exposition: include pushgateway response body in HTTP error

The pushgateway returns a descriptive message in the response body when it
rejects a payload (e.g. a malformed metric). urllib raises HTTPError before
the existing resp.code check runs, and its default message omits the body,
so the useful detail was lost. Catch HTTPError and surface the body.

Fixes #96

Signed-off-by: pritam360 <pritamchavan1212@gmail.com>

Author: pritam360

prometheus_client/exposition.py

@@ -515,7 +515,17 @@ def handle() -> None:
         request.get_method = lambda: method  # type: ignore
         for k, v in headers:
             request.add_header(k, v)
-        resp = build_opener(base_handler).open(request, timeout=timeout)
+        try:
+            resp = build_opener(base_handler).open(request, timeout=timeout)
+        except HTTPError as e:
+            # The pushgateway returns a helpful message in the response body
+            # (e.g. which metric was malformed). urllib raises HTTPError before
+            # the resp.code check below can run, and its default message drops
+            # the body, so read it here and surface it in the error.
+            body = e.read().decode('utf-8', 'replace').strip()
+            raise OSError(
+                f"error talking to pushgateway: {e.code} {e.reason}: {body}"
+            ) from e
         if resp.code >= 400:
             raise OSError(f"error talking to pushgateway: {resp.code} {resp.msg}")
 

tests/test_exposition.py

@@ -238,6 +238,17 @@ def do_PUT(self):
                     # and simulates a redirect to a url with the redirect_flag (which will produce a 201)
                     self.send_response(301)
                     self.send_header('Location', getattr(self, 'redirect_address', None))
+                elif 'error500' in self.requestline:
+                    # simulate a pushgateway rejecting the payload with a 500 and
+                    # a descriptive body, to exercise error-body surfacing.
+                    length = int(self.headers['content-length'])
+                    self.rfile.read(length)
+                    body = b'text format parsing error: duplicate metric'
+                    self.send_response(500)
+                    self.send_header('Content-Length', str(len(body)))
+                    self.end_headers()
+                    self.wfile.write(body)
+                    return
                 else:
                     self.send_response(201)
                 length = int(self.headers['content-length'])
@@ -282,6 +293,13 @@ def test_push(self):
         self.assertEqual(self.requests[0][0].headers.get('content-type'), CONTENT_TYPE_PLAIN_0_0_4)
         self.assertEqual(self.requests[0][1], b'# HELP g help\n# TYPE g gauge\ng 0.0\n')
 
+    def test_push_500_error_includes_response_body(self):
+        with self.assertRaises(OSError) as cm:
+            push_to_gateway(self.address, "my_job_error500", self.registry)
+        message = str(cm.exception)
+        self.assertIn('500', message)
+        self.assertIn('duplicate metric', message)
+
     def test_push_schemeless_url(self):
         push_to_gateway(self.address.replace('http://', ''), "my_job", self.registry)
         self.assertEqual(self.requests[0][0].command, 'PUT')