REST API 404: Bad URI, or Missing Resource?

Question

I'm building a REST API, but I've encountered a problem.

It seems that accepted practice in designing a REST API is that if the resource requested doesn't exist, a 404 is returned.

However, to me, this adds unnecessary ambiguity. HTTP 404 is more traditionally associated with a bad URI. So in effect we're saying "Either you got to the right place, but that specific record does not exist, or there's no such location on the Internets! I'm really not sure which one..."

Consider the following URI:

http://mywebsite/api/user/13

If I get a 404 back, is that because User 13 does not exist? Or is it because my URL should have been:

http://mywebsite/restapi/user/13

In the past, I've just returned a NULL result with an HTTP 200 OK response code if the record doesn't exist. It's simple, and in my opinion very clean, even if it's not necessarily accepted practice. But is there a better way to do this?

Answer 1

Paradigms

My guess to what has fueled the discussion here is that different programmers approach problems differently.

In the database paradigm selecting from a relation with a key that does not exist won't get an error but an empty result (zero tupels). Likewise if attempting to delete from a relation with no matching records. A valid request with a likewise valid response no records affected.

In the service realm a client might get more information and an error if a resource is non existant. It boils down to this: if a client requests a very specific url (/user/9) and 9 was not assigned it is just as not found as /usr/9 the resource does not exist and should yield a 404.

If however I allow the service to find resources based on something of a wildcard an empty result is not an error situation but a clear 204 Empty Result situation. So /user?Firstname=John will never be a 404 if both resource "user" exist and these Things have Firstname(s) but instead a 200 or a 204. However /user?FName=John is a malformed and should get a 400 Bad Request (not a 404 Not Found) probably with body explaining what is going on rfc7807.

Carying this thought further it would mean that /user/9 could be an 404 but /user?ID=9 would be a 204 if "user"'s are Things and have "ID"'s but ID 9 does not gel. This would help client development considerably as the first case clearly has a logic problem (the url was created based on for instance a list provided in another request) or a user problem (the user got hold of a user number 9 and attempts to search for it) which should get an empty result of some sort, not an error.

TLDR;

If user is a valid target but user 9 does not exist

• /usr/10 => 400 Bad request usr is not a Thing
• /user/8 => 200 if a user with ID 8 exist, that is
• /user/9 => 404 this resource does not exist
• /user?ID=9 => 204 valid request but no results, if IDs are Thingies
• /user?Number=9 => 400 Bad request the Thing user does not have Number
• /user?ID=.gte.9 => 200 or 204 # whether users with usernr >= 9 exist

Answer 2

Consider the following URI:

http://mywebsite/api/user/13

If I get a 404 back, is that because User 13 does not exist? Or is it because my URL should have been:

http://mywebsite/restapi/user/13

Unless you're designing with the intention that your users be manually typing out every URL, I'd say this is a non-issue. The client program shouldn't be making the user do this (unless it's curl), and if it does then the client developer is doing it wrong.

If the URL points to a specific resource and that resource cannot be found, 404 is the correct response.

This is different from a query, eg. GET /user/13 vs GET /user?id=13. The latter should return a 200 and an empty list because it asked for all matches and there were none as opposed to asking for one specific thing that should be findable. GET /uzer?id=13 should 404 because uzer isn't a thing that can be found.

Either way, the back-end behaved correctly and returned a correct and valid answer. If the client (API client, that is, i.e. a program) is hitting wrong paths, the client is misconfigured.

And, if you're doing REST and not just JSON API, then the client should have been given valid paths on GET / so there's no chance of a typo in the first place. With that out of the way, every reason to use something other than 404 disappears.

Update:

One of the key things that seems to be frequently misunderstood about REST—even by myself when I originally wrote this answer—is that a URI refers to a representation of a resource. REST makes explicit allowance for references (URIs) to resources that don't exist yet, but what the server should do with such "forward references" is not described by REST. HTTP does have an opinion: it represents not-yet-defined resources with a 404 Not Found response and some generic message.

The REST architectural style is precisely what was used in the design of HTTP/1.1. Therefore, if your HTTP API is not merely using http as a transport like SOAP or GraphQL, then it should be closely following the semantics of HTTP in order to be "RESTful."* That is to say, if the client requests a resource that doesn't exist, the correct representation in HTTP is, again, 404. Put another way, a 404 is not an error but a placeholder representation for something that cannot be represented.

Revisiting queries briefly, imo a (valid) query always has a representation because all possible queries on an extant resource always exist. If the underlying resource yields an empty set, a 200 Ok with a representation of an empty set is compliant with HTTP.

* HTTP is not a requirement of REST, of course. You could, in principle, build a RESTful GraphQL application, probably (with years of work), but HTTP is already RESTful so why reinvent the wheel?

Answer 3

This recently came up with our team. We use both 404 Not found with a message body and 204 No Content based on the following rational.

If the request URI indicates the location of a single resource, we use 404 Not found. When the request queries a URI, we use 204 No Content

• http://mywebsite/api/user/13 would return 404 when user 13 does not exist
• http://mywebsite/api/users?id=13 would return 204 no content
• http://mywebsite/api/users?firstname=test would return 204 no content

The idea here being, 'query routes' are expected to be able to return 1, many or no content.

