Only use IPv6 in the webserver when available

src/config/config.c

@@ -1364,17 +1364,30 @@ void readFTLconf(struct config *conf, const bool rewrite)
 	const in_port_t https_port = port_in_use(443) ? 8443 : 443;
 
 	// Create a string with the default ports
-	if(http_port == 80 && https_port == 443)
-		conf->webserver.port.v.s = (char*)"80,[::]:80,443s,[::]:443s";
-	else if(http_port == 8080 && https_port == 443)
-		conf->webserver.port.v.s = (char*)"8080,[::]:8080,443s,[::]:443s";
-	else if(http_port == 80 && https_port == 8443)
-		conf->webserver.port.v.s = (char*)"80,[::]:80,8443s,[::]:8443s";
-	else
-		conf->webserver.port.v.s = (char*)"8080,[::]:8080,8443s,[::]:8443s";
-
-	log_info("Initialised webserver ports at %d (HTTP) and %d (HTTPS)",
-	         http_port, https_port);
+	// Allocate memory for the string
+	char *ports = calloc(32, sizeof(char));
+	if(ports == NULL)
+	{
+		log_err("Unable to allocate memory for default ports string");
+		return;
+	}
+	// Create the string
+	snprintf(ports, 32, "%d,%ds", http_port, https_port);
+
+	// Append IPv6 ports if IPv6 is enabled
+	const bool have_ipv6 = ipv6_enabled();
+	if(have_ipv6)
+		snprintf(ports + strlen(ports), 32 - strlen(ports),
+		         ",[::]:%d,[::]:%ds", http_port, https_port);
+
+	// Set default values for webserver ports
+	if(conf->webserver.port.t == CONF_STRING_ALLOCATED)
+		free(conf->webserver.port.v.s);
+	conf->webserver.port.v.s = ports;
+	conf->webserver.port.t = CONF_STRING_ALLOCATED;
+
+	log_info("Initialised webserver ports at %d (HTTP) and %d (HTTPS), IPv6 support is %s",
+	         http_port, https_port, have_ipv6 ? "enabled" : "disabled");
 
 	// Initialize the TOML config file
 	writeFTLtoml(true);

src/daemon.c

@@ -396,3 +396,51 @@ ssize_t getrandom_fallback(void *buf, size_t buflen, unsigned int flags)
 
 	return buflen;
 }
+
+bool ipv6_enabled(void)
+{
+	// First we check a few virtual system files to see if IPv6 is disabled
+	const char *files[] = {
+		"/sys/module/ipv6/parameters/disable", // GRUB - ipv6.disable=1
+		"/proc/sys/net/ipv6/conf/all/disable_ipv6", // sysctl.conf - net.ipv6.conf.all.disable_ipv6=1
+		"/proc/sys/net/ipv6/conf/default/disable_ipv6", // sysctl.conf - net.ipv6.conf.all.disable_ipv6=1
+		NULL
+	};
+
+	// Loop over the files
+	for(int i = 0; files[i] != NULL; i++)
+	{
+		// Open file for reading
+		FILE *f = fopen(files[i], "r");
+		if(f == NULL)
+			continue;
+
+		// Read first character
+		const int c = fgetc(f);
+		fclose(f);
+		// If the first character is a 1, then IPv6 is disabled
+		if(c == '1')
+			return false;
+	}
+
+	// If the file does not exist or if it does not contain a 1, then we check
+	// if /proc/net/if_inet6 has any IPv6-capable interfaces
+	// Since Linux 2.6.25 (April 2008), files in /proc/net are a symlink to
+	// /proc/self/net and provide information about the network devices and
+	// interfaces for the network namespace of which the process is a member
+	FILE *f = fopen("/proc/net/if_inet6", "r");
+
+	if(f != NULL)
+	{
+		// If the file exists, we check if it is empty
+		const int c = fgetc(f);
+		fclose(f);
+		// If the file is empty, then there are no IPv6-capable interfaces
+		if(c == EOF)
+			return false;
+	}
+
+	// else: IPv6 is not obviously disabled and there is at least one
+	// IPv6-capable interface
+	return true;
+}

src/daemon.h

@@ -23,6 +23,7 @@ void cleanup(const int ret);
 void set_nice(void);
 void calc_cpu_usage(void);
 float get_cpu_percentage(void) __attribute__((pure));
+bool ipv6_enabled(void);
 
 #include <sys/syscall.h>
 #include <unistd.h>