Add CallerWithSkipFrameCount to the Context (#98) (#135)

Add the ability to skip a specified number of stack frames
on a per context basis. Before this toe CallerSkipFrameCount
could only be set globally.

context.go

@@ -2,6 +2,7 @@ package zerolog
 
 import (
 	"io/ioutil"
+	"math"
 	"net"
 	"time"
 )
@@ -347,14 +348,31 @@ func (c Context) Interface(key string, i interface{}) Context {
 	return c
 }
 
-type callerHook struct{}
+type callerHook struct {
-
+	callerSkipFrameCount int
-func (ch callerHook) Run(e *Event, level Level, msg string) {
-	// Extra frames to skip (added by hook infra).
-	e.caller(CallerSkipFrameCount + contextCallerSkipFrameCount)
 }
 
-var ch = callerHook{}
+func newCallerHook(skipFrameCount int) callerHook {
+	return callerHook{callerSkipFrameCount: skipFrameCount}
+}
+
+func (ch callerHook) Run(e *Event, level Level, msg string) {
+	switch ch.callerSkipFrameCount {
+	case useGlobalSkipFrameCount:
+		// Extra frames to skip (added by hook infra).
+		e.caller(CallerSkipFrameCount + contextCallerSkipFrameCount)
+	default:
+		// Extra frames to skip (added by hook infra).
+		e.caller(ch.callerSkipFrameCount + contextCallerSkipFrameCount)
+	}
+}
+
+// useGlobalSkipFrameCount acts as a flag to informat callerHook.Run
+// to use the global CallerSkipFrameCount.
+const useGlobalSkipFrameCount = math.MinInt32
+
+// ch is the default caller hook using the global CallerSkipFrameCount.
+var ch = newCallerHook(useGlobalSkipFrameCount)
 
 // Caller adds the file:line of the caller with the zerolog.CallerFieldName key.
 func (c Context) Caller() Context {
@@ -362,6 +380,14 @@ func (c Context) Caller() Context {
 	return c
 }
 
+// CallerWithSkipFrameCount adds the file:line of the caller with the zerolog.CallerFieldName key.
+// The specified skipFrameCount int will override the global CallerSkipFrameCount for this context's respective logger.
+// If set to -1 the global CallerSkipFrameCount will be used.
+func (c Context) CallerWithSkipFrameCount(skipFrameCount int) Context {
+	c.l = c.l.Hook(newCallerHook(skipFrameCount))
+	return c
+}
+
 type stackTraceHook struct{}
 
 func (sh stackTraceHook) Run(e *Event, level Level, msg string) {

log_test.go

@@ -107,6 +107,20 @@ func TestWith(t *testing.T) {
 	if got, want := decodeIfBinaryToString(out.Bytes()), `{"string":"foo","bytes":"bar","hex":"12ef","json":{"some":"json"},"error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11.101,"float64":12.30303,"time":"0001-01-01T00:00:00Z","caller":"`+caller+`"}`+"\n"; got != want {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
+
+	// Validate CallerWithSkipFrameCount.
+	out.Reset()
+	_, file, line, _ = runtime.Caller(0)
+	caller = fmt.Sprintf("%s:%d", file, line+5)
+	log = ctx.CallerWithSkipFrameCount(3).Logger()
+	func() {
+		log.Log().Msg("")
+	}()
+	// The above line is a little contrived, but the line above should be the line due
+	// to the extra frame skip.
+	if got, want := decodeIfBinaryToString(out.Bytes()), `{"string":"foo","bytes":"bar","hex":"12ef","json":{"some":"json"},"error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11.101,"float64":12.30303,"time":"0001-01-01T00:00:00Z","caller":"`+caller+`"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
 }
 
 func TestFieldsMap(t *testing.T) {