merry

Make your golang errors merry, with stacktraces, inheritance, and arbitrary additional context.

The package is largely based on http://github.com/go-errors/errors, with additional inspiration from https://github.com/go-errgo/errgo and https://github.com/amattn/deeperror.

Installation

go get github.com/ansel1/merry

Features

Merry errors work a lot like google's golang.org/x/net/context package. Merry errors wrap normal errors with a context of key/value pairs. Like contexts, merry errors are immutable: adding a key/value to an error always creates a new error which wraps the original.

merry comes with built-in support for adding information to errors:

stacktraces
overriding the error message
HTTP status codes
End user error messages

You can also add your own additional information.

The stack capturing feature can be turned off for better performance, though it's pretty fast. Benchmarks on an early 2011 MacBook Pro, with go 1.7rc1:

BenchmarkNew_withStackCapture-8      	 1000000	      1413 ns/op
BenchmarkNew_withoutStackCapture-8   	10000000	       218 ns/op

Details

New errors have a stacktrace captured where they are created

Add a stacktrace to existing errors (captured where they are wrapped)

err := lib.Read()
return merry.Wrap(err)  // no-op if err is already merry

Allow golang idiom of comparing an err value to an exported value, using Is()

var ParseError = merry.New("Parse error")

func Parse() error {
    err := ParseError.Here() // captures a stacktrace here
    merry.Is(err, ParseError)  // instead of err == ParseError
}

Change the message on an error, while still using Is() to compare to the original error

err := merry.WithMessage(ParseError, "Bad input")
merry.Is(err, ParseError) // yes it is

Is() supports hierarchies of errors

var ParseError = merry.New("Parse error")
var InvalidCharSet = merry.WithMessage(ParseError, "Invalid char set")
var InvalidSyntax = merry.WithMessage(ParseError, "Invalid syntax")

func Parse(s string) error {
    // use chainable methods to add context
    return InvalidCharSet.Here().WithMessagef("Invalid char set: %s", "UTF-8")
    // or functions
    // return merry.WithMessagef(merry.Here(InvalidCharSet), "Invalid char set: %s", "UTF-8")
}

func Check() {
    err := Parse("fields")
    merry.Is(err, ParseError) // yup
    merry.Is(err, InvalidCharSet) // yup
    merry.Is(err, InvalidSyntax) // nope
}

Add an HTTP status code

merry.HTTPCode(errors.New("regular error")) // 500
merry.HTTPCode(merry.New("merry error").WithHTTPCode(404)) // 404

Set an alternate error message for end users

e := merry.New("crash").WithUserMessage("nothing to see here")
merry.UserMessage(e)  // returns "nothing to see here"

Functions for printing error details

err := merry.New("boom")
m := merry.Stacktrace(err) // just the stacktrace
m = merry.Details(err) // error message and stacktrace
fmt.Sprintf("%+v", err) == merry.Details(err) // errors implement fmt.Formatter

Add your own context info

err := merry.New("boom").WithValue("explosive", "black powder")

Basic Usage

The package contains functions for creating new errors with stacks, or adding a stack to error instances. Functions with add context (e.g. WithValue()) work on any error, and will automatically convert them to merry errors (with a stack) if necessary.

Capturing the stack can be globally disabled with SetStackCaptureEnabled(false)

Functions which get context values from errors also accept error, and will return default values if the error is not merry, or doesn't have that key attached.

All the functions which create or attach context return concrete instances of *Error. *Error implements methods to add context to the error (they mirror the functions and do the same thing). They allow for a chainable syntax for adding context.

Example:

package main

import (
    "github.com/ansel1/merry"
    "errors"
)

var InvalidInputs = errors.New("Input is invalid")

func main() {
    // create a new error, with a stacktrace attached
    err := merry.New("bad stuff happened")
    
    // create a new error with format string, like fmt.Errorf
    err = merry.Errorf("bad input: %v", os.Args)
    
    // capture a fresh stacktrace from this callsite
    err = merry.Here(InvalidInputs)
    
    // Make err merry if it wasn't already.  The stacktrace will be captured here if the
    // error didn't already have one.  Also useful to cast to *Error 
    err = merry.Wrap(err, 0)

    // override the original error's message
    err.WithMessagef("Input is invalid: %v", os.Args)
    
    // Use Is to compare errors against values, which is a common golang idiom
    merry.Is(err, InvalidInputs) // will be true
    
    // associated an http code
    err.WithHTTPCode(400)
    
    perr := parser.Parse("blah")
    err = Wrap(perr, 0)
    // Get the original error back
    merry.Unwrap(err) == perr  // will be true
    
    // Print the error to a string, with the stacktrace, if it has one
    s := merry.Details(err)
    
    // Just print the stacktrace (empty string if err is not a RichError)
    s := merry.Stacktrace(err)

    // Get the location of the error (the first line in the stacktrace)
    file, line := merry.Location(err)
    
    // Get an HTTP status code for an error.  Defaults to 500 for non-nil errors, and 200 if err is nil.
    code := merry.HTTPCode(err)
    
}

See inline docs for more details.

License

This package is licensed under the MIT license, see LICENSE.MIT for details.

6.2 KiB Raw Blame History