blorp.go

package main

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"os"
	"os/exec"
	"sync"
	"time"
)

func main() {
	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	if err := execGitCmd(ctx, os.Stdout, []string{"notes", "--ref", "flux", "list"}); err != nil {
		println(err.Error())
		return
	}
	println("OK!")
}

type threadSafeBuffer struct {
	bytes.Buffer
	sync.Mutex
}

func (b *threadSafeBuffer) Write(p []byte) (n int, err error) {
	b.Lock()
	defer b.Unlock()
	return b.Buffer.Write(p)
}

func (b *threadSafeBuffer) ReadFrom(r io.Reader) (n int64, err error) {
	b.Lock()
	defer b.Unlock()
	return b.Buffer.ReadFrom(r)
}

// execGitCmd runs a `git` command with the supplied arguments.
func execGitCmd(ctx context.Context, out io.Writer, args []string) error {
	c := exec.CommandContext(ctx, "git", args...)

	stdOutAndStdErr := &threadSafeBuffer{}
	c.Stdout = stdOutAndStdErr
	c.Stderr = stdOutAndStdErr
	if out != nil {
		c.Stdout = io.MultiWriter(c.Stdout, out)
	}

	err := c.Run()
	if err != nil {
		if len(stdOutAndStdErr.Bytes()) > 0 {
			err = fmt.Errorf(stdOutAndStdErr.String())
		}
	}

	if ctx.Err() == context.DeadlineExceeded {
		return fmt.Errorf("running git command: %s %v: %s", "git", args, ctx.Err().Error())
	} else if ctx.Err() == context.Canceled {
		return fmt.Errorf("context was unexpectedly cancelled when running git command: %s %v", "git", args)
	}
	return err
}