feat: v0.12.0 — live device cache (_LiveCache) in sfm/server.py

Ports the intelligent-caching branch concept to a plain Python in-memory
implementation — no SQLAlchemy, no extra DB table, no new dependencies.

_LiveCache (threading.Lock + dicts) caches:
  - device info: indefinite, invalidated by POST /device/config
  - events: keyed by (conn_key, device_event_count); count-probe fast path
    (~2s poll+count_events) avoids full downloads when nothing is new
  - monitor status: 30-second TTL, invalidated by monitor start/stop
  - waveforms: permanent per (conn_key, event_index)

All four cached endpoints accept ?force=true to bypass the cache.
Removes sfm/cache.py (SQLAlchemy experiment, now superseded).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,41 @@ All notable changes to seismo-relay are documented here.
 
 ---
 
+## v0.12.0 — 2026-04-13
+
+### Added
+
+- **`sfm/server.py` — `_LiveCache`** — in-memory live device cache, eliminating
+  redundant TCP round-trips between requests.  No extra dependencies (plain Python
+  dict + threading.Lock).  Replaces the SQLAlchemy-based `sfm/cache.py` experiment
+  from the `feature/intelligent-caching` branch.
+
+  Cache behaviour by endpoint:
+
+  | Endpoint | Cache strategy |
+  |---|---|
+  | `GET /device/info` | Indefinite; invalidated by `POST /device/config` |
+  | `GET /device/events` | Count-probe fast path: quick `poll()+count_events()` (~2s); return cache if count matches; full download only when new events detected |
+  | `GET /device/monitor/status` | 30-second TTL; invalidated by monitor start/stop |
+  | `GET /device/event/{idx}/waveform` | Permanent per-index (waveforms are immutable) |
+
+- **`?force=true` param** on all four cached endpoints — bypasses cache and re-reads
+  from device.
+
+- **`POST /device/config` cache invalidation** — marks device info + events dirty so
+  the next read reflects the new compliance config.
+
+- **`POST /device/monitor/start` / `stop` cache invalidation** — evicts the monitor
+  status cache entry immediately so the next poll returns the updated state.
+
+### Removed
+
+- `sfm/cache.py` — SQLAlchemy-based cache from the experimental caching branch.
+  Its logic has been ported to the sqlite3-native `_LiveCache` class above.
+  `sqlalchemy` is no longer a dependency.
+
+---
+
 ## v0.11.0 — 2026-04-13
 
 ### Added

CLAUDE.md

@@ -2,7 +2,7 @@
 
 Ground-up Python replacement for **Blastware**, Instantel's Windows-only software for
 managing MiniMate Plus seismographs. Connects over direct RS-232 or cellular modem
-(Sierra Wireless RV50 / RV55). Current version: **v0.10.0**.
+(Sierra Wireless RV50 / RV55). Current version: **v0.12.0**.
 
 ---
 

sfm/server.py

@@ -37,6 +37,8 @@ from __future__ import annotations
 import datetime
 import logging
 import sys
+import threading
+import time
 from pathlib import Path
 from typing import Optional
 
