From b4d90b4e61160e39eaabfb8227212384a20f000e Mon Sep 17 00:00:00 2001
From: Matthew Larson <matthewjlar@gmail.com>
Date: Mon, 17 Aug 2026 11:48:59 -0500
Subject: [PATCH] Don't corrupt response stream on GET_Value errors

GET_Value calls resp.prepare() before fetching any data, so a 200 and the
transfer-encoding headers are already on the wire by the time
getSelectionData() runs. So even if the outer handler ends up with e.g.
an internal server error, that status line just gets written into the body.

This can result in odd errors like:
    `InvalidChunkLength(got length b'HTTP/1.1 500 Internal Server Error\r\n')`
which hides the underlying problem.

The paginated path in the same handler, and POST_Value, already work around this.
We just need to do the same thing in GET_Value.

Both handlers also reported the traceback via print(), so it went to stdout
instead of the log file.
---
 hsds/chunk_sn.py | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/hsds/chunk_sn.py b/hsds/chunk_sn.py
index ee77b1a2..ea9028a9 100755
--- a/hsds/chunk_sn.py
+++ b/hsds/chunk_sn.py
@@ -16,6 +16,7 @@
 
 import base64
 import math
+import traceback
 import numpy as np
 
 from json import JSONDecodeError
@@ -1071,6 +1072,7 @@ async def GET_Value(request):
 
     resp_json = {"status": 200}  # will over-write if there's a problem
     # write response
+    resp = None
     try:
         resp = StreamResponse()
         if config.get("http_compression"):
@@ -1224,11 +1226,13 @@ async def GET_Value(request):
         await resp.write_eof()
     except Exception as e:
         log.error(f"{type(e)} Exception during data write: {e}")
-        import traceback
-
-        tb = traceback.format_exc()
-        print("traceback:", tb)
-        raise HTTPInternalServerError()
+        log.error(f"traceback: {traceback.format_exc()}")
+        if resp is not None and resp.prepared:
+            # headers are already on the wire - raising here would inject a new
+            # status line into the body and corrupt the chunked stream
+            await resp.write_eof()
+        else:
+            raise HTTPInternalServerError()
 
     return resp
 
@@ -1473,11 +1477,8 @@ async def POST_Value(request):
             resp_body = resp_body.encode("utf-8")
             await resp.write(resp_body)
     except Exception as e:
-        log.error(f"{type(e)} Exception during response write")
-        import traceback
-
-        tb = traceback.format_exc()
-        print("traceback:", tb)
+        log.error(f"{type(e)} Exception during response write: {e}")
+        log.error(f"traceback: {traceback.format_exc()}")
 
     # finalize response
     await resp.write_eof()