mkio 0.1.4

Config-driven microservice framework with WebSocket, SQLite, and expression language

mkio

Config-driven microservice framework for Python. Define your schema, services, and data flows in a TOML file — zero coding required for standard configurations.

A single TCP port serves HTTP and WebSocket, backed by an embedded SQLite database. Designed for restricted environments where runtime downloads aren't possible — everything installs via pip.

Contents

• Quick Start
• Features
• Service Types
• WebSocket Protocol
• Client Libraries
• Expression Language
• Performance
• CLI Tools
• Using mkio from a Claude-Based Project
• Schema Migration
• License

Quick Start

pip install mkio

Create mkio.toml:

port = 8080

[tables.orders]
columns = { id = "TEXT PRIMARY KEY", symbol = "TEXT NOT NULL", qty = "INTEGER", status = "TEXT DEFAULT 'pending'" }

[services.add_order]
type = "transaction"
table = "orders"
op_type = "insert"
fields = ["id", "symbol", "qty"]

[services.all_orders]
type = "query"
primary_table = "orders"
filterable = ["status", "symbol"]

[static]
"/" = "./static"

Run:

mkio serve

Or programmatically:

from mkio import serve
serve("mkio.toml")
serve({...})  # or pass a dict

Features

• Single port — HTTP pages and WebSocket messages on one port
• Config-driven — define tables, transactions, and live data services in TOML
• Transaction services — insert, update, delete, upsert across multiple tables atomically
• SubPub — in-memory cache with live push to subscribers, client-side filtering, server-side where and publish formatting
• Stream — append-only ring buffer with cursor-based reconnection
• Query — snapshot + change feed from SQLite
• Expression language — safe, extensible filter and formatter expressions (qty > 100 AND status == 'pending')
• Schema migration — automatic detection of safe/destructive changes with interactive confirmation
• Write batching — hundreds of writes committed in a single SQLite transaction for high throughput
• Reconnection recovery — ref-based delta sync across all service types, persisted across server restarts via _mkio_ref column
• Client libraries — Python and JavaScript clients with auto-reconnect and ref tracking
• Graceful shutdown — drains pending writes, checkpoints WAL, clean close
• Service monitoring — tap into any service's inbound/outbound message flow via CLI or WebSocket
• Service discovery — GET /api/services list and GET /api/services/<name> detail endpoints, mkio services CLI
• CLI tools — send transactions, subscribe to live data, monitor traffic, inspect services

Service Types

Transaction

Execute INSERT, UPDATE, DELETE, or UPSERT operations. Supports multi-table atomic transactions with named ops and cross-op bind references.

[services.orders]
type = "transaction"

[services.orders.ops]
new = [
    { table = "orders", op_type = "insert", fields = ["side", "symbol", "qty", "price"] },
    { table = "audit_log", op_type = "insert", defaults = { event = "new" }, bind = { order_id = "$0.id", status = "$0.status" } },
]
accept = [
    { table = "orders", op_type = "update", key = ["id"], fields = ["status"], defaults = { status = "accepted" } },
    { table = "audit_log", op_type = "insert", defaults = { event = "accepted" }, bind = { order_id = "$0.id", status = "$0.status" } },
]

Clients select a named set by sending "op": "new" (or "accept", etc.) in the transaction message. For a service with only one workflow, ops may instead be a plain list — clients then omit the op field.

Bind references ($N.field) pull values from a prior op's RETURNING row, where N is the zero-based index of an earlier op in the same op set. Only insert, update, and upsert ops produce RETURNING rows that can be bound against. Op-level defaults provide static values the client doesn't need to send — here, event and status are set automatically per operation.

SubPub

Subscribe to get a snapshot from an in-memory cache, then receive live updates as data changes. Supports client filters, server-side where filtering (rows that don't match are never cached or published), and publish formatting with expressions including IF(cond, then, else).

[services.last_trade]
type = "subpub"
primary_table = "orders"
key = "symbol"
where = "status == 'filled'"
change_log_size = 10000

[services.last_trade.publish]
symbol = "symbol"
price = "IF(side == 'Buy', price, -price)"

Stream

Append-only data with ring buffer and ref-based cursor reconnection.

[services.audit_feed]
type = "stream"
primary_table = "audit_log"
buffer_size = 10000

Query

Snapshot from SQLite with change feed. Supports delta reconnection.

