errors package - emperror.dev/errors - Go Packages (original) (raw)

Package errors is a drop-in replacement for the standard errors package and github.com/pkg/errors.

Overview

This is a single, lightweight library merging the features of standard library `errors` package and https://github.com/pkg/errors. It also backports a few features (like Go 1.13 error handling related features).

Printing errors

If not stated otherwise, errors can be formatted with the following specifiers:

%s error message %q double-quoted error message %v error message in default format %+v error message and stack trace

This section is empty.

This section is empty.

Append appends the given errors together. Either value may be nil.

This function is a specialization of Combine for the common case where there are only two errors.

err = errors.Append(reader.Close(), writer.Close())

The following pattern may also be used to record failure of deferred operations without losing information about the original error.

func doSomething(..) (err error) { f := acquireResource() defer func() { err = errors.Append(err, f.Close()) }()

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { var err error err = errors.Append(err, errors.NewPlain("call 1 failed")) err = errors.Append(err, errors.NewPlain("call 2 failed")) fmt.Println(err) }

Output:

call 1 failed; call 2 failed

As finds the first error in err's chain that matches the type to which target points, and if so, sets the target to its value and returns true. An error matches a type if it is assignable to the target type, or if it has a method As(interface{}) bool such that As(target) returns true. As will panic if target is not a non-nil pointer to a type which implements error or is of interface type.

The As method should set the target to its value and return true if err matches the type to which target points.

package main

import ( "fmt" "os"

"emperror.dev/errors"

)

func main() { if _, err := os.Open("non-existing"); err != nil { var pathError *os.PathError if errors.As(err, &pathError) { fmt.Println("Failed at path:", pathError.Path) } else { fmt.Println(err) } }

}

Output:

Failed at path: non-existing

Cause returns the last error (root cause) in an err's chain. If err has no chain, it is returned directly.

It supports both Go 1.13 errors.Wrapper and github.com/pkg/errors.Causer interfaces (the former takes precedence).

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { ErrSomething := errors.NewPlain("something")

if err := errors.Wrap(ErrSomething, "error"); err != nil {
    if errors.Cause(err) == ErrSomething {
        fmt.Println("something went wrong")
    } else {
        fmt.Println(err)
    }
}

}

Output:

something went wrong

Combine combines the passed errors into a single error.

If zero arguments were passed or if all items are nil, a nil error is returned.

If only a single error was passed, it is returned as-is.

Combine omits nil errors so this function may be used to combine together errors from operations that fail independently of each other.

errors.Combine( reader.Close(), writer.Close(), pipe.Close(), )

If any of the passed errors is already an aggregated error, it will be flattened along with the other errors.

errors.Combine(errors.Combine(err1, err2), err3) // is the same as errors.Combine(err1, err2, err3)

The returned error formats into a readable multi-line error message if formatted with %+v.

fmt.Sprintf("%+v", errors.Combine(err1, err2))

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { err := errors.Combine( errors.NewPlain("call 1 failed"), nil, // successful request errors.NewPlain("call 3 failed"), nil, // successful request errors.NewPlain("call 5 failed"), ) fmt.Printf("%+v", err) }

Output:

the following errors occurred:

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { var errs []error

for i := 1; i < 6; i++ {
    if i%2 == 0 {
        continue
    }

    err := errors.NewPlain(fmt.Sprintf("call %d failed", i))
    errs = append(errs, err)
}

err := errors.Combine(errs...)

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

}

Output:

the following errors occurred:

Errorf returns a new error with a formatted message and annotated with stack trace at the point Errorf is called.

err := errors.Errorf("something went %s", "wrong")

func GetDetails(err error) []interface{}

GetDetails extracts the key-value pairs from err's chain.

GetErrors returns a slice containing zero or more errors that the supplied error is composed of. If the error is nil, the returned slice is empty.

err := errors.Append(r.Close(), w.Close()) errors := errors.GetErrors(err)

If the error is not composed of other errors, the returned slice contains just the error that was passed in.

Callers of this function are free to modify the returned slice.

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { err := errors.Combine( nil, // successful request errors.NewPlain("call 2 failed"), errors.NewPlain("call 3 failed"), ) err = errors.Append(err, nil) // successful request err = errors.Append(err, errors.NewPlain("call 5 failed"))

errs := errors.GetErrors(err)
for _, err := range errs {
    fmt.Println(err)
}

}

Output:

call 2 failed call 3 failed call 5 failed

Is reports whether any error in err's chain matches target.

An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { ErrSomething := errors.NewPlain("something")

if err := errors.Wrap(ErrSomething, "error"); err != nil {
    if errors.Is(err, ErrSomething) {
        fmt.Println("something went wrong")
    } else {
        fmt.Println(err)
    }
}

}

Output:

something went wrong

New returns a new error annotated with stack trace at the point New is called.

