Clean up this allocation junk

src/discord-rpc.cpp

@@ -83,12 +83,8 @@ extern "C" void Discord_UpdateConnection()
     else {
         // reads
 
-        // json parser will use this buffer first, then allocate more if needed; I seriously doubt we send any messages that would use all of this, though.
-        char parseBuffer[32 * 1024];
         for (;;) {
-            PoolAllocator pa(parseBuffer, sizeof(parseBuffer));
-            StackAllocator sa;
-            JsonDocument message(rapidjson::kObjectType, &pa, sizeof(sa.fixedBuffer_), &sa);
+            JsonDocument message;
 
             if (!Connection->Read(message)) {
                 break;

src/rpc_connection.cpp

@@ -34,10 +34,7 @@ void RpcConnection::Open()
     }
 
     if (state == State::SentHandshake) {
-        char parseBuffer[32 * 1024];
-        PoolAllocator pa(parseBuffer, sizeof(parseBuffer));
-        StackAllocator sa;
-        JsonDocument message(rapidjson::kObjectType, &pa, sizeof(sa.fixedBuffer_), &sa);
+        JsonDocument message;
         if (Read(message)) {
             auto cmd = message.FindMember("cmd");
             if (cmd == message.MemberEnd() || !cmd->value.IsString()) {

src/serialization.h

@@ -99,11 +99,24 @@ public:
 };
 
 using MallocAllocator = rapidjson::CrtAllocator;
-extern MallocAllocator MallocAllocatorInst;
 using PoolAllocator = rapidjson::MemoryPoolAllocator<MallocAllocator>;
 using UTF8 = rapidjson::UTF8<char>;
 // Writer appears to need about 16 bytes per nested object level (with 64bit size_t)
 using StackAllocator = FixedLinearAllocator<2048>;
 constexpr size_t WriterNestingLevels = 2048 / (2 * sizeof(size_t));
 using JsonWriter = rapidjson::Writer<DirectStringBuffer, UTF8, UTF8, StackAllocator, rapidjson::kWriteNoFlags>;
-using JsonDocument = rapidjson::GenericDocument<UTF8, PoolAllocator, FixedLinearAllocator<2048>>;
+using JsonDocumentBase = rapidjson::GenericDocument<UTF8, PoolAllocator, StackAllocator>;
+class JsonDocument : public JsonDocumentBase
+{
+public:
+    static const int kDefaultChunkCapacity = 32 * 1024;
+    // json parser will use this buffer first, then allocate more if needed; I seriously doubt we send any messages that would use all of this, though.
+    char parseBuffer_[32 * 1024];
+    MallocAllocator mallocAllocator_;
+    PoolAllocator poolAllocator_;
+    StackAllocator stackAllocator_;
+    JsonDocument() : JsonDocumentBase(rapidjson::kObjectType, &poolAllocator_, sizeof(stackAllocator_.fixedBuffer_), &stackAllocator_)
+        , poolAllocator_(parseBuffer_, sizeof(parseBuffer_), kDefaultChunkCapacity, &mallocAllocator_)
+        , stackAllocator_()
+    {}
+};