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package common
import (
"fmt"
"runtime"
)
//----------------------------------------
// Convenience method.
func ErrorWrap(cause interface{}, format string, args ...interface{}) Error {
if causeCmnError, ok := cause.(*cmnError); ok {
msg := fmt.Sprintf(format, args...)
return causeCmnError.Stacktrace().Trace(1, msg)
} else if cause == nil {
return newCmnError(FmtError{format, args}).Stacktrace()
} else {
// NOTE: causeCmnError is a typed nil here.
msg := fmt.Sprintf(format, args...)
return newCmnError(cause).Stacktrace().Trace(1, msg)
}
}
//----------------------------------------
// Error & cmnError
/*
Usage with arbitrary error data:
```go
// Error construction
type MyError struct{}
var err1 error = NewErrorWithData(MyError{}, "my message")
...
// Wrapping
var err2 error = ErrorWrap(err1, "another message")
if (err1 != err2) { panic("should be the same")
...
// Error handling
switch err2.Data().(type){
case MyError: ...
default: ...
}
```
*/
type Error interface {
Error() string
Stacktrace() Error
Trace(offset int, format string, args ...interface{}) Error
Data() interface{}
}
// New Error with formatted message.
// The Error's Data will be a FmtError type.
func NewError(format string, args ...interface{}) Error {
err := FmtError{format, args}
return newCmnError(err)
}
// New Error with specified data.
func NewErrorWithData(data interface{}) Error {
return newCmnError(data)
}
type cmnError struct {
data interface{} // associated data
msgtraces []msgtraceItem // all messages traced
stacktrace []uintptr // first stack trace
}
var _ Error = &cmnError{}
// NOTE: do not expose.
func newCmnError(data interface{}) *cmnError {
return &cmnError{
data: data,
msgtraces: nil,
stacktrace: nil,
}
}
// Implements error.
func (err *cmnError) Error() string {
return fmt.Sprintf("%v", err)
}
// Captures a stacktrace if one was not already captured.
func (err *cmnError) Stacktrace() Error {
if err.stacktrace == nil {
var offset = 3
var depth = 32
err.stacktrace = captureStacktrace(offset, depth)
}
return err
}
// Add tracing information with msg.
// Set n=0 unless wrapped with some function, then n > 0.
func (err *cmnError) Trace(offset int, format string, args ...interface{}) Error {
msg := fmt.Sprintf(format, args...)
return err.doTrace(msg, offset)
}
// Return the "data" of this error.
// Data could be used for error handling/switching,
// or for holding general error/debug information.
func (err *cmnError) Data() interface{} {
return err.data
}
func (err *cmnError) doTrace(msg string, n int) Error {
pc, _, _, _ := runtime.Caller(n + 2) // +1 for doTrace(). +1 for the caller.
// Include file & line number & msg.
// Do not include the whole stack trace.
err.msgtraces = append(err.msgtraces, msgtraceItem{
pc: pc,
msg: msg,
})
return err
}
func (err *cmnError) Format(s fmt.State, verb rune) {
switch verb {
case 'p':
s.Write([]byte(fmt.Sprintf("%p", &err)))
default:
if s.Flag('#') {
s.Write([]byte("--= Error =--\n"))
// Write data.
s.Write([]byte(fmt.Sprintf("Data: %#v\n", err.data)))
// Write msg trace items.
s.Write([]byte(fmt.Sprintf("Msg Traces:\n")))
for i, msgtrace := range err.msgtraces {
s.Write([]byte(fmt.Sprintf(" %4d %s\n", i, msgtrace.String())))
}
// Write stack trace.
if err.stacktrace != nil {
s.Write([]byte(fmt.Sprintf("Stack Trace:\n")))
for i, pc := range err.stacktrace {
fnc := runtime.FuncForPC(pc)
file, line := fnc.FileLine(pc)
s.Write([]byte(fmt.Sprintf(" %4d %s:%d\n", i, file, line)))
}
}
s.Write([]byte("--= /Error =--\n"))
} else {
// Write msg.
s.Write([]byte(fmt.Sprintf("%v", err.data)))
}
}
}
//----------------------------------------
// stacktrace & msgtraceItem
func captureStacktrace(offset int, depth int) []uintptr {
var pcs = make([]uintptr, depth)
n := runtime.Callers(offset, pcs)
return pcs[0:n]
}
type msgtraceItem struct {
pc uintptr
msg string
}
func (mti msgtraceItem) String() string {
fnc := runtime.FuncForPC(mti.pc)
file, line := fnc.FileLine(mti.pc)
return fmt.Sprintf("%s:%d - %s",
file, line,
mti.msg,
)
}
//----------------------------------------
// fmt error
/*
FmtError is the data type for NewError() (e.g. NewError().Data().(FmtError))
Theoretically it could be used to switch on the format string.
```go
// Error construction
var err1 error = NewError("invalid username %v", "BOB")
var err2 error = NewError("another kind of error")
...
// Error handling
switch err1.Data().(cmn.FmtError).Format() {
case "invalid username %v": ...
case "another kind of error": ...
default: ...
}
```
*/
type FmtError struct {
format string
args []interface{}
}
func (fe FmtError) Error() string {
return fmt.Sprintf(fe.format, fe.args...)
}
func (fe FmtError) String() string {
return fmt.Sprintf("FmtError{format:%v,args:%v}",
fe.format, fe.args)
}
func (fe FmtError) Format() string {
return fe.format
}