450 lines
11 KiB
Go
450 lines
11 KiB
Go
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// Copyright (c) 2019 Uber Technologies, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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// Package multierr allows combining one or more errors together.
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//
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// Overview
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//
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// Errors can be combined with the use of the Combine function.
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//
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// multierr.Combine(
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// reader.Close(),
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// writer.Close(),
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// conn.Close(),
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// )
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//
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// If only two errors are being combined, the Append function may be used
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// instead.
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//
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// err = multierr.Append(reader.Close(), writer.Close())
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//
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// This makes it possible to record resource cleanup failures from deferred
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// blocks with the help of named return values.
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//
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// func sendRequest(req Request) (err error) {
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// conn, err := openConnection()
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// if err != nil {
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// return err
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// }
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// defer func() {
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// err = multierr.Append(err, conn.Close())
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// }()
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// // ...
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// }
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//
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// The underlying list of errors for a returned error object may be retrieved
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// with the Errors function.
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//
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// errors := multierr.Errors(err)
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// if len(errors) > 0 {
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// fmt.Println("The following errors occurred:", errors)
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// }
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//
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// Advanced Usage
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//
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// Errors returned by Combine and Append MAY implement the following
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// interface.
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//
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// type errorGroup interface {
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// // Returns a slice containing the underlying list of errors.
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// //
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// // This slice MUST NOT be modified by the caller.
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// Errors() []error
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// }
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//
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// Note that if you need access to list of errors behind a multierr error, you
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// should prefer using the Errors function. That said, if you need cheap
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// read-only access to the underlying errors slice, you can attempt to cast
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// the error to this interface. You MUST handle the failure case gracefully
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// because errors returned by Combine and Append are not guaranteed to
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// implement this interface.
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//
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// var errors []error
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// group, ok := err.(errorGroup)
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// if ok {
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// errors = group.Errors()
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// } else {
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// errors = []error{err}
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// }
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package multierr // import "go.uber.org/multierr"
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import (
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"bytes"
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"fmt"
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"io"
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"strings"
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"sync"
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"go.uber.org/atomic"
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)
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var (
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// Separator for single-line error messages.
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_singlelineSeparator = []byte("; ")
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// Prefix for multi-line messages
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_multilinePrefix = []byte("the following errors occurred:")
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// Prefix for the first and following lines of an item in a list of
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// multi-line error messages.
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//
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// For example, if a single item is:
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//
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// foo
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// bar
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//
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// It will become,
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//
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// - foo
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// bar
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_multilineSeparator = []byte("\n - ")
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_multilineIndent = []byte(" ")
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)
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// _bufferPool is a pool of bytes.Buffers.
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var _bufferPool = sync.Pool{
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New: func() interface{} {
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return &bytes.Buffer{}
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},
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}
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type errorGroup interface {
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Errors() []error
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}
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// Errors returns a slice containing zero or more errors that the supplied
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// error is composed of. If the error is nil, a nil slice is returned.
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//
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// err := multierr.Append(r.Close(), w.Close())
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// errors := multierr.Errors(err)
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//
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// If the error is not composed of other errors, the returned slice contains
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// just the error that was passed in.
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//
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// Callers of this function are free to modify the returned slice.
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func Errors(err error) []error {
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if err == nil {
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return nil
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}
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// Note that we're casting to multiError, not errorGroup. Our contract is
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// that returned errors MAY implement errorGroup. Errors, however, only
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// has special behavior for multierr-specific error objects.
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//
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// This behavior can be expanded in the future but I think it's prudent to
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// start with as little as possible in terms of contract and possibility
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// of misuse.
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eg, ok := err.(*multiError)
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if !ok {
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return []error{err}
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}
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errors := eg.Errors()
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result := make([]error, len(errors))
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copy(result, errors)
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return result
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}
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// multiError is an error that holds one or more errors.
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//
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// An instance of this is guaranteed to be non-empty and flattened. That is,
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// none of the errors inside multiError are other multiErrors.
