Initial import (#1)
This is the initial import of the `multierr` library. The library
intends to provide a single common implementation of the `multierr`
type.
The implementation is slightly more complex than you would expect
because it aims to be zero-alloc for the hot-path (no errors or no
nested multierrors).
diff --git a/.deleteme b/.deleteme
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index e69de29..0000000
--- a/.deleteme
+++ /dev/null
diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/vendor
diff --git a/LICENSE.txt b/LICENSE.txt
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+++ b/LICENSE.txt
@@ -0,0 +1,19 @@
+Copyright (c) 2017 Uber Technologies, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
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+++ b/README.md
@@ -0,0 +1,25 @@
+multierr
+========
+
+Easy grouping of one or more errors into a single error.
+
+Installation
+------------
+
+ go get -u go.uber.org/multierr
+
+Usage
+-----
+
+TODO
+
+Status
+------
+
+Stable
+
+-------------------------------------------------------------------------------
+
+Released under the [MIT License].
+
+ [MIT License]: LICENSE.txt
diff --git a/error.go b/error.go
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index 0000000..66b1d50
--- /dev/null
+++ b/error.go
@@ -0,0 +1,280 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package multierr // import "go.uber.org/multierr"
+
+import (
+ "bytes"
+ "fmt"
+ "io"
+ "strings"
+ "sync"
+)
+
+var (
+ // Separator for single-line error messages.
+ _singlelineSeparator = []byte("; ")
+
+ _newline = []byte("\n")
+
+ // Prefix for multi-line messages
+ _multilinePrefix = []byte("the following errors occurred:")
+
+ // Prefix for the first and following lines of an item in a list of
+ // multi-line error messages.
+ //
+ // For example, if a single item is:
+ //
+ // foo
+ // bar
+ //
+ // It will become,
+ //
+ // - foo
+ // bar
+ _multilineSeparator = []byte("\n - ")
+ _multilineIndent = []byte(" ")
+)
+
+// _bufferPool is a pool of bytes.Buffers.
+var _bufferPool = sync.Pool{
+ New: func() interface{} {
+ return &bytes.Buffer{}
+ },
+}
+
+// multiError is an error that holds one or more errors.
+//
+// An instance of this is guaranteed to be non-empty and flattened. That is,
+// none of the errors inside multiError are other multiErrors.
+//
+// multiError formats to a semi-colon delimited list of error messages with
+// %v and with a more readable multi-line format with %+v.
+type multiError []error
+
+func (me multiError) String() string {
+ return me.Error()
+}
+
+func (me multiError) Error() string {
+ buff := _bufferPool.Get().(*bytes.Buffer)
+ buff.Reset()
+
+ me.writeSingleline(buff)
+
+ result := buff.String()
+ _bufferPool.Put(buff)
+ return result
+}
+
+func (me multiError) Format(f fmt.State, c rune) {
+ if c == 'v' && f.Flag('+') {
+ me.writeMultiline(f)
+ } else {
+ me.writeSingleline(f)
+ }
+}
+
+func (me multiError) writeSingleline(w io.Writer) {
+ first := true
+ for _, item := range me {
+ if first {
+ first = false
+ } else {
+ w.Write(_singlelineSeparator)
+ }
+ io.WriteString(w, item.Error())
+ }
+}
+
+func (me multiError) writeMultiline(w io.Writer) {
+ w.Write(_multilinePrefix)
+ for _, item := range me {
+ w.Write(_multilineSeparator)
+ writePrefixLine(w, _multilineIndent, item.Error())
+ }
+}
+
+// Writes s to the writer with the given prefix added before each line after
+// the first.
+func writePrefixLine(w io.Writer, prefix []byte, s string) {
+ first := true
+ for len(s) > 0 {
+ if first {
+ first = false
+ } else {
+ w.Write(prefix)
+ }
+
+ idx := strings.IndexByte(s, '\n')
+ if idx < 0 {
+ idx = len(s) - 1
+ }
+
+ io.WriteString(w, s[:idx+1])
+ s = s[idx+1:]
+ }
+}
+
+type inspectResult struct {
+ // Number of top-level non-nil errors
+ Count int
+
+ // Total number of errors including multiErrors
+ Capacity int
+
+ // Index of the first non-nil error in the list. Value is meaningless if
+ // Count is zero.
+ FirstErrorIdx int
+
+ // Whether the list contains at least one multiError
+ ContainsMultiError bool
+}
+
+// Inspects the given slice of errors so that we can efficiently allocate
+// space for it.
