We are using a specific endpoint on our API to test if an e-mail address is already registered in our database. When it's not, what would be the right status code to return to the client ?
We cannot take a decision between 404, 204 and 200. There are a couple of articles over the net but all state pros and cons but it's not very clear.
200 says that the request was successful
204 says that the request was successful AND that the message body included in the response is 0 bytes long.
404 says that there is no current implementation associated with the requested resource
Which of these is correct really depends on your resource design.
Consider a database query with a where clause -- if there are no matching rows, then you get SUCCESS, with an empty result set. So the analogous thing in a HTTP response would be a 2xx status code, and a body that describes an empty set.
If you were using a JSON List as your representation of the set, then the representation would be two bytes long [], and a 200 status code would be appropriate. If you were using a json lines representation, with each record on its own line, then with no records you would have no lines, therefore a 0 byte representation and 204 would be a good choice.
What about a case where we have a simple web page, that tells you if the email address is registered or not? If it's registered, the server responds with a 200 message and a html document that tells you about the registration. If it isn't registered, then you get an html message telling you that the email address isn't registered... and a 200, because we were able to find the current representation of the resource.
And 404? 404 indicates to the client that there appears to have been a spelling error in the target-uri of the http request -- that there isn't even nothing to find.
It may help to understand that status codes are metadata about the HTTP response, which is to say that they are part of the application domain of transferring documents over a network, not about the business domain. They are there so that generic components, like caches, can do interesting things without needing to know any specifics about the domain in question.
Our web API is a facade to make our domain model look like a boring document store.
I have an post api call that currently creates an appointment in my booking system.
If the api call sends the appointment request and the api can successfully create an appoinment the api returns a 201 created status code.
Currently if the appointment request is not created (due to various things such as the time is no longer available or the room is now being used) the api is returning a 400 bad request status code.
"400 Bad Request response status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error"
The data sent is not invalid syntax and potentially could be resent and be successful.
Is there a more relevant status code for this failure to create a resource. would 422 Unprocessable Entity be a valid response in this case?
409 could suit this use-case(and my personal preference):
"The request could not be completed due to a conflict with the current
state of the target resource. This code is used in situations where
the user might be able to resolve the conflict and resubmit the
request."
Typically used in PUT but could work in this scenario. For example, they could change the proposed time in the request. Or they could retry later if the room becomes available.
422 could also work to indicate a field level error.
Either way, an important thing is to accompany it with a good error message indicating the issue. From rfc7231:
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.
[... ] if the appointment request is not created (due to various things such as the time is no longer available or the room is now being used) [...]
Status codes are meant to indicate the result of the server's attempt to understand and satisfy the client's request. Given that it's a client error, the most suitable status code would be in the 4xx range.
For the situation described in your question, you could use 409:
6.5.8. 409 Conflict
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. This code is used in situations where the user might be
able to resolve the conflict and resubmit the request. The server
SHOULD generate a payload that includes enough information for a user
to recognize the source of the conflict. [...]
400 vs 422
In general, use 400 to indicate syntax errors in the payload or invalid parameters in the URL. And use 422 to indicate semantic problems in the payload. See how each status code is defined:
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.
Also consider the status codes returned by the well-known GitHub API v3 API:
There are three possible types of client errors on API calls that
receive request bodies:
Sending invalid JSON will result in a 400 Bad Request response. [...]
Sending the wrong type of JSON values will result in a 400 Bad Request response. [...]
Sending invalid fields will result in a 422 Unprocessable Entity response. [...]
Michael Kropat put together a set of diagrams that's pretty insightful when it comes to picking the most suitable status code. See the following diagram for 4xx status codes:
My suggestion would be to use 412 Precondition Failed Status code which indicated that server couldn't process the POST request due to failure/denial of additional criteria or business logic.
Refer: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/412
If the error is due to something going wrong on the server and to no fault of the client you can use the 5xx range (Server Error). 4xx errors are reserved for errors caused by the client. Most often 500 Internal Server Error is used in this case.
