examples: port header example to zig

This looks a lot nicer than its c counterpart, in my opinion.

build.zig

@@ -53,6 +53,7 @@ const Example = struct {
 
 const examples = [_]Example{
     .{ .name = "request_reply", .file = "examples/request_reply.zig" },
+    .{ .name = "headers", .file = "examples/headers.zig" },
 };
 
 pub fn add_examples(b: *std.build, options: ExampleOptions) void {

examples/headers.zig

@@ -0,0 +1,62 @@
+const std = @import("std");
+const nats = @import("nats");
+
+pub fn main() !void {
+    const connection = try nats.Connection.connectTo(nats.default_server_url);
+    defer connection.destroy();
+
+    const message = try nats.Message.create("subject", null, "message");
+    defer message.destroy();
+
+    try message.setHeaderValue("My-Key1", "value1");
+    try message.setHeaderValue("My-Key2", "value2");
+    try message.addHeaderValue("My-Key1", "value3");
+    try message.setHeaderValue("My-Key3", "value4");
+
+    try message.deleteHeader("My-Key3");
+
+    var iter = try message.headerIterator();
+    defer iter.destroy();
+
+    while (try iter.next()) |pair| {
+        std.debug.print(
+            "Key: '{s}', Value: '{s}'\n",
+            .{ pair.key, pair.value orelse "null" },
+        );
+    }
+
+    const subscription = try connection.subscribeSync("subject");
+    defer subscription.destroy();
+
+    try connection.publishMessage(message);
+    const received = try subscription.nextMessage(1000);
+    defer received.destroy();
+
+    {
+        const vals1 = try received.getAllHeaderValues("My-Key1");
+        defer std.heap.raw_c_allocator.free(vals1);
+        std.debug.print("For key 'My-Key1' got: ", .{});
+        for (vals1) |value| {
+            const val = std.mem.sliceTo(value, 0);
+
+            std.debug.print("'{s}', ", .{val});
+        }
+        std.debug.print("\n", .{});
+    }
+
+    _ = received.getHeaderValue("key-does-not-exist") catch |err| switch (err) {
+        nats.Error.NotFound => {},
+        else => {
+            std.debug.print("Should not have found that key!", .{});
+            return err;
+        },
+    };
+
+    received.deleteHeader("key-does-not-exist") catch |err| switch (err) {
+        nats.Error.NotFound => {},
+        else => {
+            std.debug.print("Should not have found that key!", .{});
+            return err;
+        },
+    };
+}