Suppose to have a REST API which updates the stock of some products in an e-commerce portal:
URL : /products/stock
METHOD : PUT
BODY :
{
"PRD001": 3,
"PRD002": 2
}
Where the request body is a map made of <<PRODUCT_CODE>> : <<USER_REQUIRED_QUANTITY>> entries
At some point, the server receives a well-formed syntactic request, but the logic behind the API fails because:
One or more of the sent PRODUCT CODES do not exist.
The USER_REQUIRED_QUANTITY requested for one of the products having PRODUCT_CODE is unavailable because of insufficient stock.
Which HTTP CODE should the REST API return for these "semantic applicative errors"?
In my opinion:
It shouldn't return 400 - BAD REQUEST because the REQUEST is well-formed from a syntactic perspective.
In the case of an inexistent product, it shouldn't return 404 -NOT FOUND because the resource is related to a stock and not to a specific product. Returning 404 - NOT FOUND could lead the client intto an error.
It could return a 409 - CONFLICT (The request could not be completed due to a conflict with the current state of the resource)
It could return a 422 Unprocessable Entity (The server understands the content type and syntax of the request entity, but still server is unable to process the request for some reason). Anyway, this status code is part of WebDAV specific and not part of the HTTP)
What do you think about this specific use case?
And, in a more general way, in which way do you handle HTTP Status codes according to applicative semantic errors?
Thank you
Important idea - status codes are metadata of the transfer of documents over a a network domain; they describe the semantics of the HTTP response so that general purpose HTTP components can do intelligent things (e.g. invalidate cached responses).
Which HTTP CODE should the REST API return for these "semantic applicative errors"?
The fact that the values in the request body are the problem strongly suggests that we want some flavor of 4xx Client Error semantics.
I'm inclined to guess that the simplest approach would be to use 403 Forbidden
The 403 (Forbidden) status code indicates that
the server understood the request but refuses
to fulfill it.
Any nuance that you need to share with the user/bespoke client is described in the body of the 403 response.
From what I can tell, 409 Conflict isn't right, but also isn't going to get you into a lot of trouble.
For a general purpose component, 403 and 409 are handled essentially the same way -- in theory a general purpose component could try to "resolve the conflict" on its own and resubmit the request, but in practice we don't have a standard for describing the nature of the conflict, which means that the component isn't going to know a way to modify the request.
So while I would decline a pull request (PR) that used a 409 here, I would also accept a PR that used a 409 and also included a decision record documenting the trade offs that the implementer had considered in this specific context (for example - it might be important that your human operators easily be able to distinguish this case from authentication issues when scanning access logs).
In other words, make the boring choice unless you have really good reasons to do something else. If you have really good reasons to do something else, write them down.
422
My doubt about this one is that it is not part to the HTTP specs.
Don't be worried at that. HTTP status codes are intended to be extensible. Anything you find in the IANA status code registry should be considered safe to use.
Also, today, the registered reference for 422 is the current HTTP Semantics specification (RFC 9110).
That said, I wouldn't use it here, because I don't think the semantics are as good a fit for your circumstance as 403.
The 422 (Unprocessable Content) status code indicates that the
server understands the content type of the request content
(hence a 415 (Unsupported Media Type) status code is inappropriate),
and the syntax of the request content is correct, but it was unable
to process the contained instructions. For example, this status
code can be sent if an XML request content contains well-formed
(i.e., syntactically correct), but semantically erroneous XML
instructions.
My interpretation of this is that we're trying to indicate that there's a problem specific to the semantics of the request body (ex: a required field is missing). It announces that we're unable to process the request, rather than announcing that the processing failed.
In other words, 422 is "I don't know what this means", where 403 is "I know what this means, but I won't do it."
We also have considered using the 403 - FORBIDDEN code, but it seems to be more related to authorization issues.
The specification gives wider latitude than the most common usage.
a request might be forbidden for reasons unrelated
to the credentials.
That said, choosing a different status code can be the right engineering trade off. If the benefits of doing the right thing are small, and the costs (in particular, the support and operational costs) are large, well... maybe being successful is more important than being right.