So:
Clients fault --> 4xx
Servers fault --> 5xx
What's the best HTTP status code to use in response to an HTTP GET for a resource that's corrupt or semantically invalid?
E.g., consider a request to GET /person/1234 where data for person ID 1234 exists on the server but violates some business rule, so the server refuses to use it.
404 doesn't apply (because the data actually exists).
4xx in general seems not ideal (because the problem is on the server end, not under the client's control).
503 seems to apply to the service as a whole, not a particular resource.
500 certainly fits, but it's very vague in actually telling the client what might be wrong.
Any suggestions?
After reading the comments and the linked resources, it looks like #RemyLebeau's approach is best:
I think 500 is the only official response code that fits this situation. And there is nothing stopping you from including a response body that describes the reason for the failure.
according to iana.org:
4xx: Client Error - The request contains bad syntax or cannot be fulfilled
5xx: Server Error - The server failed to fulfill an apparently valid request
I think none of the 4xx status code should be valid as a response to an internal server error or migration or ... where client has no responsibilities or where user's inputs are expected to be rechecked. unless user's pre-filled data are involved like maybe user's package is not allowing him to access that data after a pre-determinate and known date, in such specific case It may be valid a 403 Forbidden as #Bari did suggest.
I'm not an expert but I think when the rejection or the decision of considering endpoint data as corrupt or invalid is made by server, then it will depends on what should be done next. I see 3 possible cases:
1. It is expected that somehow this is going to be fixed and client
should be invited to request it back but at some future moment ==> 503 (Service Unavailable):
503 (Service Unavailable)
status code indicates that the server
is currently unable to handle the request due to a temporary overload
or scheduled maintenance, which will likely be alleviated after some
delay. The server MAY send a Retry-After header field
(Section 7.1.3) to suggest an appropriate amount of time for the
client to wait before retrying the request.
2. Something is wrong, it is not client responsibility but there is an alternative way to access data, maybe following a specific process or sending further details ==> 510 Not Extended
2. Server cannot fulfill the request but there is an alternative way that requires it to include further details. Example: when requested data is corrupt, server error response may include a list of older (or unsaved, unversioned) versions of it and expect client to be more specific about which version to select so it could be fetched instead of the corrupted one ==> 510 Not Extended
510 Not Extended
The policy for accessing the resource has not been met in the
request. The server should send back all the information necessary
for the client to issue an extended request. It is outside the scope
of this specification to specify how the extensions inform the
client.
If the 510 response contains information about extensions that were
not present in the initial request then the client MAY repeat the
request if it has reason to believe it can fulfill the extension
policy by modifying the request according to the information provided
in the 510 response. Otherwise the client MAY present any entity
included in the 510 response to the user, since that entity may
include relevant diagnostic information.
case 2 was updated to include an example as IMHO it may fit in such case. but again I'm not any expert and I may be
wrong about it
3. No alternative ways, nothing to be expected or none of the other cases ==> 500 should be good
500 (Internal Server Error)
status code indicates that the server
encountered an unexpected condition that prevented it from fulfilling
the request.
I'm building a server that allows clients to store objects. Those objects are fully constructed at client side, complete with object IDs that are permanent for the whole lifetime of the object.
I have defined the API so that clients can create or modify objects using PUT:
PUT /objects/{id} HTTP/1.1
...
{json representation of the object}
The {id} is the object ID, so it is part of the Request-URI.
Now, I'm also considering allowing clients to create the object using POST:
POST /objects/ HTTP/1.1
...
{json representation of the object, including ID}
Since POST is meant as "append" operation, I'm not sure what to do in case the object is already there. Should I treat the request as modification request or should I return some error code (which)?
My feeling is 409 Conflict is the most appropriate, however, seldom seen in the wild of course:
The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body SHOULD include enough information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.
According to RFC 7231, a 303 See Other MAY be used If the result of processing a POST would be equivalent to a
representation of an existing resource.
