errors

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 Go to latest Published: May 3, 2020 License: MIT Imports: 7 Imported by: 4

README

errors

Mature This project adheres to Semantic Versioning. This package is considered mature, you should expect package stability in Minor and Patch version releases

  • Major: backwards incompatible package updates
  • Minor: feature additions
  • Patch: bug fixes, backward compatible model and function changes, etc.

CHANGELOG

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bdlm/errors provides simple, concise, useful error handling and annotation.

One of the biggest frustrations with Go error handling is the lack of forensic and meta information errors should provide. By default errors are just a string and possibly a type. They can't tell you where they occurred or the path through the call stack they followed. The error implementation in Go is robust enough to control program flow but it's not very efficient for troubleshooting or analysis.

Since the idom in Go is that we pass the error back up the stack anyway:

if nil != err {
	return err
}

it's trivial to make errors much more informative with a simple error package. bdlm/errors makes this easy and supports tracing the call stack and the error callers with relative ease. Custom error types are also fully compatible with this package and can be used freely.

Install

go get github.com/bdlm/errors/v2

Quick start

See the documentation for more examples. All exported methods work with any error type as well as nil values.

Create an error
var MyError = errors.New("My error")
Create an error using formatting verbs
var MyError = errors.Errorf("My error #%d", 1)
Wrap an error
if nil != err {
	return errors.Wrap(err, "the operation failed")
}
Wrap an error with another error
err := try1()
if nil != err {
	err2 := try2()
	if nil != err2 {
		return errors.WrapE(err, err2)
	}
	return err
}
Get the previous error, if any
err := doWork()
if prevErr := errors.Unwrap(err); nil != prevErr {
	...
}
Test for a specific error type
var MyError = errors.New("My error")
func main() {
	err := doWork()
	if errors.Is(err, MyError) {
		...
	}
}
Test to see if a specific error type exists anywhere in an error stack
var MyError = errors.New("My error")
func main() {
	err := doWork()
	if errors.Has(err, MyError) {
		...
	}
}
Iterate through an error stack
err := doWork()
for nil != err {
	fmt.Println(err)
	err = errors.Unwrap(err)
}

See the documentation for more examples.

The Error interface

The exported package methods return github.com/bdlm/std/v2/errors interfaces that expose metadata and troubleshooting information:

// Error defines a robust error stack interface.
type Error interface {
	// Caller returns the associated Caller instance.
	Caller() Caller

	// Error implements error.
	Error() string

	// Has tests to see if the test error exists anywhere in the error
	// stack.
	Has(test error) bool

	// Is tests to see if the test error matches most recent error in the
	// stack.
	Is(test error) bool

	// Unwrap returns the next error, if any.
	Unwrap() Error
}

// Caller defines an interface to runtime caller results.
type Caller interface {
	// File returns the file in which the call occurred.
	File() string

	// Func returns the name of the function in which the call occurred.
	Func() string

	// Line returns the line number in the file in which the call occurred.
	Line() int

	// Pc returns the program counter.
	Pc() uintptr

	// Trace returns the call stack.
	Trace() Trace
}

// Trace defines an error trace.
type Trace []Caller

Documentation

Overview

Package errors provides simple, concise, useful error handling and annotation. 

import (
	errs "github.com/mkenney/go-errors"
)

One of the biggest frustrations with Go error handling is the lack of forensic and meta information errors can provide. Out of the box errors are just a string and possibly a type. They can't tell you where they occurred or the path through the call stack they followed. The error implementation in Go is robust enough to control program flow but it's not very efficient for troubleshooting or analysis.

Since the idom in Go is that we pass the error back up the stack anyway: 

if nil != err {
	return err
}

it's trivial to make errors much more informative with a simple error package. This package makes this easy and supports tracing the call stack and the error callers with relative ease. Custom error types are also fully compatible with this package and can be used freely.

Quick start

Create an error: 

var MyError = errors.New("My error")

Create an error using formatting verbs: 

var MyError = errors.Errorf("My error #%d", 1)

Wrap an error: 

if nil != err {
	return errors.Wrap(err, "the operation failed")
}

Wrap an error with another error: 

err := try1()
if nil != err {
	err2 := try2()
	if nil != err2 {
		return errors.Wrap(err, err2)
	}
	return err
}

Get the previous error, if any: 

err := doWork()
if prevErr := errors.Unwrap(err); nil != prevErr {
	...
}

Test for a specific error type: 

var MyError = errors.New("My error")
func main() {
	err := doWork()
	if errors.Is(err, MyError) {
		...
	}
}

Test to see if a specific error type exists anywhere in an error stack: 

var MyError = errors.New("My error")
func main() {
	err := doWork()
	if errors.Has(err, MyError) {
		...
	}
}

Iterate through an error stack: 

err := doWork()
for nil != err {
	fmt.Println(err)
	err = errors.Unwrap(err)
}

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func Caller 

func Caller(err error) std_err.Caller

Caller returns the Caller associated with an Error, if any.

func Has 

func Has(err, test error) bool

Has returns whether an error or an error stack stack is or contains the referenced error type.

func Is 

func Is(err, test error) bool

Is returns whether an error is the referenced error type.

func NewCaller 

func NewCaller() std_err.Caller

NewCaller returns a new Caller containing data for the current call stack.

func Unwrap 

func Unwrap(e error) std_err.Error

Unwrap returns the previous error.

