User Guide¶

Overview¶

chumicro-sockets provides a single TCP + TLS client API that works the same way on CircuitPython, MicroPython, and CPython. The runtimes diverge in ways the library can't paper over — CircuitPython has no socket module, only socketpool(radio); MicroPython has stdlib socket + mbedTLS-backed ssl on current builds; CPython has the full stdlib stack — so the library exposes one duck-typed TCP socket surface (send / recv_into / close / setblocking) and routes connector to a runtime-appropriate adapter. There is one connect state machine per runtime: connector() returns a tick-driven object a runner drives (or a one-shot script drives inline).

chumicro-mqtt, chumicro-requests, chumicro-http-server, and chumicro-websockets all build on this library; none of them import socketpool, socket, or ssl directly.

Getting started¶

Plain TCP¶

from chumicro_sockets import connector

# CircuitPython requires `radio=wifi.radio`; MP / CPython ignore it.
dial = connector("broker.example.com", 1883, radio=None)
while dial.state not in ("ready", "failed"):   # one-shot form; a runner
    dial.tick(0)                               # drives this for you
if dial.state == "failed":
    raise dial.last_error
sock = dial.socket
try:
    sock.send(b"PING\r\n")
    buffer = bytearray(128)
    nbytes = sock.recv_into(buffer, 128)
    print(bytes(buffer[:nbytes]))
finally:
    sock.close()

TLS — default-secure on every runtime¶

from chumicro_sockets import connector

dial = connector("api.example.com", 443, tls=True, radio=None)
# ... drive to `ready` as above, then:
dial.socket.send(b"GET / HTTP/1.0\r\n\r\n")

context=None verifies the cert chain on every runtime. Each runtime gets its trust roots from the right place:

For explicit no-verification (dev against self-signed brokers, captive-portal probes), pass context=ssl_context_no_verify() — the opt-out is named so a code reviewer can grep for it.

TLS with a custom CA¶

from chumicro_sockets import connector, ssl_context_with_ca

with open("ca.pem", "rb") as ca_file:
    ca_pem = ca_file.read()

context = ssl_context_with_ca(ca_pem)
dial = connector("api.example.com", 443, tls=True, context=context, radio=None)

ssl_context_with_ca works on every supported runtime — chumicro's minimum supported board class (256 KB MCU RAM / 2 MB physical / ~800 KB usable flash; Pi Pico W, ESP32-S2, ESP32-S3, ESP32-S3 Feather, plus any current-LTS MP/CPython host) all ships the on-board ssl module on current firmware, so the call shape is uniform. Older legacy radios that lack the ssl module (AirLift, WIZNET5K-pre-mbedTLS) aren't in scope for this library; users on those boards should pin to the existing adafruit_connection_manager ecosystem instead.

Runner pattern¶

chumicro-sockets is a passive transport — it doesn't drive its own lifecycle. Use it through chumicro-runner, which handles select.poll registration, readiness dispatch, and tick budgeting. The downstream library that owns the connection (e.g. chumicro-mqtt, chumicro-requests) exposes the runner-service contract — io_socket, io_interest(now_ms), next_deadline(now_ms) — and Runner reads those each tick to decide which sockets to register with poll. User code calls runner.add(client) and never touches poll directly.

Without a Runner, drive the same machine yourself: call connector.tick(now_ms) from your own loop and read connector.socket once connector.state == "ready", then call the connected socket's recv_into / send as usual. OSError(errno.EAGAIN) is the cross-runtime "would block" signal — re-loop, don't re-raise.

The socket read/write waits a generator yields (ReadWait / WriteWait from chumicro_sockets.waits) sit alongside the timer and completion waits in one place: the timing guide's Choosing a wait table maps each question to its primitive.

Memory notes¶

The socket itself doesn't allocate — the protocol surface is recv_into(buffer, nbytes) and send(bytes_or_memoryview) so callers control buffer lifetimes. Pre-allocate one bytearray per connection and reuse it:

RX_BUFFER = bytearray(256)

def read(sock):
    nbytes = sock.recv_into(RX_BUFFER, 256)
    return memoryview(RX_BUFFER)[:nbytes]

FakeSocket does keep an internal bytearray(sent) log — useful for tests, but don't hold the fake across long-running scenarios; replace it for each test.

Platform notes¶

CircuitPython requires a radio= kwarg pointing at the board's wifi radio (typically wifi.radio). MicroPython and CPython ignore the kwarg.

The TLS surface is uniform across runtimes because every supported board (256 KB MCU RAM / 2 MB physical / ~800 KB usable flash, current-LTS firmware — Pi Pico W, ESP32-S2, ESP32-S3, ESP32-S3 Feather native wifi) ships the on-board ssl module. Legacy radios without ssl (AirLift, WIZNET5K-pre-mbedTLS) aren't supported by this library.

Runtime + chip quirks¶

Live-AP acceptance runs against the supported boards surfaced four limitations that aren't bugs in this library — they constrain how you build certs and shape your TLS handshakes:

Tested on real CircuitPython and MicroPython boards for both plain TCP and TLS before each release.

Examples¶