Support for Censorship Circumvention API's /default route.

Fall back to trying Censorship API's /default route if no other bridges found.

At time of writing, this returns a couple of built-in obfs4 bridges.

If even that request fails, we will still fall back to our own full list of
obfs4 bridges.

cli/onionshare_cli/censorship.py

@@ -100,7 +100,7 @@ class CensorshipCircumvention(object):
             if r.status_code != 200:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_map",
+                    "request_map",
                     f"status_code={r.status_code}",
                 )
                 return False
@@ -110,7 +110,7 @@ class CensorshipCircumvention(object):
             if "errors" in result:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_map",
+                    "request_map",
                     f"errors={result['errors']}",
                 )
                 return False
@@ -138,7 +138,7 @@ class CensorshipCircumvention(object):
         if country:
             self.common.log(
                 "CensorshipCircumvention",
-                "censorship_obtain_settings",
+                "request_settings",
                 f"Trying to obtain bridges for country={country}",
             )
             data = {"country": country}
@@ -154,7 +154,7 @@ class CensorshipCircumvention(object):
             if r.status_code != 200:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_settings",
+                    "request_settings",
                     f"status_code={r.status_code}",
                 )
                 return False
@@ -164,7 +164,7 @@ class CensorshipCircumvention(object):
             if "errors" in result:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_settings",
+                    "request_settings",
                     f"errors={result['errors']}",
                 )
                 return False
@@ -175,7 +175,7 @@ class CensorshipCircumvention(object):
             if not "settings" in result:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_settings",
+                    "request_settings",
                     "No settings found for this country",
                 )
                 return False
@@ -200,7 +200,7 @@ class CensorshipCircumvention(object):
             if r.status_code != 200:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_builtin_bridges",
+                    "request_builtin_bridges",
                     f"status_code={r.status_code}",
                 )
                 return False
@@ -210,7 +210,7 @@ class CensorshipCircumvention(object):
             if "errors" in result:
                 self.common.log(
                     "CensorshipCircumvention",
-                    "censorship_obtain_builtin_bridges",
+                    "request_builtin_bridges",
                     f"errors={result['errors']}",
                 )
                 return False
@@ -237,34 +237,7 @@ class CensorshipCircumvention(object):
             f"Obtained bridges: {bridges}",
         )
         bridge_strings = bridges["bridge_strings"]
-        bridge_type = bridges["type"]
-        bridge_source = bridges["source"]
 
-        # If the recommended bridge source is to use the built-in
-        # bridges, set that in our settings, as if the user had
-        # selected the built-in bridges for a specific PT themselves.
-        #
-        if bridge_source == "builtin":
-            self.common.log(
-                "CensorshipCircumvention",
-                "save_settings",
-                "Will be using built-in bridges",
-            )
-            self.settings.set("bridges_type", "built-in")
-            if bridge_type == "obfs4":
-                self.settings.set("bridges_builtin_pt", "obfs4")
-            if bridge_type == "snowflake":
-                self.settings.set("bridges_builtin_pt", "snowflake")
-            if bridge_type == "meek":
-                self.settings.set("bridges_builtin_pt", "meek-azure")
-            bridges_ok = True
-        else:
-            self.common.log(
-                "CensorshipCircumvention",
-                "save_settings",
-                "Will be using custom bridges",
-            )
-            # Any other type of bridge we can treat as custom.
         self.settings.set("bridges_type", "custom")
 
         # Sanity check the bridges provided from the Tor API before saving
@@ -291,3 +264,42 @@ class CensorshipCircumvention(object):
                 "Could not use any of the obtained bridges.",
             )
             return False
+
+
+    def request_default_bridges(self):
+        """
+        Retrieves the list of default fall-back bridges from the Tor Project.
+
+        These are intended for when no censorship settings were found for a
+        specific country, but maybe there was some connection issue anyway.
+        """
+        if not self.api_proxies:
+            return False
+        endpoint = "https://bridges.torproject.org/moat/circumvention/defaults"
+        try:
+            r = requests.get(
+                endpoint,
+                headers={"Content-Type": "application/vnd.api+json"},
+                proxies=self.api_proxies,
+            )
+            if r.status_code != 200:
+                self.common.log(
+                    "CensorshipCircumvention",
+                    "request_default_bridges",
+                    f"status_code={r.status_code}",
+                )
+                return False
+
+            result = r.json()
+
+            if "errors" in result:
+                self.common.log(
+                    "CensorshipCircumvention",
+                    "request_default_bridges",
+                    f"errors={result['errors']}",
+                )
+                return False
+
+            return result
+        except requests.exceptions.RequestException as e:
+            raise CensorshipCircumventionError(e)

desktop/onionshare/connection_tab.py

@@ -181,7 +181,9 @@ class AutoConnectTab(QtWidgets.QWidget):
         self.tor_con.start(self.curr_settings)
 
     def _got_no_bridges(self):
-        # If we got no bridges, try connecting again using built-in obfs4 bridges
+        # If we got no bridges, even after trying the default bridges
+        # provided by the Censorship API, try connecting again using
+        # our built-in obfs4 bridges
         self.curr_settings.set("bridges_type", "built-in")
         self.curr_settings.set("bridges_builtin_pt", "obfs4")
         self.curr_settings.set("bridges_enabled", True)
@@ -244,6 +246,16 @@ class AutoConnectTab(QtWidgets.QWidget):
             bridge_settings = self.censorship_circumvention.request_settings(
                 country=country
             )
+
+            if not bridge_settings:
+                # Fall back to trying the default bridges from the API
+                self.common.log(
+                    "AutoConnectTab",
+                    "use_bridge_connect_clicked",
+                    "Falling back to trying default bridges provided by the Censorship Circumvention API",
+                )
+                bridge_settings = self.censorship_circumvention.request_default_bridges()
+
             self.common.gui.meek.cleanup()
 
             if bridge_settings and self.censorship_circumvention.save_settings(