git: Add tagging support

options.go

@@ -3,6 +3,7 @@ package git
 import (
 	"errors"
 	"regexp"
+	"strings"
 
 	"golang.org/x/crypto/openpgp"
 	"gopkg.in/src-d/go-git.v4/config"
@@ -348,8 +349,9 @@ type CommitOptions struct {
 	// Parents are the parents commits for the new commit, by default when
 	// len(Parents) is zero, the hash of HEAD reference is used.
 	Parents []plumbing.Hash
-	// A key to sign the commit with. A nil value here means the commit will not
-	// be signed. The private key must be present and already decrypted.
+	// SignKey denotes a key to sign the commit with. A nil value here means the
+	// commit will not be signed. The private key must be present and already
+	// decrypted.
 	SignKey *openpgp.Entity
 }
 
@@ -377,6 +379,41 @@ func (o *CommitOptions) Validate(r *Repository) error {
 	return nil
 }
 
+var (
+	ErrMissingName    = errors.New("name field is required")
+	ErrMissingTagger  = errors.New("tagger field is required")
+	ErrMissingMessage = errors.New("message field is required")
+)
+
+// TagObjectOptions describes how a tag object should be created.
+type TagObjectOptions struct {
+	// Tagger defines the signature of the tag creator.
+	Tagger *object.Signature
+	// Message defines the annotation of the tag. It is canonicalized during
+	// validation into the format expected by git - no leading whitespace and
+	// ending in a newline.
+	Message string
+	// SignKey denotes a key to sign the tag with. A nil value here means the tag
+	// will not be signed. The private key must be present and already decrypted.
+	SignKey *openpgp.Entity
+}
+
+// Validate validates the fields and sets the default values.
+func (o *TagObjectOptions) Validate(r *Repository, hash plumbing.Hash) error {
+	if o.Tagger == nil {
+		return ErrMissingTagger
+	}
+
+	if o.Message == "" {
+		return ErrMissingMessage
+	}
+
+	// Canonicalize the message into the expected message format.
+	o.Message = strings.TrimSpace(o.Message) + "\n"
+
+	return nil
+}
+
 // ListOptions describes how a remote list should be performed.
 type ListOptions struct {
 	// Auth credentials, if required, to use with the remote repository.

plumbing/object/tag.go

@@ -195,13 +195,14 @@ func (t *Tag) encode(o plumbing.EncodedObject, includeSig bool) (err error) {
 		return err
 	}
 
-	if t.PGPSignature != "" && includeSig {
-		// Split all the signature lines and write with a newline at the end.
-		lines := strings.Split(t.PGPSignature, "\n")
-		for _, line := range lines {
-			if _, err = fmt.Fprintf(w, "%s\n", line); err != nil {
-				return err
-			}
+	// Note that this is highly sensitive to what it sent along in the message.
+	// Message *always* needs to end with a newline, or else the message and the
+	// signature will be concatenated into a corrupt object. Since this is a
+	// lower-level method, we assume you know what you are doing and have already
+	// done the needful on the message in the caller.
+	if includeSig {
+		if _, err = fmt.Fprint(w, t.PGPSignature); err != nil {
+			return err
 		}
 	}
 

repository.go

@@ -1,15 +1,18 @@
 package git
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
 	stdioutil "io/ioutil"
 	"os"
+	"path"
 	"path/filepath"
 	"strings"
 	"time"
 
+	"golang.org/x/crypto/openpgp"
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/internal/revision"
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -31,7 +34,12 @@ var (
 	// ErrBranchExists an error stating the specified branch already exists
 	ErrBranchExists = errors.New("branch already exists")
 	// ErrBranchNotFound an error stating the specified branch does not exist
-	ErrBranchNotFound            = errors.New("branch not found")
+	ErrBranchNotFound = errors.New("branch not found")
+	// ErrTagExists an error stating the specified tag already exists
+	ErrTagExists = errors.New("tag already exists")
+	// ErrTagNotFound an error stating the specified tag does not exist
+	ErrTagNotFound = errors.New("tag not found")
+
 	ErrInvalidReference          = errors.New("invalid reference, should be a tag or a branch")
 	ErrRepositoryNotExists       = errors.New("repository does not exist")
 	ErrRepositoryAlreadyExists   = errors.New("repository already exists")
@@ -484,6 +492,153 @@ func (r *Repository) DeleteBranch(name string) error {
 	return r.Storer.SetConfig(cfg)
 }
 
