errcode

package
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 Go to latest Published: Oct 24, 2018 License: Apache-2.0 Imports: 3 Imported by: 168

Documentation

Overview

Package errcode facilitates standardized API error codes. The goal is that clients can reliably understand errors by checking against immutable error codes A Code should never be modified once committed (and released for use by clients). Instead a new Code should be created.

Error codes are represented as strings by CodeStr (see CodeStr documentation).

This package is designed to have few opinions and be a starting point for how you want to do errors in your project. The main requirement is to satisfy the ErrorCode interface by attaching a Code to an Error. See the documentation of ErrorCode. Additional optional interfaces HasClientData and HasOperation are provided for extensibility in creating structured error data representations.

Hierarchies are supported: a Code can point to a parent. This is used in the HTTPCode implementation to inherit HTTP codes found with MetaDataFromAncestors. The hierarchy is present in the Code's string representation with a dot separation.

A few generic top-level error codes are provided here. You are encouraged to create your own application customized error codes rather than just using generic errors.

See JSONFormat for an opinion on how to send back meta data about errors with the error data to a client. JSONFormat includes a body of response data (the "data field") that is by default the data from the Error serialized to JSON. This package provides no help on versioning error data.

Index

Constants

This section is empty.

Variables

View Source 
var (
	// InternalCode is equivalent to HTTP 500 Internal Server Error
	InternalCode = NewCode("internal").SetHTTP(http.StatusInternalServerError)
	// InvalidInputCode is equivalent to HTTP 400 Bad Request
	InvalidInputCode = NewCode("input").SetHTTP(http.StatusBadRequest)
	// NotFoundCode is equivalent to HTTP 404 Not Found
	NotFoundCode = NewCode("missing").SetHTTP(http.StatusNotFound)
	// StateCode is an error that is invalid due to the current object state
	// This is mapped to HTTP 400
	StateCode = NewCode("state").SetHTTP(http.StatusBadRequest)
)

Functions

func ClientData 

func ClientData(errCode ErrorCode) interface{}

ClientData retrieves data from a structure that implements HasClientData If HasClientData is not defined it will use the given ErrorCode object. Normally this function is used rather than GetClientData.

func Operation 

func Operation(v interface{}) string

Operation will return an operation string if it exists. It checks for the HasOperation interface. Otherwise it will return the zero value (empty) string.

func OperationClientData 

func OperationClientData(errCode ErrorCode) (string, interface{})

OperationClientData gives the results of both the ClientData and Operation functions. The Operation function is applied to the original ErrorCode. If that does not return an operation, it is applied to the result of ClientData. This function is used by NewJSONFormat to fill JSONFormat.

Types

type AddOp 

type AddOp func(ErrorCode) OpErrCode

AddOp is constructed by Op. It allows method chaining with AddTo.

func Op 

func Op(operation string) AddOp

Op adds an operation to an ErrorCode with AddTo. This converts the error to the type OpErrCode. 

op := errcode.Op("path.move.x")
if start < obstable && obstacle < end  {
	return op.AddTo(PathBlocked{start, end, obstacle})
}

func (AddOp) AddTo 

func (addOp AddOp) AddTo(err ErrorCode) OpErrCode

AddTo adds the operation from Op to the ErrorCode

type Code 

type Code struct {
	Parent *Code
	// contains filtered or unexported fields
}

A Code has a CodeStr representation. It is attached to a Parent to find metadata from it. The Meta field is provided for extensibility: e.g. attaching HTTP codes.

func NewCode 

func NewCode(codeRep CodeStr) Code

NewCode creates a new top-level code. A top-level code must not contain any dot separators: that will panic Most codes should be created from hierachry with the Child method.

func (Code) Child 

func (code Code) Child(childStr CodeStr) Code

Child creates a new code from a parent. For documentation purposes, a childStr may include the parent codes with dot-separation. An incorrect parent reference in the string panics.

func (Code) CodeStr 

func (code Code) CodeStr() CodeStr

CodeStr gives the full dot-separted path. This is what should be used for equality comparison.

func (Code) HTTPCode 

func (code Code) HTTPCode() int

HTTPCode retrieves the HTTP code for a code or its first ancestor with an HTTP code. If none are specified, it defaults to 400 BadRequest

func (Code) IsAncestor 

func (code Code) IsAncestor(ancestorCode Code) bool

IsAncestor looks for the given code in its ancestors.

func (Code) MetaDataFromAncestors 

func (code Code) MetaDataFromAncestors(metaData MetaData) interface{}

MetaDataFromAncestors looks for meta data starting at the current code. If not found, it traverses up the hierarchy by looking for the first ancestor with the given metadata key. This is used in the HTTPCode implementation to inherit the HTTP Code from ancestors.

func (Code) SetHTTP 

func (code Code) SetHTTP(httpCode int) Code

SetHTTP adds an HTTP code to the meta data

type CodeStr 

type CodeStr string

CodeStr is a representation of the type of a particular error. The underlying type is string rather than int. This enhances both extensibility (avoids merge conflicts) and user-friendliness. A CodeStr can have dot separators indicating a hierarchy.

func (CodeStr) String 

func (str CodeStr) String() string

type CodedError 

type CodedError struct {
	GetCode Code
	Err     error
}

CodedError is a convenience to attach a code to an error and already satisfy the ErrorCode interface. If the error is a struct, that struct will get preseneted as data to the client.

