From b3265379ddde9ef6887d8aaac6cb4c183f49de3a Mon Sep 17 00:00:00 2001
From: John Cai <jcai@gitlab.com>
Date: Wed, 11 Mar 2020 15:07:54 -0700
Subject: POC repository transactions

---
 internal/git/transaction.go      | 164 +++++++++++++++++++++++++++++++++++++++
 internal/git/transaction_test.go |  49 ++++++++++++
 2 files changed, 213 insertions(+)
 create mode 100644 internal/git/transaction.go
 create mode 100644 internal/git/transaction_test.go

diff --git a/internal/git/transaction.go b/internal/git/transaction.go
new file mode 100644
index 000000000..c98b96403
--- /dev/null
+++ b/internal/git/transaction.go
@@ -0,0 +1,164 @@
+package git
+
+import (
+	"bytes"
+	"context"
+	"encoding/gob"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os/exec"
+
+	"gitlab.com/gitlab-org/gitaly/internal/helper"
+
+	"gitlab.com/gitlab-org/gitaly/internal/git/repository"
+	"gitlab.com/gitlab-org/gitaly/internal/helper/text"
+	"gitlab.com/gitlab-org/gitaly/proto/go/gitalypb"
+)
+
+/*
+func init() {
+	gob.Register(gitalypb.Repository{})
+}
+
+*/
+
+type Transaction struct {
+	Args []string
+	repo *gitalypb.Repository
+}
+
+func NewTransaction(repo *gitalypb.Repository, args []string) *Transaction {
+	return &Transaction{
+		Args: args,
+		repo: repo,
+	}
+}
+
+func GetCurrentTransactionID(ctx context.Context, repo repository.GitRepo) (string, error) {
+	getTxID, err := SafeStdinCmd(ctx, repo, nil, SubCmd{
+		Name: "rev-parse",
+		Args: []string{"refs/tx/transaction"},
+	})
+	if err != nil {
+		return "", err
+	}
+
+	txID, err := ioutil.ReadAll(getTxID)
+	if err != nil {
+		return "", err
+	}
+
+	if err = getTxID.Wait(); err != nil {
+		return "", err
+	}
+
+	return text.ChompBytes(txID), nil
+}
+
+func GetCurrentTransaction(repo *gitalypb.Repository, transactionID string) (*Transaction, error) {
+	repoPath, err := helper.GetRepoPath(repo)
+	if err != nil {
+		return nil, err
+	}
+
+	var stdout bytes.Buffer
+	c := exec.Command("git", "-C", repoPath, "cat-file", "-p", transactionID)
+	c.Stdout = &stdout
+
+	if err := c.Run(); err != nil {
+		fmt.Printf("\n\nwhoa %v\n\n", err)
+		return nil, err
+	}
+
+	var transaction Transaction
+	if err := gob.NewDecoder(&stdout).Decode(&transaction); err != nil {
+		return nil, err
+	}
+
+	transaction.repo = repo
+
+	return &transaction, nil
+}
+
+func (t *Transaction) Begin(ctx context.Context) error {
+	// TODO: issue here of creating blobs that may never get used
+	// we don't want to clutter git's object database with these, even though they should get cleaned up during
+	// gc
+	repoPath, err := helper.GetRepoPath(t.repo)
+	if err != nil {
+		return err
+	}
+
+	r, w := io.Pipe()
+
+	var stdout, stderr bytes.Buffer
+
+	c := exec.Command("git", "-C", repoPath, "hash-object", "-w", "--stdin")
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	c.Stdin = r
+
+	if err := c.Start(); err != nil {
+		return err
+	}
+
+	if err = gob.NewEncoder(w).Encode(t); err != nil {
+		return err
+	}
+	w.Close()
+
+	if err := c.Wait(); err != nil {
+		return err
+	}
+	r.Close()
+
+	blobID := text.ChompBytes(stdout.Bytes())
+
+	lockCmd, err := SafeCmd(ctx, t.repo, nil, SubCmd{
+		Name: "update-ref",
+		Args: []string{"refs/tx/transaction", blobID, "0000000000000000000000000000000000000000"},
+	})
+	if err != nil {
+		return err
+	}
+
+	if err = lockCmd.Wait(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (t *Transaction) Commit(ctx context.Context, transactionID string) error {
+	name := t.Args[0]
+	var args []string
+
+	if len(t.Args) > 1 {
+		args = t.Args[1:]
+	}
+
+	txID, err := GetCurrentTransactionID(ctx, t.repo)
+	if err != nil {
+		return err
+	}
+
+	if txID != transactionID {
+		return errors.New("you are not allowed to commit this transaction")
+	}
+
+	c := exec.Command(name, args...)
+	if err := c.Run(); err != nil {
+		return err
+	}
+
+	repoPath, err := helper.GetRepoPath(t.repo)
+	if err != nil {
+		return err
+	}
+
+	c = exec.Command("git", "-C", repoPath, "update-ref", "-d", "refs/tx/transaction")
+
+	return c.Run()
+}
diff --git a/internal/git/transaction_test.go b/internal/git/transaction_test.go
new file mode 100644
index 000000000..792c1b00c
--- /dev/null
+++ b/internal/git/transaction_test.go
@@ -0,0 +1,49 @@
+package git
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"gitlab.com/gitlab-org/gitaly/internal/helper/text"
+	"gitlab.com/gitlab-org/gitaly/internal/testhelper"
+)
+
+func TestTransaction(t *testing.T) {
+	ctx, cancel := testhelper.Context()
+	defer cancel()
+
+	repo, testRepoPath, cleanup := testhelper.NewTestRepo(t)
+	defer cleanup()
+
+	refName, err := text.RandomHex(10)
+	require.NoError(t, err)
+
+	require.NoError(t, err)
+
+	transaction := NewTransaction(repo, []string{"git", "-C", testRepoPath, "update-ref", fmt.Sprintf("refs/heads/%s", refName), "master"})
+	require.NoError(t, transaction.Begin(ctx))
+
+	transactionID, err := GetCurrentTransactionID(ctx, repo)
+	require.NoError(t, err)
+
+	tx, err := GetCurrentTransaction(repo, transactionID)
+	require.NoError(t, err)
+	require.Equal(t, transaction, tx)
+
+	// try to create a second transaction
+	refName, err = text.RandomHex(10)
+	require.NoError(t, err)
+
+	anotherTransaction := NewTransaction(repo, []string{"git", "-C", testRepoPath, "update-ref", fmt.Sprintf("refs/heads/%s", refName), "master"})
+	require.Error(t, anotherTransaction.Begin(ctx))
+
+	// try to commit with an incorrect transaction id
+	require.Error(t, tx.Commit(ctx, "67d4350058a6f76a8a3d4133aaaaf96bf8a5698b"))
+
+	// commit the transaction
+	require.NoError(t, tx.Commit(ctx, transactionID))
+
+	// now another transaction can begin
+	require.NoError(t, anotherTransaction.Begin(ctx))
+}
-- 
cgit v1.2.3