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It is common in GraphQL to support error reporting by adding an errors block to a response. Responses can contain both data and errors, for example when some fields where resolved successfully, but other fields had errors. A field with an error is set to null, and an error is added to the errors block.

The DGS framework has an exception handler out-of-the-box that works according to the specification described in the Error Specification section on this page. This exception handler handles exceptions from data fetchers. Any RuntimeException is translated to a GraphQLError of type INTERNAL. For some specific exception types, a more specific GraphQL error type is used.

Exception type GraphQL error type description
AccessDeniedException PERMISSION_DENIED When a @Secured check fails
DgsEntityNotFoundException NOT_FOUND Thrown by the developer when a requested entity (e.g. based on query parameters) isn't found

Mapping custom exceptions

It can be useful to map application specific exceptions to meaningful exceptions back to the client. You can do this by registering a DataFetcherExceptionHandler. Make sure to either extend or delegate to the DefaultDataFetcherExceptionHandler class, this is the default exception handler of the framework. If you don't extend/delegate to this class, you lose the framework's built-in exception handler.

The following is an example of a custom exception handler implementation.

@Component
public class CustomDataFetchingExceptionHandler implements DataFetcherExceptionHandler {
    private final DefaultDataFetcherExceptionHandler defaultHandler = new DefaultDataFetcherExceptionHandler();

    @Override
    public DataFetcherExceptionHandlerResult onException(DataFetcherExceptionHandlerParameters handlerParameters) {
        if(handlerParameters.getException() instanceof MyException) {
            Map<String, Object> debugInfo = new HashMap<>();
            debugInfo.put("somefield", "somevalue");

            GraphQLError graphqlError = TypedGraphQLError.INTERNAL.message("This custom thing went wrong!")
                    .debugInfo(debugInfo)
                    .path(handlerParameters.getPath()).build();
            return DataFetcherExceptionHandlerResult.newResult()
                    .error(graphqlError)
                    .build();
        } else {
            return defaultHandler.onException(handlerParameters);
        }
    }
}

The following data fetcher throws MyException.

@DgsComponent
public class HelloDataFetcher {
    @DgsData(parentType = "Query", field = "hello")
    @DgsEnableDataFetcherInstrumentation(false)
    public String hello(DataFetchingEnvironment dfe) {

        throw new MyException();
    }
}

Querying the hello field results in the following response.

{
  "errors": [
    {
      "message": "This custom thing went wrong!",
      "locations": [],
      "path": [
        "hello"
      ],
      "extensions": {
        "errorType": "INTERNAL",
        "debugInfo": {
          "somefield": "somevalue"
        }
      }
    }
  ],
  "data": {
    "hello": null
  }
}

Error specification

There are two families of errors we typically encounter for GraphQL:

  1. Comprehensive Errors. These are unexpected errors and do not represent a condition that the end user can be expected to fix. Errors of this sort are generally applicable to many types and fields. Such errors appear in the errors array in the GraphQL response.
  2. Errors as Data. These are errors that are informative to the end user (for example: “this title is not available in your country” or “your account has been suspended”). Errors of this sort are typically specific to a particular use case and apply only to certain fields or to a certain subset of fields. These errors are part of the GraphQL schema.

The GraphQLError Interface

The GraphQL specification provides minimal guidance on the structure of an error. The only required field is a message String, which has no defined format. In Studio Edge we would like to have a stronger, more expressive contract. Here is the definition we are using:

field type description
message (non-nullable) String! a string description of the error intended for the developer as a guide to understand and correct the error
locations [Location] an array of code locations, where each location is a map with the keys line and column, both natural numbers starting from 1 that describe the beginning of an associated syntax element
path [String | Int] if the error is associated with one or more particular fields in the response, this field of the error details the paths of those response fields that experienced the error (this allows clients to identify whether a null result is intentional or caused by a runtime error)
extensions [TypedError] see “The TypedError Interface” below
"""
Error format as defined in GraphQL Spec
"""
interface GraphQLError {
    message: String! // Required by GraphQL Spec
    locations: [Location] // See GraphQL Spec
    path: [String | Int] // See GraphQL Spec
    extensions: TypedError
}

See the GraphQL specification: Errors for more information.

