Split src/common/* into headers and definitions

src/common/communication.cpp

@@ -0,0 +1,30 @@
+#include "communication.h"
+
+intptr_t send_event(boost::asio::local::stream_protocol::socket& socket,
+                    int32_t opcode,
+                    int32_t index,
+                    intptr_t value,
+                    void* data,
+                    float option) {
+    auto payload =
+        data == nullptr
+            ? std::nullopt
+            : std::make_optional(std::string(static_cast<char*>(data)));
+
+    const Event event{opcode, index, value, option, payload};
+    write_object(socket, event);
+
+    const auto response = read_object<EventResult>(socket);
+    if (response.data.has_value()) {
+        char* char_data = static_cast<char*>(data);
+
+        // For correctness we will copy the entire buffer and add a terminating
+        // null byte ourselves. In practice `response.data` will only ever
+        // contain C-style strings, but this would work with any other data
+        // format that can contain null bytes.
+        std::copy(response.data->begin(), response.data->end(), char_data);
+        char_data[response.data->size()] = 0;
+    }
+
+    return response.return_value;
+}