fix: Implement getentropy using wasi preview 1 (#178)

* fix: Implement getentropy while Emscripten gets patched

Issue: emscripten-core/emscripten#22782

Signed-off-by: Martijn Stevenson <[email protected]>

Author: martijneken

proxy_wasm_intrinsics.cc

@@ -271,3 +271,25 @@ extern "C" PROXY_WASM_KEEPALIVE void
 proxy_on_foreign_function(uint32_t context_id, uint32_t foreign_function_id, uint32_t data_size) {
   getContextBase(context_id)->onForeignFunction(foreign_function_id, data_size);
 }
+
+// Patch an Emscripten gap: https://github.com/emscripten-core/emscripten/issues/22782
+// Implement getentropy for RNG support (e.g. for absl::random).
+
+typedef uint16_t __wasi_errno_t;
+typedef size_t __wasi_size_t;
+
+__wasi_errno_t __wasi_random_get(uint8_t *buf, __wasi_size_t buf_len)
+    __attribute__((__import_module__("wasi_snapshot_preview1"), __import_name__("random_get")));
+
+extern "C" int getentropy(void *buffer, size_t len) {
+  if (len > 256) {
+    errno = EIO;
+    return -1;
+  }
+  int r = __wasi_random_get((uint8_t *)buffer, len);
+  if (r != 0) {
+    errno = r;
+    return -1;
+  }
+  return 0;
+}