ssh: introduce GIT_SSH_EXEC for external OpenSSH

We can now use the `git_process` class to invoke OpenSSH and use it as
an SSH transport. This may be preferred over libssh2 for a variety of
callers.

cmake/SelectSSH.cmake

-# find libssh2
-if(USE_SSH STREQUAL ON OR USE_SSH STREQUAL "libssh2")
+if(USE_SSH STREQUAL "exec")
+	set(GIT_SSH 1)
+	set(GIT_SSH_EXEC 1)
+
+	add_feature_info(SSH ON "using OpenSSH exec support")
+elseif(USE_SSH STREQUAL ON OR USE_SSH STREQUAL "libssh2")
 	find_pkglibraries(LIBSSH2 libssh2)
 
 	if(NOT LIBSSH2_FOUND)

src/libgit2/transports/ssh.c

@@ -5,6 +5,7 @@
  * a Linking Exception. For full terms see the included COPYING file.
  */
 
+#include "ssh_exec.h"
 #include "ssh_libssh2.h"
 
 #include "transports/smart.h"
@@ -16,6 +17,8 @@ int git_smart_subtransport_ssh(
 {
 #ifdef GIT_SSH_LIBSSH2
 	return git_smart_subtransport_ssh_libssh2(out, owner, param);
+#elif GIT_SSH_EXEC
+	return git_smart_subtransport_ssh_exec(out, owner, param);
 #else
 	GIT_UNUSED(out);
 	GIT_UNUSED(owner);

