fix: Implement getentropy while Emscripten gets patched

Issue: emscripten-core/emscripten#22782

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

proxy_wasm_intrinsics.cc

@@ -271,3 +271,30 @@ 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).
+
+int32_t __imported_wasi_snapshot_preview1_random_get(int32_t arg0, int32_t arg1)
+    __attribute__((__import_module__("wasi_snapshot_preview1"), __import_name__("random_get")));
+
+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) {
+  int32_t ret = __imported_wasi_snapshot_preview1_random_get((int32_t)buf, (int32_t)buf_len);
+  return (uint16_t)ret;
+}
+
+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;
+}