Implementation guidance for error handling

The error handling approach defined below follows the approach implemented within GPConnect and the Spine Core FHIR API Framework, based on FHIR STU3.

Guidance for error handling within a FHIR R4 implementation may differ. Refer to FHIR R4 UK Core documentation when available.

Operation outcome usage

When a RESTful interaction or operation fails an OperationOutcome resource is used to convey specific detailed processable error information back to the client as part of the HTTP response.

In the event of an error, provider systems SHALL respond by providing an OperationOutcome resource profiled to Spine-OperationOutcome-1.

The Spine-OperationOutcome-1:

  • SHALL contain a definition of severity in the OperationOutcome.issue.severity field providing a value from the valueset-issue-severity value set. In all cases described in this guidance, the value used will be error.
  • SHALL contain a definition of the type of error in the OperationOutcome.issue.code element, providing a value from the issue-type value set.
  • SHALL contain details of the Spine error code in the OperationOutcome.issue.details.coding.code and OperationOutcome.issue.details.coding.display fields. These shall be taken from the standard set of NHS Spine error codes as defined in the spine-error-or-warning-code-1 value set. The Spine error and warning codes provide a greater degree of error handling granularity, and also ensure a standardised error handling approach across NHS APIs.
  • SHOULD provide additional diagnostic details of the error in the OperationOutcome.diagnostics property where such details securely provide additional error context for consumer applications. Patient identifiable data should not be included within this property.

The sections below provide guidance on the error details to be returned in a number of key scenarios.

Identity validation errors

Provider systems SHALL respond by returning one of the following OperationOutcome error codes where FHIR resource identity error scenarios are encountered:

HTTP code Issue type Error code - code Error code - display
400 value INVALID_IDENTIFIER_SYSTEM Invalid identifier system
400 value INVALID_IDENTIFIER_VALUE Invalid identifier value
400 value INVALID_NHS_NUMBER NHS number invalid
404 not-found ORGANISATION_NOT_FOUND Organisation record not found
404 not-found PATIENT_NOT_FOUND Patient record not found
404 not-found PRACTITIONER_NOT_FOUND Practitioner record not found
404 not-found NO_RECORD_FOUND No record found

Example: Invalid NHS number supplied

If an invalid NHS number value is supplied the following error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "value",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "INVALID_NHS_NUMBER",
            "display": "Invalid NHS number"
          }
        ]
      }
    }
  ]
}

Example: Patient not found

For example, if a valid NHS number value is supplied but no local record exists for that patient, then the following error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "not-found",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "PATIENT_NOT_FOUND",
            "display": "Patient not found"
          }
        ]
      }
    }
  ]
}

Security validation errors

When a client system does not present correct security parameters, provider systems SHALL return one of the following OperationOutcome details:

HTTP code Issue type Error code - code Error code - display
403 forbidden ACCESS_DENIED Access denied

Example: Access denied

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "forbidden",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "ACCESS_DENIED",
            "display": "Access denied"
          }
        ]
      },
      "diagnostics": "Invalid authorisation token."
    }
  ]
}

Duplicate errors

When responding to consumer API requests, provider systems SHALL return one of the following OperationOutcome details when a resource could not be created or updated because it would cause a duplicate in the provider system:

HTTP code Issue type Error code - code Error code - display
409 duplicate DUPLICATE_REJECTED Create would lead to creation of a duplicate resource

For example, if the ePMA system attempted to send a MedicationRequest that is already an active record on the pharmacy system the error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "duplicate",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "DUPLICATE_REJECTED",
            "display": "Create would lead to creation of duplicate resource"
          }
        ]
      },
      "diagnostics": "MedicationRequest record already exists with that logical identifier"
    }
  ]
}

Resource validation errors

Where FHIR resource validation issues arise during processing of consumer requests, provider systems SHALL utilise one the following error details:

HTTP code Issue type Error code - code Error code - display
422 invalid INVALID_RESOURCE Submitted resource is not valid.
422 invalid INVALID_PARAMETER Submitted parameter is not valid.
422 invalid REFERENCE_NOT_FOUND Referenced resource not found.

Detailed diagnostic information MUST be supplied when erroring on the codes above.

INVALID_PARAMETER would be used in the following, or similar, scenarios:

  • An invalid date/time value specified in a custom operation parameter.

INVALID_RESOURCE would be used in situations such as the following:

  • Resource fails structural validation.
  • A resource fails to be processed because of a FHIR constraint, or other rule application, where the error is not already covered by other error codes

REFERENCE_NOT_FOUND describes a scenario where a consumer POSTs a FHIR resource which contains a FHIR reference that cannot be found.

Example: Reference not found

For example, if a MedicationRequest referenced a Practitioner resource that could not be found or resolved by the server. The following error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "invalid",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "REFERENCE_NOT_FOUND",
            "display": "FHIR reference not found"
          }
        ]
      },
      "diagnostics": "Referenced Practitioner resource not found"
    }
  ]
}

Malformed request errors

When the server cannot or will not process a request due to an apparent client error then the following BAD_REQUEST error SHALL be used to return debug details.

HTTP code Issue type Error code - code Error code - display
400 invalid BAD_REQUEST Submitted request is malformed/invalid.

BAD_REQUEST Spine error codes should be used in the following types of scenario:

  • JWT claims information is not valid JSON, is null, or has an invalid value
  • invalid FHIR resource in JWT claim (for example, Patient resource when Practitioner expected)
  • malformed JSON or XML content in request body
  • an expected header is missing or invalid
  • invalid HTTP verb used

Example: Malformed JSON Web Token in request

For example, if the request contained a null claim within a JSON Web Token (JWT), then the following error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "invalid",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "BAD_REQUEST",
            "display": "Bad request"
          }
        ]
      },
      "diagnostics": "Malformed JWT"
    }
  ]
}

Internal server errors

When the FHIR server has received a request for an operation or FHIR resource which is not (yet) implemented, then the NOT_IMPLEMENTED Spine error code SHALL be used.

HTTP code Issue type Error code - code Error code - display
501 not-supported NOT_IMPLEMENTED FHIR resource or operation not implemented at server

When the error is unexpected and the server can’t be more specific on the exact nature of the problem then the INTERNAL_SERVER_ERROR Spine error code SHALL be used, and diagnostics SHALL be included to provide detail of the error.

HTTP code Issue type Error code - code Error code - display
500 processing INTERNAL_SERVER_ERROR Unexpected internal server error.

Example: Unexpected exception

For example, if an unexpected internal exception is thrown by either an Operation or RESTful API, then the following error details would be returned:

{
  "resourceType": "OperationOutcome",
  "meta": {
    "profile": [
      "https://fhir.nhs.uk/STU3/StructureDefinition/Spine-OperationOutcome-1"
    ]
  },
  "issue": [
    {
      "severity": "error",
      "code": "exception",
      "details": {
        "coding": [
          {
            "system": "https://fhir.nhs.uk/STU3/ValueSet/Spine-ErrorOrWarningCode-1",
            "code": "INTERNAL_SERVER_ERROR",
            "display": "Internal server error"
          }
        ]
      },
      "diagnostics": "Any further internal debug details i.e. stack trace details etc."
    }
  ]
}
Tags: fhir development