+func inspect(errors []error) (res inspectResult) {
+ first := true
+ for i, err := range errors {
+ if err == nil {
+ continue
+ }
+
+ res.Count++
+ if first {
+ first = false
+ res.FirstErrorIdx = i
+ }
+
+ if me, ok := err.(multiError); ok {
+ res.Capacity += len(me)
+ res.ContainsMultiError = true
+ } else {
+ res.Capacity++
+ }
+ }
+ return
+}
+
+// fromSlice converts the given list of errors into a single error.
+func fromSlice(errors []error) error {
+ res := inspect(errors)
+ switch res.Count {
+ case 0:
+ return nil
+ case 1:
+ // only one non-nil entry
+ return errors[res.FirstErrorIdx]
+ case len(errors):
+ if !res.ContainsMultiError {
+ // already flat
+ return multiError(errors)
+ }
+ }
+
+ me := make(multiError, 0, res.Capacity)
+ for _, err := range errors[res.FirstErrorIdx:] {
+ if err == nil {
+ continue
+ }
+
+ if nested, ok := err.(multiError); ok {
+ me = append(me, nested...)
+ } else {
+ me = append(me, err)
+ }
+ }
+ return me
+}
+
+// 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.
+//
+// Combine(nil, nil) // == nil
+//
+// If only a single error was passed, it is returned as-is.
+//
+// Combine(err) // == err
+//
+// Combine skips over nil arguments so this function may be used to combine
+// together errors from operations that fail independently of each other.
+//
+// multierr.Combine(
+// reader.Close(),
+// writer.Close(),
+// pipe.Close(),
+// )
+//
+// If any of the passed errors is a multierr error, it will be flattened along
+// with the other errors.
+//
+// multierr.Combine(multierr.Combine(err1, err2), err3)
+// // is the same as
+// multierr.Combine(err1, err2, err3)
+//
+// The returned error formats into a readable multi-line error message if
+// formatted with %+v.
+//
+// fmt.Sprintf("%+v", multierr.Combine(err1, err2))
+func Combine(errors ...error) error {
+ return fromSlice(errors)
+}
+
+// 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 = multierr.Append(reader.Close(), writer.Close())
+//
+// This may be used to record failure of deferred operations without losing
+// information about the original error.
+//
+// func doSomething(..) (err error) {
+// f := acquireResource()
+// defer func() {
+// err = multierr.Append(err, f.Close())
+// }()
+func Append(left error, right error) error {
+ switch {
+ case left == nil:
+ return right
+ case right == nil:
+ return left
+ }
+
+ if _, ok := right.(multiError); !ok {
+ if l, ok := left.(multiError); ok {
+ // Common case where the error on the left is constantly being
+ // appended to.
+ return append(l, right)
+ }
+
+ // Both errors are single errors.
+ return multiError{left, right}
+ }
+
+ // Either right or both, left and right, are multiErrors. Rely on usual
+ // expensive logic.
+ errors := [2]error{left, right}
+ return fromSlice(errors[0:])
+}
diff --git a/error_test.go b/error_test.go
new file mode 100644
index 0000000..4c72c45
--- /dev/null
+++ b/error_test.go
@@ -0,0 +1,262 @@
+package multierr
+
+import (
+ "errors"
+ "fmt"
+ "testing"
+
+ "github.com/stretchr/testify/assert"
+ "github.com/stretchr/testify/require"
+)
+
+func TestCombine(t *testing.T) {
+ tests := []struct {
+ giveErrors []error
+ wantError error
+ wantMultiline string
+ wantSingleline string
+ }{
+ {
+ giveErrors: nil,
+ wantError: nil,
+ },
+ {
+ giveErrors: []error{},
+ wantError: nil,
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ nil,
+ multiError{
+ errors.New("bar"),
+ },
+ nil,
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar",
+ wantSingleline: "foo; bar",
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ multiError{
+ errors.New("bar"),
+ },
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar",
+ wantSingleline: "foo; bar",
+ },
+ {
+ giveErrors: []error{errors.New("great sadness")},
+ wantError: errors.New("great sadness"),
+ wantMultiline: "great sadness",
+ wantSingleline: "great sadness",
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar",
+ wantSingleline: "foo; bar",
+ },
+ {
+ giveErrors: []error{
+ errors.New("great sadness"),
+ errors.New("multi\n line\nerror message"),
+ errors.New("single line error message"),
+ },
+ wantError: multiError{
+ errors.New("great sadness"),
+ errors.New("multi\n line\nerror message"),
+ errors.New("single line error message"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - great sadness\n" +
+ " - multi\n" +
+ " line\n" +
+ " error message\n" +
+ " - single line error message",
+ wantSingleline: "great sadness; " +
+ "multi\n line\nerror message; " +
+ "single line error message",
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ multiError{
+ errors.New("bar"),
+ errors.New("baz"),
+ },
+ errors.New("qux"),
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ errors.New("baz"),
+ errors.New("qux"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar\n" +
+ " - baz\n" +
+ " - qux",
+ wantSingleline: "foo; bar; baz; qux",
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ nil,
+ multiError{
+ errors.New("bar"),
+ },
+ nil,
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar",
+ wantSingleline: "foo; bar",
+ },
+ {
+ giveErrors: []error{
+ errors.New("foo"),
+ multiError{
+ errors.New("bar"),
+ },
+ },
+ wantError: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ wantMultiline: "the following errors occurred:\n" +
+ " - foo\n" +
+ " - bar",
+ wantSingleline: "foo; bar",
+ },
+ }
+
+ for i, tt := range tests {
+ t.Run(fmt.Sprint(i), func(t *testing.T) {
+ err := Combine(tt.giveErrors...)