The TypedError Interface

Studio Edge defines TypedError as follows:

field type description
errorType (non-nullable) ErrorType! an enumerated error code that is meant as a fairly coarse characterization of an error, sufficient for client-side branching logic
errorDetail ErrorDetail an enumeration that provides more detail about the error, including its specific cause (the elements of this enumeration are subject to change and are not documented here)
origin String the name of the source that issued the error (for instance the name of a backend service, DGS, gateway, client library, or client app)
debugInfo DebugInfo if the request included a flag indicating that it wanted debug information, this field contains that additional information (such as a stack trace or additional reporting from an upstream service)
debugUri String the URI of a page that contains additional information that may be helpful in debugging the error (this could be a generic page for errors of this sort, or a specific page about the particular error instance)
interface TypedError {
    """
    An error code from the ErrorType enumeration.
    An errorType is a fairly coarse characterization
    of an error that should be sufficient for client
    side branching logic.
    """
    errorType: ErrorType!

    """
    The ErrorDetail is an optional field which will
    provide more fine grained information on the error
    condition. This allows the ErrorType enumeration to
    be small and mostly static so that application branching
    logic can depend on it. The ErrorDetail provides a
    more specific cause for the error. This enumeration
    will be much larger and likely change/grow over time.
    """
    errorDetail: ErrorDetail

    """
    Indicates the source that issued the error. For example, could
    be a backend service name, a domain graph service name, or a
    gateway. In the case of client code throwing the error, this
    may be a client library name, or the client app name.
    """
    origin: String

    """
    Optionally provided based on request flag
    Could include e.g. stacktrace or info from
    upstream service
    """
    debugInfo: DebugInfo

    """
    Http URI to a page detailing additional
    information that could be used to debug
    the error. This information may be general
    to the class of error or specific to this
    particular instance of the error.
    """
    debugUri: String
}

The ErrorType Enumeration

The following table shows the available ErrorType enum values:

type description HTTP analog
BAD_REQUEST This indicates a problem with the request. Retrying the same request is not likely to succeed. An example would be a query or argument that cannot be deserialized. 400 Bad Request
FAILED_PRECONDITION The operation was rejected because the system is not in a state required for the operation’s execution. For example, the directory to be deleted is non-empty, an rmdir operation is applied to a non-directory, etc. Use UNAVAILABLE instead if the client can retry just the failing call without waiting for the system state to be explicitly fixed. 400 Bad Request, or 500 Internal Server Error
INTERNAL This indicates that an unexpected internal error was encountered: some invariants expected by the underlying system have been broken. This error code is reserved for serious errors. 500 Internal Server Error
NOT_FOUND This could apply to a resource that has never existed (e.g. bad resource id), or a resource that no longer exists (e.g. cache expired). Note to server developers: if a request is denied for an entire class of users, such as gradual feature rollout or undocumented allowlist, NOT_FOUND may be used. If a request is denied for some users within a class of users, such as user-based access control, PERMISSION_DENIED must be used. 404 Not Found
PERMISSION_DENIED This indicates that the requester does not have permission to execute the specified operation. PERMISSION_DENIED must not be used for rejections caused by exhausting some resource or quota. PERMISSION_DENIED must not be used if the caller cannot be identified (use UNAUTHENTICATED instead for those errors). This error does not imply that the request is valid or the requested entity exists or satisfies other pre-conditions. 403 Forbidden
UNAUTHENTICATED This indicates that the request does not have valid authentication credentials but the route requires authentication. 401 Unauthorized
UNAVAILABLE This indicates that the service is currently unavailable. This is most likely a transient condition, which can be corrected by retrying with a backoff. 503 Unavailable
UNKNOWN This error may be returned, for example, when an error code received from another address space belongs to an error space that is not known in this address space. Errors raised by APIs that do not return enough error information may also be converted to this error. If a client sees an errorType that is not known to it, it will be interpreted as UNKNOWN. Unknown errors must not trigger any special behavior. They may be treated by an implementation as being equivalent to INTERNAL. 520 Unknown Error
The HTTP analogs are only rough mappings that are given here to provide a quick conceptual explanation of the semantics of the error by showing their analogs in the HTTP specification.