fix: preserve text/plain error body in raise_if_error() after stream is consumed

Author: stvoutsin

CHANGES.rst

@@ -4,11 +4,13 @@
 Enhancements and Fixes
 ----------------------
 
+- Preserve text/plain error body in raise_if_error() after stream is consumed. [#736]
+
 - Provide an API for SoftId-compliant management of the 'User-Agent'
-  header [#719]
+  header. [#719]
 
 - The ``astropy.samp`` module has been relocated and is now accessible under
-  ``pyvo.samp`` [#729]
+  ``pyvo.samp``. [#729]
 
 
 Deprecations and Removals

pyvo/dal/query.py

@@ -211,7 +211,10 @@ def execute_stream(self, *, post=False):
         try:
             response.raise_for_status()
         except requests.RequestException as ex:
-            # save for later use
+            # Cache the response body before returning the raw stream. If the
+            # caller consumes the stream before calling raise_if_error()
+            # this would lead to an empty error message
+            _ = response.content
             self._ex = ex
 
         return response.raw

pyvo/dal/tests/test_query.py

@@ -93,6 +93,12 @@ def register_mocks(mocker):
                 'GET', '//example.com/query/errornous',
                 text='Error', status_code=500
             )),
+            stack.enter_context(mocker.register_uri(
+                'GET', 'http://example.com/query/plaintext_error',
+                content=b'No intersection between cutout and image',
+                headers={'Content-Type': 'text/plain; charset=utf-8'},
+                status_code=500
+            )),
             stack.enter_context(mocker.register_uri(
                 'GET', 'http://example.com/query/errorstatus',
                 content=get_pkg_data_contents('data/query/errorstatus.xml')
@@ -225,6 +231,14 @@ def test_http_exception_500(self):
         else:
             assert False
 
+    def test_http_exception_message_preserved(self):
+        query = DALQuery('http://example.com/query/plaintext_error')
+        stream = query.execute_stream()
+        stream.read()
+        with pytest.raises(DALServiceError) as exc_info:
+            query.raise_if_error()
+        assert 'No intersection between cutout and image' in str(exc_info.value)
+
     def test_query_exception(self):
         service = DALService('http://example.com/query/errorstatus')