@@ -105,6 +107,136 @@ def _get_db() -> SeismoDb:
     return _db
 
 
+# ── Live device cache ─────────────────────────────────────────────────────────
+# In-memory cache for live device data.  Avoids re-dialing the device on every
+# request when the data hasn't changed.
+#
+# Keyed by conn_key ("tcp:host:port" or "serial:port:baud").
+# Does NOT persist across server restarts — this is purely an in-process cache
+# to reduce TCP round-trips and cellular data usage.
+#
+# Invalidation rules:
+#   device_info  — cached until POST /device/config marks it dirty
+#   events       — cached by (conn_key, device_event_count); re-fetched when
+#                  a quick count_events() probe shows new events on the device
+#   monitor_status — 30-second TTL (changes frequently during monitoring)
+#   waveforms    — permanent (immutable once recorded; indexed by conn_key+idx)
+#
+# All endpoints accept ?force=true to bypass the cache and re-read from device.
+
+_MONITOR_STATUS_TTL = 30.0  # seconds
+
+
+class _LiveCache:
+    """
+    Thread-safe in-memory cache for live SFM device data.
+    One singleton per server process.
+    """
+
+    def __init__(self) -> None:
+        self._lock = threading.Lock()
+        # conn_key → serialised device info dict
+        self._device_info:     dict[str, dict]               = {}
+        # conn_key → (device_event_count_when_cached, [event dicts])
+        self._events:          dict[str, tuple[int, list]]   = {}
+        # conn_key → (fetched_at_unix, status_dict)
+        self._monitor_status:  dict[str, tuple[float, dict]] = {}
+        # conn_key → bool  (True = re-read device on next /device/info)
+        self._config_dirty:    dict[str, bool]               = {}
+        # (conn_key, event_index) → waveform dict (permanent)
+        self._waveforms:       dict[tuple, dict]             = {}
+
+    # ── Connection key ────────────────────────────────────────────────────────
+
+    @staticmethod
+    def make_conn_key(
+        host: Optional[str],
+        tcp_port: int,
+        port: Optional[str],
+        baud: int,
+    ) -> str:
+        if host:
+            return f"tcp:{host}:{tcp_port}"
+        return f"serial:{port}:{baud}"
+
+    # ── Device info ───────────────────────────────────────────────────────────
+
+    def get_device_info(self, conn_key: str) -> Optional[dict]:
+        with self._lock:
+            if self._config_dirty.get(conn_key):
+                return None
+            return self._device_info.get(conn_key)
+
+    def set_device_info(self, conn_key: str, info: dict) -> None:
+        with self._lock:
+            self._device_info[conn_key] = info
+            self._config_dirty[conn_key] = False
+
+    # ── Events ────────────────────────────────────────────────────────────────
+
+    def get_events(self, conn_key: str, device_count: int) -> Optional[list]:
+        """
+        Return cached events if the device's current event count matches what
+        we had when we last fetched.  Returns None (cache miss) otherwise.
+        """
+        with self._lock:
+            if self._config_dirty.get(conn_key):
+                return None
+            entry = self._events.get(conn_key)
+            if entry is None:
+                return None
+            cached_count, events = entry
+            return events if cached_count == device_count else None
+
+    def set_events(self, conn_key: str, device_count: int, events: list) -> None:
+        with self._lock:
+            self._events[conn_key] = (device_count, events)
+
+    # ── Monitor status ────────────────────────────────────────────────────────
+
+    def get_monitor_status(self, conn_key: str) -> Optional[dict]:
+        with self._lock:
+            entry = self._monitor_status.get(conn_key)
+            if entry is None:
+                return None
+            fetched_at, status = entry
+            if time.time() - fetched_at > _MONITOR_STATUS_TTL:
+                return None
+            return status
+
+    def set_monitor_status(self, conn_key: str, status: dict) -> None:
+        with self._lock:
+            self._monitor_status[conn_key] = (time.time(), status)
+
+    def invalidate_monitor_status(self, conn_key: str) -> None:
+        with self._lock:
+            self._monitor_status.pop(conn_key, None)
+
+    # ── Config dirty flag ─────────────────────────────────────────────────────
+
+    def mark_config_dirty(self, conn_key: str) -> None:
+        """
+        Called after a successful POST /device/config write.
+        Forces next /device/info and /device/events to re-read from the device.
+        """
+        with self._lock:
+            self._config_dirty[conn_key] = True
+            self._events.pop(conn_key, None)
+
+    # ── Waveforms (permanent cache) ───────────────────────────────────────────
+
+    def get_waveform(self, conn_key: str, index: int) -> Optional[dict]:
+        with self._lock:
+            return self._waveforms.get((conn_key, index))
+
+    def set_waveform(self, conn_key: str, index: int, waveform: dict) -> None:
+        with self._lock:
+            self._waveforms[(conn_key, index)] = waveform
+
+
+_live_cache = _LiveCache()
+
+
 # ── Serialisers ────────────────────────────────────────────────────────────────
 # Plain dict helpers — avoids a Pydantic dependency in the library layer.
 
