transport: add git-send-pack support to local/ssh. (#163)

* protocol/packp: add Packfile field to ReferenceUpdateRequest.
* protocol/packp: add NewReferenceUpdateRequestFromCapabilities.
* NewReferenceUpdateRequestFromCapabilities can be used to create
  a ReferenceUpdateRequest with initial capabilities compatible with
  the server.
* protocol/packp: fix new line handling on report status.
* transport/file: test error on unexisting command.

10 files changed, 229 insertions, 47 deletions

diff --git a/plumbing/protocol/packp/capability/capability.go b/plumbing/protocol/packp/capability/capability.go
index 06fbfca..351ba0b 100644
--- a/plumbing/protocol/packp/capability/capability.go
+++ b/plumbing/protocol/packp/capability/capability.go
@@ -231,6 +231,8 @@ const (
 	SymRef Capability = "symref"
 )
 
+const DefaultAgent = "go-git/4.x"
+
 var valid = map[Capability]bool{
 	MultiACK: true, MultiACKDetailed: true, NoDone: true, ThinPack: true,
 	Sideband: true, Sideband64k: true, OFSDelta: true, Agent: true,
diff --git a/plumbing/protocol/packp/report_status.go b/plumbing/protocol/packp/report_status.go
index f480b34..ead4bb6 100644
--- a/plumbing/protocol/packp/report_status.go
+++ b/plumbing/protocol/packp/report_status.go
@@ -1,12 +1,13 @@
 package packp
 
 import (
+	"bytes"
+	"fmt"
 	"io"
+	"strings"
 
-	"fmt"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/pktline"
-	"strings"
 )
 
 const (
@@ -33,7 +34,7 @@ func (s *ReportStatus) Ok() bool {
 // Encode writes the report status to a writer.
 func (s *ReportStatus) Encode(w io.Writer) error {
 	e := pktline.NewEncoder(w)
-	if err := e.Encodef("unpack %s", s.UnpackStatus); err != nil {
+	if err := e.Encodef("unpack %s\n", s.UnpackStatus); err != nil {
 		return err
 	}
 
@@ -95,6 +96,8 @@ func (s *ReportStatus) decodeReportStatus(b []byte) error {
 		return fmt.Errorf("premature flush")
 	}
 
+	b = bytes.TrimSuffix(b, eol)
+
 	line := string(b)
 	fields := strings.SplitN(line, " ", 2)
 	if len(fields) != 2 || fields[0] != "unpack" {
@@ -106,6 +109,8 @@ func (s *ReportStatus) decodeReportStatus(b []byte) error {
 }
 
 func (s *ReportStatus) decodeCommandStatus(b []byte) error {
+	b = bytes.TrimSuffix(b, eol)
+
 	line := string(b)
 	fields := strings.SplitN(line, " ", 3)
 	status := ok
@@ -138,8 +143,8 @@ func (s *CommandStatus) Ok() bool {
 func (s *CommandStatus) encode(w io.Writer) error {
 	e := pktline.NewEncoder(w)
 	if s.Ok() {
-		return e.Encodef("ok %s", s.ReferenceName.String())
+		return e.Encodef("ok %s\n", s.ReferenceName.String())
 	}
 
-	return e.Encodef("ng %s %s", s.ReferenceName.String(), s.Status)
+	return e.Encodef("ng %s %s\n", s.ReferenceName.String(), s.Status)
 }
diff --git a/plumbing/protocol/packp/report_status_test.go b/plumbing/protocol/packp/report_status_test.go
index 064e514..168d25b 100644
--- a/plumbing/protocol/packp/report_status_test.go
+++ b/plumbing/protocol/packp/report_status_test.go
@@ -69,8 +69,8 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkOneReference(c *C) {
 	}}
 
 	s.testEncodeDecodeOk(c, rs,
-		"unpack ok",
-		"ok refs/heads/master",
+		"unpack ok\n",
+		"ok refs/heads/master\n",
 		pktline.FlushString,
 	)
 }
@@ -84,8 +84,8 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkOneReferenceFailed(c *C) {
 	}}
 