It's all about context, and also who is responsible for handling duplicates of requests (server or client or both)
If server just point the duplicate, look at 4xx:
400 Bad Request - when the server will not process a request because it's obvious client fault
409 Conflict - if the server will not process a request, but the reason for that is not the client's fault
...
For implicit handling of duplicates, look at 2XX:
200 OK
201 Created
...
if the server is expected to return something, look at 3XX:
302 Found
303 See Other
...
when the server is able to point the existing resource, it implies a redirection.
If the above is not enough, it's always a good practice to prepare some error message in the body of the response.
Personally I go with the WebDAV extension 422 Unprocessable Entity.
According to RFC 4918
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.
Late to the game maybe but I stumbled upon this semantics issue while trying to make a REST API.
To expand a little on Wrikken's answer, I think you could use either 409 Conflict or 403 Forbidden depending on the situation - in short, use a 403 error when the user can do absolutely nothing to resolve the conflict and complete the request (e.g. they can't send a DELETE request to explicitly remove the resource), or use 409 if something could possibly be done.
10.4.4 403 Forbidden
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request SHOULD NOT be repeated. If
the request method was not HEAD and the server wishes to make public
why the request has not been fulfilled, it SHOULD describe the reason
for the refusal in the entity. If the server does not wish to make
this information available to the client, the status code 404 (Not
Found) can be used instead.
Nowadays, someone says "403" and a permissions or authentication issue comes to mind, but the spec says that it's basically the server telling the client that it's not going to do it, don't ask it again, and here's why the client shouldn't.
As for PUT vs. POST... POST should be used to create a new instance of a resource when the user has no means to or shouldn't create an identifier for the resource. PUT is used when the resource's identity is known.
9.6 PUT
...
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.
I would go with 422 Unprocessable Entity, which is used when a request is invalid but the issue is not in syntax or authentication.
As an argument against other answers, to use any non-4xx error code would imply it's not a client error, and it obviously is. To use a non-4xx error code to represent a client error just makes no sense at all.
It seems that 409 Conflict is the most common answer here, but, according to the spec, that implies that the resource already exists and the new data you are applying to it is incompatible with its current state. If you are sending a POST request, with, for example, a username that is already taken, it's not actually conflicting with the target resource, as the target resource (the resource you're trying to create) has not yet been posted. It's an error specifically for version control, when there is a conflict between the version of the resource stored and the version of the resource requested. It's very useful for that purpose, for example when the client has cached an old version of the resource and sends a request based on that incorrect version which would no longer be conditionally valid. "In this case, the response representation would likely contain information useful for merging the differences based on the revision history." The request to create another user with that username is just unprocessable, having nothing to do with any version conflict.
For the record, 422 is also the status code GitHub uses when you try to create a repository by a name already in use.
After having read this and several other, years-long, discussions on status code usage, the main conclusion I came to is that the specifications have to be read carefully, focusing on the terms being used, their definition, relationship, and the surrounding context.
What often happens instead, as can be seen from different answers, is that parts of the specifications are ripped of their context and interpreted in isolation, based on feelings and assumptions.
This is going to be a pretty long answer, the short summary of which is that HTTP 409 is the most appropriate status code to report the failure of an "add new resource" operation, in case a resource with the same identifier already exists. What follows is the explanation why, based solely on what's stated in the authoritative source - RFC 7231.
So why is 409 Conflict the most appropriate status code in a situation described in the OP's question?
RFC 7231 describes 409 Conflict status code as follows:
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 key components here are the target resource and its state.
Target resource
The resource is defined by the RFC 7231 as follows:
The target of an HTTP request is called a "resource". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described in Section 2.7 of [RFC7230].
So, when using a HTTP interface, we always operate on the resources identified by URIs, by applying HTTP methods to them.
When our intention is to add a new resource, based on the OP's examples, we can:
use PUT with the resource /objects/{id};
use POST with the resource /objects.