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//
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// multiError formats to a semi-colon delimited list of error messages with
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// %v and with a more readable multi-line format with %+v.
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type multiError struct {
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copyNeeded atomic.Bool
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errors []error
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}
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var _ errorGroup = (*multiError)(nil)
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// Errors returns the list of underlying errors.
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//
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// This slice MUST NOT be modified.
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func (merr *multiError) Errors() []error {
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if merr == nil {
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return nil
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}
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return merr.errors
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}
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func (merr *multiError) Error() string {
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if merr == nil {
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return ""
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}
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buff := _bufferPool.Get().(*bytes.Buffer)
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buff.Reset()
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merr.writeSingleline(buff)
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result := buff.String()
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_bufferPool.Put(buff)
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return result
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}
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func (merr *multiError) Format(f fmt.State, c rune) {
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if c == 'v' && f.Flag('+') {
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merr.writeMultiline(f)
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} else {
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merr.writeSingleline(f)
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}
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}
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func (merr *multiError) writeSingleline(w io.Writer) {
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first := true
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for _, item := range merr.errors {
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if first {
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first = false
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} else {
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w.Write(_singlelineSeparator)
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}
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io.WriteString(w, item.Error())
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}
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}
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func (merr *multiError) writeMultiline(w io.Writer) {
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w.Write(_multilinePrefix)
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for _, item := range merr.errors {
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w.Write(_multilineSeparator)
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writePrefixLine(w, _multilineIndent, fmt.Sprintf("%+v", item))
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}
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}
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// Writes s to the writer with the given prefix added before each line after
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// the first.
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func writePrefixLine(w io.Writer, prefix []byte, s string) {
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first := true
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for len(s) > 0 {
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if first {
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first = false
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} else {
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w.Write(prefix)
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}
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idx := strings.IndexByte(s, '\n')
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if idx < 0 {
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idx = len(s) - 1
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}
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io.WriteString(w, s[:idx+1])
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s = s[idx+1:]
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}
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}
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type inspectResult struct {
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// Number of top-level non-nil errors
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Count int
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// Total number of errors including multiErrors
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Capacity int
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// Index of the first non-nil error in the list. Value is meaningless if
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// Count is zero.
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FirstErrorIdx int
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// Whether the list contains at least one multiError
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ContainsMultiError bool
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}
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// Inspects the given slice of errors so that we can efficiently allocate
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// space for it.
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func inspect(errors []error) (res inspectResult) {
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first := true
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for i, err := range errors {
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if err == nil {
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continue
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}
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res.Count++
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if first {
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first = false
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res.FirstErrorIdx = i
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}
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if merr, ok := err.(*multiError); ok {
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res.Capacity += len(merr.errors)
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res.ContainsMultiError = true
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} else {
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res.Capacity++
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}
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}
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return
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}
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// fromSlice converts the given list of errors into a single error.
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func fromSlice(errors []error) error {
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res := inspect(errors)
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switch res.Count {
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case 0:
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return nil
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case 1:
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// only one non-nil entry
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return errors[res.FirstErrorIdx]
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case len(errors):
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if !res.ContainsMultiError {
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// already flat
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return &multiError{errors: errors}
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}
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}
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nonNilErrs := make([]error, 0, res.Capacity)
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for _, err := range errors[res.FirstErrorIdx:] {
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if err == nil {
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continue
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}
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if nested, ok := err.(*multiError); ok {
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nonNilErrs = append(nonNilErrs, nested.errors...)
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} else {
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nonNilErrs = append(nonNilErrs, err)
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}
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}
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return &multiError{errors: nonNilErrs}
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}
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// Combine combines the passed errors into a single error.
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//
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// If zero arguments were passed or if all items are nil, a nil error is
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// returned.
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//
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// Combine(nil, nil) // == nil
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//
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// If only a single error was passed, it is returned as-is.
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//
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// Combine(err) // == err
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//
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// Combine skips over nil arguments so this function may be used to combine
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// together errors from operations that fail independently of each other.
