Stop reporting blocked LinkedIn responses as free usernames (#3173)

LinkedIn's 999 and its reCAPTCHA interstitial both came out as confident results, one as a free name, the other as a claimed one. Both are errors now.

maigret/error_detection.py

@@ -40,11 +40,12 @@ def detect_error_page(
         return CheckError("Rate limited", "429 status code")
     if status_code == 999:
         # LinkedIn's "Request denied", served to blocked clients for existing
-        # and non-existing profiles alike, so it is not really a not-found.
-        # Classifying it as an error would flip LinkedIn to UNKNOWN for every
-        # blocked IP, which reads as "LinkedIn is broken" to users. Kept as a
-        # pass-through on purpose: the caller's checkType branch decides.
-        return None
+        # and non-existing profiles alike. Falling through to the checkType
+        # branch turned every profile into AVAILABLE, so a blocked client was
+        # told that williamhgates has no LinkedIn. "We could not check" is the
+        # honest answer here; the cost is that a blocked IP now sees an error
+        # instead of a confident wrong "Not found!".
+        return CheckError("Access denied", "999 status code")
     if status_code >= 500:
         return CheckError("Server", f"{status_code} status code")
     return None

maigret/errors.py

@@ -84,6 +84,12 @@ COMMON_ERRORS = {
         'Captcha', 'Google rate-limit / captcha'
     ),
     'id="gs_captcha_f"': CheckError('Captcha', 'Google rate-limit / captcha'),
+    # Google reCAPTCHA interstitial: answers HTTP 200 on every path, so on a
+    # status_code site every username reads as claimed (linkedin.com). Matches
+    # the challenge page itself, not a login form that merely embeds a widget.
+    'google.com/recaptcha/challengepage/': CheckError(
+        'Captcha', 'Google reCAPTCHA interstitial'
+    ),
 }
 
 PROXY_RECOMMENDATION = (

tests/test_checking.py

@@ -149,9 +149,13 @@ def test_detect_error_page_403_ignored():
 
 
 def test_detect_error_page_999_linkedin():
-    # LinkedIn returns 999 on bot suspicion. Deliberately not an error: making
-    # it one turns LinkedIn UNKNOWN for every blocked IP.
-    assert detect_error_page("", 999, {}, ignore_403=False) is None
+    # LinkedIn returns 999 on bot suspicion, for real and made-up profiles
+    # alike. It has to be an error: passing it through made every profile
+    # look free to a blocked client.
+    err = detect_error_page("", 999, {}, ignore_403=False)
+    assert err is not None
+    assert err.type == "Access denied"
+    assert "999" in err.desc
 
 
 def test_detect_error_page_500():

tests/test_error_detection.py

@@ -40,10 +40,6 @@ def test_http_429_is_rate_limit():
     assert err.type == "Rate limited"
 
 
-def test_ignore_linkedin_999_status():
-    # 999 stays a pass-through on purpose, see detect_error_page.
-    assert detect_error_page("", 999, {}, ignore_403=False) is None
-
 def test_pow_challenge_pages_are_bot_protection():
     # Both serve a 2xx on every path, so without a marker every username
     # would read as claimed.
@@ -59,3 +55,34 @@ def test_pow_challenge_pages_are_bot_protection():
 
     assert anubis.type == "Bot protection"
     assert pow_js.type == "Bot protection"
+
+
+def test_linkedin_999_is_an_error_not_an_absence():
+    # LinkedIn serves 999 to blocked clients for existing and non-existing
+    # profiles alike. Passing it through to the status_code branch reported
+    # every profile as free, so a blocked user was told that a real account
+    # does not exist.
+    err = detect_error_page("", 999, {}, ignore_403=False)
+    assert err is not None
+    assert err.type == "Access denied"
+
+
+def test_google_recaptcha_interstitial_is_a_captcha():
+    # Answers 200 on every path, so without a marker every username reads as
+    # claimed on a status_code site.
+    err = detect_error_page(
+        '<title>Checking your browser - reCAPTCHA</title>'
+        '<script src="https://www.google.com/recaptcha/challengepage/x"></script>',
+        200, {}, ignore_403=False,
+    )
+    assert err is not None
+    assert err.type == "Captcha"
+
+
+def test_page_embedding_a_recaptcha_widget_is_not_an_error():
+    # A login form that loads the reCAPTCHA script is an ordinary page; only
+    # the challenge interstitial counts as a block.
+    assert detect_error_page(
+        '<form><script src="https://www.google.com/recaptcha/enterprise.js"></script></form>',
+        200, {}, ignore_403=False,
+    ) is None