3tears-nats
Typed NATS client wrapper, subject builders, and JetStream KV bucket primitives for 3tears applications.
What this package provides
NatsClient-- single canonical wrapper aroundnats-py. Handles connect (with bounded startup-timeout + bounded runtime reconnect ceiling), graceful shutdown/drain, typed publish, kw-only subscribe with optional Pydantic validation, request/reply withtimedeltatimeouts, and JetStream KV bucket access.Subject+Subjects-- opaque subject dataclass and factory of every canonical subject family used by 3tears applications. Replaces ad-hocf"{namespace}.tools.call"string-concatenation across the platform.NatsKvBucket-- operations against one JetStream KV bucket (get/put/delete/create/update/get_entry). Bucket name auto-prefixed by the connected client'snats_subject_namespace.nats_distributed_lock-- TTL-based distributed lock primitive built onNatsKvBucket.create(put-if-absent). Atomic acquisition + background heartbeat + automatic cleanup; on holder death the TTL expires the key.forward/serve_owner-- payload-agnostic owner-routed request/reply: send a request to whichever pod currently serves a key and get its reply back. A separate election mechanism decides who owns the key; this only carries the message.attach_pipe/serve_pipe/open_pipe-- a payload-agnostic byte pipe to whichever pod owns a key, for reaching a process that has no inbound network path. Rendezvous ridesforward; the stream then moves to its own subjects with a sequenced framing (a lost frame raises rather than being skipped) and a credit window that stops the producer reading its source when the consumer falls behind.StreamTransport-- narrow Protocol used by streaming consumers; lets test fakes substitute for the live client.- Errors --
NatsClientError,SubscribeError,PublishError,RequestError,KvError.
Why a separate package
The wrapper is consumed by the platform services (broker, gateway, registry, channel adapters, agent SDK) and any 3tears-based application. Keeping it in 3tears-nats avoids forcing those apps to depend on a host application repo just for a NATS primitive.
Mistake-proofed API
- Subscribe is keyword-only after
self. A common production bug (nc.subscribe(subject, callback)silently treating the callback as a queue group innats-py2.10+) is impossible to reproduce against this wrapper. - Publish accepts
BaseModelinstances. Raw bytes go through the explicit escape hatchpublish_raw. - Subjects are typed
Subjectobjects, not strings. The factory owns subject formatting; callers cannot accidentally interpolate the wrong shape. - Default
deadletter_on_failure=True. Uncaught subscribe-callback exceptions auto-republish to{ns}.deadletter.{path}.
Usage
from datetime import timedelta
from threetears.nats import NatsClient, Subjects
nc = await NatsClient.connect(
nats_url="nats://localhost:4222",
nats_subject_namespace="myapp",
client_name="my-service",
)
# Typed publish
await nc.publish(
subject=Subjects.audit_event("workspace.doc_set"),
message=AuditEvent(...),
)
# Typed request/reply
response = await nc.request(
subject=Subjects.tools_call(),
message=ToolCallRequest(...),
response_type=ToolCallResponse,
timeout=timedelta(seconds=5),
)
# Subscribe with Pydantic validation
sub = await nc.subscribe_typed(
subject=Subjects.audit_wildcard(),
cb=on_audit_event,
message_type=AuditEvent,
queue="audit-consumer",
)
# JetStream KV
bucket = await nc.kv_bucket(name="agent_config", ttl=timedelta(hours=2))
await bucket.put(key="agent-1", value=b"config-payload")
await nc.shutdown()
Distributed locks
nats_distributed_lock is a TTL-backed lock for "only one pod should run this body" patterns (scheduled jobs, periodic ticks, exclusive resource access). It is layered on top of NatsKvBucket.create (atomic put-if-absent), with a background heartbeat that refreshes the entry while the body runs and a TTL that bounds the orphan-lock window after a pod death.
from datetime import timedelta
from threetears.nats import LockHeld, nats_distributed_lock
try:
async with nats_distributed_lock(
nc,
"backup-job",
bucket_name="scheduler-locks", # default; override per consumer
ttl=timedelta(seconds=60), # KV entry TTL
heartbeat=timedelta(seconds=20), # heartbeat MUST be < ttl
):
await run_backup()
except LockHeld:
# another pod owns the lock; skip this run cleanly
return
client=None is a graceful no-op that yields immediately. Single-pod dev environments without NATS work unchanged. LockHeld is distinct from KvError (transport / bucket failures); callers should treat the former as the expected "another pod is running" branch and surface the latter separately.
Enforcement
Direct from nats import / from nats.aio imports are flagged by the per-repo enforcement walker tests/enforcement/test_nats_wrapper_usage.py. Strict mode by default; exemptions require a # rationale: ... line.
1 maintainer
Release files for 3tears-nats 0.51.0
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