config: Add Repository Format Extension

Relates to the SHA256 implementation, defined in #706.

Signed-off-by: Paulo Gomes <pjbgf@linux.com>

4 files changed, 149 insertions, 22 deletions

diff --git a/config/config.go b/config/config.go
index 8051bc1..83629fc 100644
--- a/config/config.go
+++ b/config/config.go
@@ -59,6 +59,8 @@ type Config struct {
 		// CommentChar is the character indicating the start of a
 		// comment for commands like commit and tag
 		CommentChar string
+		// RepositoryFormatVersion identifies the repository format and layout version.
+		RepositoryFormatVersion format.RepositoryFormatVersion
 	}
 
 	User struct {
@@ -96,6 +98,17 @@ type Config struct {
 		DefaultBranch string
 	}
 
+	Extensions struct {
+		// ObjectFormat specifies the hash algorithm to use. The
+		// acceptable values are sha1 and sha256. If not specified,
+		// sha1 is assumed. It is an error to specify this key unless
+		// core.repositoryFormatVersion is 1.
+		//
+		// This setting must not be changed after repository initialization
+		// (e.g. clone or init).
+		ObjectFormat format.ObjectFormat
+	}
+
 	// Remotes list of repository remotes, the key of the map is the name
 	// of the remote, should equal to RemoteConfig.Name.
 	Remotes map[string]*RemoteConfig
@@ -226,28 +239,31 @@ func (c *Config) Validate() error {
 }
 
 const (
-	remoteSection    = "remote"
-	submoduleSection = "submodule"
-	branchSection    = "branch"
-	coreSection      = "core"
-	packSection      = "pack"
-	userSection      = "user"
-	authorSection    = "author"
-	committerSection = "committer"
-	initSection      = "init"
-	urlSection       = "url"
-	fetchKey         = "fetch"
-	urlKey           = "url"
-	bareKey          = "bare"
-	worktreeKey      = "worktree"
-	commentCharKey   = "commentChar"
-	windowKey        = "window"
-	mergeKey         = "merge"
-	rebaseKey        = "rebase"
-	nameKey          = "name"
-	emailKey         = "email"
-	descriptionKey   = "description"
-	defaultBranchKey = "defaultBranch"
+	remoteSection              = "remote"
+	submoduleSection           = "submodule"
+	branchSection              = "branch"
+	coreSection                = "core"
+	packSection                = "pack"
+	userSection                = "user"
+	authorSection              = "author"
+	committerSection           = "committer"
+	initSection                = "init"
+	urlSection                 = "url"
+	extensionsSection          = "extensions"
+	fetchKey                   = "fetch"
+	urlKey                     = "url"
+	bareKey                    = "bare"
+	worktreeKey                = "worktree"
+	commentCharKey             = "commentChar"
+	windowKey                  = "window"
+	mergeKey                   = "merge"
+	rebaseKey                  = "rebase"
+	nameKey                    = "name"
+	emailKey                   = "email"
+	descriptionKey             = "description"
+	defaultBranchKey           = "defaultBranch"
+	repositoryFormatVersionKey = "repositoryformatversion"
+	objectFormat               = "objectformat"
 
 	// DefaultPackWindow holds the number of previous objects used to
 	// generate deltas. The value 10 is the same used by git command.
@@ -391,6 +407,7 @@ func (c *Config) unmarshalInit() {
 // Marshal returns Config encoded as a git-config file.
 func (c *Config) Marshal() ([]byte, error) {
 	c.marshalCore()
+	c.marshalExtensions()
 	c.marshalUser()
 	c.marshalPack()
 	c.marshalRemotes()
@@ -410,12 +427,24 @@ func (c *Config) Marshal() ([]byte, error) {
 func (c *Config) marshalCore() {
 	s := c.Raw.Section(coreSection)
 	s.SetOption(bareKey, fmt.Sprintf("%t", c.Core.IsBare))
+	if string(c.Core.RepositoryFormatVersion) != "" {
+		s.SetOption(repositoryFormatVersionKey, string(c.Core.RepositoryFormatVersion))
+	}
 
 	if c.Core.Worktree != "" {
 		s.SetOption(worktreeKey, c.Core.Worktree)
 	}
 }
 
+func (c *Config) marshalExtensions() {
+	// Extensions are only supported on Version 1, therefore
+	// ignore them otherwise.
+	if c.Core.RepositoryFormatVersion == format.Version_1 {
+		s := c.Raw.Section(extensionsSection)
+		s.SetOption(objectFormat, string(c.Extensions.ObjectFormat))
+	}
+}
+
 func (c *Config) marshalUser() {
 	s := c.Raw.Section(userSection)
 	if c.User.Name != "" {
diff --git a/options.go b/options.go
index 747d512..738c1ce 100644
--- a/options.go
+++ b/options.go
@@ -10,6 +10,7 @@ import (
 	"github.com/ProtonMail/go-crypto/openpgp"
 	"github.com/go-git/go-git/v5/config"
 	"github.com/go-git/go-git/v5/plumbing"
+	formatcfg "github.com/go-git/go-git/v5/plumbing/format/config"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	"github.com/go-git/go-git/v5/plumbing/protocol/packp/sideband"
 	"github.com/go-git/go-git/v5/plumbing/transport"
@@ -672,3 +673,10 @@ type PlainOpenOptions struct {
 