/objects/{id} is out of interest, because there can be no conflict when using a PUT method:
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.
If the resource with the same identifier already exists, it will be replaced by PUT.
So we'll focus on the /objects resource and POST.
RFC 7231 says about the POST:
The POST method requests that the target resource process the representation enclosed in the request according to the resource's own specific semantics. For example, POST is used for the following functions (among others): ... 3) Creating a new resource that has yet to be identified by the origin server; and 4) Appending data to a resource's existing representation(s).
Contrary to how the OP understands POST method:
Since POST is meant as "append" operation...
Appending data to a resource's existing representation is just one of the possible POST "functions". Moreover, what the OP actually does in the provided examples, is not directly appending data to the /objects representation, but creating a new independent resource /objects/{id}, which then becomes part of the /objects representation. But that's not important.
What's important is the notion of the resource representation, and it brings us to...
Resource state
RFC 7231 explains:
Considering that a resource could be anything, and that the uniform interface provided by HTTP is similar to a window through which one can observe and act upon such a thing only through the communication of messages to some independent actor on the other side, an abstraction is needed to represent ("take the place of") the current or desired state of that thing in our communications. That abstraction is called a representation [REST].
For the purposes of HTTP, a "representation" is information that is intended to reflect a past, current, or desired state of a given resource, in a format that can be readily communicated via the protocol, and that consists of a set of representation metadata and a potentially unbounded stream of representation data.
That's not all, the specification continues to describe representation parts - metadata and data, but we can summarize that a resource representation, that consists of metadata (headers) and data (payload), reflects the state of the resource.
Now we have both parts needed to understand the usage of the 409 Conflict status code.
409 Conflict
Let's reiterate:
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.
So how does it fit?
We POST to /objects => our target resource is /objects.
OP does not describe the /objects resource, but the example looks like a common scenario where /objects is a resource collection, containing all individual "object" resources. That is, the state of the /objects resource includes the knowledge about all existing /object/{id} resources.
When the /objects resource processes a POST request it has to a) create a new /object/{id} resource from the data passed in the request payload; b) modify its own state by adding the data about the newly created resource.
When a resource to be created has a duplicate identifier, that is a resource with the same /object/{id} URI already exists, the /objects resource will fail to process the POST request, because its state already includes the duplicate /object/{id} URI in it.
This is exactly the conflict with the current state of the target resource, mentioned in the 409 Conflict status code description.
In your case you can use 409 Conflict
And if you want to check another HTTPs status codes from below list
1×× Informational
100 Continue
101 Switching Protocols
102 Processing
2×× Success
200 OK
201 Created
202 Accepted
203 Non-authoritative Information
204 No Content
205 Reset Content
206 Partial Content
207 Multi-Status
208 Already Reported
226 IM Used
3×× Redirection
300 Multiple Choices
301 Moved Permanently
302 Found
303 See Other
304 Not Modified
305 Use Proxy
307 Temporary Redirect
308 Permanent Redirect
4×× Client Error
400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Payload Too Large
414 Request-URI Too Long
415 Unsupported Media Type
416 Requested Range Not Satisfiable
417 Expectation Failed
418 I’m a teapot
421 Misdirected Request
422 Unprocessable Entity
423 Locked
424 Failed Dependency
426 Upgrade Required
428 Precondition Required
429 Too Many Requests
431 Request Header Fields Too Large
444 Connection Closed Without Response
451 Unavailable For Legal Reasons
499 Client Closed Request
5×× Server Error
500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
505 HTTP Version Not Supported
506 Variant Also Negotiates
507 Insufficient Storage
508 Loop Detected
510 Not Extended
511 Network Authentication Required
599 Network Connect Timeout Error
I don't think you should do this.
The POST is, as you know, to modify the collection and it's used to CREATE a new item. So, if you send the id (I think it's not a good idea), you should modify the collection, i.e., modify the item, but it's confusing.
Use it to add an item, without id. It's the best practice.
