Add GitMiddleware

.gitignore

@@ -1,2 +1,3 @@
 smoothie
 .ssh
+.repos

git.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+
+	"github.com/gliderlabs/ssh"
+)
+
+func GitMiddleware(repoDir string) Middleware {
+	return func(sh ssh.Handler) ssh.Handler {
+		return func(s ssh.Session) {
+			cmd := s.Command()
+			if len(cmd) == 2 {
+				switch cmd[0] {
+				case "git-upload-pack", "git-receive-pack", "git-upload-archive":
+					r := cmd[1]
+					rp := fmt.Sprintf("%s%s", repoDir, r)
+					ctx := s.Context()
+					err := ensureRepo(ctx, repoDir, r)
+					if err != nil {
+						fatalGit(s, err)
+						break
+					}
+					c := exec.CommandContext(ctx, cmd[0], rp)
+					c.Dir = "./"
+					c.Stdout = s
+					c.Stdin = s
+					err = c.Run()
+					if err != nil {
+						fatalGit(s, err)
+						break
+					}
+				}
+			}
+			sh(s)
+		}
+	}
+}
+
+func fileExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return true, err
+}
+
+func fatalGit(s ssh.Session, err error) {
+	// hex length includes 4 byte length prefix and ending newline
+	logError(s, err)
+	msg := err.Error()
+	pktLine := fmt.Sprintf("%04x%s\n", len(msg)+5, msg)
+	_, err = s.Write([]byte(pktLine))
+	if err != nil {
+		logError(s, err)
+	}
+	s.Exit(1)
+}
+
+func ensureRepo(ctx context.Context, dir string, repo string) error {
+	exists, err := fileExists(dir)
+	if err != nil {
+		return err
+	}
+	if !exists {
+		err = os.MkdirAll(dir, os.ModeDir|os.FileMode(0700))
+		if err != nil {
+			return err
+		}
+	}
+	rp := fmt.Sprintf("%s%s", dir, repo)
+	exists, err = fileExists(rp)
+	if err != nil {
+		return err
+	}
+	if !exists {
+		c := exec.CommandContext(ctx, "git", "init", "--bare", rp)
+		err = c.Run()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/charmbracelet/charm v0.8.6
 	github.com/charmbracelet/lipgloss v0.2.1
 	github.com/gliderlabs/ssh v0.3.3
+	github.com/go-git/go-git/v5 v5.4.2
 	github.com/meowgorithm/babyenv v1.3.0
 	golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97
 )