diff --git a/.gitignore b/.gitignore
index 4a96461..302f16f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,4 +15,6 @@ Cargo.lock
 
 libsodium
 openssl-wasm
-boost
\ No newline at end of file
+boost
+*pb.cc
+*pb.h
\ No newline at end of file
diff --git a/README.md b/README.md
index 1dfb83b..1fe350d 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,11 @@ export PATH=$WASI_SDK_PATH/bin:$PATH
 4. Run `sh prepare-sodium.sh` to prepare `libsodium` for wasm env. You may need to install `zig` in advance.
 5. Run `sh prepare-openssl.sh` to prepare `libssl` for wasm env. Also, in some of your C++ file you need to define `pid_t getpid(void) {return 1;}` since WASI lacks process identifiers, so we nede to define some stub.
 6. Run `sh prepare-boost.sh` to prepare `boost` for wasm env.
+7. Run `sh prepare-protobuf.sh` to prepare `protobuf` for wasm env. For protobuf to work we also need to use wasi-sdk with pthreads support, e.g. https://github.com/WebAssembly/wasi-sdk/releases/tag/wasi-sdk-20%2Bthreads, and then do :
+```
+export WASI_SDK_PATH=~/Downloads/wasi-sdk-20.0+threads
+export PATH=$WASI_SDK_PATH/bin:$PATH
+```
 
 ## Build
 
@@ -36,4 +41,4 @@ This should print the following:
 [hello] Hello World from C++! (printf)
 The sodium is initialized!
 sodium randombytes: 714298213
-```
+```
\ No newline at end of file
diff --git a/build.rs b/build.rs
index 299c8ba..b57a61a 100644
--- a/build.rs
+++ b/build.rs
@@ -12,7 +12,9 @@ fn main() {
     let target = env::var("TARGET").unwrap();
 
     let mut build = cc::Build::new();
-    // build.cpp(true) // this will cause rust-lld: error: unable to find library -lstdc++
+    // build.cpp(true); // this will cause rust-lld: error: unable to find library -lstdc++
+    build.file("cpp/add.cpp");
+    build.file("cpp/wallet.pb.cc");
     build.file("cpp/my_code.cpp");
 
     if target.contains("wasm32") {
diff --git a/cpp/add.cpp b/cpp/add.cpp
new file mode 100644
index 0000000..fa1ff22
--- /dev/null
+++ b/cpp/add.cpp
@@ -0,0 +1,12 @@
+#include "add.h"
+
+Add::Add(int x, int y)
+{
+  gx = x;
+  gy = y;
+}
+
+int Add::getSum()
+{
+  return gx + gy;
+}
\ No newline at end of file
diff --git a/cpp/add.h b/cpp/add.h
new file mode 100644
index 0000000..11959c8
--- /dev/null
+++ b/cpp/add.h
@@ -0,0 +1,15 @@
+// add.h
+#ifndef add_H
+#define add_H
+
+class Add
+{
+  int gx;
+  int gy;
+
+public:
+  Add(int x, int y);
+  int getSum();
+};
+
+#endif
\ No newline at end of file
diff --git a/cpp/my_code.cpp b/cpp/my_code.cpp
index 00a1b81..78b194c 100644
--- a/cpp/my_code.cpp
+++ b/cpp/my_code.cpp
@@ -10,6 +10,10 @@
 
 #include <boost/algorithm/string.hpp>
 
+#include "wallet.pb.h"
+
+#include "add.h"
+
 struct KeyPair
 {
   std::vector<uint8_t> public_key;
@@ -17,7 +21,7 @@ struct KeyPair
 };
 
 extern "C"
-{ 
+{
   void hello()
   {
     // Test C++
@@ -82,9 +86,19 @@ extern "C"
     std::string s = "Boost Libraries";
     boost::to_upper(s);
     printf("[hello] Boost Upper Case test: %s\n", s.c_str());
+
+    // Test external class
+    //
+    Add *a1 = new Add(5, 5);
+    printf("SUM1: %d\n", a1->getSum());
+
+    // Test protobuf
+    //
+    my_wallets::MaxSupply max_supply;
   }
 
-  pid_t getpid(void) {
+  pid_t getpid(void)
+  {
     return 1;
   }
 }
\ No newline at end of file
diff --git a/prepare-protobuf.sh b/prepare-protobuf.sh
new file mode 100644
index 0000000..0d253f5
--- /dev/null
+++ b/prepare-protobuf.sh
@@ -0,0 +1,2 @@
+cd resources/proto
+protoc --cpp_out=../../cpp/ *.proto
diff --git a/resources/proto/wallet.proto b/resources/proto/wallet.proto
new file mode 100644
index 0000000..8b970a6
--- /dev/null
+++ b/resources/proto/wallet.proto
@@ -0,0 +1,10 @@
+syntax = "proto3";
+
+package my_wallets;
+
+option optimize_for = SPEED;
+
+message MaxSupply{
+	string max_supply = 1;
+	string circulation = 2;
+}