1 files changed, 196 insertions, 0 deletions

diff --git a/services/pull/temp_repo.go b/services/pull/temp_repo.go
new file mode 100644
index 0000000..36bdbde
--- /dev/null
+++ b/services/pull/temp_repo.go
@@ -0,0 +1,196 @@
+// Copyright 2019 The Gitea Authors.
+// All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pull
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	git_model "code.gitea.io/gitea/models/git"
+	issues_model "code.gitea.io/gitea/models/issues"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+	repo_module "code.gitea.io/gitea/modules/repository"
+)
+
+// Temporary repos created here use standard branch names to help simplify
+// merging code
+const (
+	baseBranch     = "base"     // equivalent to pr.BaseBranch
+	trackingBranch = "tracking" // equivalent to pr.HeadBranch
+	stagingBranch  = "staging"  // this is used for a working branch
+)
+
+type prContext struct {
+	context.Context
+	tmpBasePath string
+	pr          *issues_model.PullRequest
+	outbuf      *strings.Builder // we keep these around to help reduce needless buffer recreation,
+	errbuf      *strings.Builder // any use should be preceded by a Reset and preferably after use
+}
+
+func (ctx *prContext) RunOpts() *git.RunOpts {
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+	return &git.RunOpts{
+		Dir:    ctx.tmpBasePath,
+		Stdout: ctx.outbuf,
+		Stderr: ctx.errbuf,
+	}
+}
+
+// createTemporaryRepoForPR creates a temporary repo with "base" for pr.BaseBranch and "tracking" for  pr.HeadBranch
+// it also create a second base branch called "original_base"
+func createTemporaryRepoForPR(ctx context.Context, pr *issues_model.PullRequest) (prCtx *prContext, cancel context.CancelFunc, err error) {
+	if err := pr.LoadHeadRepo(ctx); err != nil {
+		log.Error("%-v LoadHeadRepo: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v LoadHeadRepo: %w", pr, err)
+	} else if pr.HeadRepo == nil {
+		log.Error("%-v HeadRepo %d does not exist", pr, pr.HeadRepoID)
+		return nil, nil, &repo_model.ErrRepoNotExist{
+			ID: pr.HeadRepoID,
+		}
+	} else if err := pr.LoadBaseRepo(ctx); err != nil {
+		log.Error("%-v LoadBaseRepo: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v LoadBaseRepo: %w", pr, err)
+	} else if pr.BaseRepo == nil {
+		log.Error("%-v BaseRepo %d does not exist", pr, pr.BaseRepoID)
+		return nil, nil, &repo_model.ErrRepoNotExist{
+			ID: pr.BaseRepoID,
+		}
+	} else if err := pr.HeadRepo.LoadOwner(ctx); err != nil {
+		log.Error("%-v HeadRepo.LoadOwner: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v HeadRepo.LoadOwner: %w", pr, err)
+	} else if err := pr.BaseRepo.LoadOwner(ctx); err != nil {
+		log.Error("%-v BaseRepo.LoadOwner: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v BaseRepo.LoadOwner: %w", pr, err)
+	}
+
+	// Clone base repo.
+	tmpBasePath, err := repo_module.CreateTemporaryPath("pull")
+	if err != nil {
+		log.Error("CreateTemporaryPath[%-v]: %v", pr, err)
+		return nil, nil, err
+	}
+	prCtx = &prContext{
+		Context:     ctx,
+		tmpBasePath: tmpBasePath,
+		pr:          pr,
+		outbuf:      &strings.Builder{},
+		errbuf:      &strings.Builder{},
+	}
+	cancel = func() {
+		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("Error whilst removing removing temporary repo for %-v: %v", pr, err)
+		}
+	}
+
+	baseRepoPath := pr.BaseRepo.RepoPath()
+	headRepoPath := pr.HeadRepo.RepoPath()
+
+	if err := git.InitRepository(ctx, tmpBasePath, false, pr.BaseRepo.ObjectFormatName); err != nil {
+		log.Error("Unable to init tmpBasePath for %-v: %v", pr, err)
+		cancel()
+		return nil, nil, err
+	}
+
+	remoteRepoName := "head_repo"
+	baseBranch := "base"
+
+	fetchArgs := git.TrustedCmdArgs{"--no-tags"}
+	if git.CheckGitVersionAtLeast("2.25.0") == nil {
+		// Writing the commit graph can be slow and is not needed here
+		fetchArgs = append(fetchArgs, "--no-write-commit-graph")
+	}
+
+	// addCacheRepo adds git alternatives for the cacheRepoPath in the repoPath
+	addCacheRepo := func(repoPath, cacheRepoPath string) error {
+		p := filepath.Join(repoPath, ".git", "objects", "info", "alternates")
+		f, err := os.OpenFile(p, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
+		if err != nil {
+			log.Error("Could not create .git/objects/info/alternates file in %s: %v", repoPath, err)
+			return err
+		}
+		defer f.Close()
+		data := filepath.Join(cacheRepoPath, "objects")
+		if _, err := fmt.Fprintln(f, data); err != nil {
+			log.Error("Could not write to .git/objects/info/alternates file in %s: %v", repoPath, err)
+			return err
+		}
+		return nil
+	}
+
+	// Add head repo remote.