If you want to capture an UNIQUE constraint (not the id) you can response 409, as you can do in PUT requests. But not the ID.
"302 Found" sounds logical for me. And the RFC 2616 says that it CAN be answered for other requests than GET and HEAD (and this surely includes POST)
But it still keeps the visitor going to this URL to get this "Found" resource, by the RFC. To make it to go directly to the real "Found" URL one should be using "303 See Other", which makes sense, but forces another call to GET its following URL. On the good side, this GET is cacheable.
I think that I would use "303 See Other". I dont know if I can respond with the "thing" found in the body, but I would like to do so to save one roundtrip to the server.
UPDATE: After re-reading the RFC, I still think that an inexistent "4XX+303 Found" code should be the correct. However, the "409 Conflict" is the best existing answer code (as pointed by #Wrikken), maybe including a Location header pointing to the existing resource.
I think for REST, you just have to make a decision on the behavior for that particular system in which case, I think the "right" answer would be one of a couple answers given here. If you want the request to stop and behave as if the client made a mistake that it needs to fix before continuing, then use 409. If the conflict really isn't that important and want to keep the request going, then respond by redirecting the client to the entity that was found. I think proper REST APIs should be redirecting (or at least providing the location header) to the GET endpoint for that resource following a POST anyway, so this behavior would give a consistent experience.
EDIT:
It's also worth noting that you should consider a PUT since you're providing the ID. Then the behavior is simple: "I don't care what's there right now, put this thing there." Meaning, if nothing is there, it'll be created; if something is there it'll be replaced. I think a POST is more appropriate when the server manages that ID. Separating the two concepts basically tells you how to deal with it (i.e. PUT is idempotent so it should always work so long as the payload validates, POST always creates, so if there is a collision of IDs, then a 409 would describe that conflict).
Another potential treatment is using PATCH after all. A PATCH is defined as something that changes the internal state and is not restricted to appending.
PATCH would solve the problem by allowing you to update already existing items. See: RFC 5789: PATCH
What about 208 - http://httpstatusdogs.com/208-already-reported ? Is that a option?
In my opinion, if the only thing is a repeat resource no error should be raised. After all, there is no error neither on the client or server sides.
Stumbled upon this question while checking for correct code for duplicate record.
Pardon my ignorance but I don't understand why everyone is ignoring the code "300" which clearly says "multiple choice" or "Ambiguous"
In my opinion this would be the perfect code for building a non standard or a particular system for your own use. I could be wrong as well!
https://www.rfc-editor.org/rfc/rfc7231#section-6.4.1
More likely it is 400 Bad Request
[**6.5.1. 400 Bad Request**][1]
The 400 (Bad Request) status code indicates that the server cannot or
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).
As the request contains duplicate value(value that already exists), it can be perceived as a client error. Need to change the request before the next try.
By considering these facts we can conclude as HTTP STATUS 400 Bad Request.
Since you mentioned that the object create request using post contains the ID of the object, you should make it an idempotent request. Just return the exact same response as a successful create request. Idempotent request makes APIs simpler, eg. now client doesn't have to worry about 2 different cases (success, failure). or client can safely retry the request, in case something goes wrong in connectivity/ server temporarily down.
Error 402, payment required
I.E. this resource already exists but if you give me enough money I'll delete the current one and give it to you :D
...but looking at mozilla's definition of status codes at https://developer.mozilla.org/en-US/docs/Web/HTTP/Status#client_error_responses
as a more serious answer that no one has provided here, what about 451: unavailable for legal reasons. You cannot "legally(by terms and conditions put in place by yourself)" give multiple people access to the same account information
422 is also a good option which is Unprocessable Entity
The request was well-formed but was unable to be followed due to semantic errors. since it is a perfectly valid request but due to it being semantically equal to another entry, it cannot be followed.
This is a user side fault and belongs to 4xx group. This is the right answer https://developers.rebrandly.com/docs/403-already-exists-errors