Inspired by the Caller abstraction in wasmedge-sdk (Rust), this module provides safe, idiomatic Haskell helpers for host functions to inspect and manipulate the linear memory of the calling WebAssembly guest instance.

When a WebAssembly module invokes an imported host function, WasmEdge supplies a CallingFrame. Using getCallerMemory, readCallerMemory, or writeCallerMemory, host functions can easily exchange structured data, buffers, and strings with the guest.

Example

import WasmEdge.Caller
import qualified Data.ByteString as BS

-- Host function reading a string from guest memory and logging it
logMessageHostFunc :: CallingFrame -> [WasmVal] -> IO (WasmResult [WasmVal])
logMessageHostFunc frame [WasmI32 ptr, WasmI32 len] = do
  mStr <- readCallerMemory frame 0 (fromIntegral ptr) (fromIntegral len)
  case mStr of
    Nothing -> pure (Left (WasmEdgeError ErrCategory_UserDefined 1 "Invalid memory access"))
    Just bs -> do
      putStrLn $ "Guest message: " ++ show bs
      pure (Right [])
logMessageHostFunc _ _ = pure (Left (WasmEdgeError ErrCategory_UserDefined 2 "Invalid arguments"))