Allow environment variables to be used for Name.

When the Name starts with a $, the rest will be interpreted as the name of an
environment variable containing the real Name. When Name is $HOST, but this
environment variable does not exist, gethostname() will be used to set the
Name. In both cases, illegal characters will be converted to underscores.

doc/tinc.conf.5.in

@@ -394,6 +394,19 @@ while no routing table is managed.
 .It Va Name Li = Ar name Bq required
 This is the name which identifies this tinc daemon.
 It must be unique for the virtual private network this daemon will connect to.
+The Name may only consist of alphanumeric and underscore characters.
+
+If 
+.Va Name
+starts with a
+.Li $ ,
+then the contents of the environment variable that follows will be used.
+In that case, invalid characters will be converted to underscores.
+If
+.Va Name
+is
+.Li $HOST ,
+but no such environment variable exist, the hostname will be read using the gethostnname() system call.
 
 .It Va PingInterval Li = Ar seconds Pq 60
 The number of seconds of inactivity that

doc/tinc.texi

@@ -993,6 +993,11 @@ This only has effect when Mode is set to "switch".
 This is a symbolic name for this connection.
 The name should consist only of alfanumeric and underscore characters (a-z, A-Z, 0-9 and _).
 
+If Name starts with a $, then the contents of the environment variable that follows will be used.
+In that case, invalid characters will be converted to underscores.
+If Name is $HOST, but no such environment variable exist,
+the hostname will be read using the gethostnname() system call.
+
 @cindex PingInterval
 @item PingInterval = <@var{seconds}> (60)
 The number of seconds of inactivity that tinc will wait before sending a

src/net.h

@@ -138,6 +138,7 @@ extern int setup_vpn_in_socket(const sockaddr_t *);
 extern void send_packet(const struct node_t *, vpn_packet_t *);
 extern void receive_tcppacket(struct connection_t *, const char *, int);
 extern void broadcast_packet(const struct node_t *, vpn_packet_t *);
+extern char *get_name(void);
 extern bool setup_network(void);
 extern void setup_outgoing_connection(struct outgoing_t *);
 extern void try_outgoing_connections(void);

src/net_setup.c

@@ -269,6 +269,44 @@ void load_all_subnets(void) {
 	closedir(dir);
 }
 
+char *get_name(void) {
+	char *name = NULL;
+
+	get_config_string(lookup_config(config_tree, "Name"), &name);
+
+	if(!name)
+		return NULL;
+
+	if(*name == '$') {
+		char *envname = getenv(name + 1);
+		if(!envname) {
+			if(strcmp(name + 1, "HOST")) {
+				fprintf(stderr, "Invalid Name: environment variable %s does not exist\n", name + 1);
+				return false;
+			}
+			envname = alloca(32);
+			if(gethostname(envname, 32)) {
+				fprintf(stderr, "Could not get hostname: %s\n", strerror(errno));
+				return false;
+			}
+			envname[31] = 0;
+		}
+		free(name);
+		name = xstrdup(envname);
+		for(char *c = name; *c; c++)
+			if(!isalnum(*c))
+				*c = '_';
+	}
+
+	if(!check_id(name)) {
+		logger(LOG_ERR, "Invalid name for myself!");
+		free(name);
+		return false;
+	}
+
+	return name;
+}
+
 /*
   Configure node_t myself and set up the local sockets (listen only)
 */
@@ -293,17 +331,11 @@ static bool setup_myself(void) {
 	myself->connection->options = 0;
 	myself->connection->protocol_version = PROT_CURRENT;
 
-	if(!get_config_string(lookup_config(config_tree, "Name"), &name)) {	/* Not acceptable */
+	if(!(name = get_name())) {
 		logger(LOG_ERR, "Name for tinc daemon required!");
 		return false;
 	}
 
-	if(!check_id(name)) {
-		logger(LOG_ERR, "Invalid name for myself!");
-		free(name);
-		return false;
-	}
-
 	myself->name = name;
 	myself->connection->name = xstrdup(name);
 	xasprintf(&fname, "%s/hosts/%s", confbase, name);

src/tincd.c

@@ -337,16 +337,9 @@ static void indicator(int a, int b, void *p) {
 static bool keygen(int bits) {
 	RSA *rsa_key;
 	FILE *f;
-	char *name = NULL;
+	char *name = get_name();
 	char *filename;
 
-	get_config_string(lookup_config(config_tree, "Name"), &name);
-
-	if(name && !check_id(name)) {
-		fprintf(stderr, "Invalid name for myself!\n");
-		return false;
-	}
-
 	fprintf(stderr, "Generating %d bits keys:\n", bits);
 	rsa_key = RSA_generate_key(bits, 0x10001, indicator, NULL);
 
@@ -386,8 +379,7 @@ static bool keygen(int bits) {
 	PEM_write_RSAPublicKey(f, rsa_key);
 	fclose(f);
 	free(filename);
-	if(name)
-		free(name);
+	free(name);
 
 	return true;
 }