From 8ecd388ae101a0dd88b78dc47ebfef9fe51699df Mon Sep 17 00:00:00 2001
From: Máximo Cuadros <mcuadros@gmail.com>
Date: Mon, 11 May 2020 00:17:29 +0200
Subject: Remote.Fetch: support exact SHA1 refspecs

---
 remote.go      | 33 ++++++++++++++++++++++++++++++++-
 remote_test.go | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/remote.go b/remote.go
index 242df0d..98c4acf 100644
--- a/remote.go
+++ b/remote.go
@@ -29,6 +29,7 @@ var (
 	NoErrAlreadyUpToDate     = errors.New("already up-to-date")
 	ErrDeleteRefNotSupported = errors.New("server does not support delete-refs")
 	ErrForceNeeded           = errors.New("some refs were not updated")
+	ErrExactSHA1NotSupported = errors.New("server does not support exact SHA1 refspec")
 )
 
 const (
@@ -303,6 +304,10 @@ func (r *Remote) fetch(ctx context.Context, o *FetchOptions) (sto storer.Referen
 		return nil, err
 	}
 
+	if err := r.isSupportedRefSpec(o.RefSpecs, ar); err != nil {
+		return nil, err
+	}
+
 	remoteRefs, err := ar.AllReferences()
 	if err != nil {
 		return nil, err
@@ -546,6 +551,7 @@ func (r *Remote) addReferenceIfRefSpecMatches(rs config.RefSpec,
 
 func (r *Remote) references() ([]*plumbing.Reference, error) {
 	var localRefs []*plumbing.Reference
+
 	iter, err := r.s.IterReferences()
 	if err != nil {
 		return nil, err
@@ -701,6 +707,11 @@ func doCalculateRefs(
 		return err
 	}
 
+	if s.IsExactSHA1() {
+		ref := plumbing.NewHashReference(s.Dst(""), plumbing.NewHash(s.Src()))
+		return refs.SetReference(ref)
+	}
+
 	var matched bool
 	err = iter.ForEach(func(ref *plumbing.Reference) error {
 		if !s.Match(ref.Name()) {
@@ -850,6 +861,26 @@ func (r *Remote) newUploadPackRequest(o *FetchOptions,
 	return req, nil
 }
 
+func (r *Remote) isSupportedRefSpec(refs []config.RefSpec, ar *packp.AdvRefs) error {
+	var containsIsExact bool
+	for _, ref := range refs {
+		if ref.IsExactSHA1() {
+			containsIsExact = true
+		}
+	}
+
+	if !containsIsExact {
+		return nil
+	}
+
+	if ar.Capabilities.Supports(capability.AllowReachableSHA1InWant) ||
+		ar.Capabilities.Supports(capability.AllowTipSHA1InWant) {
+		return nil
+	}
+
+	return ErrExactSHA1NotSupported
+}
+
 func buildSidebandIfSupported(l *capability.List, reader io.Reader, p sideband.Progress) io.Reader {
 	var t sideband.Type
 
@@ -883,7 +914,7 @@ func (r *Remote) updateLocalReferenceStorage(
 		}
 
 		for _, ref := range fetchedRefs {
-			if !spec.Match(ref.Name()) {
+			if !spec.Match(ref.Name()) && !spec.IsExactSHA1() {
 				continue
 			}
 
diff --git a/remote_test.go b/remote_test.go
index 6766514..0fc3449 100644
--- a/remote_test.go
+++ b/remote_test.go
@@ -20,8 +20,8 @@ import (
 	"github.com/go-git/go-git/v5/storage/memory"
 
 	"github.com/go-git/go-billy/v5/osfs"
-	. "gopkg.in/check.v1"
 	fixtures "github.com/go-git/go-git-fixtures/v4"
+	. "gopkg.in/check.v1"
 )
 
 type RemoteSuite struct {
@@ -71,6 +71,35 @@ func (s *RemoteSuite) TestFetchWildcard(c *C) {
 	})
 }
 
+func (s *RemoteSuite) TestFetchExactSHA1(c *C) {
+	r := NewRemote(memory.NewStorage(), &config.RemoteConfig{
+		URLs: []string{"https://github.com/git-fixtures/basic.git"},
+	})
+
+	s.testFetch(c, r, &FetchOptions{
+		RefSpecs: []config.RefSpec{
+			config.RefSpec("35e85108805c84807bc66a02d91535e1e24b38b9:refs/heads/foo"),
+		},
+	}, []*plumbing.Reference{
+		plumbing.NewReferenceFromStrings("refs/heads/foo", "35e85108805c84807bc66a02d91535e1e24b38b9"),
+	})
+}
+
+func (s *RemoteSuite) TestFetchExactSHA1_NotSoported(c *C) {
+	r := NewRemote(memory.NewStorage(), &config.RemoteConfig{
+		URLs: []string{s.GetBasicLocalRepositoryURL()},
+	})
+
+	err := r.Fetch(&FetchOptions{
+		RefSpecs: []config.RefSpec{
+			config.RefSpec("35e85108805c84807bc66a02d91535e1e24b38b9:refs/heads/foo"),
+		},
+	})
+
+	c.Assert(err, Equals, ErrExactSHA1NotSupported)
+
+}
+
 func (s *RemoteSuite) TestFetchWildcardTags(c *C) {
 	r := NewRemote(memory.NewStorage(), &config.RemoteConfig{
 		URLs: []string{s.GetLocalRepositoryURL(fixtures.ByTag("tags").One())},
-- 
cgit