Emscripten Fetch 总是 return 0

Question

我遵循 Emscripten 附带的同步获取示例，如下所示；

void main()
{
      emscripten_fetch_attr_t attr;
      emscripten_fetch_attr_init(&attr);
      strcpy(attr.requestMethod, "GET");
      attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY | EMSCRIPTEN_FETCH_SYNCHRONOUS;
      emscripten_fetch_t *fetch = emscripten_fetch(&attr, "https://ichef.bbci.co.uk/news/660/cpsprodpb/E9DF/production/_96317895_gettyimages-164067218.jpg");
      printf("Fetch finished with status %d\n", fetch->status);
}

它总是returns 0 来自获取状态

我用

编译

FLAGS            += -std=c++17 -stdlib=libc++ -O3
FLAGS            += -s WASM=1  -s USE_WEBGL2=1 -s FULL_ES3=1 
FLAGS            += -s ALLOW_MEMORY_GROWTH=1 
FLAGS            += -o hello.html 
FLAGS            += -s "EXTRA_EXPORTED_RUNTIME_METHODS=['ccall', 'cwrap']"    
FLAGS            += --no-heap-copy
FLAGS            +=  -s FETCH=1

然而，当我使用异步测试并读取 OnSuccess 函数中的数据时。数据打印正确

static
void ondownload_success(emscripten_fetch_t *fetch)
{
    printf("[ download ][ OK ]    %llu bytes  [ URL ]: %s\n", fetch->numBytes, fetch->url);

    printf("%c %c %c", fetch->data[0], fetch->data[3], fetch->data[2] );
    emscripten_fetch_close(fetch); // Free data associated with the fetch.
}

我的 Fetch 同步代码有什么问题？一切都与 "example_synchronous_fetch.cpp" 示例

完全相同

我运行在 Windows10。 Emscripten 1.38.29。使用Microsoft Edge 无需服务器直接浏览文件（双击hello.html）

Answer 1

同步 fetch 有一些额外的限制，您的构建标志似乎没有启用同步 fetch:

Synchronous Emscripten Fetch operations are subject to a number of restrictions, depending on which Emscripten build mode (linker flags) is used:

No flags: Only asynchronous Fetch operations are available.

–proxy-to-worker: Synchronous Fetch operations are allowed for fetches that only do an XHR but do not interact with IndexedDB.

-s USE_PTHREADS=1: Synchronous Fetch operations are available on pthreads, but not on the main thread.

–proxy-to-worker + -s USE_PTHREADS=1: Synchronous Fetch operations are available both on the main thread and pthreads.

https://emscripten.org/docs/api_reference/fetch.html#synchronous-fetches

Emscripten Fetch 总是 return 0

Emscripten Fetch always return 0

c++

xmlhttprequest

emscripten