Add support for custom smart transports (#806)

This change adds support for git smart transports. This will be then
used to implement http, https, and ssh transports that don't rely on the
libgit2 library.

clone.go

@@ -85,6 +85,7 @@ func remoteCreateCallback(
 	// clear finalizer as the calling C function will
 	// free the remote itself
 	runtime.SetFinalizer(remote, nil)
+	remote.repo.Remotes.untrackRemote(remote)
 
 	return C.int(ErrorCodeOK)
 }

git.go

@@ -128,6 +128,7 @@ var (
 type doNotCompare [0]func()
 
 var pointerHandles *HandleList
+var remotePointers *remotePointerList
 
 func init() {
 	initLibGit2()
@@ -135,6 +136,7 @@ func init() {
 
 func initLibGit2() {
 	pointerHandles = NewHandleList()
+	remotePointers = newRemotePointerList()
 
 	C.git_libgit2_init()
 
@@ -160,7 +162,11 @@ func initLibGit2() {
 // After this is called, invoking any function from this library will result in
 // undefined behavior, so make sure this is called carefully.
 func Shutdown() {
+	if err := unregisterManagedTransports(); err != nil {
+		panic(err)
+	}
 	pointerHandles.Clear()
+	remotePointers.clear()
 
 	C.git_libgit2_shutdown()
 }

git_test.go

@@ -13,6 +13,10 @@ import (
 func TestMain(m *testing.M) {
 	ret := m.Run()
 
+	if err := unregisterManagedTransports(); err != nil {
+		panic(err)
+	}
+
 	// Ensure that we are not leaking any pointer handles.
 	pointerHandles.Lock()
 	if len(pointerHandles.handles) > 0 {
@@ -23,6 +27,16 @@ func TestMain(m *testing.M) {
 	}
 	pointerHandles.Unlock()
 
+	// Or remote pointers.
+	remotePointers.Lock()
+	if len(remotePointers.pointers) > 0 {
+		for ptr, remote := range remotePointers.pointers {
+			fmt.Printf("%016p: %+v\n", ptr, remote)
+		}
+		panic("remote pointer list not empty")
+	}
+	remotePointers.Unlock()
+
 	Shutdown()
 
 	os.Exit(ret)

remote.go

@@ -15,6 +15,7 @@ import (
 	"reflect"
 	"runtime"
 	"strings"
+	"sync"
 	"unsafe"
 )
 
@@ -174,6 +175,64 @@ type Remote struct {
 	repo      *Repository
 }
 
+type remotePointerList struct {
+	sync.RWMutex
+	// stores the Go pointers
+	pointers map[*C.git_remote]*Remote
+}
+
+func newRemotePointerList() *remotePointerList {
+	return &remotePointerList{
+		pointers: make(map[*C.git_remote]*Remote),
+	}
+}
+
+// track adds the given pointer to the list of pointers to track and
+// returns a pointer value which can be passed to C as an opaque
+// pointer.
+func (v *remotePointerList) track(remote *Remote) {
+	v.Lock()
+	v.pointers[remote.ptr] = remote
+	v.Unlock()
+
+	runtime.SetFinalizer(remote, (*Remote).Free)
+}
+
+// untrack stops tracking the git_remote pointer.
+func (v *remotePointerList) untrack(remote *Remote) {
+	v.Lock()
+	delete(v.pointers, remote.ptr)
+	v.Unlock()
+}
+
+// clear stops tracking all the git_remote pointers.
+func (v *remotePointerList) clear() {
+	v.Lock()
+	var remotes []*Remote
+	for remotePtr, remote := range v.pointers {
+		remotes = append(remotes, remote)
+		delete(v.pointers, remotePtr)
+	}
+	v.Unlock()
+
+	for _, remote := range remotes {
+		remote.free()
+	}
+}
+
+// get retrieves the pointer from the given *git_remote.
+func (v *remotePointerList) get(ptr *C.git_remote) (*Remote, bool) {
+	v.RLock()
+	defer v.RUnlock()
+
+	r, ok := v.pointers[ptr]
+	if !ok {
+		return nil, false
+	}
+
+	return r, true
+}
+
 type CertificateKind uint
 
 const (
@@ -509,17 +568,42 @@ func RemoteIsValidName(name string) bool {
 	return C.git_remote_is_valid_name(cname) == 1
 }
 