 	s.testEncodeDecodeOk(c, rs,
-		"unpack my error",
-		"ng refs/heads/master command error",
+		"unpack my error\n",
+		"ng refs/heads/master command error\n",
 		pktline.FlushString,
 	)
 }
@@ -105,10 +105,10 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkMoreReferences(c *C) {
 	}}
 
 	s.testEncodeDecodeOk(c, rs,
-		"unpack ok",
-		"ok refs/heads/master",
-		"ok refs/heads/a",
-		"ok refs/heads/b",
+		"unpack ok\n",
+		"ok refs/heads/master\n",
+		"ok refs/heads/a\n",
+		"ok refs/heads/b\n",
 		pktline.FlushString,
 	)
 }
@@ -128,10 +128,10 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkMoreReferencesFailed(c *C) {
 	}}
 
 	s.testEncodeDecodeOk(c, rs,
-		"unpack my error",
-		"ok refs/heads/master",
-		"ng refs/heads/a command error",
-		"ok refs/heads/b",
+		"unpack my error\n",
+		"ok refs/heads/master\n",
+		"ng refs/heads/a command error\n",
+		"ok refs/heads/b\n",
 		pktline.FlushString,
 	)
 }
@@ -141,7 +141,7 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkNoReferences(c *C) {
 	expected.UnpackStatus = "ok"
 
 	s.testEncodeDecodeOk(c, expected,
-		"unpack ok",
+		"unpack ok\n",
 		pktline.FlushString,
 	)
 }
@@ -151,7 +151,7 @@ func (s *ReportStatusSuite) TestEncodeDecodeOkNoReferencesFailed(c *C) {
 	rs.UnpackStatus = "my error"
 
 	s.testEncodeDecodeOk(c, rs,
-		"unpack my error",
+		"unpack my error\n",
 		pktline.FlushString,
 	)
 }
@@ -165,8 +165,8 @@ func (s *ReportStatusSuite) TestDecodeErrorOneReferenceNoFlush(c *C) {
 	}}
 
 	s.testDecodeError(c, "missing flush",
-		"unpack ok",
-		"ok refs/heads/master",
+		"unpack ok\n",
+		"ok refs/heads/master\n",
 	)
 }
 
@@ -190,7 +190,7 @@ func (s *ReportStatusSuite) TestDecodeErrorMalformed(c *C) {
 	}}
 
 	s.testDecodeError(c, "malformed unpack status: unpackok",
-		"unpackok",
+		"unpackok\n",
 		pktline.FlushString,
 	)
 }
@@ -204,7 +204,7 @@ func (s *ReportStatusSuite) TestDecodeErrorMalformed2(c *C) {
 	}}
 
 	s.testDecodeError(c, "malformed unpack status: UNPACK OK",
-		"UNPACK OK",
+		"UNPACK OK\n",
 		pktline.FlushString,
 	)
 }
@@ -218,8 +218,8 @@ func (s *ReportStatusSuite) TestDecodeErrorMalformedCommandStatus(c *C) {
 	}}
 
 	s.testDecodeError(c, "malformed command status: ko refs/heads/master",
-		"unpack ok",
-		"ko refs/heads/master",
+		"unpack ok\n",
+		"ko refs/heads/master\n",
 		pktline.FlushString,
 	)
 }
@@ -233,8 +233,8 @@ func (s *ReportStatusSuite) TestDecodeErrorMalformedCommandStatus2(c *C) {
 	}}
 
 	s.testDecodeError(c, "malformed command status: ng refs/heads/master",
-		"unpack ok",
-		"ng refs/heads/master",
+		"unpack ok\n",
+		"ng refs/heads/master\n",
 		pktline.FlushString,
 	)
 }
diff --git a/plumbing/protocol/packp/ulreq.go b/plumbing/protocol/packp/ulreq.go
index faf0885..7832007 100644
--- a/plumbing/protocol/packp/ulreq.go
+++ b/plumbing/protocol/packp/ulreq.go
@@ -8,8 +8,6 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/protocol/packp/capability"
 )
 