Related
I am having trouble picking the correct HTTP Status for when an API is receives an attribute that maps additional data in the system but that additional data is not found. I was initially thinking 422 since it describes the use case but sounds like it is reserved for WebDAV. Then I was thinking maybe a 404 but I mentally associate that to a URL being incorrect. The other option was using error code 200 and have a failure message.
Example: the key nvdaKey is not a key configuration that the system knows about.
POST: pgpTool.com/encrypt
{
"message": "my secret message",
"keyConfigName": "nvdaKey"
}
The IANA HTTP Status Code Registry currently lists HTTP Semantics as the authoritative reference for status code 422
The 422 (Unprocessable Content) status code indicates that the server
understands the content type of the request content (hence a 415
(Unsupported Media Type) status code is inappropriate), and the
syntax of the request content is correct, but was unable to process
the contained instructions.
So if you think that's a winner, go for it.
403 Forbidden is also an option ("I understood your request, but I refuse to fulfill it").
Status codes are meta data in the transfer of documents over a network domain; the intended audience is general purpose HTTP components (browsers, caches, proxies....) Clients are supposed to be getting the semantics of the message from the body (in just the same way we expect humans reading the web to learn of errors by reading the returned web page, rather than by reading HTTP headers).
So apart from some purely mechanical concerns (caching, interpretation of headers) it is not necessarily critical that you produce precisely the right status code, so long as you get the class (Client Error / 4xx) correct.
Do note that a client that doesn't recognize a 422 is expected to treat the response as though it were a 400.
I found in my job that people are designing a RESTs API that has endpoints that return a single Json object (not a collection) based in query params (not path param).
For example:
/users?name=John&surname=Sparrow
with response body
{id:10, name="John", surname="Sparrow", gender="male"}
But what response code corresponds in REST API to not finding a resource due to query params?
For example:
/users?name=John&surname=Smith
(when John Smith doesn't exist).
I don't think it is a 404 error because /users endpoint exists, but I don't know if I must return a 400 error or a 200 without body (or null value) or other kind of response
Can you help me?
Thanks
What is most appropriate depends on whether an empty result list is OK or a clear failure. Whether parameters are PathParams or QueryParams has no bearing on return codes.
My general approach is that search functions such as findStuffBySearchTerms always return a successful HTTP code such as 200 and either the results or an empty list. On the other hand, fetchStuffById where I expect the entity to be found will return HTTP 404 if it is not found.
What response code corresponds in REST API to not finding a resource due to query params?
404 Not Found.
I don't think it is a 404 error because /users endpoint exists,
The resource identifier includes the query params. Which is to say, the query parameters are part of the identifier in precisely the same sense that path segments are part of the identifier.
In your request body, you can describe the circumstances of your implementation as precisely as you like.
But the audience of HTTP status codes includes general purpose components (browsers, proxies, web crawlers), for whom the response code is the primary mechanism for describing the semantics of the response:
The status-code element is a 3-digit integer code describing the result of the server's attempt to understand and satisfy the client's corresponding request. The rest of the response message is to be interpreted in light of the semantics defined for that status code. -- RFC 7230
That said, your server owns its own resources, and therefore you get to decide whether or not a resource exists, and what it's current representation looks like.
GET /users?name=Dave HTTP/1.1
200 OK
Content-Type: text/plain
Dave's not here, man.
From an HTTP/REST framing, that's a perfectly reasonable exchange; somebody asked for the latest representation of /users?name=Dave, and the latest representation is a plain text document. Absolutely fine.
The key idea here is that that HTTP status-code is metadata of the transfer of documents over a network domain.
HTTP is indifferent to the semantic meaning of the representations of resources.
That said, you should be considering in your design concerns like "what does this look like in our access logs?" If you want your operators to be able to distinguish this case from the similar case where the query parameters match information in your database, 200 vs 404 is the natural way to do that.
You'll normally prefer 404 to the other error status codes for this case because 404 indicates the response is cacheable, which is probably want you want when you are passed a request-target that has a spelling error in it somewhere.
Let's say we have an HTTP request made by the client. The endpoint exists and is accessible by the client (this rules out 401, 403, 404 and 405). The request payload is valid (this rules out 400). The server is alive and well, and is able to handle the request and return a response (this rules out 5xx).
