Add a tracer that honors GIT_TRACE

commands/command_push.go

@@ -5,6 +5,7 @@ import (
 	"github.com/github/git-media/gitmedia"
 	"github.com/github/git-media/gitmediaclient"
 	"github.com/github/git-media/pointer"
+	"github.com/github/git-media/trace"
 	"github.com/spf13/cobra"
 	"io/ioutil"
 	"os"
@@ -122,6 +123,7 @@ func pushCommand(cmd *cobra.Command, args []string) {
 // git media endpoint already has a git media object for that oid. The object will
 // not be pushed again.
 func pushAsset(oid, filename string, index, totalFiles int) *gitmedia.WrappedError {
+	trace.Trace("push_asset: %s %s %d/%d", oid, filename, index, totalFiles)
 	path, err := gitmedia.LocalMediaPath(oid)
 	if err != nil {
 		return gitmedia.Errorf(err, "Error uploading file %s (%s)", filename, oid)

git/git.go

@@ -6,6 +6,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"github.com/github/git-media/trace"
 	"io"
 	"os/exec"
 	"regexp"
@@ -149,6 +150,7 @@ func (c *gitConfig) Version() (string, error) {
 // simpleExec is a small wrapper around os/exec.Command. If the passed stdin
 // is not nil it will be hooked up to the subprocess stdin.
 func simpleExec(stdin io.Reader, name string, arg ...string) (string, error) {
+	trace.Trace("run_command: '%s' %s", name, strings.Join(arg, " "))
 	cmd := exec.Command(name, arg...)
 	if stdin != nil {
 		cmd.Stdin = stdin

trace/trace.go

@@ -0,0 +1,56 @@
+package trace
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+var tracerOut io.Writer
+
+// Trace prints tracing output following the semantics of the GIT_TRACE environment
+// variable. If GIT_TRACE is set to "1", "2", or "true", messages will be printed
+// on stderr. If the variable is set to an integer value greater than 1 and lower than
+// 10 it will be interpreted as an open file descriptor and will try to write messages
+// into this file descriptor. Alternatively, if this variable is set to an absolute
+// path, messages will be logged to that file.
+func Trace(format string, args ...interface{}) {
+	if tracerOut != nil {
+		fmt.Fprintf(tracerOut, "trace media: "+format+"\n", args...)
+	}
+}
+
+func init() {
+	trace := os.Getenv("GIT_TRACE")
+	if trace == "" || strings.ToLower(trace) == "false" {
+		return
+	}
+
+	fd, err := strconv.Atoi(trace)
+
+	if err != nil {
+		if filepath.IsAbs(trace) {
+			tracerOut, err = os.OpenFile(trace, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Could not open '%s' for tracing: %s\nDefaulting to tracing on stderr...\n", trace, err)
+				tracerOut = os.Stderr
+			}
+		} else if strings.ToLower(trace) == "true" {
+			tracerOut = os.Stderr
+		} else {
+			return
+		}
+	} else {
+		switch fd {
+		case 0:
+			return
+		case 1, 2:
+			tracerOut = os.Stderr
+		default:
+			tracerOut = os.NewFile(uintptr(fd), "trace")
+		}
+	}
+}