-const DefaultAgent = "go-git/4.x"
-
 // UploadRequest values represent the information transmitted on a
 // upload-request message.  Values from this type are not zero-value
 // safe, use the New function instead.
@@ -97,7 +95,7 @@ func NewUploadRequestFromCapabilities(adv *capability.List) *UploadRequest {
 	}
 
 	if adv.Supports(capability.Agent) {
-		r.Capabilities.Set(capability.Agent, DefaultAgent)
+		r.Capabilities.Set(capability.Agent, capability.DefaultAgent)
 	}
 
 	return r
diff --git a/plumbing/protocol/packp/updreq.go b/plumbing/protocol/packp/updreq.go
index 90d6e09..a2deb89 100644
--- a/plumbing/protocol/packp/updreq.go
+++ b/plumbing/protocol/packp/updreq.go
@@ -2,6 +2,7 @@ package packp
 
 import (
 	"errors"
+	"io"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/protocol/packp/capability"
@@ -20,6 +21,8 @@ type ReferenceUpdateRequest struct {
 	Capabilities *capability.List
 	Commands     []*Command
 	Shallow      *plumbing.Hash
+	// Packfile contains an optional packfile reader.
+	Packfile io.ReadCloser
 }
 
 // New returns a pointer to a new ReferenceUpdateRequest value.
@@ -30,6 +33,37 @@ func NewReferenceUpdateRequest() *ReferenceUpdateRequest {
 	}
 }
 
+// NewReferenceUpdateRequestFromCapabilities returns a pointer to a new
+// ReferenceUpdateRequest value, the request capabilities are filled with the
+// most optimal ones, based on the adv value (advertised capabilities), the
+// ReferenceUpdateRequest contains no commands
+//
+// It does set the following capabilities:
+//   - agent
+//   - report-status
+//   - ofs-delta
+//   - ref-delta
+// It leaves up to the user to add the following capabilities later:
+//   - atomic
+//   - ofs-delta
+//   - side-band
+//   - side-band-64k
+//   - quiet
+//   - push-cert
+func NewReferenceUpdateRequestFromCapabilities(adv *capability.List) *ReferenceUpdateRequest {
+	r := NewReferenceUpdateRequest()
+
+	if adv.Supports(capability.Agent) {
+		r.Capabilities.Set(capability.Agent, capability.DefaultAgent)
+	}
+
+	if adv.Supports(capability.ReportStatus) {
+		r.Capabilities.Set(capability.ReportStatus)
+	}
+
+	return r
+}
+
 func (r *ReferenceUpdateRequest) validate() error {
 	if len(r.Commands) == 0 {
 		return ErrEmptyCommands
diff --git a/plumbing/protocol/packp/updreq_decode.go b/plumbing/protocol/packp/updreq_decode.go
index 0740871..2ebe2a3 100644
--- a/plumbing/protocol/packp/updreq_decode.go
+++ b/plumbing/protocol/packp/updreq_decode.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/pktline"
@@ -76,23 +77,32 @@ func errMalformedCommand(err error) error {
 
 // Decode reads the next update-request message form the reader and wr
 func (req *ReferenceUpdateRequest) Decode(r io.Reader) error {
-	d := &updReqDecoder{s: pktline.NewScanner(r)}
+	var rc io.ReadCloser
+	var ok bool
+	rc, ok = r.(io.ReadCloser)
+	if !ok {
+		rc = ioutil.NopCloser(r)
+	}
+
+	d := &updReqDecoder{r: rc, s: pktline.NewScanner(r)}
 	return d.Decode(req)
 }
 
 type updReqDecoder struct {
-	s *pktline.Scanner
-	r *ReferenceUpdateRequest
+	r   io.ReadCloser
+	s   *pktline.Scanner
+	req *ReferenceUpdateRequest
 }
 
-func (d *updReqDecoder) Decode(r *ReferenceUpdateRequest) error {
-	d.r = r
+func (d *updReqDecoder) Decode(req *ReferenceUpdateRequest) error {
+	d.req = req
 	funcs := []func() error{
 		d.scanLine,
 		d.decodeShallow,
 		d.decodeCommandAndCapabilities,
 		d.decodeCommands,
-		r.validate,
+		d.setPackfile,
+		req.validate,
 	}
 
 	for _, f := range funcs {
@@ -132,7 +142,7 @@ func (d *updReqDecoder) decodeShallow() error {
 		return d.scanErrorOr(errNoCommands)
 	}
 