-// Free releases the resources of the Remote.
-func (r *Remote) Free() {
+// free releases the resources of the Remote.
+func (r *Remote) free() {
 	runtime.SetFinalizer(r, nil)
 	C.git_remote_free(r.ptr)
 	r.ptr = nil
 	r.repo = nil
 }
 
+// Free releases the resources of the Remote.
+func (r *Remote) Free() {
+	r.repo.Remotes.untrackRemote(r)
+	r.free()
+}
+
 type RemoteCollection struct {
 	doNotCompare
 	repo *Repository
+
+	sync.RWMutex
+	remotes map[*C.git_remote]*Remote
+}
+
+func (c *RemoteCollection) trackRemote(r *Remote) {
+	c.Lock()
+	c.remotes[r.ptr] = r
+	c.Unlock()
+
+	remotePointers.track(r)
+}
+
+func (c *RemoteCollection) untrackRemote(r *Remote) {
+	c.Lock()
+	delete(c.remotes, r.ptr)
+	c.Unlock()
+
+	remotePointers.untrack(r)
 }
 
 func (c *RemoteCollection) List() ([]string, error) {
@@ -554,7 +638,7 @@ func (c *RemoteCollection) Create(name string, url string) (*Remote, error) {
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
-	runtime.SetFinalizer(remote, (*Remote).Free)
+	c.trackRemote(remote)
 	return remote, nil
 }
 
@@ -570,13 +654,13 @@ func (c *RemoteCollection) CreateWithOptions(url string, option *RemoteCreateOpt
 
 	copts := populateRemoteCreateOptions(&C.git_remote_create_options{}, option, c.repo)
 	defer freeRemoteCreateOptions(copts)
+
 	ret := C.git_remote_create_with_opts(&remote.ptr, curl, copts)
 	runtime.KeepAlive(c.repo)
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
-
-	runtime.SetFinalizer(remote, (*Remote).Free)
+	c.trackRemote(remote)
 	return remote, nil
 }
 
@@ -612,7 +696,7 @@ func (c *RemoteCollection) CreateWithFetchspec(name string, url string, fetch st
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
-	runtime.SetFinalizer(remote, (*Remote).Free)
+	c.trackRemote(remote)
 	return remote, nil
 }
 
@@ -629,7 +713,7 @@ func (c *RemoteCollection) CreateAnonymous(url string) (*Remote, error) {
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
-	runtime.SetFinalizer(remote, (*Remote).Free)
+	c.trackRemote(remote)
 	return remote, nil
 }
 
@@ -646,10 +730,24 @@ func (c *RemoteCollection) Lookup(name string) (*Remote, error) {
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
-	runtime.SetFinalizer(remote, (*Remote).Free)
+	c.trackRemote(remote)
 	return remote, nil
 }
 
+func (c *RemoteCollection) Free() {
+	var remotes []*Remote
+	c.Lock()
+	for remotePtr, remote := range c.remotes {
+		remotes = append(remotes, remote)
+		delete(c.remotes, remotePtr)
+	}
+	c.Unlock()
+
+	for _, remote := range remotes {
+		remotePointers.untrack(remote)
+	}
+}
+
 func (o *Remote) Name() string {
 	s := C.git_remote_name(o.ptr)
 	runtime.KeepAlive(o)

remote_test.go

@@ -97,6 +97,7 @@ func TestRemoteConnectOption(t *testing.T) {
 
 	remote, err := repo.Remotes.CreateWithOptions("https://github.com/libgit2/TestGitRepository", option)
 	checkFatal(t, err)
+	defer remote.Free()
 
 	err = remote.ConnectFetch(nil, nil, nil)
 	checkFatal(t, err)

repository.go

@@ -46,6 +46,7 @@ func newRepositoryFromC(ptr *C.git_repository) *Repository {
 	repo := &Repository{ptr: ptr}
 
 	repo.Remotes.repo = repo
+	repo.Remotes.remotes = make(map[*C.git_remote]*Remote)
 	repo.Submodules.repo = repo
 	repo.References.repo = repo
 	repo.Notes.repo = repo
@@ -144,6 +145,7 @@ func (v *Repository) Free() {
 	ptr := v.ptr
 	v.ptr = nil
 	runtime.SetFinalizer(v, nil)
+	v.Remotes.Free()
 	if v.weak {
 		return
 	}

