aboutsummaryrefslogtreecommitdiff
path: root/vendor/github.com/pkg/errors/errors.go
blob: 1c9731ac6c13d611974e1625cb5226a404c12ee1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
// Package errors provides simple error handling primitives.
//
// The traditional error handling idiom in Go is roughly akin to
//
//     if err != nil {
//             return err
//     }
//
// which applied recursively up the call stack results in error reports
// without context or debugging information. The errors package allows
// programmers to add context to the failure path in their code in a way
// that does not destroy the original value of the error.
//
// Adding context to an error
//
// The errors.Wrap function returns a new error that adds context to the
// original error. For example
//
//     _, err := ioutil.ReadAll(r)
//     if err != nil {
//             return errors.Wrap(err, "read failed")
//     }
//
// Retrieving the cause of an error
//
// Using errors.Wrap constructs a stack of errors, adding context to the
// preceding error. Depending on the nature of the error it may be necessary
// to reverse the operation of errors.Wrap to retrieve the original error
// for inspection. Any error value which implements this interface
//
//     type causer interface {
//             Cause() error
//     }
//
// can be inspected by errors.Cause. errors.Cause will recursively retrieve
// the topmost error which does not implement causer, which is assumed to be
// the original cause. For example:
//
//     switch err := errors.Cause(err).(type) {
//     case *MyError:
//             // handle specifically
//     default:
//             // unknown error
//     }
//
// causer interface is not exported by this package, but is considered a part
// of stable public API.
//
// Formatted printing of errors
//
// All error values returned from this package implement fmt.Formatter and can
// be formatted by the fmt package. The following verbs are supported
//
//     %s    print the error. If the error has a Cause it will be
//           printed recursively
//     %v    see %s
//     %+v   extended format. Each Frame of the error's StackTrace will
//           be printed in detail.
//
// Retrieving the stack trace of an error or wrapper
//
// New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
// invoked. This information can be retrieved with the following interface.
//
//     type stackTracer interface {
//             StackTrace() errors.StackTrace
//     }
//
// Where errors.StackTrace is defined as
//
//     type StackTrace []Frame
//
// The Frame type represents a call site in the stack trace. Frame supports
// the fmt.Formatter interface that can be used for printing information about
// the stack trace of this error. For example:
//
//     if err, ok := err.(stackTracer); ok {
//             for _, f := range err.StackTrace() {
//                     fmt.Printf("%+s:%d", f)
//             }
//     }
//
// stackTracer interface is not exported by this package, but is considered a part
// of stable public API.
//
// See the documentation for Frame.Format for more details.
package errors

import (
	"fmt"
	"io"
)

// New returns an error with the supplied message.
// New also records the stack trace at the point it was called.
func New(message string) error {
	return &fundamental{
		msg:   message,
		stack: callers(),
	}
}

// Errorf formats according to a format specifier and returns the string
// as a value that satisfies error.
// Errorf also records the stack trace at the point it was called.
func Errorf(format string, args ...interface{}) error {
	return &fundamental{
		msg:   fmt.Sprintf(format, args...),
		stack: callers(),
	}
}

// fundamental is an error that has a message and a stack, but no caller.
type fundamental struct {
	msg string
	*stack
}

func (f *fundamental) Error() string { return f.msg }

func (f *fundamental) Format(s fmt.State, verb rune) {
	switch verb {
	case 'v':
		if s.Flag('+') {
			io.WriteString(s, f.msg)
			f.stack.Format(s, verb)
			return
		}
		fallthrough
	case 's':
		io.WriteString(s, f.msg)
	case 'q':
		fmt.Fprintf(s, "%q", f.msg)
	}
}

type withStack struct {
	error
	*stack
}

func (w *withStack) Cause() error { return w.error }

func (w *withStack) Format(s fmt.State, verb rune) {
	switch verb {
	case 'v':
		if s.Flag('+') {
			fmt.Fprintf(s, "%+v", w.Cause())
			w.stack.Format(s, verb)
			return
		}
		fallthrough
	case 's':
		io.WriteString(s, w.Error())
	case 'q':
		fmt.Fprintf(s, "%q", w.Error())
	}
}

// Wrap returns an error annotating err with message.
// If err is nil, Wrap returns nil.
func Wrap(err error, message string) error {
	if err == nil {
		return nil
	}
	err = &withMessage{
		cause: err,
		msg:   message,
	}
	return &withStack{
		err,
		callers(),
	}
}

// Wrapf returns an error annotating err with the format specifier.
// If err is nil, Wrapf returns nil.
func Wrapf(err error, format string, args ...interface{}) error {
	if err == nil {
		return nil
	}
	err = &withMessage{
		cause: err,
		msg:   fmt.Sprintf(format, args...),
	}
	return &withStack{
		err,
		callers(),
	}
}

type withMessage struct {
	cause error
	msg   string
}

func (w *withMessage) Error() string { return w.msg + ": " + w.cause.Error() }
func (w *withMessage) Cause() error  { return w.cause }

func (w *withMessage) Format(s fmt.State, verb rune) {
	switch verb {
	case 'v':
		if s.Flag('+') {
			fmt.Fprintf(s, "%+v\n", w.Cause())
			io.WriteString(s, w.msg)
			return
		}
		fallthrough
	case 's', 'q':
		io.WriteString(s, w.Error())
	}
}

// Cause returns the underlying cause of the error, if possible.
// An error value has a cause if it implements the following
// interface:
//
//     type causer interface {
//            Cause() error
//     }
//
// If the error does not implement Cause, the original error will
// be returned. If the error is nil, nil will be returned without further
// investigation.
func Cause(err error) error {
	type causer interface {
		Cause() error
	}

	for err != nil {
		cause, ok := err.(causer)
		if !ok {
			break
		}
		err = cause.Cause()
	}
	return err
}