-	d.r.Shallow = &h
+	d.req.Shallow = &h
 
 	return nil
 }
@@ -149,7 +159,7 @@ func (d *updReqDecoder) decodeCommands() error {
 			return err
 		}
 
-		d.r.Commands = append(d.r.Commands, c)
+		d.req.Commands = append(d.req.Commands, c)
 
 		if ok := d.s.Scan(); !ok {
 			return d.s.Err()
@@ -173,9 +183,9 @@ func (d *updReqDecoder) decodeCommandAndCapabilities() error {
 		return err
 	}
 
-	d.r.Commands = append(d.r.Commands, cmd)
+	d.req.Commands = append(d.req.Commands, cmd)
 
-	if err := d.r.Capabilities.Decode(b[i+1:]); err != nil {
+	if err := d.req.Capabilities.Decode(b[i+1:]); err != nil {
 		return err
 	}
 
@@ -186,6 +196,12 @@ func (d *updReqDecoder) decodeCommandAndCapabilities() error {
 	return nil
 }
 
+func (d *updReqDecoder) setPackfile() error {
+	d.req.Packfile = d.r
+
+	return nil
+}
+
 func parseCommand(b []byte) (*Command, error) {
 	if len(b) < minCommandLength {
 		return nil, errInvalidCommandLineLength(len(b))
diff --git a/plumbing/protocol/packp/updreq_decode_test.go b/plumbing/protocol/packp/updreq_decode_test.go
index 66d9180..6cbab2b 100644
--- a/plumbing/protocol/packp/updreq_decode_test.go
+++ b/plumbing/protocol/packp/updreq_decode_test.go
@@ -3,6 +3,7 @@ package packp
 import (
 	"bytes"
 	"io"
+	"io/ioutil"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/pktline"
@@ -156,13 +157,14 @@ func (s *UpdReqDecodeSuite) TestOneUpdateCommand(c *C) {
 	expected.Commands = []*Command{
 		{Name: name, Old: hash1, New: hash2},
 	}
+	expected.Packfile = ioutil.NopCloser(bytes.NewReader([]byte{}))
 
 	payloads := []string{
 		"1ecf0ef2c2dffb796033e5a02219af86ec6584e5 2ecf0ef2c2dffb796033e5a02219af86ec6584e5 myref\x00",
 		pktline.FlushString,
 	}
 
-	c.Assert(s.testDecodeOK(c, payloads), DeepEquals, expected)
+	s.testDecodeOkExpected(c, expected, payloads)
 }
 
 func (s *UpdReqDecodeSuite) TestMultipleCommands(c *C) {
@@ -175,6 +177,7 @@ func (s *UpdReqDecodeSuite) TestMultipleCommands(c *C) {
 		{Name: "myref2", Old: plumbing.ZeroHash, New: hash2},
 		{Name: "myref3", Old: hash1, New: plumbing.ZeroHash},
 	}
+	expected.Packfile = ioutil.NopCloser(bytes.NewReader([]byte{}))
 
 	payloads := []string{
 		"1ecf0ef2c2dffb796033e5a02219af86ec6584e5 2ecf0ef2c2dffb796033e5a02219af86ec6584e5 myref1\x00",
@@ -183,10 +186,7 @@ func (s *UpdReqDecodeSuite) TestMultipleCommands(c *C) {
 		pktline.FlushString,
 	}
 
-	c.Assert(s.testDecodeOK(c, payloads).Commands, DeepEquals, expected.Commands)
-	c.Assert(s.testDecodeOK(c, payloads).Shallow, DeepEquals, expected.Shallow)
-	c.Assert(s.testDecodeOK(c, payloads).Capabilities, DeepEquals, expected.Capabilities)
-	c.Assert(s.testDecodeOK(c, payloads), DeepEquals, expected)
+	s.testDecodeOkExpected(c, expected, payloads)
 }
 
 func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilities(c *C) {
@@ -200,6 +200,7 @@ func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilities(c *C) {
 		{Name: "myref3", Old: hash1, New: plumbing.ZeroHash},
 	}
 	expected.Capabilities.Add("shallow")
+	expected.Packfile = ioutil.NopCloser(bytes.NewReader([]byte{}))
 
 	payloads := []string{
 		"1ecf0ef2c2dffb796033e5a02219af86ec6584e5 2ecf0ef2c2dffb796033e5a02219af86ec6584e5 myref1\x00shallow",
@@ -208,7 +209,7 @@ func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilities(c *C) {
 		pktline.FlushString,
 	}
 
