#3 - DNS support + IPv6

modules/client/src/app/ClientArgs.cpp

@@ -1,6 +1,5 @@
 #include "ClientArgs.hpp"
 
-#include <arpa/inet.h>
 #include <charconv>
 #include <algorithm>
 #include <cctype>
@@ -25,12 +24,6 @@ std::string_view trim(std::string_view str) {
     return str.substr(start, end - start);
 }
 
-bool is_valid_ipv4(std::string_view ip_str) {
-    // Use inet_pton to validate IPv4 format
-    struct in_addr addr;
-    return inet_pton(AF_INET, std::string(ip_str).c_str(), &addr) == 1;
-}
-
 tl::expected<int, std::string> parse_port(std::string_view port_str) {
     if(port_str.empty()) {
         return 8080; // Default port
@@ -63,15 +56,27 @@ tl::expected<net::Address, std::string> parse_address(std::string_view text) {
         return tl::make_unexpected("address cannot be empty");
     }
 
-    // Find the colon to split host and port
-    size_t colon_pos = text.rfind(':');
-
     std::string_view host;
     std::string_view port_str;
 
-    if(colon_pos == std::string_view::npos) {
-        // No colon found: treat entire string as port or host
-        // If it's all digits, treat as port; otherwise as host (will fail validation)
+    // An IPv6 literal carries colons of its own, so the brackets it is written
+    // in are what says where the host ends. This is the form to_string() emits.
+    if(text.front() == '[') {
+        size_t closing = text.find(']');
+        if(closing == std::string_view::npos) {
+            return tl::make_unexpected("address is missing a closing bracket");
+        }
+
+        host = text.substr(1, closing - 1);
+        port_str = text.substr(closing + 1);
+
+        if(!port_str.empty()) {
+            if(port_str.front() != ':') {
+                return tl::make_unexpected("expected a port after the closing bracket");
+            }
+            port_str.remove_prefix(1);
+        }
+    } else if(size_t colon_pos = text.rfind(':'); colon_pos == std::string_view::npos) {
         bool all_digits = !text.empty() && std::all_of(text.begin(), text.end(),
             [](unsigned char c) { return std::isdigit(c); });
 
@@ -79,7 +84,6 @@ tl::expected<net::Address, std::string> parse_address(std::string_view text) {
             host = "127.0.0.1";
             port_str = text;
         } else {
-            // Treat as host with no port
             host = text;
             port_str = "";
         }
@@ -93,10 +97,6 @@ tl::expected<net::Address, std::string> parse_address(std::string_view text) {
         return tl::make_unexpected("host cannot be empty");
     }
 
-    if(!is_valid_ipv4(host)) {
-        return tl::make_unexpected("not a valid IPv4 address");
-    }
-
     // Parse port
     auto port_result = parse_port(port_str);
     if(!port_result) {
@@ -104,7 +104,13 @@ tl::expected<net::Address, std::string> parse_address(std::string_view text) {
     }
 
     int port = port_result.value();
-    return net::Address(std::optional<std::string>(std::string(host)), port);
+
+    auto address_r = net::Address::resolve(std::string(host), port);
+    if(!address_r) {
+        return tl::make_unexpected(address_r.error().message());
+    }
+
+    return address_r.value();
 }
 
 std::optional<std::string> server_arg(int argc, char** argv) {

modules/client/src/app/ClientArgs.hpp

@@ -12,10 +12,13 @@ namespace tw::app {
 /**
  * Parse an address string into a network address.
  *
- * Accepts "host:port" or a bare port number. Bare port uses 127.0.0.1.
- * Missing port defaults to 8080. Trims surrounding whitespace.
- * Validates the host with inet_pton and returns an error string
- * for non-IPv4 addresses or invalid ports.
+ * Accepts "host:port" or a bare port number, where the host may be a name as
+ * well as an address literal; an IPv6 literal has to be bracketed, as
+ * "[::1]:8080". Bare port uses 127.0.0.1. Missing port defaults to 8080.
+ * Trims surrounding whitespace.
+ *
+ * Looks the host up, so it blocks for as long as that takes, and returns an
+ * error string for a host that does not resolve or an invalid port.
  */
 tl::expected<net::Address, std::string> parse_address(std::string_view text);