Refactor git command package to improve security and maintainability (#22678)

This PR follows #21535 (and replace #22592)

## Review without space diff

https://github.com/go-gitea/gitea/pull/22678/files?diff=split&w=1

## Purpose of this PR

1. Make git module command completely safe (risky user inputs won't be
passed as argument option anymore)
2. Avoid low-level mistakes like
https://github.com/go-gitea/gitea/pull/22098#discussion_r1045234918
3. Remove deprecated and dirty `CmdArgCheck` function, hide the `CmdArg`
type
4. Simplify code when using git command

## The main idea of this PR

* Move the `git.CmdArg` to the `internal` package, then no other package
except `git` could use it. Then developers could never do
`AddArguments(git.CmdArg(userInput))` any more.
* Introduce `git.ToTrustedCmdArgs`, it's for user-provided and already
trusted arguments. It's only used in a few cases, for example: use git
arguments from config file, help unit test with some arguments.
* Introduce `AddOptionValues` and `AddOptionFormat`, they make code more
clear and simple:
    * Before: `AddArguments("-m").AddDynamicArguments(message)`
    * After: `AddOptionValues("-m", message)`
    * -
* Before: `AddArguments(git.CmdArg(fmt.Sprintf("--author='%s <%s>'",
sig.Name, sig.Email)))`
* After: `AddOptionFormat("--author='%s <%s>'", sig.Name, sig.Email)`

## FAQ

### Why these changes were not done in #21535 ?

#21535 is mainly a search&replace, it did its best to not change too
much logic.

Making the framework better needs a lot of changes, so this separate PR
is needed as the second step.


### The naming of `AddOptionXxx`

According to git's manual, the `--xxx` part is called `option`.

### How can it guarantee that `internal.CmdArg` won't be not misused?

Go's specification guarantees that. Trying to access other package's
internal package causes compilation error.

And, `golangci-lint` also denies the git/internal package. Only the
`git/command.go` can use it carefully.

### There is still a `ToTrustedCmdArgs`, will it still allow developers
to make mistakes and pass untrusted arguments?

Generally speaking, no. Because when using `ToTrustedCmdArgs`, the code
will be very complex (see the changes for examples). Then developers and
reviewers can know that something might be unreasonable.

### Why there was a `CmdArgCheck` and why it's removed?

At the moment of #21535, to reduce unnecessary changes, `CmdArgCheck`
was introduced as a hacky patch. Now, almost all code could be written
as `cmd := NewCommand(); cmd.AddXxx(...)`, then there is no need for
`CmdArgCheck` anymore.


### Why many codes for `signArg == ""` is deleted?

Because in the old code, `signArg` could never be empty string, it's
either `-S[key-id]` or `--no-gpg-sign`. So the `signArg == ""` is just
dead code.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

1 files changed, 29 insertions, 51 deletions

diff --git a/services/gitdiff/gitdiff.go b/services/gitdiff/gitdiff.go
index d3ee93ec94..4a74c1a894 100644
--- a/services/gitdiff/gitdiff.go
+++ b/services/gitdiff/gitdiff.go
@@ -1056,7 +1056,7 @@ type DiffOptions struct {
 	MaxLines           int
 	MaxLineCharacters  int
 	MaxFiles           int
-	WhitespaceBehavior git.CmdArg
+	WhitespaceBehavior git.TrustedCmdArgs
 	DirectComparison   bool
 }
 
@@ -1071,38 +1071,22 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 		return nil, err
 	}
 
-	argsLength := 6
-	if len(opts.WhitespaceBehavior) > 0 {
-		argsLength++
-	}
-	if len(opts.SkipTo) > 0 {
-		argsLength++
-	}
-	if len(files) > 0 {
-		argsLength += len(files) + 1
-	}
-
-	diffArgs := make([]git.CmdArg, 0, argsLength)
+	cmdDiff := git.NewCommand(gitRepo.Ctx)
 	if (len(opts.BeforeCommitID) == 0 || opts.BeforeCommitID == git.EmptySHA) && commit.ParentCount() == 0 {
-		diffArgs = append(diffArgs, "diff", "--src-prefix=\\a/", "--dst-prefix=\\b/", "-M")
-		if len(opts.WhitespaceBehavior) != 0 {
-			diffArgs = append(diffArgs, opts.WhitespaceBehavior)
-		}
-		// append empty tree ref
-		diffArgs = append(diffArgs, "4b825dc642cb6eb9a060e54bf8d69288fbee4904")
-		diffArgs = append(diffArgs, git.CmdArgCheck(opts.AfterCommitID))
+		cmdDiff.AddArguments("diff", "--src-prefix=\\a/", "--dst-prefix=\\b/", "-M").
+			AddArguments(opts.WhitespaceBehavior...).
+			AddArguments("4b825dc642cb6eb9a060e54bf8d69288fbee4904"). // append empty tree ref
+			AddDynamicArguments(opts.AfterCommitID)
 	} else {
 		actualBeforeCommitID := opts.BeforeCommitID
 		if len(actualBeforeCommitID) == 0 {
 			parentCommit, _ := commit.Parent(0)
 			actualBeforeCommitID = parentCommit.ID.String()
 		}
-		diffArgs = append(diffArgs, "diff", "--src-prefix=\\a/", "--dst-prefix=\\b/", "-M")
-		if len(opts.WhitespaceBehavior) != 0 {
-			diffArgs = append(diffArgs, opts.WhitespaceBehavior)
-		}
-		diffArgs = append(diffArgs, git.CmdArgCheck(actualBeforeCommitID))
-		diffArgs = append(diffArgs, git.CmdArgCheck(opts.AfterCommitID))
+
+		cmdDiff.AddArguments("diff", "--src-prefix=\\a/", "--dst-prefix=\\b/", "-M").
+			AddArguments(opts.WhitespaceBehavior...).
+			AddDynamicArguments(actualBeforeCommitID, opts.AfterCommitID)
 		opts.BeforeCommitID = actualBeforeCommitID
 	}
 
