Merge #20003: net: Exit with error message if -proxy is specified without arguments (instead of continuing without proxy server)

9b4fa0af40 net: Print error message if -proxy is specified without arguments (instead of continuing without proxy server) (practicalswift)

Pull request description:

  Exit with error message if `-proxy` is specified without arguments (instead of continuing without proxy server).

  Continuing without a proxy server when the end-user has specified `-proxy` may result in accidental loss of privacy. (The end-user might think he/she is using a proxy when he/she is not.)

  Before this patch:

  ```
  $ src/bitcoind -proxy
  …
  2020-09-23T00:24:33Z InitParameterInteraction: parameter interaction: -proxy set -> setting -listen=0
  2020-09-23T00:24:33Z InitParameterInteraction: parameter interaction: -proxy set -> setting -upnp=0
  2020-09-23T00:24:33Z InitParameterInteraction: parameter interaction: -proxy set -> setting -discover=0
  2020-09-23T00:24:33Z InitParameterInteraction: parameter interaction: -listen=0 -> setting -listenonion=0
  …
  2020-09-23T00:24:33Z init message: Starting network threads...
  ```

  `bitcoind` is now running *without* a proxy server (`GetProxy(…, …) == false`, `HaveNameProxy() == false`, etc.).

  Note that the "-proxy set" log messages above which the end-user might interpret as "good, my traffic is now routed via the proxy".

  After this patch:

  ```
  $ src/bitcoind -proxy
  Error: No proxy server specified. Use -proxy=<ip> or -proxy=<ip:port>.
  $ echo $?
  1
  ```

ACKs for top commit:
  laanwj:
    re-ACK 9b4fa0af40
  kristapsk:
    ACK 9b4fa0af40, I have tested the code.
  hebasto:
    re-ACK 9b4fa0af40

Tree-SHA512: 4ba7a011991699a54b5bb87ec68367c681231bf5dcd36f8c89ff9ddc2e8d29df453817b7e362597e652ad6b341a22b7274be0fd78d435e5f0fd8058e5221c4ce

src/init.cpp

@@ -1192,6 +1192,10 @@ bool AppInitParameterInteraction(const ArgsManager& args)
 
     nMaxTipAge = args.GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
 
+    if (args.IsArgSet("-proxy") && args.GetArg("-proxy", "").empty()) {
+        return InitError(_("No proxy server specified. Use -proxy=<ip> or -proxy=<ip:port>."));
+    }
+
     return true;
 }
 

test/functional/feature_config_args.py

@@ -78,6 +78,12 @@ class ConfArgsTest(BitcoinTestFramework):
         with open(inc_conf_file2_path, 'w', encoding='utf-8') as conf:
             conf.write('')  # clear
 
+    def test_invalid_command_line_options(self):
+        self.nodes[0].assert_start_raises_init_error(
+            expected_msg='Error: No proxy server specified. Use -proxy=<ip> or -proxy=<ip:port>.',
+            extra_args=['-proxy'],
+        )
+
     def test_log_buffer(self):
         with self.nodes[0].assert_debug_log(expected_msgs=['Warning: parsed potentially confusing double-negative -connect=0\n']):
             self.start_node(0, extra_args=['-noconnect=0'])
@@ -146,6 +152,7 @@ class ConfArgsTest(BitcoinTestFramework):
         self.test_networkactive()
 
         self.test_config_file_parser()
+        self.test_invalid_command_line_options()
 
         # Remove the -datadir argument so it doesn't override the config file
         self.nodes[0].args = [arg for arg in self.nodes[0].args if not arg.startswith("-datadir")]