Merge bitcoin/bitcoin#32660: rpc: Use type-safe exception to pass RPC help

fa94652 refactor: Use structured binding for-loop (MarcoFalke)
eeeec15 rpc: Use type-safe exception to pass RPC help (MarcoFalke)

Pull request description:

  The current "catch-all" `catch (const std::exception& e)` in `CRPCTable::help` is problematic, because it could catch exceptions unrelated to passing the help string up.

  Fix this by using a dedicated exception type.

ACKs for top commit:
  l0rinc:
    tested ACK fa94652 (edited)
  achow101:
    ACK fa94652
  rkrux:
    re-ACK fa94652

Tree-SHA512: 23dac6e0fe925561bfbf421e6a7441d546eed8c1492ac41ca4ed7dfcd12f4d2ef39c35f105a0291aac511365d98f08fbdc9a4f0bf627172873b8f23c2be45e76

Author: achow101

src/rpc/server.cpp

@@ -1,5 +1,5 @@
 // Copyright (c) 2010 Satoshi Nakamoto
-// Copyright (c) 2009-2022 The Bitcoin Core developers
+// Copyright (c) 2009-present The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -21,6 +21,7 @@
 #include <util/time.h>
 #include <validation.h>
 
+#include <algorithm>
 #include <cassert>
 #include <chrono>
 #include <memory>
@@ -79,15 +80,13 @@ std::string CRPCTable::help(const std::string& strCommand, const JSONRPCRequest&
 
     for (const auto& entry : mapCommands)
         vCommands.emplace_back(entry.second.front()->category + entry.first, entry.second.front());
-    sort(vCommands.begin(), vCommands.end());
+    std::ranges::sort(vCommands);
 
     JSONRPCRequest jreq = helpreq;
     jreq.mode = JSONRPCRequest::GET_HELP;
     jreq.params = UniValue();
 
-    for (const std::pair<std::string, const CRPCCommand*>& command : vCommands)
-    {
-        const CRPCCommand *pcmd = command.second;
+    for (const auto& [_, pcmd] : vCommands) {
         std::string strMethod = pcmd->name;
         if ((strCommand != "" || pcmd->category == "hidden") && strMethod != strCommand)
             continue;
@@ -97,11 +96,8 @@ std::string CRPCTable::help(const std::string& strCommand, const JSONRPCRequest&
             UniValue unused_result;
             if (setDone.insert(pcmd->unique_id).second)
                 pcmd->actor(jreq, unused_result, /*last_handler=*/true);
-        }
-        catch (const std::exception& e)
-        {
-            // Help text is returned in an exception
-            std::string strHelp = std::string(e.what());
+        } catch (const HelpResult& e) {
+            std::string strHelp{e.what()};
             if (strCommand == "")
             {
                 if (strHelp.find('\n') != std::string::npos)

src/rpc/util.cpp

@@ -645,7 +645,7 @@ UniValue RPCHelpMan::HandleRequest(const JSONRPCRequest& request) const
      * the user is asking for help information, and throw help when appropriate.
      */
     if (request.mode == JSONRPCRequest::GET_HELP || !IsValidNumArgs(request.params.size())) {
-        throw std::runtime_error(ToString());
+        throw HelpResult{ToString()};
     }
     UniValue arg_mismatch{UniValue::VOBJ};
     for (size_t i{0}; i < m_args.size(); ++i) {

src/rpc/util.h

@@ -67,6 +67,10 @@ class FillableSigningProvider;
 class CScript;
 struct Sections;
 
+struct HelpResult : std::runtime_error {
+    explicit HelpResult(const std::string& msg) : std::runtime_error{msg} {}
+};
+
 /**
  * Gets all existing output types formatted for RPC help sections.
  *