@@ -1111,16 +1095,11 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 	// the skipping for us
 	parsePatchSkipToFile := opts.SkipTo
 	if opts.SkipTo != "" && git.CheckGitVersionAtLeast("2.31") == nil {
-		diffArgs = append(diffArgs, git.CmdArg("--skip-to="+opts.SkipTo))
+		cmdDiff.AddOptionFormat("--skip-to=%s", opts.SkipTo)
 		parsePatchSkipToFile = ""
 	}
 
-	if len(files) > 0 {
-		diffArgs = append(diffArgs, "--")
-		for _, file := range files {
-			diffArgs = append(diffArgs, git.CmdArg(file)) // it's safe to cast it to CmdArg because there is a "--" before
-		}
-	}
+	cmdDiff.AddDashesAndList(files...)
 
 	reader, writer := io.Pipe()
 	defer func() {
@@ -1128,10 +1107,9 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 		_ = writer.Close()
 	}()
 
-	go func(ctx context.Context, diffArgs []git.CmdArg, repoPath string, writer *io.PipeWriter) {
-		cmd := git.NewCommand(ctx, diffArgs...)
-		cmd.SetDescription(fmt.Sprintf("GetDiffRange [repo_path: %s]", repoPath))
-		if err := cmd.Run(&git.RunOpts{
+	go func() {
+		cmdDiff.SetDescription(fmt.Sprintf("GetDiffRange [repo_path: %s]", repoPath))
+		if err := cmdDiff.Run(&git.RunOpts{
 			Timeout: time.Duration(setting.Git.Timeout.Default) * time.Second,
 			Dir:     repoPath,
 			Stderr:  os.Stderr,
@@ -1141,7 +1119,7 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 		}
 
 		_ = writer.Close()
-	}(gitRepo.Ctx, diffArgs, repoPath, writer)
+	}()
 
 	diff, err := ParsePatch(opts.MaxLines, opts.MaxLineCharacters, opts.MaxFiles, reader, parsePatchSkipToFile)
 	if err != nil {
@@ -1201,16 +1179,16 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 		separator = ".."
 	}
 
-	shortstatArgs := []git.CmdArg{git.CmdArgCheck(opts.BeforeCommitID + separator + opts.AfterCommitID)}
+	diffPaths := []string{opts.BeforeCommitID + separator + opts.AfterCommitID}
 	if len(opts.BeforeCommitID) == 0 || opts.BeforeCommitID == git.EmptySHA {
-		shortstatArgs = []git.CmdArg{git.EmptyTreeSHA, git.CmdArgCheck(opts.AfterCommitID)}
+		diffPaths = []string{git.EmptyTreeSHA, opts.AfterCommitID}
 	}
-	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(gitRepo.Ctx, repoPath, shortstatArgs...)
+	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(gitRepo.Ctx, repoPath, nil, diffPaths...)
 	if err != nil && strings.Contains(err.Error(), "no merge base") {
 		// git >= 2.28 now returns an error if base and head have become unrelated.
 		// previously it would return the results of git diff --shortstat base head so let's try that...
-		shortstatArgs = []git.CmdArg{git.CmdArgCheck(opts.BeforeCommitID), git.CmdArgCheck(opts.AfterCommitID)}
-		diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(gitRepo.Ctx, repoPath, shortstatArgs...)
+		diffPaths = []string{opts.BeforeCommitID, opts.AfterCommitID}
+		diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(gitRepo.Ctx, repoPath, nil, diffPaths...)
 	}
 	if err != nil {
 		return nil, err
@@ -1324,17 +1302,17 @@ func CommentMustAsDiff(c *issues_model.Comment) *Diff {
 }
 
 // GetWhitespaceFlag returns git diff flag for treating whitespaces
-func GetWhitespaceFlag(whitespaceBehavior string) git.CmdArg {
-	whitespaceFlags := map[string]string{
-		"ignore-all":    "-w",
-		"ignore-change": "-b",
-		"ignore-eol":    "--ignore-space-at-eol",
-		"show-all":      "",
+func GetWhitespaceFlag(whitespaceBehavior string) git.TrustedCmdArgs {
+	whitespaceFlags := map[string]git.TrustedCmdArgs{
+		"ignore-all":    {"-w"},
+		"ignore-change": {"-b"},
+		"ignore-eol":    {"--ignore-space-at-eol"},
+		"show-all":      nil,
 	}
 
 	if flag, ok := whitespaceFlags[whitespaceBehavior]; ok {
-		return git.CmdArg(flag)
+		return flag
 	}
 	log.Warn("unknown whitespace behavior: %q, default to 'show-all'", whitespaceBehavior)
-	return ""
+	return nil
 }