Merge bitcoin/bitcoin#26612: refactor: RPC: pass named argument value as string_view

545ff924ab6303ffabd91fdfc4f0a4962daf133c refactor: use string_view for RPC named argument values (stickies-v)
7727603e44f8f674e0fc8389e78047e2b56e6052 refactor: reduce unnecessary complexity in ParseNonRFCJSONValue (stickies-v)
1d02e599012721549d4c20b1b37fcc5ee7b961b6 test: add cases to JSON parsing (stickies-v)

Pull request description:

  Inspired by MarcoFalke's [comment](https://github.com/bitcoin/bitcoin/pull/26506#discussion_r1036149426). Main purpose of this PR is to minimize copying (potentially large) RPC named arguments when calling `.substr()` by using `std::string_view` instead of `std::string`. Furthermore, cleans up the code by removing unnecessary complexity in `ParseNonRFCJSONValue()` (done first to avoid refactoring required to concatenate `string` and `string_view`), updates some naming and adds a few test cases. Should not introduce any behaviour change.

  ## Questions
  - ~Was there actually any merit to `ParseNonRFCJSONValue()` surrounding the value with brackets and then parsing it as an array? I don't see it, and the new approach doesn't fail any tests. Still a bit suspicious about it though.~
    - Cleared up by https://github.com/bitcoin/bitcoin/pull/26506#pullrequestreview-1211984059
    - If there are no objections to 7727603e44f8f674e0fc8389e78047e2b56e6052, I think we should follow up with a PR to rename `ParseNonRFCJSONValue()` to a local `Parse()` helper function (that throws if invalid), remove it from `client.h` and merge the test coverage we currently have on `ParseNonRFCJSONValue()` with the coverage we have on `UniValue::read()`.

ACKs for top commit:
  ryanofsky:
    Code review ACK 545ff924ab6303ffabd91fdfc4f0a4962daf133c
  MarcoFalke:
    review ACK 545ff924ab6303ffabd91fdfc4f0a4962daf133c 📻

Tree-SHA512: b1c89fb010ac9c3054b023cac1acbba2a539a09cf39a7baffbd7f7571ee268d5a6d98701c7ac10d68a814526e8fd0fe96ac1d1fb072f272033e415b753f64a5c

2 files changed, 20 insertions, 16 deletions

diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index eb91a151b5..9449b9d197 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -4,10 +4,13 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <rpc/client.h>
+#include <tinyformat.h>
 #include <util/system.h>
 
 #include <set>
 #include <stdint.h>
+#include <string>
+#include <string_view>
 
 class CRPCConvertParam
 {
@@ -229,15 +232,15 @@ public:
     CRPCConvertTable();
 
     /** Return arg_value as UniValue, and first parse it if it is a non-string parameter */
-    UniValue ArgToUniValue(const std::string& arg_value, const std::string& method, int param_idx)
+    UniValue ArgToUniValue(std::string_view arg_value, const std::string& method, int param_idx)
     {
-        return members.count(std::make_pair(method, param_idx)) > 0 ? ParseNonRFCJSONValue(arg_value) : arg_value;
+        return members.count({method, param_idx}) > 0 ? ParseNonRFCJSONValue(arg_value) : arg_value;
     }
 
     /** Return arg_value as UniValue, and first parse it if it is a non-string parameter */
-    UniValue ArgToUniValue(const std::string& arg_value, const std::string& method, const std::string& param_name)
+    UniValue ArgToUniValue(std::string_view arg_value, const std::string& method, const std::string& param_name)
     {
-        return membersByName.count(std::make_pair(method, param_name)) > 0 ? ParseNonRFCJSONValue(arg_value) : arg_value;
+        return membersByName.count({method, param_name}) > 0 ? ParseNonRFCJSONValue(arg_value) : arg_value;
     }
 };
 
@@ -254,13 +257,11 @@ static CRPCConvertTable rpcCvtTable;
 /** Non-RFC4627 JSON parser, accepts internal values (such as numbers, true, false, null)
  * as well as objects and arrays.
  */
-UniValue ParseNonRFCJSONValue(const std::string& strVal)
+UniValue ParseNonRFCJSONValue(std::string_view raw)
 {
-    UniValue jVal;
-    if (!jVal.read(std::string("[")+strVal+std::string("]")) ||
-        !jVal.isArray() || jVal.size()!=1)
-        throw std::runtime_error(std::string("Error parsing JSON: ") + strVal);
-    return jVal[0];
+    UniValue parsed;
+    if (!parsed.read(raw)) throw std::runtime_error(tfm::format("Error parsing JSON: %s", raw));
+    return parsed;
 }
 
 UniValue RPCConvertValues(const std::string &strMethod, const std::vector<std::string> &strParams)
@@ -268,8 +269,8 @@ UniValue RPCConvertValues(const std::string &strMethod, const std::vector<std::s
     UniValue params(UniValue::VARR);
 
     for (unsigned int idx = 0; idx < strParams.size(); idx++) {
-        const std::string& strVal = strParams[idx];
-        params.push_back(rpcCvtTable.ArgToUniValue(strVal, strMethod, idx));
+        std::string_view value{strParams[idx]};
+        params.push_back(rpcCvtTable.ArgToUniValue(value, strMethod, idx));
     }
 
     return params;
@@ -280,15 +281,15 @@ UniValue RPCConvertNamedValues(const std::string &strMethod, const std::vector<s
     UniValue params(UniValue::VOBJ);
     UniValue positional_args{UniValue::VARR};
 
-    for (const std::string &s: strParams) {
+    for (std::string_view s: strParams) {
         size_t pos = s.find('=');
         if (pos == std::string::npos) {
             positional_args.push_back(rpcCvtTable.ArgToUniValue(s, strMethod, positional_args.size()));
             continue;
         }
 
-        std::string name = s.substr(0, pos);
-        std::string value = s.substr(pos+1);
+        std::string name{s.substr(0, pos)};
+        std::string_view value{s.substr(pos+1)};
 
         // Intentionally overwrite earlier named values with later ones as a
         // convenience for scripts and command line users that want to merge
diff --git a/src/rpc/client.h b/src/rpc/client.h
index b9fee5bbb3..3c5c4fc4d6 100644
--- a/src/rpc/client.h
+++ b/src/rpc/client.h
@@ -6,6 +6,9 @@
 #ifndef BITCOIN_RPC_CLIENT_H
 #define BITCOIN_RPC_CLIENT_H
 
+#include <string>
+#include <string_view>
+
 #include <univalue.h>
 
 /** Convert positional arguments to command-specific RPC representation */
@@ -17,6 +20,6 @@ UniValue RPCConvertNamedValues(const std::string& strMethod, const std::vector<s
 /** Non-RFC4627 JSON parser, accepts internal values (such as numbers, true, false, null)
  * as well as objects and arrays.
  */
-UniValue ParseNonRFCJSONValue(const std::string& strVal);
+UniValue ParseNonRFCJSONValue(std::string_view raw);
 
 #endif // BITCOIN_RPC_CLIENT_H