+// CreateTag creates a tag. If opts is included, the tag is an annotated tag,
+// otherwise a lightweight tag is created.
+func (r *Repository) CreateTag(name string, hash plumbing.Hash, opts *TagObjectOptions) (*plumbing.Reference, error) {
+	rname := plumbing.ReferenceName(path.Join("refs", "tags", name))
+
+	_, err := r.Storer.Reference(rname)
+	switch err {
+	case nil:
+		// Tag exists, this is an error
+		return nil, ErrTagExists
+	case plumbing.ErrReferenceNotFound:
+		// Tag missing, available for creation, pass this
+	default:
+		// Some other error
+		return nil, err
+	}
+
+	var target plumbing.Hash
+	if opts != nil {
+		target, err = r.createTagObject(name, hash, opts)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		target = hash
+	}
+
+	ref := plumbing.NewHashReference(rname, target)
+	if err = r.Storer.SetReference(ref); err != nil {
+		return nil, err
+	}
+
+	return ref, nil
+}
+
+func (r *Repository) createTagObject(name string, hash plumbing.Hash, opts *TagObjectOptions) (plumbing.Hash, error) {
+	if err := opts.Validate(r, hash); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	rawobj, err := object.GetObject(r.Storer, hash)
+	if err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	tag := &object.Tag{
+		Name:       name,
+		Tagger:     *opts.Tagger,
+		Message:    opts.Message,
+		TargetType: rawobj.Type(),
+		Target:     hash,
+	}
+
+	if opts.SignKey != nil {
+		sig, err := r.buildTagSignature(tag, opts.SignKey)
+		if err != nil {
+			return plumbing.ZeroHash, err
+		}
+
+		tag.PGPSignature = sig
+	}
+
+	obj := r.Storer.NewEncodedObject()
+	if err := tag.Encode(obj); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	return r.Storer.SetEncodedObject(obj)
+}
+
+func (r *Repository) buildTagSignature(tag *object.Tag, signKey *openpgp.Entity) (string, error) {
+	encoded := &plumbing.MemoryObject{}
+	if err := tag.Encode(encoded); err != nil {
+		return "", err
+	}
+
+	rdr, err := encoded.Reader()
+	if err != nil {
+		return "", err
+	}
+
+	var b bytes.Buffer
+	if err := openpgp.ArmoredDetachSign(&b, signKey, rdr, nil); err != nil {
+		return "", err
+	}
+
+	return b.String(), nil
+}
+
+// Tag fetches a tag from the repository.
+//
+// If you want to check to see if the tag is an annotated tag, you can call
+// TagObject on the hash of the reference in ForEach:
+//
+//   ref, err := r.Tag("v0.1.0")
+//   if err != nil {
+//     // Handle error
+//   }
+//
+//   obj, err := r.TagObject(ref.Hash())
+//   switch err {
+//   case nil:
+//     // Tag object present
+//   case plumbing.ErrObjectNotFound:
+//     // Not a tag object
+//   default:
+//     // Some other error
+//   }
+//
+func (r *Repository) Tag(name string) (*plumbing.Reference, error) {
+	ref, err := r.Reference(plumbing.ReferenceName(path.Join("refs", "tags", name)), false)
+	if err != nil {
+		if err == plumbing.ErrReferenceNotFound {
+			// Return a friendly error for this one, versus just ReferenceNotFound.
+			return nil, ErrTagNotFound
+		}
+
+		return nil, err
+	}
+
+	return ref, nil
+}
+
+// DeleteTag deletes a tag from the repository.
+func (r *Repository) DeleteTag(name string) error {
+	ref, err := r.Tag(name)
+	if err != nil {
+		return err
+	}
+
+	obj, err := r.TagObject(ref.Hash())
+	if err != nil && err != plumbing.ErrObjectNotFound {
+		return err
+	}
+
+	if err = r.Storer.RemoveReference(plumbing.ReferenceName(path.Join("refs", "tags", name))); err != nil {
+		return err
+	}
+
+	// Delete the tag object if this was an annotated tag.
+	if obj != nil {
+		return r.DeleteObject(obj.Hash)
+	}
+
+	return nil
+}
+
 func (r *Repository) resolveToCommitHash(h plumbing.Hash) (plumbing.Hash, error) {
 	obj, err := r.Storer.EncodedObject(plumbing.AnyObject, h)
 	if err != nil {
@@ -845,9 +1000,31 @@ func (r *Repository) Log(o *LogOptions) (object.CommitIter, error) {
 	return nil, fmt.Errorf("invalid Order=%v", o.Order)
 }
 
-// Tags returns all the References from Tags. This method returns only lightweight
-// tags. Note that not all the tags are lightweight ones. To return annotated tags
-// too, you need to call TagObjects() method.
+// Tags returns all the tag References in a repository.
+//
+// If you want to check to see if the tag is an annotated tag, you can call
+// TagObject on the hash Reference passed in through ForEach:
+//
+//   iter, err := r.Tags()
+//   if err != nil {
+//     // Handle error
+//   }
+//
+//   if err := iter.ForEach(func (ref *plumbing.Reference) error {
+//     obj, err := r.TagObject(ref.Hash())
+//     switch err {
+//     case nil:
+//       // Tag object present
+//     case plumbing.ErrObjectNotFound:
+//       // Not a tag object
+//     default:
+//       // Some other error
+//       return err
+//     }
+//   }); err != nil {
+//     // Handle outer iterator error
+//   }
+//
 func (r *Repository) Tags() (storer.ReferenceIter, error) {
 	refIter, err := r.Storer.IterReferences()
 	if err != nil {