@@ -272,10 +404,11 @@ def webapp():
 
 @app.get("/device/info")
 def device_info(
-    port:     Optional[str] = Query(None,          description="Serial port (e.g. COM5, /dev/ttyUSB0)"),
+    port:     Optional[str] = Query(None,             description="Serial port (e.g. COM5, /dev/ttyUSB0)"),
-    baud:     int           = Query(38400,          description="Serial baud rate (default 38400)"),
+    baud:     int           = Query(38400,             description="Serial baud rate (default 38400)"),
-    host:     Optional[str] = Query(None,          description="TCP host — modem IP or ACH relay (e.g. 203.0.113.5)"),
+    host:     Optional[str] = Query(None,             description="TCP host — modem IP or ACH relay (e.g. 203.0.113.5)"),
     tcp_port: int           = Query(DEFAULT_TCP_PORT, description=f"TCP port (default {DEFAULT_TCP_PORT})"),
+    force:    bool          = Query(False,             description="Bypass cache and re-read from device"),
 ) -> dict:
     """
     Connect to the device, perform the POLL startup handshake, and return
@@ -283,8 +416,18 @@ def device_info(
 
     Supply either *port* (serial) or *host* (TCP/modem).
     Equivalent to POST /device/connect — provided as GET for convenience.
+
+    Response is cached until a POST /device/config write invalidates it.
+    Pass ?force=true to bypass the cache.
     """
-    log.info("GET /device/info  port=%s host=%s tcp_port=%d", port, host, tcp_port)
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
+    log.info("GET /device/info  port=%s host=%s tcp_port=%d force=%s", port, host, tcp_port, force)
+
+    if not force:
+        cached = _live_cache.get_device_info(conn_key)
+        if cached is not None:
+            log.debug("device_info cache hit for %s", conn_key)
+            return cached
 
     try:
         def _do():
@@ -304,7 +447,9 @@ def device_info(
     except Exception as exc:
         raise HTTPException(status_code=500, detail=f"Device error: {exc}") from exc
 
-    return _serialise_device_info(info)
+    result = _serialise_device_info(info)
+    _live_cache.set_device_info(conn_key, result)
+    return result
 
 
 @app.post("/device/connect")
@@ -323,11 +468,12 @@ def device_connect(
 
 @app.get("/device/events")
 def device_events(
-    port:     Optional[str] = Query(None,          description="Serial port (e.g. COM5)"),
+    port:     Optional[str] = Query(None,             description="Serial port (e.g. COM5)"),
-    baud:     int           = Query(38400,          description="Serial baud rate"),
+    baud:     int           = Query(38400,             description="Serial baud rate"),
-    host:     Optional[str] = Query(None,          description="TCP host — modem IP or ACH relay"),
+    host:     Optional[str] = Query(None,             description="TCP host — modem IP or ACH relay"),
     tcp_port: int           = Query(DEFAULT_TCP_PORT, description=f"TCP port (default {DEFAULT_TCP_PORT})"),
-    debug:    bool          = Query(False,          description="Include raw record hex for field-layout inspection"),
+    debug:    bool          = Query(False,             description="Include raw record hex for field-layout inspection"),
+    force:    bool          = Query(False,             description="Bypass cache and re-download from device"),
 ) -> dict:
     """
     Connect to the device, read the event index, and download all stored
@@ -335,14 +481,48 @@ def device_events(
 
     Supply either *port* (serial) or *host* (TCP/modem).
 
+    **Caching:** a quick count_events() probe (~2s) is performed first.  If the
+    device's event count matches the cached count, the cached response is returned
+    immediately without a full download.  Pass ?force=true to skip this and always
+    re-download.
+
     Pass debug=true to include raw_record_hex in each event — useful for
     verifying field offsets against the protocol reference.
 
     This does NOT download raw ADC waveform samples — those are large and
-    fetched separately via GET /device/event/{idx}/waveform (future endpoint).
+    fetched separately via GET /device/event/{idx}/waveform.
     """
-    log.info("GET /device/events  port=%s host=%s debug=%s", port, host, debug)
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
+    log.info("GET /device/events  port=%s host=%s debug=%s force=%s", port, host, debug, force)
 
