I am currently contributing to a REST API written in Go and I was facing an existential question.
How are we supposed to handle an empty body in a PATCH? Knowing that a PATCH is used to update an existing data, are we supposed to return an error code (4XX) or an ok status (2XX)?
For example, if I have the following route: /user/:id
And a user has the following structure:
type User struct {
Name string
Email string
}
So if we PATCH a specific user, we will either have a body containing the name or the email.
What should we do if it is empty?
The RFC5789 was not a real help (2.2 for error handling)
https://datatracker.ietf.org/doc/rfc5789/?include_text=1
How are we supposed to handle an empty body in a PATCH?
That depends: what's wrong with an empty patch body?
If an empty patch body is an error, then your response should communicate the nature of the error to the client.
If the empty patch body is not an error, then apply the empty patch. That's probably a no-op, in which case, success! So you return a response that explains that applying empty patches is trivial, and here's where they can go to see the updated implementation. Alternatively, you can 204 as shown in the example. I don't see things explicitly spelled out, but I think you can draw upon the pattern described in RFC 7231 section 6.3.1.
Some examples that might help.
Suppose the client were using JSON Patch as the media type for the request. Now, a "JSON Patch document is a JSON [RFC4627] document that represents an array of objects". An empty request body is not a valid JSON document, and certainly isn't a valid array of objects, so that's a malformed patch document, and as described in section 2.2 you should be thinking about sending a 400 response.
Suppose the client were to send a json patch with an empty array of operations
[]
Semantically, that's a no-op -- except that a response indicating that the patch was successfully applied will invalidate cached values. So you could certainly report success (200) with not doing anything. You may be able to prevent the cached entries from being invalidated by returning an error (I think the Patch spec isn't quite describing the semantics correctly, but I don't see an errata filed).
A similar argument applies for application/merge-patch+json.
You may also want to consider the errata for RFC 5789
If a server receives a PATCH request with a media type whose specification does not define semantics specific to PATCH, the server SHOULD reject the request by returning the 415 Unsupported Media Type status code, unless a more specific error status code takes priority.
In particular, servers SHOULD NOT assume PATCH semantics for generic media types that don't define them, such as "application/xml" or "application/json".
The MDN used 204 No Content in an example here:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/PATCH#response
I have skimmed over the HTTP/1.1 protocol spec at RFC-2616 and I am trying to understand which status code should be returned when a particular REST method is invoked. As far as I have studied the protocol (links), I tried to parse REST methods to the correct status code:
GET
to return 200 (ok) in case at least one resource is found.
should I return 204 (not found) if nothing is found (i.e. empty list is returned)?
PUT
to return 200 (ok) or 204 (not found) based if the resource is modified or not
moreover to return 501 (unimplemented) if the request is malformed or not understood.
POST
the same like PUT method with the difference the 201 (created) is returned if the new reource has been added to the orign
based on common recommendation, POST sould be used for creating a new reource, PUT for modifying an existing one. If I decide follow this recommendation, what should I return in case of attempt to modify an existing resource ex. POST api/v1/person/1?
PATCH
the same like PUT method with the difference it doesn't replace the whole resource like PUT does, but itmodifies a resource partially
there is no word about PATCH REST method in W3 protocol RFC-2616, should it be treated the same like PUT?
DELETE
to return 200 (ok) if the resource was deleted and [204 (not found)] in case there is no resource existing to remove (id not found). Does it copy the GET responses principe in case of REST implementation?
Is my "table" correct (especially the statements with the quotation marks ?? Is right that only GET should return the request itself in the body and the rest of methods just an URI link to an amended resource (new added, modified..) included in the header?
Is my understanding correct and does exist another source describing REST methods officially which is recommended (or are we "obligated") to follow? I am quite confused of wide range of sources giving me a bit different answers to each method as well of this really verbose RFC-2616 protocol.
The best would be the existence of a table describing briefly and clearly all these 5 methods with possibilites of status returned, body content and headers.