[services.all_orders]
type = "query"
primary_table = "orders"
filterable = ["status"]

WebSocket Protocol

Connect to /ws (general) or /ws/{service_name} (per-service).

// Transaction
{"service": "add_order", "ref": "...", "data": {"id": "1", "symbol": "AAPL", "qty": 100}}

// Named op transaction
{"service": "orders", "ref": "...", "op": "new", "data": {"side": "Buy", "symbol": "AAPL", "qty": 100, "price": 150}}

// Transaction with msgid (echoed back on result/error for async correlation)
{"service": "orders", "ref": "...", "op": "new", "msgid": "req-42", "data": {"side": "Buy", "symbol": "AAPL", "qty": 100, "price": 150}}

// Subscribe
{"service": "all_orders", "type": "subscribe", "filter": "status == 'pending'"}

// Reconnect with ref (resumes from last seen position)
{"service": "audit_feed", "type": "subscribe", "ref": "20260404 15:30:45.123456000000"}

Client Libraries

Python

from mkio.client import MkioClient

async with MkioClient("ws://localhost:8080/ws") as client:
    result = await client.send("add_order", {"id": "1", "symbol": "AAPL", "qty": 100})

    async for msg in client.subscribe("all_orders", filter="status == 'pending'"):
        print(msg)
        # msg["ref"] tracks position for recovery on reconnect

JavaScript

Auto-served at /mkio.js — no CDN or bundler needed.

<script src="/mkio.js"></script>
<script>
const client = new MkioClient("ws://localhost:8080/ws");
await client.connect();

client.subscribe("all_orders", {
    filter: "status == 'pending'",
    onSnapshot: (rows) => renderTable(rows),
    onUpdate: (op, row) => updateRow(op, row),
});
</script>

Compatibility: Runs in all evergreen browsers (Chrome, Edge, Firefox, Safari) with no polyfills. Also works in Node.js ≥22, where WebSocket, TextDecoder, and performance are available as globals. On Node 18–21, assign a WebSocket polyfill to globalThis before importing:

globalThis.WebSocket = require("ws");
const { MkioClient } = require("./mkio.js");

The file uses CommonJS module.exports; load it via require(...) in Node, or <script src="/mkio.js"> in the browser.

Debugging from the browser console

Once /mkio.js is loaded, a mkio object is available in DevTools with methods that mirror the mkio CLI (the <url> argument is dropped since the page already holds the connection):

mkio.help()                                // show help
mkio.services()                            // list services this tab has talked to
mkio.services("orders")                    // detail for one service (via /api/services)
mkio.monitor()                             // log every frame to/from any service
mkio.monitor("orders")                     // filter to one service (call again to add more)
mkio.monitor("off")                        // stop
mkio.send("orders", {side:"Buy",...}, {op:"new"})
mkio.subscribe("all_orders", {filter:"status == 'pending'"})

mkio.monitor(...) only taps this tab's traffic. For traffic across all connected clients use the CLI's server-side mkio monitor instead.

Expression Language

Used for client filters, server-side where filters, and publish formatters.

Category	Syntax
Comparison	==, !=, >, <, >=, <=
Logical	AND, OR, NOT
Arithmetic	+, -, *, /
String	CONTAINS, STARTS_WITH
Null	IS NULL, IS NOT NULL
Functions	UPPER(), LOWER(), ROUND(), ABS(), COALESCE(), IF()
Membership	IN (right side is a list/tuple/set supplied by host code)
Grouping	( ... )

Data types: string (single-quoted, e.g. 'pending'), integer, float, boolean (TRUE/FALSE), and NULL.

Operator precedence (lowest to highest):

1. OR
2. AND
3. NOT
4. Comparisons: == != < > <= >=, IS NULL / IS NOT NULL, IN, CONTAINS, STARTS_WITH
5. Additive: + -
6. Multiplicative: * /
7. Unary minus: -x
8. Primary: literals, field references, function calls, parenthesized expressions

Use parentheses to override precedence, e.g. (status == 'new' OR status == 'pending') AND qty > 100.

Built-in Functions

Function	Signature	Description
UPPER	UPPER(s)	Uppercase a string. Non-string values pass through unchanged.
LOWER	LOWER(s)	Lowercase a string. Non-string values pass through unchanged.
ROUND	ROUND(x, n=0)	Round numeric x to n decimal places. n defaults to 0.
ABS	ABS(x)	Absolute value of a numeric.
COALESCE	COALESCE(a, b, ...)	Returns the first non-NULL argument, or NULL if all are NULL. Variadic (1+ args).
IF	IF(cond, then, else)	Returns then if cond is truthy, else else. Short-circuits — only the taken branch is evaluated.