+    # ── Cache fast path ───────────────────────────────────────────────────────
+    # Do a quick poll + count_events() probe (~2s over cellular) to check if the
+    # device has any new events.  If the count matches the cache, return early.
+    if not force and not debug:
+        try:
+            def _count():
+                with _build_client(port, baud, host, tcp_port) as client:
+                    try:
+                        client.poll()
+                    except Exception:
+                        client.poll()
+                    return client.count_events()
+            device_count = _run_with_retry(_count, is_tcp=_is_tcp(host))
+            cached_events = _live_cache.get_events(conn_key, device_count)
+            if cached_events is not None:
+                log.info("  events cache hit (%d events, count=%d)", len(cached_events), device_count)
+                # Also serve cached device info if available
+                cached_info = _live_cache.get_device_info(conn_key)
+                return {
+                    "device":      cached_info or {},
+                    "event_count": len(cached_events),
+                    "events":      cached_events,
+                    "cached":      True,
+                }
+        except Exception as exc:
+            log.warning("  count probe failed (%s) — falling through to full download", exc)
+
+    # ── Full download ─────────────────────────────────────────────────────────
     try:
         def _do():
             with _build_client(port, baud, host, tcp_port) as client:
@@ -358,15 +538,12 @@ def device_events(
         raise HTTPException(status_code=500, detail=f"Device error: {exc}") from exc
 
     # Fill sample_rate from compliance config where the event record doesn't supply it.
-    # sample_rate is a device-level setting, not stored per-event in the waveform record.
     if info.compliance_config and info.compliance_config.sample_rate:
         for ev in events:
             if ev.sample_rate is None:
                 ev.sample_rate = info.compliance_config.sample_rate
 
     # Backfill event.project_info fields that the 210-byte waveform record doesn't carry.
-    # The waveform record only stores "Project:" — client/operator/sensor_location/notes
-    # live in the SUB 1A compliance config, not in the per-event record.
     if info.compliance_config:
         cc = info.compliance_config
         for ev in events:
@@ -378,10 +555,19 @@ def device_events(
             if pi.sensor_location is None: pi.sensor_location = cc.sensor_location
             if pi.notes           is None: pi.notes           = cc.notes
 
+    serialised_info   = _serialise_device_info(info)
+    serialised_events = [_serialise_event(ev, debug=debug) for ev in events]
+
+    # Update cache (skip if debug=True — raw hex blobs shouldn't pollute the cache)
+    if not debug:
+        _live_cache.set_device_info(conn_key, serialised_info)
+        _live_cache.set_events(conn_key, len(events), serialised_events)
+
     return {
-        "device":      _serialise_device_info(info),
+        "device":      serialised_info,
         "event_count": len(events),
-        "events":      [_serialise_event(ev, debug=debug) for ev in events],
+        "events":      serialised_events,
+        "cached":      False,
     }
 
 
@@ -429,10 +615,11 @@ def device_event(
 @app.get("/device/event/{index}/waveform")
 def device_event_waveform(
     index:    int,
-    port:     Optional[str] = Query(None,          description="Serial port (e.g. COM5)"),
+    port:     Optional[str] = Query(None,             description="Serial port (e.g. COM5)"),
-    baud:     int           = Query(38400,          description="Serial baud rate"),
+    baud:     int           = Query(38400,             description="Serial baud rate"),
-    host:     Optional[str] = Query(None,          description="TCP host — modem IP or ACH relay"),
+    host:     Optional[str] = Query(None,             description="TCP host — modem IP or ACH relay"),
     tcp_port: int           = Query(DEFAULT_TCP_PORT, description=f"TCP port (default {DEFAULT_TCP_PORT})"),
+    force:    bool          = Query(False,             description="Bypass cache and re-download waveform"),
 ) -> dict:
     """
     Download the full raw ADC waveform for a single event (0-based index).
@@ -451,8 +638,18 @@ def device_event_waveform(
     - **sample_rate**: samples per second (from compliance config)
     - **channels**: dict of channel name → list of signed int16 ADC counts
       (keys: "Tran", "Vert", "Long", "Mic")
+
+    Waveforms are immutable once recorded and are cached permanently per
+    (connection, event index).  Pass ?force=true to re-download.
     """
-    log.info("GET /device/event/%d/waveform  port=%s host=%s", index, port, host)
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
+    log.info("GET /device/event/%d/waveform  port=%s host=%s force=%s", index, port, host, force)
+
+    if not force:
+        cached_waveform = _live_cache.get_waveform(conn_key, index)
+        if cached_waveform is not None:
+            log.debug("waveform cache hit: %s event %d", conn_key, index)
+            return cached_waveform
 
     try:
         def _do():
@@ -486,7 +683,7 @@ def device_event_waveform(
     if sample_rate is None and info.compliance_config:
         sample_rate = info.compliance_config.sample_rate
 
