404 Not Found or Bad Request?

Question

Let's say that we have the following REST call:

GET api/companies/5 

(get company with id 5)

If company '5' doesn't exist, we would typically return a 404 Not Found response.

But now, let's take this call:

GET api/companies/5/invoices/10 

(get invoice 10 from company 5)

Now, if company '5' doesn't exist, do we still return a 404 Not Found? Or should a 404 only be returned if the outer most resource can not be found (invoice 10, in this case).

Would Bad Request perhaps be a better option?

Answer 1

404 is your best response. According the HTTP RFC, http://www.ietf.org/rfc/rfc2616.txt, a 400 Bad Request means:

The request could not be understood by the server due to malformed syntax.

Whereas, a 404 states:

The server has not found anything matching the Request-URI.

The entire URI is your resource identifier, and you're not finding a matching resource for that particular identifier.

Answer 2

404 may cause a confusion - is the resource missing or is the actual URL incorrect?

I'd personally go for the 422 code:

   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.