Example 
err1 := errors.New("error 1")
err2 := errors.Wrap(err1, "error 2")
err := errors.Unwrap(err2)

fmt.Println(err)

Output:

error 1
Example (IterateStack) 
err := loadConfig()

// Iterate through an error stack, last in - first out.
for err != nil {
	fmt.Printf("%+v\n", err)
	err = errors.Unwrap(err)
}

Output:

service configuration could not be loaded - #0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig); could not decode configuration data - #1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig); could not read configuration file - #2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig); read: end of input - #3 print.go:597 (fmt.(*pp).handleMethods);
could not decode configuration data - #0 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig); could not read configuration file - #1 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig); read: end of input - #2 print.go:597 (fmt.(*pp).handleMethods);
could not read configuration file - #0 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig); read: end of input - #1 print.go:597 (fmt.(*pp).handleMethods);
read: end of input - #0 examples_test.go:168 (github.com/bdlm/errors/v2_test.ExampleUnwrap_iterateStack);

Types

type E 

type E struct {
	// contains filtered or unexported fields
}

E is a github.com/bdlm/std.Error interface implementation and simply wraps the exported package methods as a convenience.

func Errorf 

func Errorf(msg string, data ...interface{}) *E

Errorf formats according to a format specifier and returns an error that contains caller data.

func New 

func New(msg string) *E

New returns an error that contains caller data.

Example 
err := errors.New("this is an error message")

fmt.Println(err)

Output:

this is an error message

func Trace 

func Trace(e error) *E

Trace adds an additional caller line to the error trace trace on an error to aid in debugging and forensic analysis.

func Track 

func Track(e error) *E

Track updates the error stack with additional caller data.

func Wrap 

func Wrap(e error, msg string, data ...interface{}) *E

Wrap returns a new error that wraps the provided error.

Example 
// Wrap an error with additional metadata.
err := loadConfig()
err = errors.Wrap(err, "loadConfig returned an error")

fmt.Printf("% +v", err)

Output:

loadConfig returned an error - #0 examples_test.go:180 (github.com/bdlm/errors/v2_test.ExampleWrap);
service configuration could not be loaded - #1 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig);
could not decode configuration data - #2 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig);
could not read configuration file - #3 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig);
read: end of input - #4 print.go:597 (fmt.(*pp).handleMethods);

func WrapE 

func WrapE(e, err error) *E

WrapE returns a new error that wraps the provided error.

Example 
var internalServerError = grpcErrors.Error(
	grpcCodes.Internal,
	"internal server error",
)

// Wrap an error with another error to maintain context.
err := loadConfig()
if nil != err {
	err = errors.WrapE(err, internalServerError)
}

fmt.Printf("% +v", err)

Output:

rpc error: code = Internal desc = internal server error - #0 examples_test.go:199 (github.com/bdlm/errors/v2_test.ExampleWrapE);
service configuration could not be loaded - #1 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig);
could not decode configuration data - #2 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig);
could not read configuration file - #3 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig);
read: end of input - #4 print.go:597 (fmt.(*pp).handleMethods);

func (*E) Caller 

func (e *E) Caller() std_err.Caller

Caller implements std.Error.

func (*E) Error 

func (e *E) Error() string

Error implements std.Error.

func (*E) Format 

func (e *E) Format(state fmt.State, verb rune)

Format implements fmt.Formatter. https://golang.org/pkg/fmt/#hdr-Printing

Verbs: 

%s      Returns the error string of the last error added
%v      Alias for %s

Flags: 

#      JSON formatted output, useful for logging
-      Output caller details, useful for troubleshooting
+      Output full error stack details, useful for debugging
' '    (space) Add whitespace formatting for readability, useful for development

Examples: 

%s:    An error occurred
%v:    An error occurred
%-v:   #0 stack_test.go:40 (github.com/bdlm/error_test.TestErrors) - An error occurred
%+v:   #0 stack_test.go:40 (github.com/bdlm/error_test.TestErrors) - An error occurred #1 stack_test.go:39 (github.com/bdlm/error_test.TestErrors) - An error occurred
%#v:   {"error":"An error occurred"}
%#-v:  {"caller":"#0 stack_test.go:40 (github.com/bdlm/error_test.TestErrors)","error":"An error occurred"}
%#+v:  [{"caller":"#0 stack_test.go:40 (github.com/bdlm/error_test.TestErrors)","error":"An error occurred"},{"caller":"#0 stack_test.go:39 (github.com/bdlm/error_test.TestErrors)","error":"An error occurred"}]
Example (Json) 
err := loadConfig()
fmt.Printf("%#v", err)