The error arises within the processing of the request. Examples of such errors may include:
Business validation error.
Querying for an entity in a database that does not exist. Assume that the database lookup is only one part of the request processing pipeline (e.g. not the client request itself).
The server that handles the original client request makes an internal HTTP request that fails. In this case, the handling server is alive and well, while the internal HTTP request may return a 5xx. Assume that the internal HTTP request is only one part of the request processing pipeline (e.g. not the client request itself).
What is the appropriate HTTP code to assign for these responses?
I've seen API docs use 402 (Stripe) and 422 (PayPal), though I haven't come across anything definitive.
Thoughts from the community welcome! Thanks.
What is the appropriate HTTP code to assign for these responses?
Two important ideas
First - your API is a facade, designed to make it look your service/business logic/etc is just another HTTP compliant document store (aka the "uniform interface" constraint). For the purposes of designing your responses, the specific nature of your resources and the implementation details are not significant.
Second - the important point of a status code is how that status code will be understood by general purpose components (think browsers, web caches, reverse proxies, spiders...). We're trying to help these components broadly categorize the nature of the response. (This is one reason why there are relatively few codes in the 5xx class; there just isn't much that a general purpose component can do differently if the servers handling of the request fails).
And here's the thing: if the general purpose handling of two status codes isn't significantly different. 403 Forbidden and 409 Conflict have different semantics associated with them, but the differences in the standardized handling of those codes, if any, are pretty subtle.
You should make an effort to get 4xx vs 5xx right. It's often less important to precisely identify which 4xx code to use.
Business validation error
Common choices here would be 409 Conflict (your request is not consistent with my copy of the data), or 403 Forbidden (I understood your request, but I'm not going to fulfill it).
If the problem is the data within the request itself (ie: somebody submitted the wrong form) you are more likely to see a 422 Unprocessable Entity (yes, I accept application/json, but not this application/json).
Querying for an entity in a database that does not exist.
The implementation details don't matter; can you trace the problem back to the HTTP request?
If the problem traces back to the URI (we parse the target uri for some information, and use that information to lookup information in our data store), then 404 Not Found is often a good choice. If the problem traces back to the body of the request (we expected some option in the form to match an entry in our enumerated list, but it doesn't), then 409 Conflict is reasonable.
If the server's data is flat out issing, then you are probably looking at a 500 Internal Server Error.
The server that handles the original client request makes an internal HTTP request that fails.
A failure of the server to connect to some other HTTP server is purely an implementation detail, like not being able to connect to a database or a file system.
Unless that failure is a consequence of information in the request, you are going to end up with the 500 Internal Server Error.
This may be where the use of custom defined error response codes may come in, As long as you respect the already defined response codes. For example you could define 600 as your response code and in your API Docs specify what these custom codes mean in detail. For more information of all existing codes I would reference Iana: http://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
Now if your goal is to stay within existing http response boundaries I would recommend something along the lines of:
Unprocessable failure: Status 422
Authorization failure: Status 403
Unable to process could mean many things such as the aforementioned business validation error.
Business validation error.
This could be 400, 422, 403, 409 depending on what business validation means.
Querying for an entity in a database that does not exist. Assume that the database lookup is only one part of the request processing pipeline (e.g. not the client request itself).
Sounds like 400, 409 or 422.
The server that handles the original client request makes an internal HTTP request that fails. In this case, the handling server is alive and well, while the internal HTTP request may return a 5xx. Assume that the internal HTTP request is only one part of the request processing pipeline (e.g. not the client request itself).
The client doesn't know/care about internal http requests. The point is that it's failed, and it's a bug/system failure so this is a 5xx error.
The most important thing to remember when choosing a HTTP status code is:
Make sure you have the general class correct, so 4xx and 5xx depending on this is a client/server error.
If you need something more specific, ask yourself why. Is your client going to be able to make a better decision if it received a 400 or 409? If not, maybe it's not that important.
I wrote a ton about error codes here, and would suggest you read a bunch of the 4xx entries.
Also a great blog post from one of the authors of the HTTP standards, which goes more into the idea that finding the perfect status code for a case is not that important.