Whatever pattern you choose, the most important things is to be consistent - so get buy in from your team.

Answer 4

Since this discussion seems to be able to survive the end of time I'll throw in the JSON:API Specifications

404 Not Found A server MUST respond with 404 Not Found when processing a request to fetch a single resource that does not exist, except when the request warrants a 200 OK response with null as the primary data (as described above).

HTTP/1.1 200 OK
Content-Type: application/vnd.api+json

{
  "links": {
    "self": "http://example.com/articles/1/author"
  },
  "data": null
}

Also please see this Stackoverflow question

Answer 5

For this scenario HTTP 404 is response code for the response from the REST API Like 400, 401, 404 , 422 unprocessable entity

use the Exception handling to check the full exception message.

try{
  // call the rest api
} catch(RestClientException e) {
     //process exception
     if(e instanceof HttpStatusCodeException){
        String responseText=((HttpStatusCodeException)e).getResponseBodyAsString();
         //now you have the response, construct json from it, and extract the errors
         System.out.println("Exception :" +responseText);
     }

}

This exception block give you the proper message thrown by the REST API

Answer 6

That is an very old post but I faced to a similar problem and I would like to share my experience with you guys.

I am building microservice architecture with rest APIs. I have some rest GET services, they collect data from back-end system based on the request parameters.

I followed the rest API design documents and I sent back HTTP 404 with a perfect JSON error message to client when there was no data which align to the query conditions (for example zero record was selected).

When there was no data to sent back to the client I prepared an perfect JSON message with internal error code, etc. to inform the client about the reason of the "Not Found" and it was sent back to the client with HTTP 404. That works fine.

Later I have created a rest API client class which is an easy helper to hide the HTTP communication related code and I used this helper all the time when I called my rest APIs from my code.

BUT I needed to write confusing extra code just because HTTP 404 had two different functions:

• the real HTTP 404 when the rest API is not available in the given url, it is thrown by the application server or web-server where the rest API application runs
• client get back HTTP 404 as well when there is no data in database based on the where condition of the query.

Important: My rest API error handler catches all the exceptions appears in the back-end service which means in case of any error my rest API always returns with a perfect JSON message with the message details.

This is the 1st version of my client helper method which handles the two different HTTP 404 response:

public static String getSomething(final String uuid) {
    String serviceUrl = getServiceUrl();
    String path = "user/" + , uuid);
    String requestUrl = serviceUrl + path;
    String httpMethod = "GET";

    Response response = client
            .target(serviceUrl)
            .path(path)
            .request(ExtendedMediaType.APPLICATION_UTF8)
            .get();

    if (response.getStatus() == Response.Status.OK.getStatusCode()) {
        // HTTP 200
        return response.readEntity(String.class);
    } else {
        // confusing code comes here just because
        // I need to decide the type of HTTP 404...

        // trying to parse response body
        try {
            String responseBody = response.readEntity(String.class);
            ObjectMapper mapper = new ObjectMapper();
            ErrorInfo errorInfo = mapper.readValue(responseBody, ErrorInfo.class);

            // re-throw the original exception
            throw new MyException(errorInfo);

        } catch (IOException e) {
            // this is a real HTTP 404
            throw new ServiceUnavailableError(response, requestUrl, httpMethod);
        }

    // this exception will never be thrown
    throw new Exception("UNEXPECTED ERRORS, BETTER IF YOU DO NOT SEE IT IN THE LOG");
}

BUT, because my Java or JavaScript client can receive two kind of HTTP 404 somehow I need to check the body of the response in case of HTTP 404. If I can parse the response body then I am sure I got back a response where there was no data to send back to the client.

If I am not able to parse the response that means I got back a real HTTP 404 from the web server (not from the rest API application).

It is so confusing and the client application always needs to do extra parsing to check the real reason of HTTP 404.

Honestly I do not like this solution. It is confusing, needs to add extra bullshit code to clients all the time.

So instead of using HTTP 404 in this two different scenarios I decided that I will do the following:

• I am not using HTTP 404 as a response HTTP code in my rest application anymore.
• I am going to use HTTP 204 (No Content) instead of HTTP 404.

In that case client code can be more elegant:

public static String getString(final String processId, final String key) {
    String serviceUrl = getServiceUrl();
    String path = String.format("key/%s", key);
    String requestUrl = serviceUrl + path;
    String httpMethod = "GET";

    log(requestUrl);

    Response response = client
            .target(serviceUrl)
            .path(path)
            .request(ExtendedMediaType.APPLICATION_JSON_UTF8)
            .header(CustomHttpHeader.PROCESS_ID, processId)
            .get();

    if (response.getStatus() == Response.Status.OK.getStatusCode()) {
        return response.readEntity(String.class);
    } else {
        String body = response.readEntity(String.class);
        ObjectMapper mapper = new ObjectMapper();
        ErrorInfo errorInfo = mapper.readValue(body, ErrorInfo.class);
        throw new MyException(errorInfo);
    }

    throw new AnyServerError(response, requestUrl, httpMethod);
}

I think this handles that issue better.