-	c.Assert(s.testDecodeOK(c, payloads), DeepEquals, expected)
+	s.testDecodeOkExpected(c, expected, payloads)
 }
 
 func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilitiesShallow(c *C) {
@@ -223,6 +224,7 @@ func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilitiesShallow(c *C) {
 	}
 	expected.Capabilities.Add("shallow")
 	expected.Shallow = &hash1
+	expected.Packfile = ioutil.NopCloser(bytes.NewReader([]byte{}))
 
 	payloads := []string{
 		"shallow 1ecf0ef2c2dffb796033e5a02219af86ec6584e5",
@@ -232,7 +234,31 @@ func (s *UpdReqDecodeSuite) TestMultipleCommandsAndCapabilitiesShallow(c *C) {
 		pktline.FlushString,
 	}
 
-	c.Assert(s.testDecodeOK(c, payloads), DeepEquals, expected)
+	s.testDecodeOkExpected(c, expected, payloads)
+}
+
+func (s *UpdReqDecodeSuite) TestWithPackfile(c *C) {
+	hash1 := plumbing.NewHash("1ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+	hash2 := plumbing.NewHash("2ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+	name := "myref"
+
+	expected := NewReferenceUpdateRequest()
+	expected.Commands = []*Command{
+		{Name: name, Old: hash1, New: hash2},
+	}
+	packfileContent := []byte("PACKabc")
+	expected.Packfile = ioutil.NopCloser(bytes.NewReader(packfileContent))
+
+	payloads := []string{
+		"1ecf0ef2c2dffb796033e5a02219af86ec6584e5 2ecf0ef2c2dffb796033e5a02219af86ec6584e5 myref\x00",
+		pktline.FlushString,
+	}
+	var buf bytes.Buffer
+	e := pktline.NewEncoder(&buf)
+	c.Assert(e.EncodeString(payloads...), IsNil)
+	buf.Write(packfileContent)
+
+	s.testDecodeOkRaw(c, expected, buf.Bytes())
 }
 
 func (s *UpdReqDecodeSuite) testDecoderErrorMatches(c *C, input io.Reader, pattern string) {
@@ -251,3 +277,32 @@ func (s *UpdReqDecodeSuite) testDecodeOK(c *C, payloads []string) *ReferenceUpda
 
 	return r
 }
+
+func (s *UpdReqDecodeSuite) testDecodeOkRaw(c *C, expected *ReferenceUpdateRequest, raw []byte) {
+	req := NewReferenceUpdateRequest()
+	c.Assert(req.Decode(bytes.NewBuffer(raw)), IsNil)
+	c.Assert(req.Packfile, NotNil)
+	s.compareReaders(c, req.Packfile, expected.Packfile)
+	req.Packfile = nil
+	expected.Packfile = nil
+	c.Assert(req, DeepEquals, expected)
+}
+
+func (s *UpdReqDecodeSuite) testDecodeOkExpected(c *C, expected *ReferenceUpdateRequest, payloads []string) {
+	req := s.testDecodeOK(c, payloads)
+	c.Assert(req.Packfile, NotNil)
+	s.compareReaders(c, req.Packfile, expected.Packfile)
+	req.Packfile = nil
+	expected.Packfile = nil
+	c.Assert(req, DeepEquals, expected)
+}
+
+func (s *UpdReqDecodeSuite) compareReaders(c *C, a io.ReadCloser, b io.ReadCloser) {
+	pba, err := ioutil.ReadAll(a)
+	c.Assert(err, IsNil)
+	c.Assert(a.Close(), IsNil)
+	pbb, err := ioutil.ReadAll(b)
+	c.Assert(err, IsNil)
+	c.Assert(b.Close(), IsNil)
+	c.Assert(pba, DeepEquals, pbb)
+}
diff --git a/plumbing/protocol/packp/updreq_encode.go b/plumbing/protocol/packp/updreq_encode.go
index b2b7944..44c0573 100644
--- a/plumbing/protocol/packp/updreq_encode.go
+++ b/plumbing/protocol/packp/updreq_encode.go
@@ -29,6 +29,14 @@ func (r *ReferenceUpdateRequest) Encode(w io.Writer) error {
 		return err
 	}
 