I am writing a new API and documenting it using Swagger/OpenAPI. It seems to be a good standard to document error responses, that the developer can expect to encounter.
But I cannot find any guide lines or best practices about Internal Server Error. Every path could in theory throw an unhandled exception. I do not expect it to happen, but it might. Should all paths have a response with status code 500 "Internal Server Error" or should I only document responses the developer can do anything about, i.e. 2xx, 3xx and 4xx?
The offical documentation shows an example for specifying all 5xx status codes in the responses section, but it does not go into details about the specific status code, or the message returned. It also mentions that the API specification should only contain known errors:
Note that an API specification does not necessarily need to cover all possible HTTP response codes, since they may not be known in advance. However, it is expected to cover successful responses and any known errors. By “known errors” we mean, for example, a 404 Not Found response for an operation that returns a resource by ID, or a 400 Bad Request response in case of invalid operation parameters.
You could follow the same approach and specify it like in the example. I think it's not important or even recommended to try to describe it more specifically, since you might not be able to cover all cases anyway and the client is not expected to act on the message returned for internal server errors (possibly other than retrying later). So for example, I would not recommend specifying a message format for it.
Omitting any responses with 5xx HTTP error codes makes sense as well.
I am developing iOS application running against a remote server, having another developer behind it. The project and an API draft we are writing are in initial phase.
The problem we are faced with is that we are not satisfied with existing amount of conventional status codes described by HTTP/REST specifications: there are cases where we are uncertain about what code to pick up.
Examples to provide minimal context:
Server-side validation errors. Fx. Client-side validations are ok, but server API has recently been changed slightly, so a server should return something indicating that it is exactly the validation problem.
An attempt to register user that already exists. SO topics do not provide any precise point on that.
A user is registered, and tries to log in without having the password confirmation procedure accomplished.
Two obvious approaches we see here:
Use fx 400 error for the cases when an appropriate conventional status code could not be found. This will lead us to parsing error text messages from JSON responses. Obviously, this approach will introduce superfluous complication in a client-side code.
Create our own sub-codes system and rely on it in our code. This one involves too much artificial conventions, which will lead us towards becoming too opinionated and arbitrary.
Feeling that the number of such cases is going to grow, we are thinking about an introduction of custom sub-codes in JSON responses our server should give (i.e. choose the second approach).
What I'm asking here:
What are the recommended approaches, strategies, even glues or hacks for these kinds of situations?
What are pros-cons of moving away from strictly following REST/HTTP conventions for status codes?
Thanks!
For validation problems, I use 422 Unprocessable Entity (WebDAV; RFC 4918)
The request was well-formed but was unable to be followed due to semantic errors. This is because the request did not fail because of malformed syntax, but because of semantics.
Then in order to communicate you just need to decide on your errors format, so for situation 1 if there is a required field you might return a 422 with the following.
{
"field": ["required"]
}
I would treat number two as a validation problem, since really it is a validation problem on username, so a 422 with the following.
{
"username": ["conflict"]
}
Number three I would treat as a 403 Forbidden because passing an authorization header will not help and will be forbidden until they do something other than pass credentials.
You could do something like oauth2 does and return a human readable description, a constant that people can code against that further clarifies the error and a uri for more information.
{
"error": "unfinished_registration",
"error_description": "Must finish the user registration process",
"error_uri": "http://yourdocumentation.com"
}
Note: you will find that people disagree on what http codes map to what situation and if 422 should be used since is part of the WebDAV extensions, and that is fine, the most important thing you can do is document what the codes mean and be consistent rather than being perfect with what they mean.
There's no such thing as "sub-codes" in HTTP (Microsoft IIS is clearly violating the spec, and should be flogged).
If there's an appropriate status code, use it; don't say "this status code means that in my application" because that's losing the value of generic status codes; you might as well design your own protocol.
After that, if you need to refine the semantics of the status code, use headers and/or the body.
For the use cases you have described, you could use these error codes:
1) 400 Bad Request
The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
2) 409 Conflict
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.
3) 401 Not Authorized
The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (section 14.8). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
For any other use case that you have, it varies. I would probably go with number 2 if there is truly no standard way of encoding specific errors.