src/libgit2/transports/ssh_exec.c

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "ssh_exec.h"
+
+#ifdef GIT_SSH_EXEC
+
+#include "common.h"
+
+#include "net.h"
+#include "path.h"
+#include "futils.h"
+#include "process.h"
+
+typedef struct {
+	git_smart_subtransport_stream parent;
+} ssh_exec_subtransport_stream;
+
+typedef struct {
+	git_smart_subtransport parent;
+	git_transport *owner;
+
+	ssh_exec_subtransport_stream *current_stream;
+
+	git_smart_service_t action;
+	git_process *process;
+} ssh_exec_subtransport;
+
+static int ssh_exec_subtransport_stream_read(
+	git_smart_subtransport_stream *s,
+	char *buffer,
+	size_t buf_size,
+	size_t *bytes_read)
+{
+	ssh_exec_subtransport *transport;
+	ssh_exec_subtransport_stream *stream = (ssh_exec_subtransport_stream *)s;
+	ssize_t ret;
+
+	GIT_ASSERT_ARG(stream);
+	GIT_ASSERT(stream->parent.subtransport);
+
+	transport = (ssh_exec_subtransport *)stream->parent.subtransport;
+
+	if ((ret = git_process_read(transport->process, buffer, buf_size)) < 0)
+		return (int)ret;
+
+	*bytes_read = (size_t)ret;
+	return 0;
+}
+
+static int ssh_exec_subtransport_stream_write(
+        git_smart_subtransport_stream *s,
+        const char *buffer,
+        size_t len)
+{
+	ssh_exec_subtransport *transport;
+	ssh_exec_subtransport_stream *stream = (ssh_exec_subtransport_stream *)s;
+	ssize_t ret;
+
+	GIT_ASSERT(stream && stream->parent.subtransport);
+
+	transport = (ssh_exec_subtransport *)stream->parent.subtransport;
+
+	while (len > 0) {
+		if ((ret = git_process_write(transport->process, buffer, len)) < 0)
+			return (int)ret;
+
+		len -= ret;
+	}
+
+	return 0;
+}
+
+static void ssh_exec_subtransport_stream_free(git_smart_subtransport_stream *s)
+{
+	ssh_exec_subtransport_stream *stream = (ssh_exec_subtransport_stream *)s;
+
+	git__free(stream);
+}
+
+static int ssh_exec_subtransport_stream_init(
+	ssh_exec_subtransport_stream **out,
+	ssh_exec_subtransport *transport)
+{
+	GIT_ASSERT_ARG(out);
+
+	*out = git__calloc(sizeof(ssh_exec_subtransport_stream), 1);
+	GIT_ERROR_CHECK_ALLOC(*out);
+
+	(*out)->parent.subtransport = &transport->parent;
+	(*out)->parent.read = ssh_exec_subtransport_stream_read;
+	(*out)->parent.write = ssh_exec_subtransport_stream_write;
+	(*out)->parent.free = ssh_exec_subtransport_stream_free;
+
+	return 0;
+}
+
+GIT_INLINE(int) ensure_transport_state(
+	ssh_exec_subtransport *transport,
+	git_smart_service_t expected,
+	git_smart_service_t next)
+{
+	if (transport->action != expected && transport->action != next) {
+		git_error_set(GIT_ERROR_NET, "invalid transport state");
+
+		return -1;
+	}
+
+	return 0;
+}
+
+static int start_ssh(
+	ssh_exec_subtransport *transport,
+	git_smart_service_t action,
+	const char *sshpath)
+{
+	const char *args[6];
+	const char *env[] = { "GIT_DIR=" };
+
+	git_process_options process_opts = GIT_PROCESS_OPTIONS_INIT;
+	git_net_url url = GIT_NET_URL_INIT;
+	git_str userhost = GIT_STR_INIT;
+	const char *command;
+	int error;
+
+	process_opts.capture_in = 1;
+	process_opts.capture_out = 1;
+	process_opts.capture_err = 1;
+
+	switch (action) {
+	case GIT_SERVICE_UPLOADPACK_LS:
+		command = "git-upload-pack";
+		break;
+	case GIT_SERVICE_RECEIVEPACK_LS:
+		command = "git-receive-pack";
+		break;
+	default:
+		git_error_set(GIT_ERROR_NET, "invalid action");
+		error = -1;
+		goto done;
+	}
+
+	if (git_net_str_is_url(sshpath))
+		error = git_net_url_parse(&url, sshpath);
+	else
+		error = git_net_url_parse_scp(&url, sshpath);
+
+	if (error < 0)
+		goto done;
+
+	if (url.username) {
+		git_str_puts(&userhost, url.username);
+		git_str_putc(&userhost, '@');
+	}
+	git_str_puts(&userhost, url.host);
+
+	args[0] = "/usr/bin/ssh";
+	args[1] = "-p";
+	args[2] = url.port;
+	args[3] = userhost.ptr;
+	args[4] = command;
+	args[5] = url.path;
+
+	if ((error = git_process_new(&transport->process, args, ARRAY_SIZE(args), env, ARRAY_SIZE(env), &process_opts)) < 0 ||
+	    (error = git_process_start(transport->process)) < 0) {
+		git_process_free(transport->process);
+		transport->process = NULL;
+		goto done;
+	}
+
+done:
+	git_str_dispose(&userhost);
+	git_net_url_dispose(&url);
+	return error;
+}
+
+static int ssh_exec_subtransport_action(
+	git_smart_subtransport_stream **out,
+	git_smart_subtransport *t,
+	const char *sshpath,
+	git_smart_service_t action)
+{
+	ssh_exec_subtransport *transport = (ssh_exec_subtransport *)t;
+	ssh_exec_subtransport_stream *stream = NULL;
+	git_smart_service_t expected;
+	int error;
+
+	switch (action) {
+	case GIT_SERVICE_UPLOADPACK_LS:
+	case GIT_SERVICE_RECEIVEPACK_LS:
+		if ((error = ensure_transport_state(transport, 0, 0)) < 0 ||
+		    (error = ssh_exec_subtransport_stream_init(&stream, transport)) < 0 ||
+		    (error = start_ssh(transport, action, sshpath)) < 0)
+		    goto on_error;
+
+		transport->current_stream = stream;
+		break;
+
+	case GIT_SERVICE_UPLOADPACK:
+	case GIT_SERVICE_RECEIVEPACK:
+		expected = (action == GIT_SERVICE_UPLOADPACK) ?
+			GIT_SERVICE_UPLOADPACK_LS : GIT_SERVICE_RECEIVEPACK_LS;
+
+		if ((error = ensure_transport_state(transport, expected, action)) < 0)
+			goto on_error;
+
+		break;
+
+	default:
+		git_error_set(GIT_ERROR_INVALID, "invalid service request");
+		goto on_error;
+	}
+
+	transport->action = action;
+	*out = &transport->current_stream->parent;
+
+	return 0;
+
+on_error:
+	if (stream != NULL)
+		ssh_exec_subtransport_stream_free(&stream->parent);
+
+	return -1;
+}
+
+static int ssh_exec_subtransport_close(git_smart_subtransport *t)
+{
+	ssh_exec_subtransport *transport = (ssh_exec_subtransport *)t;
+
+	if (transport->process) {
+		git_process_close(transport->process);
+		git_process_free(transport->process);
+		transport->process = NULL;
+	}
+
+	transport->action = 0;
+
+	return 0;
+}
+
+static void ssh_exec_subtransport_free(git_smart_subtransport *t)
+{
+	ssh_exec_subtransport *transport = (ssh_exec_subtransport *)t;
+
+	git__free(transport);
+}
+
+int git_smart_subtransport_ssh_exec(
+	git_smart_subtransport **out,
+	git_transport *owner,
+	void *payload)
+{
+	ssh_exec_subtransport *transport;
+
+	GIT_UNUSED(payload);
+
+	transport = git__calloc(sizeof(ssh_exec_subtransport), 1);
+	GIT_ERROR_CHECK_ALLOC(transport);
+
+	transport->owner = owner;
+	transport->parent.action = ssh_exec_subtransport_action;
+	transport->parent.close = ssh_exec_subtransport_close;
+	transport->parent.free = ssh_exec_subtransport_free;
+
+	*out = (git_smart_subtransport *) transport;
+	return 0;
+}
+
+#endif

src/libgit2/transports/ssh_exec.h

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_transports_ssh_exec_h__
+#define INCLUDE_transports_ssh_exec_h__
+
+#include "common.h"
+
+#include "git2.h"
+#include "git2/transport.h"
+#include "git2/sys/transport.h"
+
+int git_smart_subtransport_ssh_exec(
+	git_smart_subtransport **out,
+	git_transport *owner,
+	void *param);
+
+int git_smart_subtransport_ssh_exec_set_paths(
+	git_smart_subtransport *subtransport,
+	const char *cmd_uploadpack,
+	const char *cmd_receivepack);
+
+#endif

src/util/git2_features.h.in

@@ -30,6 +30,7 @@
 #cmakedefine GIT_QSORT_MSC
 
 #cmakedefine GIT_SSH 1
+#cmakedefine GIT_SSH_EXEC 1
 #cmakedefine GIT_SSH_LIBSSH2 1
 #cmakedefine GIT_SSH_LIBSSH2_MEMORY_CREDENTIALS 1