New is a shorthand for:

WithStack(NewPlain(message))

NewPlain returns a simple error without any annotated context, like stack trace. Useful for creating sentinel errors and in testing.

var ErrSomething = errors.NewPlain("something went wrong")

func NewWithDetails(message string, details ...interface{}) error

NewWithDetails returns a new error annotated with stack trace at the point NewWithDetails is called, and the supplied details.

Unwrap returns the result of calling the Unwrap method on err, if err implements Unwrap. Otherwise, Unwrap returns nil.

It supports both Go 1.13 Unwrap and github.com/pkg/errors.Causer interfaces (the former takes precedence).

package main

import ( "fmt"

"emperror.dev/errors"

)

func main() { ErrSomething := errors.NewPlain("something")

if err := errors.WithMessage(ErrSomething, "error"); err != nil {
    if errors.Unwrap(err) == ErrSomething {
        fmt.Println("something went wrong")
    } else {
        fmt.Println(err)
    }
}

}

Output:

something went wrong

UnwrapEach loops through an error chain and calls a function for each of them.

The provided function can return false to break the loop before it reaches the end of the chain.

It supports both Go 1.13 errors.Wrapper and github.com/pkg/errors.Causer interfaces (the former takes precedence).

func WithDetails(err error, details ...interface{}) error

WithDetails annotates err with with arbitrary key-value pairs.

WithMessage annotates err with a new message. If err is nil, WithMessage returns nil.

WithMessage is useful when the error already contains a stack trace, but adding additional info to the message helps in debugging.

Errors returned by WithMessage are formatted slightly differently:

%s error messages separated by a colon and a space (": ") %q double-quoted error messages separated by a colon and a space (": ") %v one error message per line %+v one error message per line and stack trace (if any)

WithMessagef annotates err with the format specifier. If err is nil, WithMessagef returns nil.

WithMessagef is useful when the error already contains a stack trace, but adding additional info to the message helps in debugging.

The same formatting rules apply as in case of WithMessage.

WithStack annotates err with a stack trace at the point WithStack was called. If err is nil, WithStack returns nil.

WithStack is commonly used with sentinel errors and errors returned from libraries not annotating errors with stack trace:

var ErrSomething = errors.NewPlain("something went wrong")

func doSomething() error { return errors.WithStack(ErrSomething) }

WithStackDepth annotates err with a stack trace at the given call depth. Zero identifies the caller of WithStackDepth itself. If err is nil, WithStackDepth returns nil.

WithStackDepth is generally used in other error constructors:

func MyWrapper(err error) error { return WithStackDepth(err, 1) }

WithStackDepthIf behaves the same way as WithStackDepth except it does not annotate the error with a stack trace if there is already one in err's chain.

WithStackIf behaves the same way as WithStack except it does not annotate the error with a stack trace if there is already one in err's chain.

Wrap returns an error annotating err with a stack trace at the point Wrap is called, and the supplied message. If err is nil, Wrap returns nil.

Wrap is a shorthand for:

WithStack(WithMessage(err, message))

WrapIf behaves the same way as Wrap except it does not annotate the error with a stack trace if there is already one in err's chain.

If err is nil, WrapIf returns nil.

WrapIfWithDetails returns an error annotating err with a stack trace at the point WrapIfWithDetails is called, and the supplied message and details. If err is nil, WrapIfWithDetails returns nil.

WrapIfWithDetails is a shorthand for:

WithDetails(WithStackIf(WithMessage(err, message, details...))

WrapIff behaves the same way as Wrapf except it does not annotate the error with a stack trace if there is already one in err's chain.

If err is nil, WrapIff returns nil.

WrapWithDetails returns an error annotating err with a stack trace at the point WrapWithDetails is called, and the supplied message and details. If err is nil, WrapWithDetails returns nil.

WrapWithDetails is a shorthand for:

WithDetails(WithStack(WithMessage(err, message, details...))

Wrapf returns an error annotating err with a stack trace at the point Wrapf is called, and the format specifier. If err is nil, Wrapf returns nil.

Wrapf is a shorthand for:

WithStack(WithMessagef(err, format, a...))

Frame represents a program counter inside a stack frame. For historical reasons if Frame is interpreted as a uintptr its value represents the program counter + 1.

It is an alias of the same type in github.com/pkg/errors.

Sentinel is a simple error without any annotated context, like stack trace. Useful for creating sentinel errors.

const ErrSomething = errors.Sentinel("something went wrong")

See https://dave.cheney.net/2016/04/07/constant-errors

nolint: unused

package main

import ( "emperror.dev/errors" )

func main() { const ErrSomething = errors.Sentinel("something went wrong")

}

StackTrace is stack of Frames from innermost (newest) to outermost (oldest).

It is an alias of the same type in github.com/pkg/errors.