server/protocol: Protocol version negotiation

7 files changed, 63 insertions, 1 deletions

diff --git a/TODO.txt b/TODO.txt
index 7771749..8e7ac3b 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -4,3 +4,7 @@
 - Message replies: referenced message should be msgid
 - Somehow communicate (push? poll?) to room members whether a particular user is currently _active_, not just online.
 - A session is marked inactive 2 minutes after the latest activity on that session. Make the number "2" configurable and not a hard-coded constant.
+- Use poll(2), not select(2)
+- Fix OOM dos vector
+- Sub-linear hash table of conn_data's in main.c
+- Constant-time lookup of commands in command.c
diff --git a/command.c b/command.c
index 5121ddf..6e73ce3 100644
--- a/command.c
+++ b/command.c
@@ -25,6 +25,22 @@ struct cmd_retval{
 #define RET_MEMZERO ((struct cmd_retval){.socket_close=false,.memzero=true})
 #define RET_MEMZERO_CLOSE(close_) ((struct cmd_retval){.socket_close=(close_),.memzero=true})
 
+static struct cmd_retval cmd_version(struct conn_data *data,const char *tag,const char **args){
+	i64 version;
+	if (!parse_i64(args[0], &version)
+			|| version < MIN_SUPPORTED_PROTOCOL_VERSION
+			|| version > PROTOCOL_VERSION) {
+		data->protversion = -1;
+		net_send_error(data->fd, tag, "Version not supported");
+		return RET_OK;
+	}
+
+	data->protversion = version;
+
+	net_send_ok(data->fd, tag);
+	return RET_OK;
+}
+
 static struct cmd_retval cmd_register(struct conn_data *data,const char *tag,const char **args){
 	i64 userid=db_find_user(args[0]);
 	if(userid!=-1){
@@ -375,6 +391,7 @@ struct cmd_info{
 };
 
 static const struct cmd_info commands[]={
+	{"version",1,false,cmd_version},
 	{"register",2,true,cmd_register},
 	{"login",2,true,cmd_login},
 	{"logout",0,false,cmd_logout},
@@ -423,6 +440,13 @@ bool handle_input_line(struct conn_data *data,char *line,size_t linelen){
 		return true;
 	}
 
+	// Ensure first command is 'version'
+	if(data->protversion==-1&&strcmp(commands[cmdi].cmdname,"version")!=0){
+		debug("Command %s before version negotiation on connection %d",
+				commands[cmdi].cmdname,data->fd);
+		return true;
+	}
+
 	int nargs=commands[cmdi].nargs;
 	char *args[nargs];
 	size_t cursor=cmdlen+1;
diff --git a/command.h b/command.h
index 3b01f42..e1226a5 100644
--- a/command.h
+++ b/command.h
@@ -4,6 +4,10 @@
 #include "conn_data.h"
 
 
+#define PROTOCOL_VERSION 1
+#define MIN_SUPPORTED_PROTOCOL_VERSION 1
+
+
 // Returns true if socket should be closed.
 // Modifies some bytes in `line`, AS WELL AS line[linelen]!
 bool handle_input_line(struct conn_data *data,char *line,size_t linelen);
diff --git a/conn_data.c b/conn_data.c
index 1b237b4..fa2da10 100644
--- a/conn_data.c
+++ b/conn_data.c
@@ -7,6 +7,7 @@ void conn_data_init(struct conn_data *data,int fd){
 	data->buflen=0;
 	data->buffer=malloc(data->bufsz,char);
 
+	data->protversion=-1;
 	data->userid=-1;
 }
 
@@ -16,5 +17,6 @@ void conn_data_nullify(struct conn_data *data){
 	data->bufsz=0;
 	data->buflen=0;
 
+	data->protversion=-1;
 	data->userid=-1;
 }
diff --git a/conn_data.h b/conn_data.h
index dae100f..4c6ab07 100644
--- a/conn_data.h
+++ b/conn_data.h
@@ -8,6 +8,7 @@ struct conn_data{
 	i64 bufsz,buflen;
 	char *buffer;
 
+	i64 protversion;  // -1 if not negotiated yet
 	i64 userid;  // -1 if not logged in
 };
 
diff --git a/main.c b/main.c
index 77237bf..78c98cb 100644
--- a/main.c
+++ b/main.c
@@ -125,6 +125,8 @@ static bool server_socket_callback(int fd){
 }
 
 static bool timeout_callback(int fd){
+	// Note: this does not check the protocol version. If the protocol changes
+	// significantly regarding push messages, perhaps that should change.
 	return net_send_raw_text(fd,"_push ping\n",11);
 }
 
diff --git a/protocol.md b/protocol.md
index 4094b79..2d7ec63 100644
--- a/protocol.md
+++ b/protocol.md
@@ -1,4 +1,4 @@
-# tomsg protocol
+# tomsg protocol (version 1)
 
 The underlying transport of the protocol is a plain TCP socket. The individual
 messages are all line-based; this means that a single message, both
@@ -16,6 +16,11 @@ There are three kinds of messages: commands from the client, command responses
 from the server, and push messages from the server (not to be confused with push
 _notifications_). These three kinds are described below.
 
+Note that the first message the client must send is the `version` command, with
+which server and client can agree (or not) on a protocol version; if a `version`
+message has not yet been replied to with an `ok` response, no other commands are
+valid. See the definition of the `version` command for more information.
+
 In the syntax descriptions below, `<name>` indicates an argument called "name";
 the angle brackets are not part of the syntax. The type of the argument may be
 indicated with the notation `<name:type>`; possible types are `i64` (a 64-bit
@@ -63,6 +68,26 @@ arguments are zero or more words, except if for the command in question the last
 argument is of type `string...` (in which case it may contain spaces and
 ranges until the end of the line).
 
+- `<tag> version <version:word>`
+  - Indicates that the client wishes to speak the protocol with the specified
+    version. For the version of the protocol described in this document, see the
+    header at the top of the file.
+
+    After the server has replied to this command with `ok`, the rest of the
+    protocol of (only) the specified version may be used. Before that, or if the
+    server replies with `error`, no commands other than `version` are valid.
+
+    If the client sends subsequent `version` messages after the first one, the
+    server may choose to handle those subsequent messages and switch versions,
+    or always return `error`, or some arbitrary mix. However, sending multiple
+    `version` messages is always valid (though not recommended).
+
+    It is probable that the server can only speak one version of the protocol,
+    but it may support multiple versions. Note also that the version is a
+    _word_, not an integer; though this document describes an integer-versioned
+    protocol, future versions may use other printable ASCII characters (but not
+    any outside that range).
+  - Returns `ok` or `error`.
 - `<tag> register <user:word> <pass:string...>`
   - Register a new user on the server. The password may contain spaces.
   - Returns `ok` or `error`.