transport.go

@@ -0,0 +1,431 @@
+package git
+
+/*
+#include <git2.h>
+#include <git2/sys/transport.h>
+
+typedef struct {
+	git_smart_subtransport parent;
+	void *handle;
+} _go_managed_smart_subtransport;
+
+typedef struct {
+	git_smart_subtransport_stream parent;
+	void *handle;
+} _go_managed_smart_subtransport_stream;
+
+int _go_git_transport_register(const char *prefix, void *handle);
+int _go_git_transport_smart(git_transport **out, git_remote *owner, int stateless, _go_managed_smart_subtransport *subtransport_payload);
+void _go_git_setup_smart_subtransport_stream(_go_managed_smart_subtransport_stream *stream);
+*/
+import "C"
+import (
+	"errors"
+	"fmt"
+	"io"
+	"reflect"
+	"runtime"
+	"sync"
+	"unsafe"
+)
+
+var (
+	// globalRegisteredSmartTransports is a mapping of global, git2go-managed
+	// transports.
+	globalRegisteredSmartTransports = struct {
+		sync.Mutex
+		transports map[string]*RegisteredSmartTransport
+	}{
+		transports: make(map[string]*RegisteredSmartTransport),
+	}
+)
+
+// unregisterManagedTransports unregisters all git2go-managed transports.
+func unregisterManagedTransports() error {
+	globalRegisteredSmartTransports.Lock()
+	originalTransports := globalRegisteredSmartTransports.transports
+	globalRegisteredSmartTransports.transports = make(map[string]*RegisteredSmartTransport)
+	globalRegisteredSmartTransports.Unlock()
+
+	var err error
+	for protocol, managed := range originalTransports {
+		unregisterErr := managed.Free()
+		if err == nil && unregisterErr != nil {
+			err = fmt.Errorf("failed to unregister transport for %q: %v", protocol, unregisterErr)
+		}
+	}
+	return err
+}
+
+// SmartServiceAction is an action that the smart transport can ask a
+// subtransport to perform.
+type SmartServiceAction int
+
+const (
+	// SmartServiceActionUploadpackLs is used upon connecting to a remote, and is
+	// used to perform reference discovery prior to performing a pull operation.
+	SmartServiceActionUploadpackLs SmartServiceAction = C.GIT_SERVICE_UPLOADPACK_LS
+
+	// SmartServiceActionUploadpack is used when performing a pull operation.
+	SmartServiceActionUploadpack SmartServiceAction = C.GIT_SERVICE_UPLOADPACK
+
+	// SmartServiceActionReceivepackLs is used upon connecting to a remote, and is
+	// used to perform reference discovery prior to performing a push operation.
+	SmartServiceActionReceivepackLs SmartServiceAction = C.GIT_SERVICE_RECEIVEPACK_LS
+
+	// SmartServiceActionReceivepack is used when performing a push operation.
+	SmartServiceActionReceivepack SmartServiceAction = C.GIT_SERVICE_RECEIVEPACK
+)
+
+// Transport encapsulates a way to communicate with a Remote.
+type Transport struct {
+	doNotCompare
+	ptr *C.git_transport
+}
+
+// SmartCredentials calls the credentials callback for this transport.
+func (t *Transport) SmartCredentials(user string, methods CredentialType) (*Credential, error) {
+	cred := newCredential()
+	var cstr *C.char
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if user != "" {
+		cstr = C.CString(user)
+		defer C.free(unsafe.Pointer(cstr))
+	}
+	ret := C.git_transport_smart_credentials(&cred.ptr, t.ptr, cstr, C.int(methods))
+	if ret != 0 {
+		cred.Free()
+		return nil, MakeGitError(ret)
+	}
+
+	return cred, nil
+}
+
+// SmartSubtransport is the interface for custom subtransports which carry data
+// for the smart transport.
+type SmartSubtransport interface {
+	// Action creates a SmartSubtransportStream for the provided url and
+	// requested action.
+	Action(url string, action SmartServiceAction) (SmartSubtransportStream, error)
+
+	// Close closes the SmartSubtransport.
+	//
+	// Subtransports are guaranteed a call to Close between
+	// calls to Action, except for the following two "natural" progressions
+	// of actions against a constant URL.
+	//
+	// 1. UPLOADPACK_LS -> UPLOADPACK
+	// 2. RECEIVEPACK_LS -> RECEIVEPACK
+	Close() error
+
+	// Free releases the resources of the SmartSubtransport.
+	Free()
+}
+
+// SmartSubtransportStream is the interface for streams used by the smart
+// transport to read and write data from a subtransport.
+type SmartSubtransportStream interface {
+	io.Reader
+	io.Writer
+
+	// Free releases the resources of the SmartSubtransportStream.
+	Free()
+}
+
+// SmartSubtransportCallback is a function which creates a new subtransport for
+// the smart transport.
+type SmartSubtransportCallback func(remote *Remote, transport *Transport) (SmartSubtransport, error)
+