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//
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// multierr.Combine(
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// reader.Close(),
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// writer.Close(),
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// pipe.Close(),
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// )
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//
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// If any of the passed errors is a multierr error, it will be flattened along
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// with the other errors.
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//
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// multierr.Combine(multierr.Combine(err1, err2), err3)
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// // is the same as
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// multierr.Combine(err1, err2, err3)
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//
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// The returned error formats into a readable multi-line error message if
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// formatted with %+v.
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//
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// fmt.Sprintf("%+v", multierr.Combine(err1, err2))
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func Combine(errors ...error) error {
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return fromSlice(errors)
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}
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// Append appends the given errors together. Either value may be nil.
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//
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// This function is a specialization of Combine for the common case where
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// there are only two errors.
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//
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// err = multierr.Append(reader.Close(), writer.Close())
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//
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// The following pattern may also be used to record failure of deferred
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// operations without losing information about the original error.
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//
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// func doSomething(..) (err error) {
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// f := acquireResource()
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// defer func() {
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// err = multierr.Append(err, f.Close())
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// }()
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func Append(left error, right error) error {
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switch {
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case left == nil:
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return right
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case right == nil:
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return left
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}
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if _, ok := right.(*multiError); !ok {
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if l, ok := left.(*multiError); ok && !l.copyNeeded.Swap(true) {
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// Common case where the error on the left is constantly being
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// appended to.
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errs := append(l.errors, right)
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return &multiError{errors: errs}
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} else if !ok {
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// Both errors are single errors.
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return &multiError{errors: []error{left, right}}
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}
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}
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// Either right or both, left and right, are multiErrors. Rely on usual
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// expensive logic.
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errors := [2]error{left, right}
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return fromSlice(errors[0:])
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}
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// AppendInto appends an error into the destination of an error pointer and
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// returns whether the error being appended was non-nil.
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//
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// var err error
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// multierr.AppendInto(&err, r.Close())
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|
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// multierr.AppendInto(&err, w.Close())
|
||
|
|
//
|
||
|
|
// The above is equivalent to,
|
||
|
|
//
|
||
|
|
// err := multierr.Append(r.Close(), w.Close())
|
||
|
|
//
|
||
|
|
// As AppendInto reports whether the provided error was non-nil, it may be
|
||
|
|
// used to build a multierr error in a loop more ergonomically. For example:
|
||
|
|
//
|
||
|
|
// var err error
|
||
|
|
// for line := range lines {
|
||
|
|
// var item Item
|
||
|
|
// if multierr.AppendInto(&err, parse(line, &item)) {
|
||
|
|
// continue
|
||
|
|
// }
|
||
|
|
// items = append(items, item)
|
||
|
|
// }
|
||
|
|
//
|
||
|
|
// Compare this with a verison that relies solely on Append:
|
||
|
|
//
|
||
|
|
// var err error
|
||
|
|
// for line := range lines {
|
||
|
|
// var item Item
|
||
|
|
// if parseErr := parse(line, &item); parseErr != nil {
|
||
|
|
// err = multierr.Append(err, parseErr)
|
||
|
|
// continue
|
||
|
|
// }
|
||
|
|
// items = append(items, item)
|
||
|
|
// }
|
||
|
|
func AppendInto(into *error, err error) (errored bool) {
|
||
|
|
if into == nil {
|
||
|
|
// We panic if 'into' is nil. This is not documented above
|
||
|
|
// because suggesting that the pointer must be non-nil may
|
||
|
|
// confuse users into thinking that the error that it points
|
||
|
|
// to must be non-nil.
|
||
|
|
panic("misuse of multierr.AppendInto: into pointer must not be nil")
|
||
|
|
}
|
||
|
|
|
||
|
|
if err == nil {
|
||
|
|
return false
|
||
|
|
}
|
||
|
|
*into = Append(*into, err)
|
||
|
|
return true
|
||
|
|
}
|