From 73c1a9c7da22e4e093bd5ee28c7a432984134f4c Mon Sep 17 00:00:00 2001
From: Shubham Padkonde <shubhampadkonde12@gmail.com>
Date: Thu, 24 Sep 2026 04:22:41 +0000
Subject: [PATCH] Fix q=0 crash and ordering in get_choice_from_headers

- A header entry with q=0 (e.g. "Accept-Language: fr;q=0, en") raised
  ZeroDivisionError from 1 / q_value. q=0 means "not acceptable", so
  such entries are now skipped; if nothing acceptable remains, None is
  returned as for a missing header.
- With all=True the choices were returned in heap order rather than
  sorted order, e.g. "a;q=0.1,b;q=0.2,c;q=0.3,d;q=0.4,e;q=0.9" gave
  ['e', 'd', 'b', 'a', 'c']. Choices are now sorted by descending q,
  keeping header order for ties.
- An unparsable q value such as "q=1.2.3" is skipped instead of raising.
---
 pygeoapi/util.py         | 19 ++++++++++++-------
 tests/other/test_util.py | 16 ++++++++++++++++
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/pygeoapi/util.py b/pygeoapi/util.py
index b60e187a08..f0962929ba 100644
--- a/pygeoapi/util.py
+++ b/pygeoapi/util.py
@@ -35,7 +35,6 @@
 from datetime import date, datetime, time, timezone
 from decimal import Decimal
 from enum import Enum
-from heapq import heappush
 import ipaddress
 import json
 import logging
@@ -743,14 +742,20 @@ def get_choice_from_headers(headers: dict,
         match = re.match(r'^([^;]+)(?:;q=([\d.]+))?$', part.strip())
         if match:
             value, q_value = match.groups()
-            q_value = float(q_value) if q_value else 1.0
+            try:
+                q_value = float(q_value) if q_value else 1.0
+            except ValueError:
+                continue
 
-            # Sort choices by q value and index
-            if 0 <= q_value <= 1:
-                heappush(choices, (1 / q_value, i, value))
+            # q=0 means "not acceptable" (RFC 9110, section 12.4.2)
+            if 0 < q_value <= 1:
+                choices.append((-q_value, i, value))
 
-    # Drop q value
-    sorted_choices = [choice[-1] for choice in choices]
+    if not choices:
+        return
+
+    # Highest q value first; ties keep header order
+    sorted_choices = [choice[-1] for choice in sorted(choices)]
 
     # Return one or all choices
     return sorted_choices if all else sorted_choices[0]
diff --git a/tests/other/test_util.py b/tests/other/test_util.py
index 7cb321019d..5ede22b81b 100644
--- a/tests/other/test_util.py
+++ b/tests/other/test_util.py
@@ -330,6 +330,22 @@ def test_get_choice_from_headers():
     assert util.get_choice_from_headers(
         {'accept-language': 'en_US', 'accept': '*/*'}, 'accept') == '*/*'
 
+    # all=True returns every choice ordered by q value, ties in header order
+    assert util.get_choice_from_headers(
+        {'accept-language': 'a;q=0.1,b;q=0.2,c;q=0.3,d;q=0.4,e;q=0.9,f'},
+        'accept-language', all=True) == ['f', 'e', 'd', 'c', 'b', 'a']
+    assert util.get_choice_from_headers(
+        {'accept': 'text/html,application/json'},
+        'accept', all=True) == ['text/html', 'application/json']
+
+    # q=0 means "not acceptable" and must not raise ZeroDivisionError
+    assert util.get_choice_from_headers(
+        {'accept-language': 'fr;q=0,en'}, 'accept-language') == 'en'
+    assert util.get_choice_from_headers(
+        {'accept-language': 'fr;q=0'}, 'accept-language') is None
+    assert util.get_choice_from_headers(
+        {'accept-language': 'fr;q=0'}, 'accept-language', all=True) is None
+
 
 @pytest.mark.parametrize('url,allow_internal,result', [
     ['http://127.0.0.1/test', False, False],