+	if err := addCacheRepo(tmpBasePath, baseRepoPath); err != nil {
+		log.Error("%-v Unable to add base repository to temporary repo [%s -> %s]: %v", pr, pr.BaseRepo.FullName(), tmpBasePath, err)
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add base repository to temporary repo [%s -> tmpBasePath]: %w", pr.BaseRepo.FullName(), err)
+	}
+
+	if err := git.NewCommand(ctx, "remote", "add", "-t").AddDynamicArguments(pr.BaseBranch).AddArguments("-m").AddDynamicArguments(pr.BaseBranch).AddDynamicArguments("origin", baseRepoPath).
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to add base repository as origin [%s -> %s]: %v\n%s\n%s", pr, pr.BaseRepo.FullName(), tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add base repository as origin [%s -> tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), err, prCtx.outbuf.String(), prCtx.errbuf.String())
+	}
+
+	if err := git.NewCommand(ctx, "fetch", "origin").AddArguments(fetchArgs...).AddDashesAndList(pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to fetch origin base branch [%s:%s -> base, original_base in %s]: %v:\n%s\n%s", pr, pr.BaseRepo.FullName(), pr.BaseBranch, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to fetch origin base branch [%s:%s -> base, original_base in tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+	}
+
+	if err := git.NewCommand(ctx, "symbolic-ref").AddDynamicArguments("HEAD", git.BranchPrefix+baseBranch).
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to set HEAD as base branch in [%s]: %v\n%s\n%s", pr, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to set HEAD as base branch in tmpBasePath: %w\n%s\n%s", err, prCtx.outbuf.String(), prCtx.errbuf.String())
+	}
+
+	if err := addCacheRepo(tmpBasePath, headRepoPath); err != nil {
+		log.Error("%-v Unable to add head repository to temporary repo [%s -> %s]: %v", pr, pr.HeadRepo.FullName(), tmpBasePath, err)
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add head base repository to temporary repo [%s -> tmpBasePath]: %w", pr.HeadRepo.FullName(), err)
+	}
+
+	if err := git.NewCommand(ctx, "remote", "add").AddDynamicArguments(remoteRepoName, headRepoPath).
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to add head repository as head_repo [%s -> %s]: %v\n%s\n%s", pr, pr.HeadRepo.FullName(), tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add head repository as head_repo [%s -> tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), err, prCtx.outbuf.String(), prCtx.errbuf.String())
+	}
+
+	trackingBranch := "tracking"
+	objectFormat := git.ObjectFormatFromName(pr.BaseRepo.ObjectFormatName)
+	// Fetch head branch
+	var headBranch string
+	if pr.Flow == issues_model.PullRequestFlowGithub {
+		headBranch = git.BranchPrefix + pr.HeadBranch
+	} else if len(pr.HeadCommitID) == objectFormat.FullLength() { // for not created pull request
+		headBranch = pr.HeadCommitID
+	} else {
+		headBranch = pr.GetGitRefName()
+	}
+	if err := git.NewCommand(ctx, "fetch").AddArguments(fetchArgs...).AddDynamicArguments(remoteRepoName, headBranch+":"+trackingBranch).
+		Run(prCtx.RunOpts()); err != nil {
+		cancel()
+		if !git.IsBranchExist(ctx, pr.HeadRepo.RepoPath(), pr.HeadBranch) {
+			return nil, nil, git_model.ErrBranchNotExist{
+				BranchName: pr.HeadBranch,
+			}
+		}
+		log.Error("%-v Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr, pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		return nil, nil, fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), headBranch, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+	}
+	prCtx.outbuf.Reset()
+	prCtx.errbuf.Reset()
+
+	return prCtx, cancel, nil
+}