafe methods is to allow automated retrieval processes (spiders) and cache performance optimization (pre-fetching) to work without fear of causing harm.

Safe methods allow user agents to represent other methods, such as POST, PUT and DELETE, in a unique way so that the user is made aware of the fact that a possibly unsafe action is being requested – and they can update/delete the resource on the server and so should be used carefully.

7.2. Idempotent Methods

The term idempotent is used more comprehensively to describe an operation that will produce the same results if executed once or multiple times.

In HTTP specification, the PUT, DELETE and safe methods (GET, HEAD, OPTIONS, TRACE) are idempotent methods.

Idempotence is a handy property in many situations, as it means that an operation can be repeated or retried as often as necessary without causing unintended effects.

With non-idempotent operations, the algorithm may have to keep track of whether the operation was already performed or not.

Like the definition of safe methods, the idempotent property only applies to what has been requested by the user; a server is free to log each request separately or retain a revision control history.

References:

https://www.w3.org/Protocols/rfc2616/rfc2616.txt
http://tools.ietf.org/html/rfc6902
https://en.wikipedia.org/wiki/Idempotence#Computer_science_meaning

Was this article helpful?

Comments

  1. I have a service that validates entries for a sport. It can accept multiple entries, and each entry contains the id of the entrant and other details of the entry, all wrapped up in a JSON list of objects.
    Validation doesn’t change anything – it just checks the data and returns response – is the entry valid, and if not, why not.
    The service is most definitely idempotent – you can call it again and again without anything changing.

    So, it should be GET, but GET doesn’t allow for a payload like POST does – and it is POST I use for this purpose.

    These verbs may well have made sense when the web started, but since the advent of Web services and API’s, which provide complex responses to complex data, but don’t make changes, there is a gap in the described functionality.

    Maybe we need to extend ‘GET’ to allow for a payload?

    Reply
    • Some implementations will allow payload in GET but it certainly isn’t standard and I would avoid it where possible. Nothing wrong with overloading POST where it doesn’t fit the REST definition. Remember POST and GET were all we had once upon a time. Having said that if the payload isn’t too crazy you could try passing it as query params.

      Reply
    • Have you tried using query parameters?

      GET weburl.com/validate?id=1&id=3&id=4

      or GET weburl.com/validate?id=1,2,3,4,5,221
      or even GET weburl.com/validate?id_in=1,2,3&id_get=220 (where id_get means ids greater or equal to)

      How you parse the query parameters is up to you – any of these options should work.

      The only key consideration is the 2048 character url name limit.

      Reply
  2. I have a query on GET /users (collection resource)
    1) If Database Table has data
    2) If Database Table doesn’t have data

    what should return response and status code? is empty [] with 200 status code or 404?

    Please provide some clarity.

    Reply

Leave a Comment