If you have any better solution please share it with us.

Answer 7

So in essence, it sounds like the answer could depend on how the request is formed.

If the requested resource forms part of the URI as per a request to http://mywebsite/restapi/user/13 and user 13 does not exist, then a 404 is probably appropriate and intuitive because the URI is representative of a non-existent user/entity/document/etc. The same would hold for the more secure technique using a GUID http://mywebsite/api/user/3dd5b770-79ea-11e1-b0c4-0800200c9a66 and the api/restapi argument above.

However, if the requested resource ID was included in the request header [include your own example], or indeed, in the URI as a parameter, eg http://mywebsite/restapi/user/?UID=13 then the URI would still be correct (because the concept of a USER does exits at http://mywebsite/restapi/user/); and therefore the response could reasonable be expected to be a 200 (with an appropriately verbose message) because the specific user known as 13 does not exist but the URI does. This way we are saying the URI is good, but the request for data has no content.

Personally a 200 still doesn't feel right (though I have previously argued it does). A 200 response code (without a verbose response) could cause an issue not to be investigated when an incorrect ID is sent for example.

A better approach would be to send a 204 - No Contentresponse. This is compliant with w3c's description *The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation.*1 The confusion, in my opinion is caused by the Wikipedia entry stating 204 No Content - The server successfully processed the request, but is not returning any content. Usually used as a response to a successful delete request. The last sentence is highly debateable. Consider the situation without that sentence and the solution is easy - just send a 204 if the entity does not exist. There is even an argument for returning a 204 instead of a 404, the request has been processed and no content has been returned! Please be aware though, 204's do not allow content in the response body

Sources

http://en.wikipedia.org/wiki/List_of_HTTP_status_codes 1. http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

Answer 8

This old but excellent article... http://www.infoq.com/articles/webber-rest-workflow says this about it...

404 Not Found - The service is far too lazy (or secure) to give us a real reason why our request failed, but whatever the reason, we need to deal with it.

Answer 9

404 Not Found technically means that uri does not currently map to a resource. In your example, I interpret a request to http://mywebsite/api/user/13 that returns a 404 to imply that this url was never mapped to a resource. To the client, that should be the end of conversation.

To address concerns with ambiguity, you can enhance your API by providing other response codes. For example, suppose you want to allow clients to issue GET requests the url http://mywebsite/api/user/13, you want to communicate that clients should use the canonical url http://mywebsite/restapi/user/13. In that case, you may want to consider issuing a permanent redirect by returning a 301 Moved Permanently and supply the canonical url in the Location header of the response. This tells the client that for future requests they should use the canonical url.

Answer 10

The Uniform Resource Identifier is a unique pointer to the resource. A poorly form URI doesn't point to the resource and therefore performing a GET on it will not return a resource. 404 means The server has not found anything matching the Request-URI. If you put in the wrong URI or bad URI that is your problem and the reason you didn't get to a resource whether a HTML page or IMG.

Answer 11

Use 404 if the resource does not exist. Don't return 200 with an empty body.

This is akin to undefined vs empty string (e.g. "") in programming. While very similar, there is definitely a difference.

404 means that nothing exists at that URI (like an undefined variable in programming). Returning 200 with an empty body means that something does exist there and that something is just empty right now (like an empty string in programming).

404 doesn't mean it was a "bad URI". There are special HTTP codes that are intended for URI errors (e.g. 414 Request-URI Too Long).

Answer 12

As with most things, "it depends". But to me, your practice is not bad and is not going against the HTTP spec per se. However, let's clear some things up.

First, URI's should be opaque. Even if they're not opaque to people, they are opaque to machines. In other words, the difference between http://mywebsite/api/user/13, http://mywebsite/restapi/user/13 is the same as the difference between http://mywebsite/api/user/13 and http://mywebsite/api/user/14 i.e. not the same is not the same period. So a 404 would be completely appropriate for http://mywebsite/api/user/14 (if there is no such user) but not necessarily the only appropriate response.

You could also return an empty 200 response or more explicitly a 204 (No Content) response. This would convey something else to the client. It would imply that the resource identified by http://mywebsite/api/user/14 has no content or is essentially nothing. It does mean that there is such a resource. However, it does not necessarily mean that you are claiming there is some user persisted in a data store with id 14. That's your private concern, not the concern of the client making the request. So, if it makes sense to model your resources that way, go ahead.

There are some security implications to giving your clients information that would make it easier for them to guess legitimate URI's. Returning a 200 on misses instead of a 404 may give the client a clue that at least the http://mywebsite/api/user part is correct. A malicious client could just keep trying different integers. But to me, a malicious client would be able to guess the http://mywebsite/api/user part anyway. A better remedy would be to use UUID's. i.e. http://mywebsite/api/user/3dd5b770-79ea-11e1-b0c4-0800200c9a66 is better than http://mywebsite/api/user/14. Doing that, you could use your technique of returning 200's without giving much away.

Answer 13

404 is just the HTTP response code. On top of that, you can provide a response body and/or other headers with a more meaningful error message that developers will see.