Should a RESTful API return 400 or 404 when passed an invalid id

Question

When building a RESTful API and a user provides an id of resource that does not exist, should you return 404 Not Found or 400 Bad Request

Answer 1

According to the RFC (https://tools.ietf.org/html/rfc2616#section-10.4) the API should return 404 when

"The server has not found anything matching the Request-URI",

which is your example.

400 would be when the resource is found, but the request itself is malformed.

For instance: i. https://api.domain.com/v1/resource/foobar

where foobar DOES NOT exist should return 404

ii. https://api.domain.com/v1/resource/foobar where foobar DOES exist, but the request is wrong ({age:"NOTANINTEGER"}, a string instead of an int for example), it should return 400.

Hope I could help.