+ require.Equal(t, tt.wantError, err)
+
+ if tt.wantMultiline != "" {
+ assert.Equal(t, tt.wantMultiline, fmt.Sprintf("%+v", err))
+ }
+
+ if tt.wantSingleline != "" {
+ assert.Equal(t, tt.wantSingleline, err.Error())
+ if s, ok := err.(fmt.Stringer); ok {
+ assert.Equal(t, tt.wantSingleline, s.String())
+ }
+ assert.Equal(t, tt.wantSingleline, fmt.Sprintf("%v", err))
+ }
+ })
+ }
+}
+
+func TestCombineDoesNotModifySlice(t *testing.T) {
+ errors := []error{
+ errors.New("foo"),
+ nil,
+ errors.New("bar"),
+ }
+
+ assert.NotNil(t, Combine(errors...))
+ assert.Len(t, errors, 3)
+ assert.Nil(t, errors[1], 3)
+}
+
+func TestAppend(t *testing.T) {
+ tests := []struct {
+ left error
+ right error
+ want error
+ }{
+ {
+ left: nil,
+ right: nil,
+ want: nil,
+ },
+ {
+ left: nil,
+ right: errors.New("great sadness"),
+ want: errors.New("great sadness"),
+ },
+ {
+ left: errors.New("great sadness"),
+ right: nil,
+ want: errors.New("great sadness"),
+ },
+ {
+ left: errors.New("foo"),
+ right: errors.New("bar"),
+ want: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ },
+ {
+ left: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ right: errors.New("baz"),
+ want: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ errors.New("baz"),
+ },
+ },
+ {
+ left: errors.New("baz"),
+ right: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ want: multiError{
+ errors.New("baz"),
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ },
+ {
+ left: multiError{
+ errors.New("foo"),
+ },
+ right: multiError{
+ errors.New("bar"),
+ },
+ want: multiError{
+ errors.New("foo"),
+ errors.New("bar"),
+ },
+ },
+ }
+
+ for _, tt := range tests {
+ assert.Equal(t, tt.want, Append(tt.left, tt.right))
+ }
+}
diff --git a/glide.lock b/glide.lock
new file mode 100644
index 0000000..15c5fa4
--- /dev/null
+++ b/glide.lock
@@ -0,0 +1,16 @@
+hash: cb430176250bcfe8bafd93aa48d285fa35b08af59b5f9971dcf553a1d6c236ec
+updated: 2017-03-17T16:22:25.024129734-07:00
+imports: []
+testImports:
+- name: github.com/davecgh/go-spew
+ version: 346938d642f2ec3594ed81d874461961cd0faa76
+ subpackages:
+ - spew
+- name: github.com/pmezard/go-difflib
+ version: 792786c7400a136282c1664665ae0a8db921c6c2
+ subpackages:
+ - difflib
+- name: github.com/stretchr/testify
+ version: 4d4bfba8f1d1027c4fdbe371823030df51419987
+ subpackages:
+ - assert
diff --git a/glide.yaml b/glide.yaml
new file mode 100644
index 0000000..67951f5
--- /dev/null
+++ b/glide.yaml
@@ -0,0 +1,6 @@
+package: go.uber.org/multierr
+import: []
+testImport:
+- package: github.com/stretchr/testify
+ subpackages:
+ - assert
