Parse multicall commands once per call

Keep the change to d, f, p and t multicalls. Parse each column lazily on first use and evaluate it through rpc::call_object, preserving per-target argument expansion.

Compared unpatched and patched builds on macOS: output was byte-identical across the test harness, including an erase-mid-call check.

test/rpc/test_command.cc

@@ -2,7 +2,10 @@
 
 #include "test/rpc/test_command.h"
 
+#include <torrent/exceptions.h>
+
 #include "rpc/command.h"
+#include "rpc/parse_commands.h"
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestCommand);
 
@@ -83,3 +86,50 @@ TestCommand::test_stack_double() {
   rpc::command_base::pop_stack(&stack_first, last_stack_first);
   CPPUNIT_ASSERT(command_stack_all_empty());
 }
+
+void
+TestCommand::test_preparsed_commands() {
+  unsigned int prepare_count = 0;
+  rpc::preparsed_commands commands([&prepare_count](auto& prepared) {
+    ++prepare_count;
+    // Reentrant access must not invoke the same callback recursively.
+    prepared.prepare_if_needed();
+    prepared.push_back(rpc::parse_command_object("string.length=abc"));
+  });
+
+  CPPUNIT_ASSERT_EQUAL(0u, prepare_count);
+  CPPUNIT_ASSERT(commands.empty());
+
+  commands.prepare_if_needed();
+  CPPUNIT_ASSERT_EQUAL(1u, prepare_count);
+
+  size_t count = 0;
+  for (auto& itr : commands) {
+    CPPUNIT_ASSERT(itr.is_dict_key());
+    ++count;
+  }
+
+  CPPUNIT_ASSERT_EQUAL(size_t(1), count);
+  CPPUNIT_ASSERT_EQUAL(1u, prepare_count);
+
+  for (auto& itr : commands)
+    CPPUNIT_ASSERT(itr.is_dict_key());
+
+  CPPUNIT_ASSERT_EQUAL(1u, prepare_count);
+}
+
+void
+TestCommand::test_parse_command_object() {
+  auto command = rpc::parse_command_object("\tstring.length=abc  ");
+  CPPUNIT_ASSERT(command.is_dict_key());
+  CPPUNIT_ASSERT_EQUAL(std::string("string.length"), command.as_dict_key());
+
+  // This helper has no way to return the next-command pointer, so it must not
+  // silently accept a multipart command separated by ';'.
+  CPPUNIT_ASSERT_THROW(rpc::parse_command_object("string.length=abc;string.length=def"), torrent::input_error);
+
+  // Unlike parse_command (which parses command files), this helper handles one
+  // multicall command and must reject newline boundaries, including CRLF.
+  CPPUNIT_ASSERT_THROW(rpc::parse_command_object("string.length=abc\nstring.length=def"), torrent::input_error);
+  CPPUNIT_ASSERT_THROW(rpc::parse_command_object("string.length=abc\r\nstring.length=def"), torrent::input_error);
+}

test/rpc/test_command.h

@@ -5,10 +5,14 @@ class TestCommand : public test_fixture {
 
   CPPUNIT_TEST(test_stack);
   CPPUNIT_TEST(test_stack_double);
+  CPPUNIT_TEST(test_preparsed_commands);
+  CPPUNIT_TEST(test_parse_command_object);
 
   CPPUNIT_TEST_SUITE_END();
 
 public:
   void test_stack();
   void test_stack_double();
+  void test_preparsed_commands();
+  void test_parse_command_object();
 };