From RFC 7230
This HTTP/1.1 specification obsoletes RFC 2616
So any attempt to work out patterns for status codes should start from there
Is my "table" correct
Not really; take a look at Kropat's (unofficial) flow charts in Stop Making it Hard.
We have an endpoint which when you post create a new version of resource and returns a 201 and the location of the newly created resource. It determines the new version number based on a comparison of the current version and the version being posted (using a semver like ruleset).
If the version you post is identical to the existing version then no version number is updated. What should we return in this case?
We could just return a 201 even though we have not technically created anything.
I don't want to return a 409 as its not really a conflict, like when you post something with the same id. If you posted the same thing when the existing version was slightly different then you would happily get a 201.
We could just return a 200, but then that would seem weird, and increases the response codes that the users have to deal with
Does the idempotency of the 201 response matter?
Any better suggestions?
How about 303 - See Other? Seems to fit. I draw your attention to this sentence
from the spec at https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource.
That sounds like what you want to do to me. Here's the rest of it.
10.3.4 303 See Other
The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre-HTTP/1.1 user agents do not understand the 303
status. When interoperability with such clients is a concern, the
302 status code may be used instead, since most user agents react
to a 302 response as described here for 303
I am a bit puzzled by the other answers as some get it almost right. So, let's clear up things a bit. If all requests are indeed performed with the POST method, in the context of ReSTfulness, they are supposed to modify state on the target server. Otherwise, the meaning of POST is a bit relaxed as you can see in RFC 7231, sec. 4.3.3.
Since the intent of the requests is to create a new version of a resource, they have failed if a version with the given presentation already exists. This would disqualify any 2xx-class response codes. From section 6.3:
The 2xx (Successful) class of status code indicates that the client's request was successfully received, understood, and accepted.
If you absolutely wanted to, you could go for 202/Accepted, which "is intentionally noncommittal." This is a bit of a stretch, though, as this status code is intended for queued processing. I would advise against it.
The 204/No Content code suggested by others is a bit of a poor choice. It were absolutely correct if you POSTed to the resource you were updating, though.
As the result is neither informational (1xx) nor a fault by the server (5xx). Let us have a look at the 3xx class first. From section 6.4:
The 3xx (Redirection) class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request.
One of the most prominent one here would be 304/Not Modified. While sounding like a perfect fit, this code is unfortunately not applicable here. It can only be returned in response to conditional GET or HEAD requests.
302/Found may sound like the next best fit. However, this code is intended for temporary redirects, which is in all likelyhood not what you want.
As has been suggested here, 303/See Other is indeed a good choice:
The 303 (See Other) status code indicates that the server is redirecting the user agent to a different resource [...] which is intended to provide an indirect response to the original request.
[...]
This status code is applicable to any HTTP method. It is primarily used to allow the output of a POST action to redirect the user agent to a selected resource
All other 3xx codes are dealing with various forms of redirects that hardly relate to the situation here.
A final look, 4xx-class of status codes. From RFC 7231, sec. 6.5:
The 4xx (Client Error) class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server SHOULD send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method.
Very few of these are actually deeling with the request body. Two of those who do would stand out here: One is 400/Bad Request, which is by design overly broad. It is - if you will - a catch-all solution. However, this would imply that the request body is malformed (as in syntactically incorrect) in some way, which is probably not the case.
More interesting is 409/Conflict. From the RFC (emphasis mine):
The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource.
The wording of the definition places this code close to the PUT method, but is not exclusive. To reiterate the definition of the 4xx codes:
These status codes are applicable to any request method.
422/Unprocessable Entity is a contender, but it implies a semantic error, which really isn't the case here.
Ultimately (drumroll) the final piece of the puzzle could be found in section 4.3.3:
If the result of processing a POST would be equivalent to a representation of an existing resource, an origin server MAY redirect the user agent to that resource by sending a 303 (See Other) response with the existing resource's identifier in the Location field.
