pldmd: fix unsupported command handling

A request with a valid PLDM type but an unregistered command
currently results in std::out_of_range from the command handler
lookup.

Unsupported commands are protocol-level errors and should return
a PLDM completion code instead of propagating a C++ exception.

Replace the throwing command lookup with a guarded lookup and
return PLDM_ERROR_UNSUPPORTED_PLDM_CMD when a command is not
registered.

Update the registration test to verify that unsupported commands
return the expected completion code rather than throwing an
exception.

Tested:
- meson test -C build pldmd_registration_test --print-errorlogs

Change-Id: Ia85d86fd4d22f7510e8ee52876f31643470eee70
Signed-off-by: Meghana Vangapandu <meghanav@ami.com>

pldmd/handler.hpp

diff --git a/pldmd/handler.hpp b/pldmd/handler.hpp
index 89b8a7f..9709f80 100644
--- a/pldmd/handler.hpp
+++ b/pldmd/handler.hpp
@@ -36,7 +36,12 @@
     Response handle(pldm_tid_t tid, Command pldmCommand,
                     const pldm_msg* request, size_t reqMsgLen)
     {
-        return handlers.at(pldmCommand)(tid, request, reqMsgLen);
+        auto handler = handlers.find(pldmCommand);
+        if (handler == handlers.end())
+        {
+            return ccOnlyResponse(request, PLDM_ERROR_UNSUPPORTED_PLDM_CMD);
+        }
+        return handler->second(tid, request, reqMsgLen);
     }
 
     /** @brief Create a response message containing only cc

test/pldmd_registration_test.cpp

diff --git a/test/pldmd_registration_test.cpp b/test/pldmd_registration_test.cpp
index e98bb21..6247e2d 100644
--- a/test/pldmd_registration_test.cpp
+++ b/test/pldmd_registration_test.cpp
@@ -55,6 +55,8 @@
     Invoker invoker{};
     const Response kExpectedBadTypeResponse = {0x01, 0x02, 0x03,
                                                PLDM_ERROR_INVALID_PLDM_TYPE};
+    const Response kExpectedBadCmdResponse = {0x01, 0x02, 0x03,
+                                              PLDM_ERROR_UNSUPPORTED_PLDM_CMD};
     const std::array<uint8_t, sizeof(pldm_msg)> kDummyPldmRequestBacking = {
         0x01, 0x02, 0x03};
     const pldm_msg* kDummyPldmRequest =
@@ -65,6 +67,6 @@
 
     invoker.registerHandler(testType, std::make_unique<TestHandler>());
     uint8_t badCmd = 0xFE;
-    ASSERT_THROW(invoker.handle(tid, testType, badCmd, nullptr, 0),
-                 std::out_of_range);
+    EXPECT_EQ(invoker.handle(tid, testType, badCmd, kDummyPldmRequest, 0),
+              kExpectedBadCmdResponse);
 }