+// RegisteredSmartTransport represents a transport that has been registered.
+type RegisteredSmartTransport struct {
+	doNotCompare
+	name      string
+	stateless bool
+	callback  SmartSubtransportCallback
+	handle    unsafe.Pointer
+}
+
+// NewRegisteredSmartTransport adds a custom transport definition, to be used
+// in addition to the built-in set of transports that come with libgit2.
+func NewRegisteredSmartTransport(
+	name string,
+	stateless bool,
+	callback SmartSubtransportCallback,
+) (*RegisteredSmartTransport, error) {
+	return newRegisteredSmartTransport(name, stateless, callback, false)
+}
+
+func newRegisteredSmartTransport(
+	name string,
+	stateless bool,
+	callback SmartSubtransportCallback,
+	global bool,
+) (*RegisteredSmartTransport, error) {
+	if !global {
+		// Check if we had already registered a smart transport for this protocol. If
+		// we had, free it. The user is now responsible for this transport for the
+		// lifetime of the library.
+		globalRegisteredSmartTransports.Lock()
+		if managed, ok := globalRegisteredSmartTransports.transports[name]; ok {
+			delete(globalRegisteredSmartTransports.transports, name)
+			globalRegisteredSmartTransports.Unlock()
+
+			err := managed.Free()
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			globalRegisteredSmartTransports.Unlock()
+		}
+	}
+
+	cstr := C.CString(name)
+	defer C.free(unsafe.Pointer(cstr))
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	registeredSmartTransport := &RegisteredSmartTransport{
+		name:      name,
+		stateless: stateless,
+		callback:  callback,
+	}
+	registeredSmartTransport.handle = pointerHandles.Track(registeredSmartTransport)
+
+	ret := C._go_git_transport_register(cstr, registeredSmartTransport.handle)
+	if ret != 0 {
+		pointerHandles.Untrack(registeredSmartTransport.handle)
+		return nil, MakeGitError(ret)
+	}
+
+	runtime.SetFinalizer(registeredSmartTransport, (*RegisteredSmartTransport).Free)
+	return registeredSmartTransport, nil
+}
+
+// Free releases all resources used by the RegisteredSmartTransport and
+// unregisters the custom transport definition referenced by it.
+func (t *RegisteredSmartTransport) Free() error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	cstr := C.CString(t.name)
+	defer C.free(unsafe.Pointer(cstr))
+
+	if ret := C.git_transport_unregister(cstr); ret < 0 {
+		return MakeGitError(ret)
+	}
+
+	pointerHandles.Untrack(t.handle)
+	runtime.SetFinalizer(t, nil)
+	t.handle = nil
+	return nil
+}
+
+//export smartTransportCallback
+func smartTransportCallback(
+	errorMessage **C.char,
+	out **C.git_transport,
+	owner *C.git_remote,
+	handle unsafe.Pointer,
+) C.int {
+	registeredSmartTransport := pointerHandles.Get(handle).(*RegisteredSmartTransport)
+	remote, ok := remotePointers.get(owner)
+	if !ok {
+		err := errors.New("remote pointer not found")
+		return setCallbackError(errorMessage, err)
+	}
+
+	managed := &managedSmartSubtransport{
+		remote:       remote,
+		callback:     registeredSmartTransport.callback,
+		subtransport: (*C._go_managed_smart_subtransport)(C.calloc(1, C.size_t(unsafe.Sizeof(C._go_managed_smart_subtransport{})))),
+	}
+	managedHandle := pointerHandles.Track(managed)
+	managed.handle = managedHandle
+	managed.subtransport.handle = managedHandle
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	ret := C._go_git_transport_smart(out, owner, cbool(registeredSmartTransport.stateless), managed.subtransport)
+	if ret != 0 {
+		pointerHandles.Untrack(managedHandle)
+	}
+	return ret
+}
+
+//export smartTransportSubtransportCallback
+func smartTransportSubtransportCallback(
+	errorMessage **C.char,
+	wrapperPtr *C._go_managed_smart_subtransport,
+	owner *C.git_transport,
+) C.int {
+	subtransport := pointerHandles.Get(wrapperPtr.handle).(*managedSmartSubtransport)
+
+	underlyingSmartSubtransport, err := subtransport.callback(subtransport.remote, &Transport{ptr: owner})
+	if err != nil {
+		return setCallbackError(errorMessage, err)
+	}
+	subtransport.underlying = underlyingSmartSubtransport
+	return C.int(ErrorCodeOK)
+}
+
+type managedSmartSubtransport struct {
+	owner                *C.git_transport
+	callback             SmartSubtransportCallback
+	remote               *Remote
+	subtransport         *C._go_managed_smart_subtransport
+	underlying           SmartSubtransport
+	handle               unsafe.Pointer
+	currentManagedStream *managedSmartSubtransportStream
+}
+
+func getSmartSubtransportInterface(subtransport *C.git_smart_subtransport) *managedSmartSubtransport {
