ssh: introduce a 'simple' ssh variant

When using the 'ssh' transport, the '-o' option is used to specify an
environment variable which should be set on the remote end.  This allows
git to send additional information when contacting the server,
requesting the use of a different protocol version via the
'GIT_PROTOCOL' environment variable like so: "-o SendEnv=GIT_PROTOCOL".

Unfortunately not all ssh variants support the sending of environment
variables to the remote end.  To account for this, only use the '-o'
option for ssh variants which are OpenSSH compliant.  This is done by
checking that the basename of the ssh command is 'ssh' or the ssh
variant is overridden to be 'ssh' (via the ssh.variant config).

Other options like '-p' and '-P', which are used to specify a specific
port to use, or '-4' and '-6', which are used to indicate that IPV4 or
IPV6 addresses should be used, may also not be supported by all ssh
variants.

Currently if an ssh command's basename wasn't 'plink' or
'tortoiseplink' git assumes that the command is an OpenSSH variant.
Since user configured ssh commands may not be OpenSSH compliant, tighten
this constraint and assume a variant of 'simple' if the basename of the
command doesn't match the variants known to git.  The new ssh variant
'simple' will only have the host and command to execute ([username@]host
command) passed as parameters to the ssh command.

Update the Documentation to better reflect the command-line options sent
to ssh commands based on their variant.

Reported-by: Jeffrey Yasskin <jyasskin@google.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 61 insertions, 47 deletions

diff --git a/connect.c b/connect.c
index b8695a2fa2..7fbd396b35 100644
--- a/connect.c
+++ b/connect.c
@@ -776,37 +776,44 @@ static const char *get_ssh_command(void)
 	return NULL;
 }
 
-static int override_ssh_variant(int *port_option, int *needs_batch)
+enum ssh_variant {
+	VARIANT_SIMPLE,
+	VARIANT_SSH,
+	VARIANT_PLINK,
+	VARIANT_PUTTY,
+	VARIANT_TORTOISEPLINK,
+};
+
+static int override_ssh_variant(enum ssh_variant *ssh_variant)
 {
-	char *variant;
+	const char *variant = getenv("GIT_SSH_VARIANT");
 
-	variant = xstrdup_or_null(getenv("GIT_SSH_VARIANT"));
-	if (!variant &&
-	    git_config_get_string("ssh.variant", &variant))
+	if (!variant && git_config_get_string_const("ssh.variant", &variant))
 		return 0;
 
-	if (!strcmp(variant, "plink") || !strcmp(variant, "putty")) {
-		*port_option = 'P';
-		*needs_batch = 0;
-	} else if (!strcmp(variant, "tortoiseplink")) {
-		*port_option = 'P';
-		*needs_batch = 1;
-	} else {
-		*port_option = 'p';
-		*needs_batch = 0;
-	}
-	free(variant);
+	if (!strcmp(variant, "plink"))
+		*ssh_variant = VARIANT_PLINK;
+	else if (!strcmp(variant, "putty"))
+		*ssh_variant = VARIANT_PUTTY;
+	else if (!strcmp(variant, "tortoiseplink"))
+		*ssh_variant = VARIANT_TORTOISEPLINK;
+	else if (!strcmp(variant, "simple"))
+		*ssh_variant = VARIANT_SIMPLE;
+	else
+		*ssh_variant = VARIANT_SSH;
+
 	return 1;
 }
 
-static void handle_ssh_variant(const char *ssh_command, int is_cmdline,
-			       int *port_option, int *needs_batch)
+static enum ssh_variant determine_ssh_variant(const char *ssh_command,
+					      int is_cmdline)
 {
+	enum ssh_variant ssh_variant = VARIANT_SIMPLE;
 	const char *variant;
 	char *p = NULL;
 
-	if (override_ssh_variant(port_option, needs_batch))
-		return;
+	if (override_ssh_variant(&ssh_variant))
+		return ssh_variant;
 
 	if (!is_cmdline) {
 		p = xstrdup(ssh_command);
@@ -825,19 +832,22 @@ static void handle_ssh_variant(const char *ssh_command, int is_cmdline,
 			free(ssh_argv);
 		} else {
 			free(p);
-			return;
+			return ssh_variant;
 		}
 	}
 
