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package git
import (
"context"
"fmt"
"os"
"os/exec"
"path/filepath"
"github.com/charmbracelet/wish"
"github.com/gliderlabs/ssh"
"github.com/go-git/go-git/v5"
"github.com/go-git/go-git/v5/plumbing"
)
// ErrNotAuthed represents unauthorized access.
var ErrNotAuthed = fmt.Errorf("you are not authorized to do this")
// ErrSystemMalfunction represents a general system error returned to clients.
var ErrSystemMalfunction = fmt.Errorf("something went wrong")
// AccessLevel is the level of access allowed to a repo.
type AccessLevel int
const (
NoAccess AccessLevel = iota
ReadOnlyAccess
ReadWriteAccess
AdminAccess
)
// GitHooks is an interface that allows for custom authorization
// implementations and post push/fetch notifications. Prior to git access,
// AuthRepo will be called with the ssh.Session public key and the repo name.
// Implementers return the appropriate AccessLevel.
type GitHooks interface {
AuthRepo(string, ssh.PublicKey) AccessLevel
Push(string, ssh.PublicKey)
Fetch(string, ssh.PublicKey)
}
// Middleware adds Git server functionality to the ssh.Server. Repos are stored
// in the specified repo directory. The provided GitHooks implementation will be
// checked for access on a per repo basis for a ssh.Session public key.
// GitHooks.Push and GitHooks.Fetch will be called on successful completion of
// their commands.
func Middleware(repoDir string, gh GitHooks) wish.Middleware {
return func(sh ssh.Handler) ssh.Handler {
return func(s ssh.Session) {
cmd := s.Command()
if len(cmd) == 2 {
gc := cmd[0]
repo := cmd[1] // cmd[1] will be `/REPO`
if len(repo) > 0 && repo[0] == '/' {
repo = repo[1:]
}
pk := s.PublicKey()
access := gh.AuthRepo(repo, pk)
switch gc {
case "git-receive-pack":
switch access {
case ReadWriteAccess, AdminAccess:
err := gitReceivePack(s, gc, repoDir, repo)
if err != nil {
fatalGit(s, ErrSystemMalfunction)
} else {
gh.Push(repo, pk)
}
default:
fatalGit(s, ErrNotAuthed)
}
case "git-upload-archive", "git-upload-pack":
switch access {
case ReadOnlyAccess, ReadWriteAccess, AdminAccess:
err := gitUploadPack(s, gc, repoDir, repo)
if err != nil {
fatalGit(s, ErrSystemMalfunction)
} else {
gh.Fetch(repo, pk)
}
default:
fatalGit(s, ErrNotAuthed)
}
}
}
sh(s)
}
}
}
func gitReceivePack(s ssh.Session, gitCmd string, repoDir string, repo string) error {
ctx := s.Context()
err := ensureRepo(ctx, repoDir, repo)
if err != nil {
return err
}
rp := filepath.Join(repoDir, repo)
err = runCmd(s, "./", gitCmd, rp)
if err != nil {
return err
}
err = ensureDefaultBranch(s, rp)
if err != nil {
return err
}
err = runCmd(s, rp, "git", "update-server-info")
if err != nil {
return err
}
return nil
}
func gitUploadPack(s ssh.Session, gitCmd string, repoDir string, repo string) error {
rp := filepath.Join(repoDir, repo)
if exists, err := fileExists(rp); exists && err == nil {
err = runCmd(s, "./", gitCmd, rp)
if err != nil {
return err
}
}
return nil
}
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
msg := err.Error()
pktLine := fmt.Sprintf("%04x%s\n", len(msg)+5, msg)
_, _ = s.Write([]byte(pktLine))
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 := filepath.Join(dir, repo)
exists, err = fileExists(rp)
if err != nil {
return err
}
if !exists {
_, err := git.PlainInit(rp, true)
if err != nil {
return err
}
}
return nil
}
func runCmd(s ssh.Session, dir, name string, args ...string) error {
usi := exec.CommandContext(s.Context(), name, args...)
usi.Dir = dir
usi.Stdout = s
usi.Stdin = s
err := usi.Run()
if err != nil {
return err
}
return nil
}
func ensureDefaultBranch(s ssh.Session, repoPath string) error {
r, err := git.PlainOpen(repoPath)
if err != nil {
return err
}
brs, err := r.Branches()
if err != nil {
return err
}
defer brs.Close()
fb, err := brs.Next()
if err != nil {
return err
}
// Rename the default branch to the first branch available
_, err = r.Head()
if err == plumbing.ErrReferenceNotFound {
err = runCmd(s, repoPath, "git", "branch", "-M", fb.Name().Short())
if err != nil {
return err
}
}
if err != nil && err != plumbing.ErrReferenceNotFound {
return err
}
return nil
}
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