+	wrapperPtr := (*C._go_managed_smart_subtransport)(unsafe.Pointer(subtransport))
+	return pointerHandles.Get(wrapperPtr.handle).(*managedSmartSubtransport)
+}
+
+//export smartSubtransportActionCallback
+func smartSubtransportActionCallback(
+	errorMessage **C.char,
+	out **C.git_smart_subtransport_stream,
+	t *C.git_smart_subtransport,
+	url *C.char,
+	action C.git_smart_service_t,
+) C.int {
+	subtransport := getSmartSubtransportInterface(t)
+
+	underlyingStream, err := subtransport.underlying.Action(C.GoString(url), SmartServiceAction(action))
+	if err != nil {
+		return setCallbackError(errorMessage, err)
+	}
+
+	// It's okay to do strict equality here: we expect both to be identical.
+	if subtransport.currentManagedStream == nil || subtransport.currentManagedStream.underlying != underlyingStream {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+
+		stream := (*C._go_managed_smart_subtransport_stream)(C.calloc(1, C.size_t(unsafe.Sizeof(C._go_managed_smart_subtransport_stream{}))))
+		managed := &managedSmartSubtransportStream{
+			underlying: underlyingStream,
+			streamPtr:  stream,
+		}
+		managedHandle := pointerHandles.Track(managed)
+		managed.handle = managedHandle
+		stream.handle = managedHandle
+
+		C._go_git_setup_smart_subtransport_stream(stream)
+
+		subtransport.currentManagedStream = managed
+	}
+
+	*out = &subtransport.currentManagedStream.streamPtr.parent
+	return C.int(ErrorCodeOK)
+}
+
+//export smartSubtransportCloseCallback
+func smartSubtransportCloseCallback(errorMessage **C.char, t *C.git_smart_subtransport) C.int {
+	subtransport := getSmartSubtransportInterface(t)
+
+	subtransport.currentManagedStream = nil
+
+	if subtransport.underlying != nil {
+		err := subtransport.underlying.Close()
+		if err != nil {
+			return setCallbackError(errorMessage, err)
+		}
+	}
+
+	return C.int(ErrorCodeOK)
+}
+
+//export smartSubtransportFreeCallback
+func smartSubtransportFreeCallback(t *C.git_smart_subtransport) {
+	subtransport := getSmartSubtransportInterface(t)
+
+	if subtransport.underlying != nil {
+		subtransport.underlying.Free()
+		subtransport.underlying = nil
+	}
+	pointerHandles.Untrack(subtransport.handle)
+	C.free(unsafe.Pointer(subtransport.subtransport))
+	subtransport.handle = nil
+	subtransport.subtransport = nil
+}
+
+type managedSmartSubtransportStream struct {
+	owner      *C.git_smart_subtransport_stream
+	streamPtr  *C._go_managed_smart_subtransport_stream
+	underlying SmartSubtransportStream
+	handle     unsafe.Pointer
+}
+
+func getSmartSubtransportStreamInterface(subtransportStream *C.git_smart_subtransport_stream) *managedSmartSubtransportStream {
+	managedSubtransportStream := (*C._go_managed_smart_subtransport_stream)(unsafe.Pointer(subtransportStream))
+	return pointerHandles.Get(managedSubtransportStream.handle).(*managedSmartSubtransportStream)
+}
+
+//export smartSubtransportStreamReadCallback
+func smartSubtransportStreamReadCallback(
+	errorMessage **C.char,
+	s *C.git_smart_subtransport_stream,
+	buffer *C.char,
+	bufSize C.size_t,
+	bytesRead *C.size_t,
+) C.int {
+	stream := getSmartSubtransportStreamInterface(s)
+
+	var p []byte
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&p))
+	header.Cap = int(bufSize)
+	header.Len = int(bufSize)
+	header.Data = uintptr(unsafe.Pointer(buffer))
+
+	n, err := stream.underlying.Read(p)
+	*bytesRead = C.size_t(n)
+	if n == 0 && err != nil {
+		if err == io.EOF {
+			return C.int(ErrorCodeOK)
+		}
+
+		return setCallbackError(errorMessage, err)
+	}
+
+	return C.int(ErrorCodeOK)
+}
+
+//export smartSubtransportStreamWriteCallback
+func smartSubtransportStreamWriteCallback(
+	errorMessage **C.char,
+	s *C.git_smart_subtransport_stream,
+	buffer *C.char,
+	bufLen C.size_t,
+) C.int {
+	stream := getSmartSubtransportStreamInterface(s)
+
+	var p []byte
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&p))
+	header.Cap = int(bufLen)
+	header.Len = int(bufLen)
+	header.Data = uintptr(unsafe.Pointer(buffer))
+
+	if _, err := stream.underlying.Write(p); err != nil {
+		return setCallbackError(errorMessage, err)
+	}
+
+	return C.int(ErrorCodeOK)
+}
+
+//export smartSubtransportStreamFreeCallback
+func smartSubtransportStreamFreeCallback(s *C.git_smart_subtransport_stream) {
+	stream := getSmartSubtransportStreamInterface(s)
+
+	stream.underlying.Free()
+	pointerHandles.Untrack(stream.handle)
+	C.free(unsafe.Pointer(stream.streamPtr))
+	stream.handle = nil
+	stream.streamPtr = nil
+}

