From 27aa8c0bb1cb453753ccf0cde05cfb56aeaae652 Mon Sep 17 00:00:00 2001
From: Thor Whalen <1906276+thorwhalen@users.noreply.github.com>
Date: Tue, 13 Oct 2026 09:05:26 +0000
Subject: [PATCH 1/2] Implement flask_error_handler: error statuses and
 WWW-Authenticate for Flask apps (#37)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 py2http/default_configs.py           |  8 ++++++-
 py2http/tests/test_error_statuses.py | 34 ++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/py2http/default_configs.py b/py2http/default_configs.py
index f0c51f9..afe17f8 100644
--- a/py2http/default_configs.py
+++ b/py2http/default_configs.py
@@ -150,7 +150,13 @@ def bottle_error_handler(error: Exception):
 
 
 def flask_error_handler(error: Exception):
-    raise NotImplementedError()
+    """The ``(body, status, headers)`` a Flask view returns for an error, mapped like
+    the bottle handler (``OPAQUE_ERRORS`` hides the text of a 500)."""
+    message = str(error)
+    status = error_status(error)
+    if status == 500 and os.getenv("OPAQUE_ERRORS", None):
+        message = "Internal server error"
+    return {"error": message}, status, _status_headers(status)
 
 
 def default_error_handler(error: Exception):
diff --git a/py2http/tests/test_error_statuses.py b/py2http/tests/test_error_statuses.py
index ad43571..9de4af7 100644
--- a/py2http/tests/test_error_statuses.py
+++ b/py2http/tests/test_error_statuses.py
@@ -63,3 +63,37 @@ def test_aiohttp_error_handler(error, status):
     assert caught.value.status == status
     if status == 500:
         assert "internal detail" not in caught.value.text
+
+
+@pytest.mark.parametrize("error, status", CASES)
+def test_flask_error_handler(error, status, monkeypatch):
+    flask = pytest.importorskip("flask")
+    monkeypatch.delenv("PY2HTTP_WWW_AUTHENTICATE", raising=False)
+    monkeypatch.setenv("PY2HTTP_FRAMEWORK", "flask")
+    from py2http.default_configs import default_error_handler
+
+    app = flask.Flask(__name__)
+
+    @app.route("/fail")
+    def fail():
+        return default_error_handler(error)
+
+    response = app.test_client().get("/fail")
+    assert response.status_code == status
+    assert set(response.get_json()) == {"error"}
+    if status == 401:
+        assert response.headers["WWW-Authenticate"] == "Bearer"
+    else:
+        assert "WWW-Authenticate" not in response.headers
+    if status == 500:
+        assert "internal detail" in response.get_json()["error"]
+
+
+def test_flask_opaque_errors_hides_500_text(monkeypatch):
+    flask = pytest.importorskip("flask")
+    monkeypatch.setenv("OPAQUE_ERRORS", "1")
+    from py2http.default_configs import flask_error_handler
+
+    app = flask.Flask(__name__)
+    app.add_url_rule("/f", "f", lambda: flask_error_handler(KeyError("internal detail")))
+    assert app.test_client().get("/f").get_json() == {"error": "Internal server error"}

From a460be7c3b65dbf4d53b13d56efd26f42b28e1c6 Mon Sep 17 00:00:00 2001
From: Thor Whalen <1906276+thorwhalen@users.noreply.github.com>
Date: Tue, 13 Oct 2026 09:06:38 +0000
Subject: [PATCH 2/2] flask_error_handler: 400 status line names the error,
 like bottle (#37)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 py2http/default_configs.py           | 3 ++-
 py2http/tests/test_error_statuses.py | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/py2http/default_configs.py b/py2http/default_configs.py
index afe17f8..baab228 100644
--- a/py2http/default_configs.py
+++ b/py2http/default_configs.py
@@ -156,7 +156,8 @@ def flask_error_handler(error: Exception):
     status = error_status(error)
     if status == 500 and os.getenv("OPAQUE_ERRORS", None):
         message = "Internal server error"
-    return {"error": message}, status, _status_headers(status)
+    status_line = f"400 {type(error).__name__}" if status == 400 else status
+    return {"error": message}, status_line, _status_headers(status)
 
 
 def default_error_handler(error: Exception):
diff --git a/py2http/tests/test_error_statuses.py b/py2http/tests/test_error_statuses.py
index 9de4af7..e71e9ef 100644
--- a/py2http/tests/test_error_statuses.py
+++ b/py2http/tests/test_error_statuses.py
@@ -81,6 +81,8 @@ def fail():
     response = app.test_client().get("/fail")
     assert response.status_code == status
     assert set(response.get_json()) == {"error"}
+    if status == 400:  # as the bottle handler: the status line names the error
+        assert response.status == f"400 {type(error).__name__}"
     if status == 401:
         assert response.headers["WWW-Authenticate"] == "Bearer"
     else: