add pre-receive hook command

message: add pre-receive hook command
change_hash: ACKwl15k0EUU9zt2guC/yV0qA13f+YQbri/CRMENSNjc
credentials:
- type: pgp_signature
  pub_key_id: 95C46FA6A41148AC
  body: 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
  account: mediocregopher

cmd/dehub/main.go

@@ -1,39 +1,57 @@
 package main
 
 import (
+	"bufio"
 	"dehub"
 	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 )
 
+func exitErr(err error) {
+	fmt.Fprintf(os.Stderr, "exiting: %v\n", err)
+	os.Stderr.Sync()
+	os.Stdout.Sync()
+	os.Exit(1)
+}
+
 type subCmdCtx struct {
-	repo *dehub.Repo
+	repo func() *dehub.Repo
+	flag *flag.FlagSet
 	args []string
 }
 
-var subCmds = []struct {
+func (sctx subCmdCtx) flagParse() {
+	if err := sctx.flag.Parse(sctx.args); err != nil {
+		exitErr(err)
+	}
+}
+
+type subCmd struct {
 	name, descr string
 	body        func(sctx subCmdCtx) error
-}{
+}
+
+var subCmds = []subCmd{
 	{
 		name:  "commit",
 		descr: "commits staged changes to the head of the current branch",
 		body: func(sctx subCmdCtx) error {
-			flag := flag.NewFlagSet("commit", flag.ExitOnError)
-			msg := flag.String("msg", "", "Commit message to use")
-			accountID := flag.String("account-id", "", "Account to sign commit as")
-			flag.Parse(sctx.args)
+			msg := sctx.flag.String("msg", "", "Commit message to use")
+			accountID := sctx.flag.String("account-id", "", "Account to sign commit as")
+			sctx.flagParse()
 
 			if *msg == "" || *accountID == "" {
+				flag.PrintDefaults()
 				return errors.New("-msg and -account-id are both required")
 			}
 
-			cfg, err := sctx.repo.LoadConfig()
+			cfg, err := sctx.repo().LoadConfig()
 			if err != nil {
 				return err
 			}
@@ -58,7 +76,7 @@ var subCmds = []struct {
 				return fmt.Errorf("could not cast %+v to SignifierInterface: %w", sig, err)
 			}
 
-			_, hash, err := sctx.repo.CommitMaster(*msg, *accountID, sigInt)
+			_, hash, err := sctx.repo().CommitMaster(*msg, *accountID, sigInt)
 			if err != nil {
 				return err
 			}
@@ -70,16 +88,15 @@ var subCmds = []struct {
 		name:  "verify",
 		descr: "verifies one or more commits as having the proper credentials",
 		body: func(sctx subCmdCtx) error {
-			flag := flag.NewFlagSet("verify", flag.ExitOnError)
-			rev := flag.String("rev", "HEAD", "Revision of commit to verify")
-			flag.Parse(sctx.args)
+			rev := sctx.flag.String("rev", "HEAD", "Revision of commit to verify")
+			sctx.flagParse()
 
-			h, err := sctx.repo.GitRepo.ResolveRevision(plumbing.Revision(*rev))
+			h, err := sctx.repo().GitRepo.ResolveRevision(plumbing.Revision(*rev))
 			if err != nil {
 				return fmt.Errorf("could not resolve revision %q: %w", *rev, err)
 			}
 
-			if err := sctx.repo.VerifyMasterCommit(*h); err != nil {
+			if err := sctx.repo().VerifyMasterCommit(*h); err != nil {
 				return fmt.Errorf("could not verify commit at %q (%s): %w", *rev, *h, err)
 			}
 
@@ -87,50 +104,173 @@ var subCmds = []struct {
 			return nil
 		},
 	},
-}
+	{
+		name:  "hook",
+		descr: "use dehub as a git hook",
+		body: func(sctx subCmdCtx) error {
+			preRcv := sctx.flag.Bool("pre-receive", false, "Use dehub as a server-side pre-receive hook")
+			sctx.flagParse()
 
-func printHelp() {
-	fmt.Printf("USAGE: %s <command> [-h]\n\n", os.Args[0])
-	fmt.Println("COMMANDS")
-	for _, subCmd := range subCmds {
-		fmt.Printf("\t%s : %s\n", subCmd.name, subCmd.descr)
-	}
-}
+			if !*preRcv {
+				flag.PrintDefaults()
+				return errors.New("must set the hook type")
+			}
 
-func exitErr(err error) {
-	fmt.Fprintf(os.Stderr, "exiting: %v\n", err)
-	os.Stderr.Sync()
-	os.Stdout.Sync()
-	os.Exit(1)
+			br := bufio.NewReader(os.Stdin)
+			for {
+				line, err := br.ReadString('\n')
+				if errors.Is(err, io.EOF) {
+					return nil
+				} else if err != nil {
+					return fmt.Errorf("error reading next line from stdin: %w", err)
+				}
+
+				lineParts := strings.Fields(line)
+				if len(lineParts) < 3 {
+					return fmt.Errorf("malformed pre-receive hook stdin line %q", line)
+				}
+
+				if plumbing.ReferenceName(lineParts[2]) != plumbing.Master {
+					return fmt.Errorf("only commits to the master branch are allowed at the moment (tried to push to %q)", lineParts[2])
+				}
+
+				// the zeroRevision gets sent on the very first push
+				const zeroRevision plumbing.Revision = "0000000000000000000000000000000000000000"
+
+				fromRev := plumbing.Revision(lineParts[0])
+				var fromHash *plumbing.Hash
+				if fromRev != zeroRevision {
+					fromHash, err = sctx.repo().GitRepo.ResolveRevision(fromRev)
+					if err != nil {
+						return fmt.Errorf("unable to resolve revision %q: %w", fromRev, err)
+					}
+				}
+
+				toRev := plumbing.Revision(lineParts[1])
+				toHash, err := sctx.repo().GitRepo.ResolveRevision(toRev)
+				if err != nil {
+					return fmt.Errorf("unable to resolve revision %q: %w", toRev, err)
+				}
+
+				toCommit, err := sctx.repo().GitRepo.CommitObject(*toHash)
+				if err != nil {
+					return fmt.Errorf("unable to find commit %q: %w", *toHash, err)
+				}
+
+				var hashesToCheck []plumbing.Hash
+				var found bool
+				for currCommit := toCommit; ; {
+					hashesToCheck = append(hashesToCheck, currCommit.Hash)
+					if currCommit.NumParents() == 0 {
+						break
+					} else if currCommit.NumParents() > 1 {
+						return fmt.Errorf("commit %q has more than one parent: %+v",
+							currCommit.Hash, currCommit.ParentHashes)
+					}
+
+					parentCommit, err := currCommit.Parent(0)
+					if err != nil {
+						return fmt.Errorf("unable to get parent of commit %q: %w", currCommit.Hash, err)
+					} else if fromHash != nil && parentCommit.Hash == *fromHash {
+						found = true
+						break
+					}
+					currCommit = parentCommit
+				}
+				if !found && fromHash != nil {
+					return fmt.Errorf("unable to find commit %q as an ancestor of %q", *fromHash, *toHash)
+				}
+
+				for i := len(hashesToCheck) - 1; i >= 0; i-- {
+					hash := hashesToCheck[i]
+					fmt.Printf("Verifying master commit %q\n", hash)
+					if err := sctx.repo().VerifyMasterCommit(hash); err != nil {
+						return fmt.Errorf("could not verify master commit %q", hash)
+					}
+				}
+				fmt.Println("All pushed commits have been verified, well done.")
+				return nil
+			}
+		},
+	},
 }
 
