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.

1 files changed, 431 insertions, 0 deletions

diff --git a/transport.go b/transport.go
new file mode 100644
index 0000000..94c9ffa
--- /dev/null
+++ b/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
+}