utils: move trace to utils

Without exposing `trace`, we can't set a target to enable tracing from
out of go-git.

Fixes: https://github.com/go-git/go-git/pull/916

1 files changed, 55 insertions, 0 deletions

diff --git a/utils/trace/trace.go b/utils/trace/trace.go
new file mode 100644
index 0000000..3e15c5b
--- /dev/null
+++ b/utils/trace/trace.go
@@ -0,0 +1,55 @@
+package trace
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"sync/atomic"
+)
+
+var (
+	// logger is the logger to use for tracing.
+	logger = newLogger()
+
+	// current is the targets that are enabled for tracing.
+	current atomic.Int32
+)
+
+func newLogger() *log.Logger {
+	return log.New(os.Stderr, "", log.Ltime|log.Lmicroseconds|log.Lshortfile)
+}
+
+// Target is a tracing target.
+type Target int32
+
+const (
+	// General traces general operations.
+	General Target = 1 << iota
+
+	// Packet traces git packets.
+	Packet
+)
+
+// SetTarget sets the tracing targets.
+func SetTarget(target Target) {
+	current.Store(int32(target))
+}
+
+// SetLogger sets the logger to use for tracing.
+func SetLogger(l *log.Logger) {
+	logger = l
+}
+
+// Print prints the given message only if the target is enabled.
+func (t Target) Print(args ...interface{}) {
+	if int32(t)&current.Load() != 0 {
+		logger.Output(2, fmt.Sprint(args...)) // nolint: errcheck
+	}
+}
+
+// Printf prints the given message only if the target is enabled.
+func (t Target) Printf(format string, args ...interface{}) {
+	if int32(t)&current.Load() != 0 {
+		logger.Output(2, fmt.Sprintf(format, args...)) // nolint: errcheck
+	}
+}