errors

Documentation

Overview

Package errors defines an error representation that associates an error message to an error code.

It's meant to allow translation to other kinds of errors (e.g., gRPC errors) without information loss, while at the same time keeping the implementation independent of specific libraries.

Errors created by this package are meant to be user-visible, therefore care must be taken to ensure that both messages and error codes are chosen according to the perspective of the RPC caller. For example, a function that reads a file may be tempted to return an error with a NotFound code, but from the perspective of the RPC caller, FailedPrecondition would be clearer (as it indicates a bad argument on the request).

Index

• func Errorf(code Code, format string, a ...interface{}) error
• func New(code Code, msg string) error
• type Code
  • func ErrorCode(err error) Code
  • func (i Code) String() string
• type TrillianError

Functions

func Errorf

func Errorf(code Code, format string, a ...interface{}) error

Errorf creates a TrillianError from the specified code and message.

Note that errors created by this package are meant to be user-visible, therefore both code and message should be chosen from the perspective of the RPC caller.

func New

func New(code Code, msg string) error

New creates a TrillianError from the specified code and message.

Note that errors created by this package are meant to be user-visible, therefore both code and message should be chosen from the perspective of the RPC caller.

Types

type Code

type Code uint32

Code mirrors gRPC's codes.Code.

const (
	// OK is returned on success.
	OK Code = 0

	// Canceled indicates the operation was cancelled (typically by the caller).
	Canceled Code = 1

	// 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.
	Unknown Code = 2

	// InvalidArgument indicates client specified an invalid argument.
	// Note that this differs from FailedPrecondition. It indicates arguments
	// that are problematic regardless of the state of the system
	// (e.g., a malformed file name).
	InvalidArgument Code = 3

	// DeadlineExceeded means operation expired before completion.
	// 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.
	DeadlineExceeded Code = 4

	// NotFound means some requested entity (e.g., file or directory) was
	// not found.
	NotFound Code = 5

	// AlreadyExists means an attempt to create an entity failed because one
	// already exists.
	AlreadyExists Code = 6

	// PermissionDenied indicates the caller does not have permission to
	// execute the specified operation. It must not be used for rejections
	// caused by exhausting some resource (use ResourceExhausted
	// instead for those errors).  It must not be
	// used if the caller cannot be identified (use Unauthenticated
	// instead for those errors).
	PermissionDenied Code = 7

	// Unauthenticated indicates the request does not have valid
	// authentication credentials for the operation.
	Unauthenticated Code = 16

	// ResourceExhausted indicates some resource has been exhausted, perhaps
	// a per-user quota, or perhaps the entire file system is out of space.
	ResourceExhausted Code = 8

	// FailedPrecondition indicates 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 FailedPrecondition, Aborted, and Unavailable:
	//  (a) Use Unavailable if the client can retry just the failing call.
	//  (b) Use Aborted if the client should retry at a higher-level
	//      (e.g., restarting a read-modify-write sequence).
	//  (c) Use FailedPrecondition 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, FailedPrecondition
	//      should be returned since the client should not retry unless
	//      they have first fixed up the directory by deleting files from it.
	//  (d) Use FailedPrecondition 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.
	FailedPrecondition Code = 9

	// Aborted indicates the operation was aborted, typically due to a
	// concurrency issue like sequencer check failures, transaction aborts,
	// etc.
	//
	// See litmus test above for deciding between FailedPrecondition,
	// Aborted, and Unavailable.
	Aborted Code = 10

	// OutOfRange means operation was attempted past the valid range.
	// E.g., seeking or reading past end of file.
	//
	// Unlike InvalidArgument, this error indicates a problem that may
	// be fixed if the system state changes. For example, a 32-bit file
	// system will generate InvalidArgument if asked to read at an
	// offset that is not in the range [0,2^32-1], but it will generate
	// OutOfRange if asked to read from an offset past the current
	// file size.
	//
	// There is a fair bit of overlap between FailedPrecondition and
	// OutOfRange.  We recommend using OutOfRange (the more specific
	// error) when it applies so that callers who are iterating through
	// a space can easily look for an OutOfRange error to detect when
	// they are done.
	OutOfRange Code = 11

	// Unimplemented indicates operation is not implemented or not
	// supported/enabled in this service.
	Unimplemented Code = 12

	// Internal errors.  Means some invariants expected by underlying
	// system has been broken.  If you see one of these errors,
	// something is very broken.
	Internal Code = 13

	// Unavailable indicates the service is currently unavailable.
	// This is a most likely a transient condition and may be corrected
	// by retrying with a backoff.
	//
	// See litmus test above for deciding between FailedPrecondition,
	// Aborted, and Unavailable.
	Unavailable Code = 14

	// DataLoss indicates unrecoverable data loss or corruption.
	DataLoss Code = 15
)

Descriptions are copied from https://github.com/grpc/grpc-go/blob/master/codes/codes.go for developer convenience.

func ErrorCode

func ErrorCode(err error) Code

ErrorCode returns the assigned Code if err is a TrillianError. If err is nil, OK is returned. If err is not a TrillianError, Unknown is returned.

func (Code) String

func (i Code) String() string

type TrillianError

type TrillianError interface {
	error

	// Code returns the corresponding code to the error.
	Code() Code
}

TrillianError associates an error message with a failure code in order to make error translation possible by other layers (e.g., TrillianError to gRPC).

TrillianError instances contain user-visible messages and codes, both of which should be chosen from the perspective of the RPC caller.