compiler: Add source code length to bytecode buffer

compiler/compiler.cpp

@@ -49,7 +49,7 @@ bool Compiler::CompileModule(const std::string& fileName, bool compileDependenci
     }
 
     // Write the bytecode to file
-    std::vector<uint8_t> bytecodeResult = CreateBytecodeBuffer(cache->data, cache->length);
+    std::vector<uint8_t> bytecodeResult = CreateBytecodeBuffer(cache->data, cache->length, sourceCode.size());
     bool writeResult = package->WriteFile(fileName, (void*)bytecodeResult.data(), bytecodeResult.size());
     if(!writeResult)
     {
@@ -101,21 +101,22 @@ bool Compiler::IsBytecodeFile(void* buffer, size_t size)
     return true;
 }
 
-std::vector<uint8_t> Compiler::CreateBytecodeBuffer(const uint8_t* buffer, int length)
+std::vector<uint8_t> Compiler::CreateBytecodeBuffer(const uint8_t* buffer, int length, int sourceLength)
 {
     // Make necessary changes to the bytecode
     FixBytecode(buffer);
 
     // Create our own custom bytecode buffer by appending our magic bytes
     // at the front, and then the bytecode itself at the end
     std::vector<uint8_t> buf;
-    size_t bufSize = magicBytes.size() + length;
+    size_t bufSize = magicBytes.size() + sizeof(int) + length;
     buf.resize(bufSize);
 
     memcpy(buf.data(), magicBytes.data(), magicBytes.size());
-    memcpy(buf.data() + magicBytes.size(), buffer, length);
+    memcpy(buf.data() + magicBytes.size(), &sourceLength, sizeof(int));
+    memcpy(buf.data() + magicBytes.size() + sizeof(int), buffer, length);
 
-    return std::move(buf);
+    return buf;
 }
 
 // Hash for empty module ("")

compiler/compiler.h

@@ -73,7 +73,7 @@ namespace BytecodeCompiler
         bool IsBytecodeFile(void* buffer, size_t size);
 
     private:
-        std::vector<uint8_t> CreateBytecodeBuffer(const uint8_t* buffer, int length);
+        std::vector<uint8_t> CreateBytecodeBuffer(const uint8_t* buffer, int length, int sourceLength);
 
         static void FixBytecode(const uint8_t* buffer);
     };

docs/internal.md

@@ -50,5 +50,7 @@ so that the module is working again.
 ## Format
 
 The bytecode we send to the client has exactly *5 bytes* of magic bytes at the front, these bytes are `ALTBC` to identify the data as alt:V bytecode, when we write it to file.
-To read this bytecode, we need to check for these 5 magic bytes at the front,  if they match, remove them from the buffer,
+After that there are *4 bytes* that form a 4-byte integer that corresponds to the size of the original source code (this is needed because V8 sometimes uses the source code buffer,
+when compiling functions, and if the buffer is too small, it crashes) that will be used to create a string to pass to the script compiler with the length of the original source code.
+To read this bytecode, we need to check for these 5 magic bytes at the front, if they match, remove them and the 4 bytes from the source code length from the buffer,
 and the remaining buffer is the full bytecode generated by V8, which we can then use to instantiate the script.