Output:

[{"error":"service configuration could not be loaded"}]
Example (JsonDetail) 
err := loadConfig()
fmt.Printf("%#-v", err)

Output:

[{"caller":"#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)","error":"service configuration could not be loaded"}]
Example (JsonDetailPreformat) 
err := loadConfig()
fmt.Printf("% #-v", err)

Output:

[
    {
        "caller": "#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)",
        "error": "service configuration could not be loaded"
    }
]
Example (JsonPreformat) 
err := loadConfig()
fmt.Printf("% #v", err)

Output:

[
    {
        "error": "service configuration could not be loaded"
    }
]
Example (JsonTrace) 
err := loadConfig()
fmt.Printf("%#+v", err)

Output:

[{"caller":"#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)","error":"service configuration could not be loaded"},{"caller":"#1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig)","error":"could not decode configuration data"},{"caller":"#2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig)","error":"could not read configuration file"},{"caller":"#3 print.go:597 (fmt.(*pp).handleMethods)","error":"read: end of input"}]
Example (JsonTracePreformat) 
err := loadConfig()
fmt.Printf("% #+v", err)

Output:

[
    {
        "caller": "#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)",
        "error": "service configuration could not be loaded"
    },
    {
        "caller": "#1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig)",
        "error": "could not decode configuration data"
    },
    {
        "caller": "#2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig)",
        "error": "could not read configuration file"
    },
    {
        "caller": "#3 print.go:597 (fmt.(*pp).handleMethods)",
        "error": "read: end of input"
    }
]
Example (String) 
err := loadConfig()
fmt.Println(err)

Output:

service configuration could not be loaded
Example (StringDetail) 
err := loadConfig()
fmt.Printf("%-v", err)

Output:

service configuration could not be loaded - #0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig);
Example (StringDetailPreformat) 
err := loadConfig()
fmt.Printf("% -v", err)

Output:

service configuration could not be loaded - #0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig);
Example (StringPreformat) 
err := loadConfig()
fmt.Printf("% v", err)

Output:

service configuration could not be loaded
Example (StringTrace) 
err := loadConfig()
fmt.Printf("%+v", err)

Output:

service configuration could not be loaded - #0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig); could not decode configuration data - #1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig); could not read configuration file - #2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig); read: end of input - #3 print.go:597 (fmt.(*pp).handleMethods);
Example (StringTracePreformat) 
err := loadConfig()
fmt.Printf("% +v", err)

Output:

service configuration could not be loaded - #0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig);
could not decode configuration data - #1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig);
could not read configuration file - #2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig);
read: end of input - #3 print.go:597 (fmt.(*pp).handleMethods);

func (*E) Has 

func (e *E) Has(test error) bool

Has implements std.Error.

func (*E) Is 

func (e *E) Is(test error) bool

Is implements std.Error.

func (*E) MarshalJSON 

func (e *E) MarshalJSON() ([]byte, error)

MarshalJSON implements the json.Marshaller interface.

Example (Marshal) 
err := loadConfig()
jsn, _ := json.Marshal(err)

fmt.Println(string(jsn))

Output:

[{"caller":"#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)","error":"service configuration could not be loaded"},{"caller":"#1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig)","error":"could not decode configuration data"},{"caller":"#2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig)","error":"could not read configuration file"},{"caller":"#3 encode.go:477 (encoding/json.marshalerEncoder)","error":"read: end of input"}]
Example (MarshalIndent) 
err := loadConfig()
jsn, _ := json.MarshalIndent(err, "", "    ")

fmt.Println(string(jsn))

Output:

[
    {
        "caller": "#0 mocks_test.go:16 (github.com/bdlm/errors/v2_test.loadConfig)",
        "error": "service configuration could not be loaded"
    },
    {
        "caller": "#1 mocks_test.go:21 (github.com/bdlm/errors/v2_test.decodeConfig)",
        "error": "could not decode configuration data"
    },
    {
        "caller": "#2 mocks_test.go:26 (github.com/bdlm/errors/v2_test.readConfig)",
        "error": "could not read configuration file"
    },
    {
        "caller": "#3 encode.go:477 (encoding/json.marshalerEncoder)",
        "error": "read: end of input"
    }
]

func (*E) Unwrap 

func (e *E) Unwrap() std_err.Error

Unwrap implements std.Error.

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