-	if (!strcasecmp(variant, "plink") ||
-	    !strcasecmp(variant, "plink.exe"))
-		*port_option = 'P';
+	if (!strcasecmp(variant, "ssh") ||
+	    !strcasecmp(variant, "ssh.exe"))
+		ssh_variant = VARIANT_SSH;
+	else if (!strcasecmp(variant, "plink") ||
+		 !strcasecmp(variant, "plink.exe"))
+		ssh_variant = VARIANT_PLINK;
 	else if (!strcasecmp(variant, "tortoiseplink") ||
-		 !strcasecmp(variant, "tortoiseplink.exe")) {
-		*port_option = 'P';
-		*needs_batch = 1;
-	}
+		 !strcasecmp(variant, "tortoiseplink.exe"))
+		ssh_variant = VARIANT_TORTOISEPLINK;
+
 	free(p);
+	return ssh_variant;
 }
 
 /*
@@ -937,8 +947,7 @@ struct child_process *git_connect(int fd[2], const char *url,
 		conn->in = conn->out = -1;
 		if (protocol == PROTO_SSH) {
 			const char *ssh;
-			int needs_batch = 0;
-			int port_option = 'p';
+			enum ssh_variant variant;
 			char *ssh_host = hostandport;
 			const char *port = NULL;
 			transport_check_allowed("ssh");
@@ -965,10 +974,9 @@ struct child_process *git_connect(int fd[2], const char *url,
 				die("strange hostname '%s' blocked", ssh_host);
 
 			ssh = get_ssh_command();
-			if (ssh)
-				handle_ssh_variant(ssh, 1, &port_option,
-						   &needs_batch);
-			else {
+			if (ssh) {
+				variant = determine_ssh_variant(ssh, 1);
+			} else {
 				/*
 				 * GIT_SSH is the no-shell version of
 				 * GIT_SSH_COMMAND (and must remain so for
@@ -979,32 +987,38 @@ struct child_process *git_connect(int fd[2], const char *url,
 				ssh = getenv("GIT_SSH");
 				if (!ssh)
 					ssh = "ssh";
-				else
-					handle_ssh_variant(ssh, 0,
-							   &port_option,
-							   &needs_batch);
+				variant = determine_ssh_variant(ssh, 0);
 			}
 
 			argv_array_push(&conn->args, ssh);
 
-			if (get_protocol_version_config() > 0) {
+			if (variant == VARIANT_SSH &&
+			    get_protocol_version_config() > 0) {
 				argv_array_push(&conn->args, "-o");
 				argv_array_push(&conn->args, "SendEnv=" GIT_PROTOCOL_ENVIRONMENT);
 				argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
 						 get_protocol_version_config());
 			}
 
-			if (flags & CONNECT_IPV4)
-				argv_array_push(&conn->args, "-4");
-			else if (flags & CONNECT_IPV6)
-				argv_array_push(&conn->args, "-6");
-			if (needs_batch)
+			if (variant != VARIANT_SIMPLE) {
+				if (flags & CONNECT_IPV4)
+					argv_array_push(&conn->args, "-4");
+				else if (flags & CONNECT_IPV6)
+					argv_array_push(&conn->args, "-6");
+			}
+
+			if (variant == VARIANT_TORTOISEPLINK)
 				argv_array_push(&conn->args, "-batch");
-			if (port) {
-				argv_array_pushf(&conn->args,
-						 "-%c", port_option);
+
+			if (port && variant != VARIANT_SIMPLE) {
+				if (variant == VARIANT_SSH)
+					argv_array_push(&conn->args, "-p");
+				else
+					argv_array_push(&conn->args, "-P");
+
 				argv_array_push(&conn->args, port);
 			}
+
 			argv_array_push(&conn->args, ssh_host);
 		} else {
 			transport_check_allowed("file");