+	if r.Packfile != nil {
+		if _, err := io.Copy(w, r.Packfile); err != nil {
+			return err
+		}
+
+		return r.Packfile.Close()
+	}
+
 	return nil
 }
 
diff --git a/plumbing/protocol/packp/updreq_encode_test.go b/plumbing/protocol/packp/updreq_encode_test.go
index 47958fd..14f9975 100644
--- a/plumbing/protocol/packp/updreq_encode_test.go
+++ b/plumbing/protocol/packp/updreq_encode_test.go
@@ -7,6 +7,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/format/pktline"
 
 	. "gopkg.in/check.v1"
+	"io/ioutil"
 )
 
 type UpdReqEncodeSuite struct{}
@@ -117,3 +118,27 @@ func (s *UpdReqEncodeSuite) TestMultipleCommandsAndCapabilitiesShallow(c *C) {
 
 	s.testEncode(c, r, expected)
 }
+
+func (s *UpdReqEncodeSuite) TestWithPackfile(c *C) {
+	hash1 := plumbing.NewHash("1ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+	hash2 := plumbing.NewHash("2ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+	name := "myref"
+
+	packfileContent := []byte("PACKabc")
+	packfileReader := bytes.NewReader(packfileContent)
+	packfileReadCloser := ioutil.NopCloser(packfileReader)
+
+	r := NewReferenceUpdateRequest()
+	r.Commands = []*Command{
+		{Name: name, Old: hash1, New: hash2},
+	}
+	r.Packfile = packfileReadCloser
+
+	expected := pktlines(c,
+		"1ecf0ef2c2dffb796033e5a02219af86ec6584e5 2ecf0ef2c2dffb796033e5a02219af86ec6584e5 myref\x00",
+		pktline.FlushString,
+	)
+	expected = append(expected, packfileContent...)
+
+	s.testEncode(c, r, expected)
+}
diff --git a/plumbing/protocol/packp/updreq_test.go b/plumbing/protocol/packp/updreq_test.go
new file mode 100644
index 0000000..2412fbf
--- /dev/null
+++ b/plumbing/protocol/packp/updreq_test.go
@@ -0,0 +1,39 @@
+package packp
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing/protocol/packp/capability"
+
+	. "gopkg.in/check.v1"
+)
+
+type UpdReqSuite struct{}
+
+var _ = Suite(&UpdReqSuite{})
+
+func (s *UpdReqSuite) TestNewReferenceUpdateRequestFromCapabilities(c *C) {
+	cap := capability.NewList()
+	cap.Set(capability.Sideband)
+	cap.Set(capability.Sideband64k)
+	cap.Set(capability.Quiet)
+	cap.Set(capability.ReportStatus)
+	cap.Set(capability.DeleteRefs)
+	cap.Set(capability.PushCert, "foo")
+	cap.Set(capability.Atomic)
+	cap.Set(capability.Agent, "foo")
+
+	r := NewReferenceUpdateRequestFromCapabilities(cap)
+	c.Assert(r.Capabilities.String(), Equals,
+		"agent=go-git/4.x report-status",
+	)
+
+	cap = capability.NewList()
+	cap.Set(capability.Agent, "foo")
+
+	r = NewReferenceUpdateRequestFromCapabilities(cap)
+	c.Assert(r.Capabilities.String(), Equals, "agent=go-git/4.x")
+
+	cap = capability.NewList()
+
+	r = NewReferenceUpdateRequestFromCapabilities(cap)
+	c.Assert(r.Capabilities.String(), Equals, "")
+}