golog to print stack when PRINT_STACK=true

Author: fffw

src/github.com/getlantern/golog/golog.go

@@ -1,11 +1,13 @@
 // package golog implements logging functions that log errors to stderr and
-// debug messages to stdout. Trace logging is also supported. Trace logs go to
-// stdout as well, but they are only written if the program is run with
-// environment variable "TRACE=true"
+// debug messages to stdout. Trace logging is also supported.
+// Trace logs go to stdout as well, but they are only written if the program
+// is run with environment variable "TRACE=true".
+// A stack dump will be printed after the message if "PRINT_STACK=true".
 package golog
 
 import (
 	"bufio"
+	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -106,16 +108,20 @@ func LoggerFor(prefix string) Logger {
 		l.traceOut = ioutil.Discard
 	}
 
+	printStack := os.Getenv("PRINT_STACK")
+	l.printStack, _ = strconv.ParseBool(printStack)
+
 	return l
 }
 
 type logger struct {
-	prefix    string
-	traceOn   bool
-	traceOut  io.Writer
-	outs      atomic.Value
-	pc        []uintptr
-	funcForPc *runtime.Func
+	prefix     string
+	traceOn    bool
+	traceOut   io.Writer
+	printStack bool
+	outs       atomic.Value
+	pc         []uintptr
+	funcForPc  *runtime.Func
 }
 
 // attaches the file and line number corresponding to
@@ -132,13 +138,19 @@ func (l *logger) print(out io.Writer, skipFrames int, severity string, arg inter
 	if err != nil {
 		errorOnLogging(err)
 	}
+	if l.printStack {
+		l.doPrintStack()
+	}
 }
 
 func (l *logger) printf(out io.Writer, skipFrames int, severity string, message string, args ...interface{}) {
 	_, err := fmt.Fprintf(out, severity+" "+l.linePrefix(skipFrames)+message+"\n", args...)
 	if err != nil {
 		errorOnLogging(err)
 	}
+	if l.printStack {
+		l.doPrintStack()
+	}
 }
 
 func (l *logger) Debug(arg interface{}) {
@@ -232,6 +244,24 @@ func (l *logger) AsStdLogger() *log.Logger {
 	return log.New(&errorWriter{l}, "", 0)
 }
 
+func (l *logger) doPrintStack() {
+	var b []byte
+	buf := bytes.NewBuffer(b)
+	for _, pc := range l.pc {
+		funcForPc := runtime.FuncForPC(pc)
+		if funcForPc == nil {
+			break
+		}
+		file, line := funcForPc.FileLine(pc)
+		name := funcForPc.Name()
+		if strings.HasPrefix(name, "runtime.") {
+			break
+		}
+		fmt.Fprintf(buf, "\t%s\t%s: %d\n", name, file, line)
+	}
+	buf.WriteTo(os.Stderr)
+}
+
 func errorOnLogging(err error) {
 	fmt.Fprintf(os.Stderr, "Unable to log: %v\n", err)
 }