Parser of GitLab error responses fails

[mdeknowis]

We are using 4.8.50 of gitlab4j-api.

We experienced that GitLab returns errors e.g. in case of POST api/v4/groups as

{"error":"path is missing"}

Hence org.gitlab4j.api.GitLabApiException.GitLabApiException(Response) fails to parse the body, because it only supports this structure:

public class ErrorMessage {

    private String message;
...
}

So we have no chance to get the error message.

So it would be very helpful to support also error, so the message of GitLabApiException is filled with the error message.

[gmessner]

As per https://docs.gitlab.com/ee/api/#data-validation-and-error-reporting, all errors except 404 have this structure:

{ "message":"400 (Bad request) \"title\" not given" }

404 errors have this:

{ "error": "404 Not Found" }

If I understand, you are asking for GitLabApiException to add reading of response with the "error" field so that regardless of the error response it will always end up as message property of the GitLabApiException.

[mdeknowis]

That would be great. I'm not sure, if the error response is originally a bug on GitLab side.

But that was the response of our invalid request:

org.gitlab4j.api.GitLabApi               : 1 * Sending client request on thread http-nio-14080-exec-1
1 > POST https://xxx/api/v4/groups
1 > Accept: application/json
1 > Content-Type: application/x-www-form-urlencoded
1 > PRIVATE-TOKEN: xxx
name=managed-solutions&request_access_enabled=false

org.gitlab4j.api.GitLabApi               : 1 * Client response received on thread http-nio-14080-exec-1
1 < 400
1 < Cache-Control: no-cache
1 < Connection: keep-alive
1 < Content-Length: 27
1 < Content-Type: application/json
1 < Date: Thu, 25 Oct 2018 13:40:53 GMT
1 < Vary: Origin
1 < X-Content-Type-Options: nosniff
1 < X-Frame-Options: SAMEORIGIN
1 < X-Request-Id: xxx
1 < X-Runtime: 0.021161
{"error":"path is missing"}

[mdeknowis]

It looks like, the structure can extremely vary:

org.gitlab4j.api.GitLabApi               : 1 * Sending client request on thread http-nio-14080-exec-7
1 > POST https://xxx/api/v4/projects
1 > Accept: application/json
1 > Content-Type: application/x-www-form-urlencoded
1 > PRIVATE-TOKEN: xxx
name=MDE%27s+MCA...

org.gitlab4j.api.GitLabApi               : 1 * Client response received on thread http-nio-14080-exec-7
1 < 400
...
{"message":{"name":["can contain only letters, digits, emojis, '_', '.', dash, space. It must start with letter, digit, emoji or '_'."],"limit_reached":[]}}

Or also

{"message":{"name":["has already been taken"],"path":["has already been taken"],"limit_reached":[]}}

[gmessner]

@mdeknowis
After further examination of the documentation and actual return values, there are 3 possible things in the content when an exception occurs:

1. An attribute is missing "message" as a String (HTTP Status 400)
2. Validation error "message" as a Map<String, String[]> (HTTP Status 400)
3. Unknown route "error" as a String (HTTP Status 404)

I have also seen non 400 and 404 errors, like a 500, but I do not recall what the format was. So my proposal would be as follows:

Modify getMessage() as follows:
Since getMessage() is from the base Exception class and must always return a String, will return the content of the "message" or "error" field as a java.lang.String

Add the following methods to GitLabApiException:
public boolean hasValidationErrors()
public Map<String, String[]> getValidationErrors()

When there are validation errors getMessage() will return a message formatted as follows:

The following fields have validation errors: field1, field2, ...

Making these mods will ensure all possibilities are covered and allowGitLabApiException to be easily used to display error messages in a UI for form validation etc...

[gmessner]

@mdeknowis
I've released GitLab4J-API 4.8.52 with the functionality as described above.

[gmessner]

@mdeknowis
If this addresses your issues, please close once verified.

[mdeknowis]

Thanks. Looks fine!