big refactor of waveform protocol.

sfm/server.py

@@ -37,6 +37,7 @@ from __future__ import annotations
 import datetime
 import logging
 import sys
+import tempfile
 import threading
 import time
 from pathlib import Path
@@ -863,8 +864,8 @@ def device_event_blastware_file(
 
     Supply either *port* (serial) or *host* (TCP/modem).
 
-    The file is written to /tmp and streamed back as a binary download.
-    Blastware can open it directly — filename encodes serial + timestamp.
+    The file is written to the OS temp directory and streamed back as a binary
+    download.  Blastware can open it directly — filename encodes serial + timestamp.
 
     Filename format: <prefix><serial3><stem><AB>0<W|H>
       - prefix letter = chr(ord('B') + floor(serial_numeric / 1000))
@@ -885,26 +886,13 @@ def device_event_blastware_file(
         def _do():
             with _build_client(port, baud, host, tcp_port, timeout=120.0) as client:
                 info = client.connect()
-                # Use stop_after_metadata=True (full_waveform=False) with 1 extra
-                # chunk after "Project:".  The extra chunk is required to prime the
-                # device over TCP: termination at term_counter=metadata_counter+0x0400
-                # returns only ~90 bytes (no useful footer) over TCP/cellular, but
-                # termination at metadata_counter+0x0800 (one chunk later) returns
-                # the full 737-byte frame containing the footer.
-                #
-                # Confirmed from 4-26-26 BW RS-232 capture: BW terminates at 0x1800
-                # without an extra chunk (works on RS-232 but not TCP).
-                # write_blastware_file() automatically skips the extra chunk's
-                # contribution — only the probe+ADC+metadata+terminator bytes appear
-                # in the output file.
-                #
-                # full_waveform=True (natural end-of-stream) downloads ALL chunks
-                # including post-event silence (35+ chunks for a 9-sec event at
-                # 1024 sps) — this produces 24KB+ files that Blastware rejects.
+                # Under v0.14.0 BW-exact 5A walk, the chunk loop is bounded by
+                # the event end_offset extracted from STRT.  No more
+                # stop_after_metadata / extra_chunks gymnastics — these
+                # kwargs are now no-ops.
                 events = client.get_events(
                     full_waveform=False,
                     stop_after_index=index,
-                    extra_chunks_after_metadata=1,
                 )
                 matching = [ev for ev in events if ev.index == index]
                 return matching[0] if matching else None, info
@@ -940,8 +928,18 @@ def device_event_blastware_file(
     # Build filename using the same algorithm Blastware uses
     filename = blastware_filename(ev, serial)
 
-    # Write to /tmp so FastAPI can stream it back
-    out_path = Path("/tmp") / filename
+    # Write to OS temp dir (cross-platform: /tmp on Linux/macOS,
+    # %TEMP% on Windows) so FastAPI can stream it back via FileResponse.
+    out_path = Path(tempfile.gettempdir()) / filename
+    # Delete any stale file at this path before writing.  On Windows we have
+    # observed the new (smaller) file getting trailing zero-bytes from the
+    # previous (larger) file when filesystem semantics around open(...,"wb")
+    # don't truncate cleanly (e.g. through a synced folder).  Explicit unlink
+    # eliminates that ambiguity.
+    try:
+        out_path.unlink()
+    except FileNotFoundError:
+        pass
     write_blastware_file(ev, a5_frames, out_path)
     log.info(
         "blastware_file: wrote %s (%d A5 frames, serial=%s)",