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I am implementing a PATCH method on a dropwizard REST resource. Currently only a subset of the properties of the resource an be patched. And currently only the replace operation can be fulfilled.

Which HTTP code should I return if I see a PATCH request for a property/path that is not suppported? And what should I return if the unsupported add or remove operations are requested?

cassiomolin
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Manolo
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2 Answers2

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Which HTTP code should I return if I see a PATCH request for a property/path that is not suppported?

In this situation, the server should return 405 to indicate that a HTTP method is not supported by the target resource. Besides the status code, the server must return an Allow header listing the supported methods for that resource:

6.5.5. 405 Method Not Allowed

The 405 (Method Not Allowed) status code indicates that the method received in the request-line is known by the origin server but not supported by the target resource. The origin server MUST generate an Allow header field in a 405 response containing a list of the target resource's currently supported methods.

And what should I return if the unsupported add or remove operations are requested?

I assume you mean add and remove operations from JSON Patch, a JSON document that describes a sequence of operations to apply to a JSON document and is suitable to be used with the PATCH HTTP method.

So have a look a the error handling section of the RFC 5789, the document that defines the PATCH HTTP method.

The situation described in your question is, in fact, an entity that cannot be processed by the server due to semantic reasons. So 422 is a reasonable choice, according to the RFC 5789:

Unprocessable request: Can be specified with a 422 (Unprocessable Entity) response when the server understands the patch document and the syntax of the patch document appears to be valid, but the server is incapable of processing the request. This might include attempts to modify a resource in a way that would cause the resource to become invalid; for instance, a modification to a well-formed XML document that would cause it to no longer be well-formed. [...]

Also keep in mind the following recommendation from the same document:

The entity body of error responses SHOULD contain enough information to communicate the nature of the error to the client. The content- type of the response entity can vary across implementations.

The RFC 7807 defines document formats that can be used for reporting problems in HTTP APIs.

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cassiomolin
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    I realize my post can be interpreted as two questions. So I'll choose this as the answer. The answer to the question I intended to ask is the second one, code 422. What I meant was that the PATCH verb is supported. But only for certain values of "path" in the json patch document (not url path). And only for "op:replace". – Manolo Oct 29 '18 at 11:25
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My vote would be 405:

405 Method Not Allowed

A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.

Coupled with the suggestion that Cassio makes regarding providing enough information to describe the error.

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stdunbar
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    `405` is not suitable for this situation once it will indicate that `PATCH` itself is not supported by the resource. Quoting the [RFC 7231](https://tools.ietf.org/html/rfc7231#section-6.5.5): _"The `405` (Method Not Allowed) status code indicates that **the method received in the request-line** is known by the origin server but not supported by the target resource."_ – cassiomolin Oct 19 '18 at 14:18
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    @CassioMazzochiMolin - the OP said "Which HTTP code should I return if I see a PATCH request for a property/path that is not supported". Isn't that exactly what you just quoted - "the method is not supported by the resource"? Using a WEBDAV specific code seems the wrong way to go to me. – stdunbar Oct 19 '18 at 15:18
  • Turns out that the OP has **two** different questions (and I initially overlooked that). Your answer addresses the situation where `PATCH` is not supported by a particular resource. Hence I've upvoted your answer. – cassiomolin Oct 19 '18 at 15:33