transport_test.go

@@ -0,0 +1,72 @@
+package git
+
+import (
+	"io"
+	"reflect"
+	"testing"
+)
+
+type testSmartSubtransport struct {
+}
+
+func (t *testSmartSubtransport) Action(url string, action SmartServiceAction) (SmartSubtransportStream, error) {
+	return &testSmartSubtransportStream{}, nil
+}
+
+func (t *testSmartSubtransport) Close() error {
+	return nil
+}
+
+func (t *testSmartSubtransport) Free() {
+}
+
+type testSmartSubtransportStream struct {
+}
+
+func (s *testSmartSubtransportStream) Read(buf []byte) (int, error) {
+	payload := "" +
+		"001e# service=git-upload-pack\n" +
+		"0000005d0000000000000000000000000000000000000000 HEAD\x00symref=HEAD:refs/heads/master agent=libgit\n" +
+		"003f0000000000000000000000000000000000000000 refs/heads/master\n" +
+		"0000"
+
+	return copy(buf, []byte(payload)), io.EOF
+}
+
+func (s *testSmartSubtransportStream) Write(buf []byte) (int, error) {
+	return 0, io.EOF
+}
+
+func (s *testSmartSubtransportStream) Free() {
+}
+
+func TestTransport(t *testing.T) {
+	t.Parallel()
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	callback := func(remote *Remote, transport *Transport) (SmartSubtransport, error) {
+		return &testSmartSubtransport{}, nil
+	}
+	registeredSmartTransport, err := NewRegisteredSmartTransport("foo", true, callback)
+	checkFatal(t, err)
+	defer registeredSmartTransport.Free()
+
+	remote, err := repo.Remotes.Create("test", "foo://bar")
+	checkFatal(t, err)
+	defer remote.Free()
+
+	err = remote.ConnectFetch(nil, nil, nil)
+	checkFatal(t, err)
+
+	remoteHeads, err := remote.Ls()
+	checkFatal(t, err)
+
+	expectedRemoteHeads := []RemoteHead{
+		{&Oid{}, "HEAD"},
+		{&Oid{}, "refs/heads/master"},
+	}
+	if !reflect.DeepEqual(expectedRemoteHeads, remoteHeads) {
+		t.Errorf("mismatched remote heads. expected %v, got %v", expectedRemoteHeads, remoteHeads)
+	}
+}

