bitcoin-cli: Provide a better error message when bitcoind is not running

Before this patch:

```
$ bitcoin-cli -testnet echo 'hello world'
error: Could not locate RPC credentials. No authentication cookie could be found, and RPC password is not set.  See -rpcpassword and -stdinrpcpass.  Configuration file: (/root/.bitcoin/bitcoin.conf)
```

After this patch:

```
$ bitcoin-cli -testnet echo 'hello world'
error: Could not connect to the server 127.0.0.1:18332

Make sure the bitcoind server is running and that you are connecting to the correct RPC port.
```

src/bitcoin-cli.cpp

@@ -313,13 +313,11 @@ static UniValue CallRPC(BaseRequestHandler *rh, const std::string& strMethod, co
 
     // Get credentials
     std::string strRPCUserColonPass;
+    bool failedToGetAuthCookie = false;
     if (gArgs.GetArg("-rpcpassword", "") == "") {
         // Try fall back to cookie-based authentication if no password is provided
         if (!GetAuthCookie(&strRPCUserColonPass)) {
-            throw std::runtime_error(strprintf(
-                _("Could not locate RPC credentials. No authentication cookie could be found, and RPC password is not set.  See -rpcpassword and -stdinrpcpass.  Configuration file: (%s)"),
-                    GetConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME)).string().c_str()));
-
+            failedToGetAuthCookie = true;
         }
     } else {
         strRPCUserColonPass = gArgs.GetArg("-rpcuser", "") + ":" + gArgs.GetArg("-rpcpassword", "");
@@ -358,11 +356,21 @@ static UniValue CallRPC(BaseRequestHandler *rh, const std::string& strMethod, co
 
     event_base_dispatch(base.get());
 
-    if (response.status == 0)
-        throw CConnectionFailed(strprintf("couldn't connect to server: %s (code %d)\n(make sure server is running and you are connecting to the correct RPC port)", http_errorstring(response.error), response.error));
-    else if (response.status == HTTP_UNAUTHORIZED)
-        throw std::runtime_error("incorrect rpcuser or rpcpassword (authorization failed)");
-    else if (response.status >= 400 && response.status != HTTP_BAD_REQUEST && response.status != HTTP_NOT_FOUND && response.status != HTTP_INTERNAL_SERVER_ERROR)
+    if (response.status == 0) {
+        std::string responseErrorMessage;
+        if (response.error != -1) {
+            responseErrorMessage = strprintf(" (error code %d - \"%s\")", response.error, http_errorstring(response.error));
+        }
+        throw CConnectionFailed(strprintf("Could not connect to the server %s:%d%s\n\nMake sure the bitcoind server is running and that you are connecting to the correct RPC port.", host, port, responseErrorMessage));
+    } else if (response.status == HTTP_UNAUTHORIZED) {
+        if (failedToGetAuthCookie) {
+            throw std::runtime_error(strprintf(
+                _("Could not locate RPC credentials. No authentication cookie could be found, and RPC password is not set.  See -rpcpassword and -stdinrpcpass.  Configuration file: (%s)"),
+                GetConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME)).string().c_str()));
+        } else {
+            throw std::runtime_error("Authorization failed: Incorrect rpcuser or rpcpassword");
+        }
+    } else if (response.status >= 400 && response.status != HTTP_BAD_REQUEST && response.status != HTTP_NOT_FOUND && response.status != HTTP_INTERNAL_SERVER_ERROR)
         throw std::runtime_error(strprintf("server returned HTTP error %d", response.status));
     else if (response.body.empty())
         throw std::runtime_error("no response from server");

test/functional/interface_bitcoin_cli.py

@@ -29,11 +29,11 @@ class TestBitcoinCli(BitcoinTestFramework):
 
         self.log.info("Test -stdinrpcpass option")
         assert_equal(0, self.nodes[0].cli('-rpcuser=%s' % user, '-stdinrpcpass', input=password).getblockcount())
-        assert_raises_process_error(1, "incorrect rpcuser or rpcpassword", self.nodes[0].cli('-rpcuser=%s' % user, '-stdinrpcpass', input="foo").echo)
+        assert_raises_process_error(1, "Incorrect rpcuser or rpcpassword", self.nodes[0].cli('-rpcuser=%s' % user, '-stdinrpcpass', input="foo").echo)
 
         self.log.info("Test -stdin and -stdinrpcpass")
         assert_equal(["foo", "bar"], self.nodes[0].cli('-rpcuser=%s' % user, '-stdin', '-stdinrpcpass', input=password + "\nfoo\nbar").echo())
-        assert_raises_process_error(1, "incorrect rpcuser or rpcpassword", self.nodes[0].cli('-rpcuser=%s' % user, '-stdin', '-stdinrpcpass', input="foo").echo)
+        assert_raises_process_error(1, "Incorrect rpcuser or rpcpassword", self.nodes[0].cli('-rpcuser=%s' % user, '-stdin', '-stdinrpcpass', input="foo").echo)
 
         self.log.info("Make sure that -getinfo with arguments fails")
         assert_raises_process_error(1, "-getinfo takes no arguments", self.nodes[0].cli('-getinfo').help)