Note the "MAY." So you can really choose between 303 and 409. I feel 409 were the better fit, as clearly an earlier request introduced a state that is incompatible with the current one. OTOH, 303 may be the politer way to go and is closer to the standard. Either way, as a consumer of your API, I would really like to know if my requests failed. And be it by not having any effect whatsoever.
If nothing has been created by the operation, 201 is not suitable for that:
6.3.2. 201 Created
The 201 (Created) status code indicates that the request has been fulfilled and has resulted in one or more new resources being created. [...]
See below some options you could consider if the operation succeeds:
6.3.1. 200 OK
The 200 (OK) status code indicates that the request has succeeded. The payload sent in a 200 response depends on the request method. For the methods defined by this specification, the intended meaning of the payload can be summarized as:
[...]
POST: a representation of the status of, or results obtained from, the action;
[...]
Aside from responses to CONNECT, a 200 response always has a payload, though an origin server MAY generate a payload body of zero length. If no payload is desired, an origin server ought to send 204 (No Content) instead. [...]
6.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body. [...]
If the operation fails:
6.5.1. 400 Bad Request
The 400 (Bad Request) status code indicates that the server cannot will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).
11.2. 422 Unprocessable Entity
The 422 (Unprocessable Entity) status code means the server understands the content type of the request entity (hence a 415 (Unsupported Media Type) status code is inappropriate), and the syntax of the request entity is correct (thus a 400 (Bad Request) status code is inappropriate) but was unable to process the contained instructions. For example, this error condition may occur if an XML request body contains well-formed (i.e., syntactically correct), but semantically erroneous, XML instructions.
A 201 Created should be used whenever you creating a new resource without doubt.
As defined in HTTP Method Definitions RFC, either200 Ok or 204 No Contentis an appropriate response if the operation does not create a new resource depending on the response body content.
The action performed by the POST method might not result in a resource
that can be identified by a URI. In this case, either 200 (OK) or 204
(No Content) is the appropriate response status, depending on whether
or not the response includes an entity that describes the result.
If a resource has been created on the origin server, the response
SHOULD be 201 (Created) and contain an entity which describes the
status of the request and refers to the new resource, and a Location
header (see section 14.30).
Now, coming back to your original question about what to use when the operation is successful and there is nothing to return, you should use 204 No Content. This status code is specifically meant for scenarios where the requested operation is successfully completed but there is no additional relevant information that the server can provide.
The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body.
I don't think that for this case the idempotency is an issue, because the state of the system is not the same as it was in the inicial request, because the entity now exists, so you can respond with a different code.
200 should be fine, but it is a little weird as you said.
I have never use this, but I read that for some case you should redirect with a 302, to make a get for other resource, in this case I think this apply, return a 302 and make a get pointing for the old semver, assuming that you have a get endpoint for this entity.
If the POST'd resource has the same version number, but different data, then a 409 would be fitting. But if the data is the same as what's already stored, then a 409 might not be required. Through process of elimination I would say 200 OK would be fine.
We could just return a 200, but then that would seem weird, and increases the response codes that the users have to deal with
If this is a costly concern, consider eliminating the 201, not the 200. The fact of the matter is that for any decently complex service there may be at some point a situation where a 20X (where X is not 0) is applicable. So does that mean we code with each of the 20X responses in mind and spend time checking if our services has situations where 20X is preferred over 200? I suspect not. So unless there is a specific reason to respond with a 20X, for example to deal with a specific use case, then just use 200 and reduce the amount of coding and documenting required. I suspect for most scenarios, the calling client does not care.
Ultimately, the correct answer probably depends on whatever client is consuming your API. If you are building the client too, you could do whatever you prefer... (Just don't get too crazy.)
Assuming you are writing the API and client:
My opinion/suggestion is...
If there IS a new version number: The 201 HTTP status code would fit will.
If there is NOT a new version number: The 200 or 204 HTTP status code would fit well.
If there is no benefit to the client knowing the version number has changed or is the same: Send the 200 HTTP status code.
If you don't control the client consuming your API: Obviously defer to what they expect.
