I didn't find useful information about which methods status is correct for absent object in db.
For example I have deleted user with id = 1, but someone try to get it's information thought GET method with query params id=1.
Which status will be right: 404, 204, 400,406 or 410?
I didn't find useful information about which methods status is correct for absent object in db.
Yup, that's right - HTTP status codes don't tell you anything about rows in a database, what they tell you about are documents ( "resources" ) in a document store.
More precisely, the HTTP status code is metadata that tells general purpose components (like a web browser, or a cache) what's in the message-body of the response.
Depending on what document you put into the message-body, the appropriate status code could be any of:
200
404
410
200 announce that the message-body is a document (more broadly, a current representation of the resource). 404 and 410 (and all 4xx and 5xx status codes) announce that the message-body is a representation of the explanation of the error.
404 indicates that the document identified by the effective target uri of the request doesn't exist right now, but it might exist later; you can attach caching metadata to communicate when the might check again.
410 indicates that the document identified by the effective target uri of the request doesn't exist right now, and that condition is likely permanent. That permanence implies that clients can delete bookmarks, and remote links to the document should be removed, and so on.
If you recycle ids, or if deletes ids can be restored, then 410 isn't an appropriate choice.
In some APIs, resources have current representations even when there is no matching information in the database.
In other words, the current representation of the resource might be an empty document
200 OK HTTP/2
Content-Type: text/plain
Content-Length: 0
or it could be a null object
200 OK HTTP/2
Content-Type: application/json
Content-Length: 4
null
or it could be an empty list
200 OK HTTP/2
Content-Type: application/json
Content-Length: 2
[]
or an empty object
200 OK HTTP/2
Content-Type: application/json
Content-Length: 2
{}
or a meme
200 OK HTTP/2
Content-Type: text/plain
Content-Length: 36
This space intentionally left blank.
The status code to use follows from the decision to use a sort of "default" representation of our document when there is no specific information available.
The more common decision, of course, is to choose not to provide default representations, but instead announce that the client has made a mistake (in which case the 4xx class of status code is the correct starting point).
Isn't it write to return 204(NO CONTENT) status or something similar? 'Cause I think 200 is not fully informative status
Maybe - there's some ambiguity in the HTTP standard, and because of that ambiguity I tend to be biased against 204 (today; if you look up some of my older answers, I was much likely to try 204 in the past).
RFC 7231, Section 6.3.1
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.
So we have two different ways to send zero bytes of data back to the client; either 200 with Content-Length set to zero, or 204.
Are those two things the same?
The answer seems to be "not quite"; there's a subtle difference documented in section 6.3.5
The 204 response allows a server to indicate that the action has been successfully applied to the target resource, while implying that the user agent does not need to traverse away from its current "document view" (if any).
Now, think about that in the context of a web browser. If I click a link that points to an empty file, a 200 response would mean that the browser would traverse away from the current "document view" to show me the empty file. But the language of 204 suggests that instead the browser should stay put, and just indicate that the empty file was successfully downloaded.
Note: I haven't done any experiments to see if browsers do act that way; my only claim is that staying in place is the specified behavior.
My reading of the specification is that 204 is designed to support a use case that only arises in the context of unsafe actions, like PUT. You can see hints of that as far back as HTTP/1.0
This response is primarily intended to allow input for scripts or other actions to take place without causing a change to the user agent's active document view. The response may include new metainformation in the form of entity headers, which should apply to the document currently in the user agent's active view.
In short, responding with a 204 to a GET request is placing a bet that the authors of general purpose components have interpreted an ambiguous part of the specification the same way that you do -- and I don't like that bet at all. Much more reliable to use the well understood 200 response, and avoid the unnecessary ambiguity.
Can a GET request message ever return a HTTP status code of 201?
A conforming HTTP server should never do this. GET is a safe method, and is not supposed to have any side effects.
201 means a new resource was created on the server, which really is a side-effect.
So if a GET results in a 201, something is wrong. However, if you are building a client want to know in advance which success codes you might get, you should simply support every code between 200 and 299 (inclusive) and treat them all as success codes.
Yes. The API has control over what status code to send.
In practice, the status code is meant to communicate the status of the response - so it’s unlikely that a 201 (“Created”) should be returned from a GET request.
201 - created.
We can return code 201 for GET, but normally we use POST to send some data in server. So I don't think it is good to return 201 for GET
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.
I am sometimes getting 102 response from a web server. This response indicates that the server is processing the request but is not the final response for it (http://en.wikipedia.org/wiki/List_of_HTTP_status_codes#1xx_Informational). The request(>) response (<) sequence might look like this:
>GET some_url
<HTTP/1.1 102 Processing
<HTTP/1.1 102 Processing
<HTTP/1.1 102 Processing
<HTTP/1.1 200 OK
The server can be considered reliable in the sense that the final response is ultimately sent.
Using LWP::UserAgent (6.02) I can recognise that I've received a 102 using HTTP::Status::is_info() but what I then need to do is consume at least one and maybe more subsequent responses for the original request and I can't see a way to do that once I have the response.
I thought I might be able to do it with a handler (http://metacpan.org/pod/LWP::UserAgent#Handlers) which I use successfully elsewhere, but I can't find a way to force continuing to listen.
I've also looked for a way to turn on "102 awareness" within LWP and just have the library take care of listening for the final response which it then returns, but I can't see that either.
Tell me I'm missing something obvious, please.
What is the appropriate way of giving an estimate for request completion when the server returns a 202 - Accepted status code for asynchronous requests?
From the HTTP spec (italics added by me):
202 Accepted
The request has been accepted for processing, but the processing has not been completed. [...]
The entity returned with this response SHOULD include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the user can expect the request to be fulfilled.
Here are some of thoughts:
I have glanced at the max-age directive, but using it would be abusing Cache-Control?
Return the expected wait time in the response body?
Add an application specific X- response header, but the X-headers was deprecated in RFC 6648?
Add a (non X-) specific response header? If so, how should it be named? The SO question Custom HTTP headers : naming conventions gave some ideas, but after the deprecation it only answers how HTTP headers are formatted, not how they should be named.
Other suggestions?
Definitely do not abuse existing HTTP headers for this. Since it's your own server, you get to define what the response looks like. You can (and should) pick whatever response works best for the intended recipient of this information and return the actual information in the response body.
For example, if you are only interested in displaying a human-readable message then you could return text/plain saying "Your request is likely to be processed in the next 30 minutes.".
At the other end of the spectrum, you might want to go all the REST way and return application/json, perhaps formatted like this (I totally made this up on the spot):
{
"status": "pending",
"completion": {
"estimate": "Thu Sep 08 2011 12:00:00 GMT-0400",
"rejected-after": "Fri Sep 09 2011 12:00:00 GMT-0400",
},
"tracking": {
"url": "http://server/status?id=myUniqueId"
}
}
You can use the Location header to specify the URL of the status monitor. Things like current status and estimate can either go in custom headers (which noone but your own software would use), or in the response body (which a web browser would display to a user, at least).
Although not explicitly mentioned specifically for the 202 - Accepted response code, the Retry-After header seems to be a suitable option. From the documentation:
The Retry-After response-header field can be used [...] to indicate how long the service is expected to be unavailable to the requesting client.