KV Store

zero exposes a unified, type-erased KV store so handlers don't depend on a specific backend. The Redis client (when configured) is auto-registered as the default store; additional stores are registered at startup.

See examples/zero-redis and examples/zero-nats-publisher for runnable examples.

Backends

Backend	Notes
.redis	okredis — the default store when Redis is configured
.nats_kv	NATS JetStream KV (reuses the nats dependency; needs a JetStream connection)
.memory	in-memory, zero dependencies — handy for tests
.sqlite	reuses the SQLite datasource (kv(k,v,exp) table)

Register stores

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);

    // backend: .redis | .nats_kv | .memory | .sqlite
    try app.addKVStore("feature-flags", .memory, .{});
    try app.addKVStore("sessions", .nats_kv, .{ .bucket = "sessions" });

    try app.run();
}

Use a store in a handler

pub fn handler(ctx: *Context) !void {
    // default store (Redis when configured), or a named store
    const kv = ctx.KV orelse ctx.GetKVStore("sessions") orelse return error.NoKV;
    try kv.set(ctx, "user:1", "active");

    const v = try kv.get(ctx, "user:1");      // ?[]const u8, caller-owned (free with ctx.allocator)
    defer if (v) |s| ctx.allocator.free(s);

    const has = try kv.exists(ctx, "user:1");

    try kv.delete(ctx, "user:1");

    try kv.expire(ctx, "user:1", 60_000);     // ms; unsupported on nats_kv
}

Circuit breaker

The cache store (including the default cache store) can be wrapped in a circuit breaker. Enable it with CACHE_CIRCUIT_BREAKER_ENABLE=true.

The breaker opens after 5 consecutive failures and stays open for 30s (cooldown); while open, cache calls return error.CircuitOpen instead of piling up against an unhealthy backend.

See Resilience → Circuit breakers for the shared behavior and the app_circuit_open_total metric.