Add CLI to specify dest for relay messages

The dest can be specified as a 4 char ASCII string, or as an IPv4 address.

src/Client.zig

@@ -39,10 +39,10 @@ fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocato
     _ = try sock.sendTo(dest_addr, msg_bytes);
 }
 
-pub fn sendRelay(payload: []const u8, allocator: Allocator) !void {
+pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
     const msg = SaprusMessage{
         .relay = .{
-            .header = .{ .dest = .{ 70, 70, 70, 70 } },
+            .header = .{ .dest = dest },
             .payload = payload,
         },
     };

src/main.zig

@@ -23,6 +23,7 @@ pub fn main() !void {
     const params = comptime clap.parseParamsComptime(
         \\-h, --help           Display this help and exit.
         \\-r, --relay <str>    A relay message to send.
+        \\-d, --dest <str>     An IPv4 or <= 4 ASCII byte string.
         \\-c, --connect <str>  A connection message to send.
         \\
     );
@@ -49,7 +50,12 @@ pub fn main() !void {
     }
 
     if (res.args.relay) |r| {
-        try SaprusClient.sendRelay(if (r.len > 0) r else "Hello darkness my old friend", gpa);
+        const dest = parseDest(res.args.dest) catch .{ 70, 70, 70, 70 };
+        try SaprusClient.sendRelay(
+            if (r.len > 0) r else "Hello darkness my old friend",
+            dest,
+            gpa,
+        );
         // std.debug.print("Sent: {s}\n", .{r});
         return;
     } else if (res.args.connect) |c| {
@@ -69,6 +75,20 @@ pub fn main() !void {
     return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
 }
 
+fn parseDest(in: ?[]const u8) ![4]u8 {
+    if (in) |dest| {
+        if (dest.len <= 4) {
+            var res: [4]u8 = @splat(0);
+            @memcpy(res[0..dest.len], dest);
+            return res;
+        }
+
+        const addr = try std.net.Ip4Address.parse(dest, 0);
+        return @bitCast(addr.sa.addr);
+    }
+    return .{ 70, 70, 70, 70 };
+}
+
 const builtin = @import("builtin");
 const std = @import("std");
 const DebugAllocator = std.heap.DebugAllocator(.{});