To override the http code or the data representation or just for clearer documentation, you are encouraged to wrap CodeError with your own struct that inherits it. Look at the implementation of invalidInput, internalError, and notFound.

func NewCodedError 

func NewCodedError(err error, code Code) CodedError

NewCodedError is for constructing broad error kinds (e.g. those representing HTTP codes) Which could have many different underlying go errors. Eventually you may want to give your go errors more specific codes. The second argument is the broad code.

If the error given is already an ErrorCode, that will be used as the code instead of the second argument.

func (CodedError) Code 

func (e CodedError) Code() Code

Code returns the GetCode field

func (CodedError) Error 

func (e CodedError) Error() string

func (CodedError) GetClientData 

func (e CodedError) GetClientData() interface{}

GetClientData returns the underlying Err field.

type EmbedOp 

type EmbedOp struct{ Op string }

EmbedOp is designed to be embedded into your existing error structs. It provides the HasOperation interface already, which can reduce your boilerplate.

func (EmbedOp) GetOperation 

func (e EmbedOp) GetOperation() string

GetOperation satisfies the HasOperation interface

type ErrorCode 

type ErrorCode interface {
	Error() string // The Error interface
	Code() Code
}

ErrorCode is the interface that ties an error and RegisteredCode together.

Note that there are additional interfaces (HasClientData, HasOperation, please see the docs) that can be defined by an ErrorCode to customize finding structured data for the client.

ErrorCode allows error codes to be defined without being forced to use a particular struct such as CodedError. CodedError is convenient for generic errors that wrap many different errors with similar codes. Please see the docs for CodedError. For an application specific error with a 1:1 mapping between a go error structure and a RegisteredCode, You probably want to use this interface directly. Example: 

// First define a normal error type
type PathBlocked struct {
	start     uint64 `json:"start"`
	end       uint64 `json:"end"`
	obstacle  uint64 `json:"end"`
}

func (e PathBlocked) Error() string {
	return fmt.Sprintf("The path %d -> %d has obstacle %d", e.start, e.end, e.obstacle)
}

// Now define the code
var PathBlockedCode = errcode.StateCode.Child("state.blocked")

// Now attach the code to the error type
func (e PathBlocked) Code() Code {
	return PathBlockedCode
}

func NewInternalErr 

func NewInternalErr(err error) ErrorCode

NewInternalErr creates an internalError from an err If the given err is an ErrorCode that is a descendant of InternalCode, its code will be used. This ensures the intention of sending an HTTP 50x.

func NewInvalidInputErr 

func NewInvalidInputErr(err error) ErrorCode

NewInvalidInputErr creates an invalidInput from an err If the error is already an ErrorCode it will use that code Otherwise it will use InvalidInputCode which gives HTTP 400

func NewNotFoundErr 

func NewNotFoundErr(err error) ErrorCode

NewNotFoundErr creates a notFound from an err If the error is already an ErrorCode it will use that code Otherwise it will use NotFoundCode which gives HTTP 404

type HasClientData 

type HasClientData interface {
	GetClientData() interface{}
}

HasClientData is used to defined how to retrieve the data portion of an ErrorCode to be returned to the client. Otherwise the struct itself will be assumed to be all the data by the ClientData method. This is provided for exensibility, but may be unnecessary for you. Data should be retrieved with the ClientData method.

type HasOperation 

type HasOperation interface {
	GetOperation() string
}

HasOperation is an interface to retrieve the operation that occurred during an error. The end goal is to be able to see a trace of operations in a distributed system to quickly have a good understanding of what occurred. Inspiration is taken from upspin error handling: https://commandcenter.blogspot.com/2017/12/error-handling-in-upspin.html The relationship to error codes is not one-to-one. A given error code can be triggered by multiple different operations, just as a given operation could result in multiple different error codes.

GetOperation is defined, but generally the operation should be retrieved with Operation(). Operation() will check if a HasOperation interface exists. As an alternative to defining this interface you can use an existing wrapper (OpErrCode via AddOp) or embedding (EmbedOp) that has already defined it.

type JSONFormat 

type JSONFormat struct {
	Data      interface{} `json:"data"`
	Msg       string      `json:"msg"`
	Code      CodeStr     `json:"code"`
	Operation string      `json:"operation,omitempty"`
}

JSONFormat is an opinion on how to serialize an ErrorCode to JSON. Msg is the string from Error(). The Data field is filled in by GetClientData

func NewJSONFormat 

func NewJSONFormat(errCode ErrorCode) JSONFormat

NewJSONFormat turns an ErrorCode into a JSONFormat

type MetaData 

type MetaData map[CodeStr]interface{}

MetaData is a pattern for attaching meta data to codes and inheriting it from a parent. See MetaDataFromAncestors. This is used to attach an HTTP code to a Code.

type OpErrCode 

type OpErrCode struct {
	Operation string
	Err       ErrorCode
}

OpErrCode is an ErrorCode with an "Operation" field attached. This may be used as a convenience to record the operation information for the error. However, it isn't required to be used, see the HasOperation documentation for alternatives.

func (OpErrCode) Code 

func (e OpErrCode) Code() Code

Code returns the unerlying Code of Err.

func (OpErrCode) Error 

func (e OpErrCode) Error() string

Error prefixes the operation to the underlying Err Error.

func (OpErrCode) GetClientData 

func (e OpErrCode) GetClientData() interface{}

GetClientData returns the ClientData of the underlying Err.

func (OpErrCode) GetOperation 

func (e OpErrCode) GetOperation() string

GetOperation satisfies the HasOperation interface.

Source Files

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