1 package errors
2 3 import (
4 "fmt"
5 "io"
6 "path"
7 "runtime"
8 "strconv"
9 "strings"
10 )
11 12 // Frame represents a program counter inside a stack frame.
13 // For historical reasons if Frame is interpreted as a uintptr
14 // its value represents the program counter + 1.
15 type Frame uintptr
16 17 // pc returns the program counter for this frame;
18 // multiple frames may have the same PC value.
19 func (f Frame) pc() uintptr { return uintptr(f) - 1 }
20 21 // file returns the full path to the file that contains the
22 // function for this Frame's pc.
23 func (f Frame) file() string {
24 fn := runtime.FuncForPC(f.pc())
25 if fn == nil {
26 return "unknown"
27 }
28 file, _ := fn.FileLine(f.pc())
29 return file
30 }
31 32 // line returns the line number of source code of the
33 // function for this Frame's pc.
34 func (f Frame) line() int {
35 fn := runtime.FuncForPC(f.pc())
36 if fn == nil {
37 return 0
38 }
39 _, line := fn.FileLine(f.pc())
40 return line
41 }
42 43 // name returns the name of this function, if known.
44 func (f Frame) name() string {
45 fn := runtime.FuncForPC(f.pc())
46 if fn == nil {
47 return "unknown"
48 }
49 return fn.Name()
50 }
51 52 // Format formats the frame according to the fmt.Formatter interface.
53 //
54 // %s source file
55 // %d source line
56 // %n function name
57 // %v equivalent to %s:%d
58 //
59 // Format accepts flags that alter the printing of some verbs, as follows:
60 //
61 // %+s function name and path of source file relative to the compile time
62 // GOPATH separated by \n\t (<funcname>\n\t<path>)
63 // %+v equivalent to %+s:%d
64 func (f Frame) Format(s fmt.State, verb rune) {
65 switch verb {
66 case 's':
67 switch {
68 case s.Flag('+'):
69 io.WriteString(s, f.name())
70 io.WriteString(s, "\n\t")
71 io.WriteString(s, f.file())
72 default:
73 io.WriteString(s, path.Base(f.file()))
74 }
75 case 'd':
76 io.WriteString(s, strconv.Itoa(f.line()))
77 case 'n':
78 io.WriteString(s, funcname(f.name()))
79 case 'v':
80 f.Format(s, 's')
81 io.WriteString(s, ":")
82 f.Format(s, 'd')
83 }
84 }
85 86 // MarshalText formats a stacktrace Frame as a text string. The output is the
87 // same as that of fmt.Sprintf("%+v", f), but without newlines or tabs.
88 func (f Frame) MarshalText() ([]byte, error) {
89 name := f.name()
90 if name == "unknown" {
91 return []byte(name), nil
92 }
93 return []byte(fmt.Sprintf("%s %s:%d", name, f.file(), f.line())), nil
94 }
95 96 // StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
97 type StackTrace []Frame
98 99 // Format formats the stack of Frames according to the fmt.Formatter interface.
100 //
101 // %s lists source files for each Frame in the stack
102 // %v lists the source file and line number for each Frame in the stack
103 //
104 // Format accepts flags that alter the printing of some verbs, as follows:
105 //
106 // %+v Prints filename, function, and line number for each Frame in the stack.
107 func (st StackTrace) Format(s fmt.State, verb rune) {
108 switch verb {
109 case 'v':
110 switch {
111 case s.Flag('+'):
112 for _, f := range st {
113 io.WriteString(s, "\n")
114 f.Format(s, verb)
115 }
116 case s.Flag('#'):
117 fmt.Fprintf(s, "%#v", []Frame(st))
118 default:
119 st.formatSlice(s, verb)
120 }
121 case 's':
122 st.formatSlice(s, verb)
123 }
124 }
125 126 // formatSlice will format this StackTrace into the given buffer as a slice of
127 // Frame, only valid when called with '%s' or '%v'.
128 func (st StackTrace) formatSlice(s fmt.State, verb rune) {
129 io.WriteString(s, "[")
130 for i, f := range st {
131 if i > 0 {
132 io.WriteString(s, " ")
133 }
134 f.Format(s, verb)
135 }
136 io.WriteString(s, "]")
137 }
138 139 // stack represents a stack of program counters.
140 type stack []uintptr
141 142 func (s *stack) Format(st fmt.State, verb rune) {
143 switch verb {
144 case 'v':
145 switch {
146 case st.Flag('+'):
147 for _, pc := range *s {
148 f := Frame(pc)
149 fmt.Fprintf(st, "\n%+v", f)
150 }
151 }
152 }
153 }
154 155 func (s *stack) StackTrace() StackTrace {
156 f := make([]Frame, len(*s))
157 for i := 0; i < len(f); i++ {
158 f[i] = Frame((*s)[i])
159 }
160 return f
161 }
162 163 func callers() *stack {
164 const depth = 32
165 var pcs [depth]uintptr
166 n := runtime.Callers(3, pcs[:])
167 var st stack = pcs[0:n]
168 return &st
169 }
170 171 // funcname removes the path prefix component of a function's name reported by func.Name().
172 func funcname(name string) string {
173 i := strings.LastIndex(name, "/")
174 name = name[i+1:]
175 i = strings.Index(name, ".")
176 return name[i+1:]
177 }
178