NATS Subscriber

This document demonstrates subscribing to a NATS subject using zero's built-in pubsub client.

It is the continuation of the Publisher demo — prefer to read that first.

// listens for upcoming event and injects into the subscriber handler
// for further actions.
app.addPubSubSubscription("subject", subscriberHandler);

Broker selection

Same as the publisher — set PUBSUB_BACKEND=NATS and PUBSUB_BROKER.

PUBSUB_BACKEND=NATS
PUBSUB_BROKER=nats://localhost:4222

Example

src/main.zig

const std = @import("std");
const zero = @import("zero");

const App = zero.App;
const Context = zero.Context;
const utils = zero.utils;

pub fn main(init: std.process.Init) !void {
    var gpa: std.heap.DebugAllocator(.{}) = .init;
    const allocator = gpa.allocator();
    const app = try App.new(allocator, init.io, init.environ_map);

    try app.addPubSubSubscription("zero", onMessage);
    try app.run();
}

fn onMessage(ctx: *Context) !void {
    if (ctx.message) |message| {
        const m = message.nats;
        var buf: [256]u8 = undefined;
        const line = std.fmt.bufPrint(&buf, "received on [{s}] {s}", .{ m.subject, m.payload }) catch "decode error";
        ctx.info(line);
    }
}

The inbound message is available on ctx.message.?.nats, which exposes .subject and .payload (both []const u8). See examples/zero-nats-subscriber for a runnable example.