Notes:

• IF is a special form, not a regular function: the non-taken branch is never evaluated, so it's safe to guard against nulls or division-by-zero, e.g. IF(qty > 0, price / qty, 0).
• UPPER / LOWER are null-safe via passthrough: UPPER(NULL) returns NULL.
• Function names are case-insensitive at parse time but conventionally written uppercase.
• Custom functions registered via register_function appear alongside these built-ins.

Worked example combining several functions:

IF(status == 'filled', UPPER(symbol), COALESCE(note, '-'))

Extend with custom functions:

from mkio import register_function

register_function("MASK_PAN", lambda s: "****" + s[-4:])

Performance

• Write batching — collects writes over a 2ms window, commits as single SQLite transaction with per-request SAVEPOINTs
• WAL mode — dual connections (write + read) for concurrent reads during writes
• Zero-copy fan-out — change events serialized once, same bytes sent to all subscribers
• Optional acceleration — pip install mkio[fast] for orjson (5-10x JSON) and uvloop (2-4x I/O)

CLI Tools

List and inspect services

mkio services http://localhost:8080                # List all services
mkio services http://localhost:8080 orders         # Show detail for one service

Detail view shows fields, types, required/optional, auto-generated columns, and example commands.

Send transactions

mkio send http://localhost:8080 orders --op new '{"side":"Buy","symbol":"AAPL","qty":100,"price":150}'
mkio send http://localhost:8080 orders --op new orders.json    # From JSON file
mkio send http://localhost:8080 orders --op new orders.csv     # From CSV file
mkio send http://localhost:8080 orders mixed.csv                 # CSV with per-row op column

Subscribe to live data

mkio subscribe http://localhost:8080 all_orders
mkio subscribe http://localhost:8080 all_orders --filter "status == 'pending'"
mkio subscribe http://localhost:8080 all_orders --ref "20260404 15:30:45.123456000000"  # Resume from ref

Monitor a service

Tap into a service's inbound and outbound message flow in real time:

mkio monitor http://localhost:8080 last_trade

[15:30:45.123] >> IN  subscribe
{ "type": "subscribe", "service": "last_trade" }

[15:30:45.125] << OUT snapshot
{ "type": "snapshot", "rows": [...] }

The monitor protocol is a native framework feature — any mkio application supports it.

Using mkio from a Claude-Based Project

mkio ships agent-facing docs inside the package for AI-assisted integration. Three files in src/mkio/agents/:

• AGENTS.md — protocol, refs, discovery, service types (always needed)
• AGENTS.python.md — Python client API + worked example
• AGENTS.js.md — JS client API + worked example

Option A: Reference in your project's CLAUDE.md

# Python-only consumer
@/path/to/mkio/src/mkio/agents/AGENTS.md
@/path/to/mkio/src/mkio/agents/AGENTS.python.md

# JS-only consumer
@/path/to/mkio/src/mkio/agents/AGENTS.md
@/path/to/mkio/src/mkio/agents/AGENTS.js.md

# Both
@/path/to/mkio/src/mkio/agents/AGENTS.md
@/path/to/mkio/src/mkio/agents/AGENTS.python.md
@/path/to/mkio/src/mkio/agents/AGENTS.js.md

To find the installed path: python -c "import mkio, os; print(os.path.join(os.path.dirname(mkio.__file__), 'agents'))"

Option B: Install the Claude Code skill

cp -r <mkio-checkout>/skills/mkio ~/.claude/skills/

The skill auto-triggers on mkio-related work and reads the agent docs from the installed package.

Runtime service discovery

A stdlib-only helper fetches service descriptors as LLM-friendly JSON:

python -m mkio.skill_helpers.discover http://localhost:8080           # list services
python -m mkio.skill_helpers.discover http://localhost:8080 orders    # full descriptor

Schema Migration

When the config schema changes between restarts, mkio detects and classifies each difference:

• Safe (new table, nullable column) — applied automatically
• Potentially destructive (type change, PK change) — requires confirmation
• Destructive (remove column/table) — requires confirmation

Set auto_migrate = true in config for non-interactive environments.

License

Apache-2.0