 func main() {
-	if len(os.Args) < 2 {
-		printHelp()
+	var pickedSubCmd bool
+	var subCmd subCmd
+	flagSet := flag.NewFlagSet("dehub", flag.ContinueOnError)
+	flagSet.Usage = func() {
+		cmd := "<command>"
+		if pickedSubCmd {
+			cmd = subCmd.name
+		}
+		fmt.Printf("USAGE: %s [global flags] %s [command flags]\n\n", os.Args[0], cmd)
+
+		if !pickedSubCmd {
+			fmt.Println("COMMANDS")
+			for _, subCmd := range subCmds {
+				fmt.Printf("\t%s : %s\n", subCmd.name, subCmd.descr)
+			}
+			fmt.Println("")
+		}
+
+		fmt.Println("GLOBAL FLAGS")
+		flagSet.PrintDefaults()
+		fmt.Println("")
+	}
+
+	bare := flagSet.Bool("bare", false, "If set then dehub will expect to be working with a bare repo")
+	if err := flagSet.Parse(os.Args[1:]); err != nil {
+		exitErr(err)
 		return
 	}
 
-	subCmdName := strings.ToLower(os.Args[1])
-	for _, subCmd := range subCmds {
-		if subCmd.name != subCmdName {
-			continue
-		}
+	args := flagSet.Args()
+	if len(args) < 1 {
+		flagSet.Usage()
+		exitErr(errors.New("no command selected"))
+	}
 
-		r, err := dehub.OpenRepo(".")
-		if err != nil {
-			exitErr(err)
+	subCmdName, args := strings.ToLower(args[0]), args[1:]
+	for _, subCmd = range subCmds {
+		if pickedSubCmd = subCmd.name == subCmdName; pickedSubCmd {
+			break
 		}
+	}
 
-		err = subCmd.body(subCmdCtx{
-			repo: r,
-			args: os.Args[2:],
-		})
-		if err != nil {
+	if !pickedSubCmd {
+		flagSet.Usage()
+		exitErr(fmt.Errorf("unknown command %q", subCmdName))
+	}
+
+	subFlagSet := flag.NewFlagSet(subCmd.name, flag.ExitOnError)
+	subFlagSet.Usage = func() {
+		flagSet.Usage()
+		fmt.Println("COMMAND FLAGS")
+		subFlagSet.PrintDefaults()
+		fmt.Println("")
+	}
+
+	var r *dehub.Repo
+	repoFn := func() *dehub.Repo {
+		if r != nil {
+			return r
+		}
+		var err error
+		if r, err = dehub.OpenRepo(".", dehub.OpenBare(*bare)); err != nil {
+			wd, _ := os.Getwd()
+			err = fmt.Errorf("failed to OpenRepo at %q: %w", wd, err)
 			exitErr(err)
 		}
-		return
+		return r
 	}
 
-	fmt.Printf("unknown command %q\n\n", subCmdName)
-	printHelp()
+	err := subCmd.body(subCmdCtx{
+		repo: repoFn,
+		flag: subFlagSet,
+		args: args,
+	})
+	if err != nil {
+		exitErr(err)
+	}
 }

repo.go

@@ -26,6 +26,22 @@ var (
 	ConfigPath = filepath.Join(DehubDir, "config.yml")
 )
 
+type repoOpts struct {
+	bare bool
+}
+
+// OpenOption is an option which can be passed to the OpenRepo function to
+// affect the Repo's behavior.
+type OpenOption func(*repoOpts)
+
+// OpenBare returns an OpenOption which, if true is given, causes the OpenRepo
+// function to expect to open a bare repo.
+func OpenBare(bare bool) OpenOption {
+	return func(o *repoOpts) {
+		o.bare = bare
+	}
+}
+
 // Repo is an object which allows accessing and modifying the dehub repo.
 type Repo struct {
 	GitRepo *git.Repository
@@ -36,11 +52,16 @@ type Repo struct {
 //
 // The given path is expected to have a git repo and .dehub folder already
 // initialized.
-func OpenRepo(path string) (*Repo, error) {
+func OpenRepo(path string, options ...OpenOption) (*Repo, error) {
+	var opts repoOpts
+	for _, opt := range options {
+		opt(&opts)
+	}
+
 	r := Repo{}
 	var err error
 	openOpts := &git.PlainOpenOptions{
-		DetectDotGit: true,
+		DetectDotGit: !opts.bare,
 	}
 	if r.GitRepo, err = git.PlainOpenWithOptions(path, openOpts); err != nil {
 		return nil, fmt.Errorf("could not open git repo: %w", err)