gRPC defined 18 status codes for returning different types of errors.
I think they’re a pretty good reference if you want to design clear error handling for API.
Status Codes
OK = 0
Not an error; returned on success.
CANCELLED = 1
The operation was cancelled (typically by the caller).
UNKNOWN = 2
Unknown error. An example of where this error may be returned is if a Status value received from another address space belongs to an error-space that is not known in this address space. Also errors raised by APIs that do not return enough error information may be converted to this error.
INVALID_ARGUMENT = 3,
Client specified an invalid argument. Note that this differs from FAILED_PRECONDITION. INVALID_ARGUMENT indicates arguments that are problematic regardless of the state of the system (e.g., a malformed file name).
DEADLINE_EXCEEDED = 4,
Deadline expired before operation could complete. For operations that change the state of the system, this error may be returned even if the operation has completed successfully. For example, a successful response from a server could have been delayed long enough for the deadline to expire.
NOT_FOUND = 5,
Some requested entity (e.g., file or directory) was not found.
ALREADY_EXISTS = 6,
Some entity that we attempted to create (e.g., file or directory) already exists.
PERMISSION_DENIED = 7,
The caller does not have permission to execute the specified operation. PERMISSION_DENIED must not be used for rejections caused by exhausting some resource (use RESOURCE_EXHAUSTED instead for those errors). PERMISSION_DENIED must not be used if the caller can not be identified (use UNAUTHENTICATED instead for those errors).
UNAUTHENTICATED = 16,
The request does not have valid authentication credentials for the operation.
RESOURCE_EXHAUSTED = 8,
Some resource has been exhausted, perhaps a per-user quota, or perhaps the entire file system is out of space.
FAILED_PRECONDITION = 9,
Operation was rejected because the system is not in a state required for the operation’s execution. For example, directory to be deleted may be non-empty, an rmdir operation is applied to a non-directory, etc.
A litmus test that may help a service implementor in deciding between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE:
- Use UNAVAILABLE if the client can retry just the failing call.
- Use ABORTED if the client should retry at a higher-level (e.g., restarting a read-modify-write sequence).
- Use FAILED_PRECONDITION if the client should not retry until the system state has been explicitly fixed. E.g., if an “rmdir” fails because the directory is non-empty, FAILED_PRECONDITION should be returned since the client should not retry unless they have first fixed up the directory by deleting files from it.
- Use FAILED_PRECONDITION if the client performs conditional REST Get/Update/Delete on a resource and the resource on the server does not match the condition. E.g., conflicting read-modify-write on the same resource.
ABORTED = 10,
The operation was aborted, typically due to a concurrency issue like sequencer check failures, transaction aborts, etc.
See litmus test above for deciding between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE.
OUT_OF_RANGE = 11,
Operation was attempted past the valid range. E.g., seeking or reading past end of file.
Unlike INVALID_ARGUMENT, this error indicates a problem that may be fixed if the system state changes. For example, a 32-bit file system will generate INVALID_ARGUMENT if asked to read at an offset that is not in the range [0,2^32-1], but it will generate OUT_OF_RANGE if asked to read from an offset past the current file size.
There is a fair bit of overlap between FAILED_PRECONDITION and OUT_OF_RANGE. We recommend using OUT_OF_RANGE (the more specific error) when it applies so that callers who are iterating through a space can easily look for an OUT_OF_RANGE error to detect when they are done.
UNIMPLEMENTED = 12,
Operation is not implemented or not supported/enabled in this service.
INTERNAL = 13,
Internal errors. Means some invariants expected by underlying System has been broken. If you see one of these errors, Something is very broken.
UNAVAILABLE = 14,
The service is currently unavailable. This is a most likely a transient condition and may be corrected by retrying with a backoff.
warning Although data MIGHT not have been transmitted when this status occurs, there is NOT A GUARANTEE that the server has not seen anything. So in general it is unsafe to retry on this status code if the call is non-idempotent.
See litmus test above for deciding between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE.
DATA_LOSS = 15,
Unrecoverable data loss or corruption.