add backoff to the git plugin

.drone.yml

@@ -25,7 +25,7 @@ pipeline:
     image: plugins/docker:17.05
     pull: true
     repo: plugins/git
-    tags: [ latest, 1.3.0, 1.3, 1 ]
+    tags: [ latest, 1.4.0, 1.4, 1 ]
     secrets: [ docker_username, docker_password ]
     dockerfile: Dockerfile
     when:

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"time"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/joho/godotenv"
@@ -91,6 +92,18 @@ func main() {
 			EnvVar: "PLUGIN_SUBMODULE_OVERRIDE",
 			Value:  &MapFlag{},
 		},
+		cli.DurationFlag{
+			Name:   "backoff",
+			Usage:  "backoff duration",
+			EnvVar: "PLUGIN_BACKOFF",
+			Value:  5 * time.Second,
+		},
+		cli.IntFlag{
+			Name:   "backoff-attempts",
+			Usage:  "backoff attempts",
+			EnvVar: "PLUGIN_ATTEMPTS",
+			Value:  5,
+		},
 		cli.StringFlag{
 			Name:  "env-file",
 			Usage: "source env file",
@@ -131,6 +144,10 @@ func run(c *cli.Context) error {
 			SubmoduleRemote: c.Bool("submodule-update-remote"),
 			Submodules:      c.Generic("submodule-override").(*MapFlag).Get(),
 		},
+		Backoff: Backoff{
+			Attempts: c.Int("backoff-attempts"),
+			Duration: c.Duration("backoff"),
+		},
 	}
 
 	return plugin.Exec()

plugin.go

@@ -1,17 +1,22 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
+	"time"
 )
 
 type Plugin struct {
-	Repo   Repo
-	Build  Build
-	Netrc  Netrc
-	Config Config
+	Repo    Repo
+	Build   Build
+	Netrc   Netrc
+	Config  Config
+	Backoff Backoff
 }
 
 func (p Plugin) Exec() error {
@@ -56,19 +61,55 @@ func (p Plugin) Exec() error {
 	}
 
 	for _, cmd := range cmds {
+		buf := new(bytes.Buffer)
 		cmd.Dir = p.Build.Path
-		cmd.Stdout = os.Stdout
-		cmd.Stderr = os.Stderr
+		cmd.Stdout = io.MultiWriter(os.Stdout, buf)
+		cmd.Stderr = io.MultiWriter(os.Stderr, buf)
 		trace(cmd)
 		err := cmd.Run()
-		if err != nil {
+		switch {
+		case err != nil && shouldRetry(buf.String()):
+			err = retryExec(cmd, p.Backoff.Duration, p.Backoff.Attempts)
+			if err != nil {
+				return err
+			}
+		case err != nil:
 			return err
 		}
 	}
 
 	return nil
 }
 
+// shouldRetry returns true if the command should be re-executed. Currently
+// this only returns true if the remote ref does not exist.
+func shouldRetry(s string) bool {
+	return strings.Contains(s, "find remote ref")
+}
+
+// retryExec is a helper function that retries a command.
+func retryExec(cmd *exec.Cmd, backoff time.Duration, retries int) (err error) {
+	for i := 0; i < retries; i++ {
+		// signal intent to retry
+		fmt.Printf("retry in %v\n", backoff)
+
+		// wait 5 seconds before retry
+		<-time.After(backoff)
+
+		// copy the original command
+		retry := exec.Command(cmd.Args[0], cmd.Args[1:]...)
+		retry.Dir = cmd.Dir
+		retry.Stdout = os.Stdout
+		retry.Stderr = os.Stderr
+		trace(retry)
+		err = retry.Run()
+		if err == nil {
+			return
+		}
+	}
+	return
+}
+
 // Creates an empty git repository.
 func initGit() *exec.Cmd {
 	return exec.Command(

types.go

@@ -1,6 +1,9 @@
 package main
 
-import "encoding/json"
+import (
+	"encoding/json"
+	"time"
+)
 
 type (
 	Repo struct {
@@ -29,6 +32,11 @@ type (
 		Submodules      map[string]string
 		SubmoduleRemote bool
 	}
+
+	Backoff struct {
+		Attempts int
+		Duration time.Duration
+	}
 )
 
 // below are special types used for unmarshaling structured data