You may also wish review all of the HTTP Status Codes in the HTTP RFC spec. The above status codes also link directly to the relevant section.
201 : when new version is created
202 : when existing version is updated
204 : when request is accepted but no processing is done
by def, 204 = No Content
The server has fulfilled the request but does not need to return an
entity-body, and might want to return updated metainformation. The
response MAY include new or updated metainformation in the form of
entity-headers, which if present SHOULD be associated with the
requested variant.
If the client is a user agent, it SHOULD NOT change its document view
from that which caused the request to be sent. This response is
primarily intended to allow input for actions to take place without
causing a change to the user agent's active document view, although
any new or updated metainformation SHOULD be applied to the document
currently in the user agent's active view.
The 204 response MUST NOT include a message-body, and thus is always
terminated by the first empty line after the header fields.
So its slight tangential to your needs but I think its the best fit.
Assume the system manages users. Users are exposed via the following URL - /users. A particular user is exposed via the following URL - /users/{id}. Users have reports exposed via the following URL - /users/{id}/reports.
One operation consists of generating a report. The appropriate HTTP request is a POST on /users/{id}/reports. However, under certain conditions, a generated report would be exactly the same as the last generated report. Therefore, I thought that returning the last generated report in this case is a good approach.
I also know that in such case, no resource will be created.
Is there a correct RESTful way to handle this case? Maybe returning a special code?
Is there a correct RESTful way to handle this case? Maybe returning a special code?
Stepping back for a moment: a perfectly straight forward way to handle the "create" use case looks like
client POSTs a request to /users/1/reports
the origin server creates a new resource and calculates a new identifier for this resource (/users/1/reports/a)
the server returns a response that indicates that a new resource has been created, the location of that resource, and its current representation.
The indication that a new resource has been created is the status-code: 201.
The location of the newly created resource is described by the Location response header.
The location of the content is described by the Content-Location response header
The current representation is the message body of the response (no surprise).
HTTP/1.1 201 Created
Location: /users/1/reports/a
Content-Location: /users/1/reports/a
...
<representation of the report goes here>
In your case, where the resource already exists, then things look pretty much the same. To avoid implying that we have created a new resource, the status-code is changed to 200, and the Location header is dropped.
HTTP/1.1 200 OK
Content-Location: /users/1/reports/a
...
<representation of the report goes here>
If you prefer that the client retrieve the report representation using the identifier of the previously generated report, then you should use 303 See Other
It is primarily used to allow the output of a POST action to redirect the user agent to a selected resource, since doing so provides the information corresponding to the POST response in a form that can be separately identified, bookmarked, and cached, independent of the original request.
HTTP/1.1 303 See Other
Location: /users/1/reports/a
...
This pattern is commonly referred to as Post/Redirect/Get
i'd use 304 Not Modified in cases where the report is not modified. This should tell everyone, that the ressource didn't change since the last export and normally no further content is transmitted. This could also be used to instead refer to your older results if you cache those. Generally the 304 is not used for posts, but the use of a post to jus trigger the creation of a log can be considered a bit exotic as well.
If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields.
RFC containing explanation of the 304 Status Code
If the creation worked i'd send a 201 created and use the location header as pointer to the new file.
So i've got a website that accepts an HTTP-PUT for a particular resource, eg. /contact which will allow the consumer to update a contact, assuming they have passed validation.
So I update the record, all is great .. and now I need to return something to the consumer.
What's the HTTP Status Code I should be returning?
If this was an HTTP-POST (ie. Creating a -new- resource), then I would return an 201 Created and add a Location header attribute.
But .. I can't find any clues about what to do for an Update.
Cheers :)
200 is especially appropriate if you are returning a representation of the action (although the work-in-progress-but-nearing-last-call "HTTP bis" oddly doesn't mention PUT in its description of 200 OK).
If you're not returning any sort of representation, use 204 No Content to indicate to the client that it doesn't need to change its current "document view".
200 is the appropriate status code assuming the PUT only did an update and did not create a resource.