From b85c1a60bf7f27e37fe2a86b26aa83ff198e208e Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Sun, 28 Jun 2020 22:18:57 +0200
Subject: server/protocol: Protocol version negotiation

---
 command.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

(limited to '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;
-- 
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