Fix MessageId::getDataAsString() crashed with MSVC debug config (#108)

Fixes #107

### Motivation

The `MessageId::getDataAsString()` API returns a `std::string` to the
application side. In most cases it's not an issue. However, when
building Windows DLLs with `LINK_STATIC=ON`, the library will be
built with `/MTd` or `/MT` option to link 3rd party dependencies
statically. In this case, the DLL and the application have different C
runtime libraries that allocate or deallocate memory. The returned
`std::string` object is allocated inside the DLL, while it will be
destroyed in the application. The destruction could crash because the
application C runtime cannot find the heap address from the C runtime in
DLL.

### Modifications

For MSVC debug build, change the API to return a const reference to
`std::string`. Then the original `std::string` object will be
deallocated inside the DLL.

Author: BewareMyPower

include/pulsar/Message.h

@@ -90,8 +90,15 @@ class PULSAR_PUBLIC Message {
      * Get string representation of the message
      *
      * @return the string representation of the message payload
+     *
+     * NOTE: For MSVC with debug mode, return a thread local std::string object to avoid memory allocation
+     * across DLLs and applications, which could lead to a crash.
      */
+#if defined(_MSC_VER) && !defined(NDEBUG)
+    const std::string& getDataAsString() const;
+#else
     std::string getDataAsString() const;
+#endif
 
     /**
      * Get key value message.

lib/Message.cc

@@ -54,7 +54,15 @@ const void* Message::getData() const { return impl_->payload.data(); }
 
 std::size_t Message::getLength() const { return impl_->payload.readableBytes(); }
 
+#if defined(_MSC_VER) && !defined(NDEBUG)
+const std::string& Message::getDataAsString() const {
+    thread_local std::string value;
+    value = std::string{static_cast<const char*>(getData()), getLength()};
+    return value;
+}
+#else
 std::string Message::getDataAsString() const { return std::string((const char*)getData(), getLength()); }
+#endif
 
 Message::Message() : impl_() {}