-    return {
+    result = {
         "index":           ev.index,
         "record_type":     ev.record_type,
         "timestamp":       _serialise_timestamp(ev.timestamp),
@@ -498,6 +695,8 @@ def device_event_waveform(
         "peak_values":     _serialise_peak_values(ev.peak_values),
         "channels":        raw,
     }
+    _live_cache.set_waveform(conn_key, index, result)
+    return result
 
 
 # ── Write endpoints ───────────────────────────────────────────────────────────
@@ -582,6 +781,7 @@ def device_config(
         422 if neither port nor host is provided.
     """
     changed = body.model_dump(exclude_none=True)
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
     log.info("POST /device/config  port=%s host=%s  fields=%s", port, host, list(changed.keys()))
 
     try:
@@ -612,6 +812,10 @@ def device_config(
     except Exception as exc:
         raise HTTPException(status_code=500, detail=f"Device error: {exc}") from exc
 
+    # Config was written — invalidate cached device info and events so the next
+    # /device/info or /device/events call re-reads fresh data from the device.
+    _live_cache.mark_config_dirty(conn_key)
+
     return {
         "status": "ok",
         "updated_fields": changed,
@@ -639,6 +843,7 @@ def device_monitor_status(
     baud:     int           = Query(38400,             description="Serial baud rate"),
     host:     Optional[str] = Query(None,             description="TCP host — modem IP or ACH relay"),
     tcp_port: int           = Query(DEFAULT_TCP_PORT, description=f"TCP port (default {DEFAULT_TCP_PORT})"),
+    force:    bool          = Query(False,             description="Bypass cache and re-read from device"),
 ) -> dict:
     """
     Read monitoring status from the device.
@@ -650,7 +855,17 @@ def device_monitor_status(
 
     Returns is_monitoring bool, battery voltage, and memory usage (total + free
     bytes).  Battery and memory are only present when the unit is idle.
+
+    **Caching:** response is cached for 30 seconds.  Pass ?force=true to bypass.
     """
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
+
+    if not force:
+        cached = _live_cache.get_monitor_status(conn_key)
+        if cached is not None:
+            log.debug("monitor_status cache hit for %s", conn_key)
+            return cached
+
     with _build_client(port=port, baud=baud, host=host, tcp_port=tcp_port) as client:
         try:
             client.poll()
@@ -668,6 +883,8 @@ def device_monitor_status(
     if status.memory_free is not None:
         result["memory_free_bytes"] = status.memory_free
         result["memory_free_kb"]    = round(status.memory_free / 1024, 1)
+
+    _live_cache.set_monitor_status(conn_key, result)
     return result
 
 
@@ -683,6 +900,7 @@ def device_monitor_start(
 
     Sends SUB 0x96 and waits for ack SUB 0x69.
     """
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
     with _build_client(port=port, baud=baud, host=host, tcp_port=tcp_port) as client:
         try:
             client.poll()
@@ -690,6 +908,7 @@ def device_monitor_start(
             log.warning("start monitoring poll retry: %s", exc)
             client.poll()
         client.start_monitoring()
+    _live_cache.invalidate_monitor_status(conn_key)
     return {"status": "started"}
 
 
@@ -705,6 +924,7 @@ def device_monitor_stop(
 
     Sends SUB 0x97 and waits for ack SUB 0x68.
     """
+    conn_key = _live_cache.make_conn_key(host, tcp_port, port, baud)
     with _build_client(port=port, baud=baud, host=host, tcp_port=tcp_port) as client:
         try:
             client.poll()
@@ -712,6 +932,7 @@ def device_monitor_stop(
             log.warning("stop monitoring poll retry: %s", exc)
             client.poll()
         client.stop_monitoring()
+    _live_cache.invalidate_monitor_status(conn_key)
     return {"status": "stopped"}