wrapper.c

@@ -504,3 +504,116 @@ int _go_git_indexer_new(
 	indexer_options.progress_cb_payload = progress_cb_payload;
 	return git_indexer_new(out, path, mode, odb, &indexer_options);
 }
+
+static int smart_transport_callback(
+		git_transport **out,
+		git_remote *owner,
+		void *param)
+{
+	char *error_message = NULL;
+	const int ret = smartTransportCallback(
+			&error_message,
+			out,
+			owner,
+			param);
+	return set_callback_error(error_message, ret);
+}
+
+int _go_git_transport_register(const char *prefix, void *param)
+{
+	return git_transport_register(prefix, smart_transport_callback, param);
+}
+
+static int smart_subtransport_action_callback(
+		git_smart_subtransport_stream **out,
+		git_smart_subtransport *transport,
+		const char *url,
+		git_smart_service_t action)
+{
+	char *error_message = NULL;
+	const int ret = smartSubtransportActionCallback(
+			&error_message,
+			out,
+			transport,
+			(char *)url,
+			action);
+	return set_callback_error(error_message, ret);
+}
+
+static int smart_subtransport_close_callback(git_smart_subtransport *transport)
+{
+	char *error_message = NULL;
+	const int ret = smartSubtransportCloseCallback(
+			&error_message,
+			transport);
+	return set_callback_error(error_message, ret);
+}
+
+static int smart_subtransport_callback(
+		git_smart_subtransport **out,
+		git_transport *owner,
+		void *param)
+{
+	_go_managed_smart_subtransport *subtransport = (_go_managed_smart_subtransport *)param;
+	subtransport->parent.action = smart_subtransport_action_callback;
+	subtransport->parent.close = smart_subtransport_close_callback;
+	subtransport->parent.free = smartSubtransportFreeCallback;
+
+	*out = &subtransport->parent;
+	char *error_message = NULL;
+	const int ret = smartTransportSubtransportCallback(&error_message, subtransport, owner);
+	return set_callback_error(error_message, ret);
+}
+
+int _go_git_transport_smart(
+		git_transport **out,
+		git_remote *owner,
+		int stateless,
+		_go_managed_smart_subtransport *subtransport_payload)
+{
+	git_smart_subtransport_definition definition = {
+		smart_subtransport_callback,
+		stateless,
+		subtransport_payload,
+	};
+
+	return git_transport_smart(out, owner, &definition);
+}
+
+static int smart_subtransport_stream_read_callback(
+		git_smart_subtransport_stream *stream,
+		char *buffer,
+		size_t buf_size,
+		size_t *bytes_read)
+{
+	char *error_message = NULL;
+	const int ret = smartSubtransportStreamReadCallback(
+			&error_message,
+			stream,
+			buffer,
+			buf_size,
+			bytes_read);
+	return set_callback_error(error_message, ret);
+}
+
+static int smart_subtransport_stream_write_callback(
+		git_smart_subtransport_stream *stream,
+		const char *buffer,
+		size_t len)
+{
+	char *error_message = NULL;
+	const int ret = smartSubtransportStreamWriteCallback(
+			&error_message,
+			stream,
+			(char *)buffer,
+			len);
+	return set_callback_error(error_message, ret);
+}
+
+void _go_git_setup_smart_subtransport_stream(_go_managed_smart_subtransport_stream *stream)
+{
+	_go_managed_smart_subtransport_stream *managed_stream = (_go_managed_smart_subtransport_stream *)stream;
+	managed_stream->parent.read = smart_subtransport_stream_read_callback;
+	managed_stream->parent.write = smart_subtransport_stream_write_callback;
+	managed_stream->parent.free = smartSubtransportStreamFreeCallback;
+}