 // Validate validates the fields and sets the default values.
 func (o *PlainOpenOptions) Validate() error { return nil }
+
+type PlainInitOptions struct {
+	ObjectFormat formatcfg.ObjectFormat
+}
+
+// Validate validates the fields and sets the default values.
+func (o *PlainInitOptions) Validate() error { return nil }
diff --git a/plumbing/format/config/format.go b/plumbing/format/config/format.go
new file mode 100644
index 0000000..4873ea9
--- /dev/null
+++ b/plumbing/format/config/format.go
@@ -0,0 +1,53 @@
+package config
+
+// RepositoryFormatVersion represents the repository format version,
+// as per defined at:
+//
+//	https://git-scm.com/docs/repository-version
+type RepositoryFormatVersion string
+
+const (
+	// Version_0 is the format defined by the initial version of git,
+	// including but not limited to the format of the repository
+	// directory, the repository configuration file, and the object
+	// and ref storage.
+	//
+	// Specifying the complete behavior of git is beyond the scope
+	// of this document.
+	Version_0 = "0"
+
+	// Version_1 is identical to version 0, with the following exceptions:
+	//
+	//   1. When reading the core.repositoryformatversion variable, a git
+	//		implementation which supports version 1 MUST also read any
+	//		configuration keys found in the extensions section of the
+	//		configuration file.
+	//
+	//	 2. If a version-1 repository specifies any extensions.* keys that
+	//		the running git has not implemented, the operation MUST NOT proceed.
+	//		Similarly, if the value of any known key is not understood by the
+	//		implementation, the operation MUST NOT proceed.
+	//
+	// Note that if no extensions are specified in the config file, then
+	// core.repositoryformatversion SHOULD be set to 0 (setting it to 1 provides
+	// no benefit, and makes the repository incompatible with older
+	// implementations of git).
+	Version_1 = "1"
+
+	// DefaultRepositoryFormatVersion holds the default repository format version.
+	DefaultRepositoryFormatVersion = Version_0
+)
+
+// ObjectFormat defines the object format.
+type ObjectFormat string
+
+const (
+	// SHA1 represents the object format used for SHA1.
+	SHA1 ObjectFormat = "sha1"
+
+	// SHA256 represents the object format used for SHA256.
+	SHA256 ObjectFormat = "sha256"
+
+	// DefaultObjectFormat holds the default object format.
+	DefaultObjectFormat = SHA1
+)
diff --git a/repository.go b/repository.go
index 2a06f8b..56ae976 100644
--- a/repository.go
+++ b/repository.go
@@ -3,6 +3,7 @@ package git
 import (
 	"bytes"
 	"context"
+	"crypto"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -21,7 +22,9 @@ import (
 	"github.com/go-git/go-git/v5/internal/revision"
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/cache"
+	formatcfg "github.com/go-git/go-git/v5/plumbing/format/config"
 	"github.com/go-git/go-git/v5/plumbing/format/packfile"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/storage"
@@ -57,6 +60,7 @@ var (
 	ErrIsBareRepository          = errors.New("worktree not available in a bare repository")
 	ErrUnableToResolveCommit     = errors.New("unable to resolve commit")
 	ErrPackedObjectsNotSupported = errors.New("packed objects not supported")
+	ErrSHA256NotSupported        = errors.New("go-git was not compiled with SHA256 support")
 )
 
 // Repository represents a git repository
@@ -228,6 +232,39 @@ func PlainInit(path string, isBare bool) (*Repository, error) {
 	return Init(s, wt)
 }
 
+func PlainInitWithOptions(path string, opts *PlainInitOptions) (*Repository, error) {
+	wt := osfs.New(path)
+	dot, _ := wt.Chroot(GitDirName)
+
+	s := filesystem.NewStorage(dot, cache.NewObjectLRUDefault())
+
+	r, err := Init(s, wt)
+	if err != nil {
+		return nil, err
+	}
+
+	cfg, err := r.Config()
+	if err != nil {
+		return nil, err
+	}
+
+	if opts != nil {
+		if opts.ObjectFormat == formatcfg.SHA256 && hash.CryptoType != crypto.SHA256 {
+			return nil, ErrSHA256NotSupported
+		}
+
+		cfg.Core.RepositoryFormatVersion = formatcfg.Version_1
+		cfg.Extensions.ObjectFormat = opts.ObjectFormat
+	}
+
+	err = r.Storer.SetConfig(cfg)
+	if err != nil {
+		return nil, err
+	}
+
+	return r, err
+}
+
 // PlainOpen opens a git repository from the given path. It detects if the
 // repository is bare or a normal one. If the path doesn't contain a valid
 // repository ErrRepositoryNotExists is returned