8 files changed, 154 insertions, 32 deletions
diff --git a/utils/binary/read.go b/utils/binary/read.go
index a14d48d..b8f9df1 100644
--- a/utils/binary/read.go
+++ b/utils/binary/read.go
@@ -1,4 +1,4 @@
-// Package binary implements sintax-sugar functions on top of the standard
+// Package binary implements syntax-sugar functions on top of the standard
 // library binary package
 package binary
 
diff --git a/utils/ioutil/common.go b/utils/ioutil/common.go
index b0ace4e..235af71 100644
--- a/utils/ioutil/common.go
+++ b/utils/ioutil/common.go
@@ -195,7 +195,7 @@ func NewWriterOnError(w io.Writer, notify func(error)) io.Writer {
 }
 
 // NewWriteCloserOnError returns a io.WriteCloser that call the notify function
-//when an unexpected (!io.EOF) error happens, after call Write function.
+// when an unexpected (!io.EOF) error happens, after call Write function.
 func NewWriteCloserOnError(w io.WriteCloser, notify func(error)) io.WriteCloser {
 	return NewWriteCloser(NewWriterOnError(w, notify), w)
 }
@@ -208,13 +208,3 @@ func (r *writerOnError) Write(p []byte) (n int, err error) {
 
 	return
 }
-
-type PipeReader interface {
-	io.ReadCloser
-	CloseWithError(err error) error
-}
-
-type PipeWriter interface {
-	io.WriteCloser
-	CloseWithError(err error) error
-}
diff --git a/utils/ioutil/pipe.go b/utils/ioutil/pipe.go
deleted file mode 100644
index f30c452..0000000
--- a/utils/ioutil/pipe.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// +build !js
-
-package ioutil
-
-import "io"
-
-func Pipe() (PipeReader, PipeWriter) {
-	return io.Pipe()
-}
diff --git a/utils/ioutil/pipe_js.go b/utils/ioutil/pipe_js.go
deleted file mode 100644
index cf102e6..0000000
--- a/utils/ioutil/pipe_js.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// +build js
-
-package ioutil
-
-import "github.com/acomagu/bufpipe"
-
-func Pipe() (PipeReader, PipeWriter) {
-	return bufpipe.New(nil)
-}
diff --git a/utils/merkletrie/difftree.go b/utils/merkletrie/difftree.go
index 9f5145a..8090942 100644
--- a/utils/merkletrie/difftree.go
+++ b/utils/merkletrie/difftree.go
@@ -55,7 +55,7 @@ package merkletrie
 // Here is a full list of all the cases that are similar and how to
 // merge them together into more general cases.  Each general case
 // is labeled with an uppercase letter for further reference, and it
-// is followed by the pseudocode of the checks you have to perfrom
+// is followed by the pseudocode of the checks you have to perform
 // on both noders to see if you are in such a case, the actions to
 // perform (i.e. what changes to output) and how to advance the
 // iterators of each tree to continue the comparison process.
diff --git a/utils/merkletrie/internal/fsnoder/file.go b/utils/merkletrie/internal/fsnoder/file.go
index 0bb908b..453efee 100644
--- a/utils/merkletrie/internal/fsnoder/file.go
+++ b/utils/merkletrie/internal/fsnoder/file.go
@@ -32,7 +32,7 @@ func newFile(name, contents string) (*file, error) {
 func (f *file) Hash() []byte {
 	if f.hash == nil {
 		h := fnv.New64a()
-		h.Write([]byte(f.contents)) // it nevers returns an error.
+		h.Write([]byte(f.contents)) // it never returns an error.
 		f.hash = h.Sum(nil)
 	}
 
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
+	}
+}
diff --git a/utils/trace/trace_test.go b/utils/trace/trace_test.go
new file mode 100644
index 0000000..6f8f140
--- /dev/null
+++ b/utils/trace/trace_test.go
@@ -0,0 +1,95 @@
+package trace
+
+import (
+	"bytes"
+	"io"
+	"log"
+	"testing"
+)
+
+func TestMain(m *testing.M) {
+	defer SetLogger(newLogger())
+	if code := m.Run(); code != 0 {
+		panic(code)
+	}
+}
+
+func setUpTest(t testing.TB, buf *bytes.Buffer) {
+	t.Cleanup(func() {
+		if buf != nil {
+			buf.Reset()
+		}
+		SetTarget(0)
+	})
+	w := io.Discard
+	if buf != nil {
+		w = buf
+	}
+	SetLogger(log.New(w, "", 0))
+}
+
+func TestEmpty(t *testing.T) {
+	var buf bytes.Buffer
+	setUpTest(t, &buf)
+	General.Print("test")
+	if buf.String() != "" {
+		t.Error("expected empty string")
+	}
+}
+
+func TestOneTarget(t *testing.T) {
+	var buf bytes.Buffer
+	setUpTest(t, &buf)
+	SetTarget(General)
+	General.Print("test")
+	if buf.String() != "test\n" {
+		t.Error("expected 'test'")
+	}
+}
+
+func TestMultipleTargets(t *testing.T) {
+	var buf bytes.Buffer
+	setUpTest(t, &buf)
+	SetTarget(General | Packet)
+	General.Print("a")
+	Packet.Print("b")
+	if buf.String() != "a\nb\n" {
+		t.Error("expected 'a\nb\n'")
+	}
+}
+
+func TestPrintf(t *testing.T) {
+	var buf bytes.Buffer
+	setUpTest(t, &buf)
+	SetTarget(General)
+	General.Printf("a %d", 1)
+	if buf.String() != "a 1\n" {
+		t.Error("expected 'a 1\n'")
+	}
+}
+
+func TestDisabledMultipleTargets(t *testing.T) {
+	var buf bytes.Buffer
+	setUpTest(t, &buf)
+	SetTarget(General)
+	General.Print("a")
+	Packet.Print("b")
+	if buf.String() != "a\n" {
+		t.Error("expected 'a\n'")
+	}
+}
+
+func BenchmarkDisabledTarget(b *testing.B) {
+	setUpTest(b, nil)
+	for i := 0; i < b.N; i++ {
+		General.Print("test")
+	}
+}
+
+func BenchmarkEnabledTarget(b *testing.B) {
+	setUpTest(b, nil)
+	SetTarget(General)
+	for i := 0; i < b.N; i++ {
+		General.Print("test")
+	}
+}