如何使用 Rust 将带有 JavaScript 的文件读取到 WebAssembly? [英] How to read a file with JavaScript to WebAssembly using Rust?
问题描述
如何传递 File 以在 WebAssembly 内存上下文中读取?
How can I pass a File to be read within the WebAssembly memory context?
使用 JavaScript 在浏览器中读取文件很容易:
Reading a file in the browser with JavaScript is easy:
<input class="file-selector" type="file" id="files" name="files[]" />
我能够使用 crate stdweb 引导用 Rust 编写的 WebAssembly 代码，添加一个事件监听器到DOM 元素并启动一个 FileReader:
I was able to bootstrap WebAssembly code written in Rust with the crate stdweb, add an event listener to the DOM element and fire up a FileReader:
let reader = FileReader::new();
let file_input_element: InputElement = document().query_selector(".file-selector").unwrap().unwrap().try_into().unwrap();
file_input_element.add_event_listener(enclose!( (reader, file_input_element) move |event: InputEvent| {
// mystery part
}));
在 JavaScript 中，我会从元素中获取文件并将其传递给阅读器，但是，stdweb 的 API 需要以下签名:
In JavaScript, I would get the file from the element and pass it to the reader, however, the API of stdweb needs the following signature:
pub fn read_as_array_buffer<T: IBlob>(&self, blob: &T) -> Result<(), TODO>
我不知道如何实现 IBlob，而且我确信无论是使用 stdweb API 还是我对 WebAssembly/Rust 的理解，我都遗漏了一些明显的东西.我希望有比 更简洁的东西将内容转换为 UTF-8.
I have no idea how to implement IBlob and I am sure that I am missing something obvious either with the stdweb API or in my understanding of WebAssembly/Rust. I was hoping that there is something less verbose than converting stuff to UTF-8.
推荐答案
它在 FileReader 本身从 JavaScript 传递到 WebAssembly 时起作用.这似乎也是一种干净的方法，因为无论如何都必须通过 JavaScript API 读取数据 - 无需从 WASM 调用 JS.
It works when the FileReader itself is passed from JavaScript to WebAssembly. It also seems like a clean approach because the data has to be read by the JavaScript API anyway - no need to call JS from WASM.
index.html
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Read to wasm</title>
</head>
<body>
<input type="file" id="file-input"/>
<script src="reader.js"></script>
<script>
var fileReader = new FileReader();
fileReader.onloadend = e => Rust.reader
.then(reader=> {
window.alert(reader.print_result(fileReader));
});
var fileInputElement = document.getElementById("file-input");
fileInputElement.addEventListener("change", e => fileReader.readAsText(fileInputElement.files[0]));
</script>
</body>
</html>
main.rs
#![feature(proc_macro)]
#[macro_use]
extern crate stdweb;
use stdweb::js_export;
use stdweb::web::FileReader;
use stdweb::web::FileReaderResult;
#[js_export]
fn print_result(file_reader: FileReader) -> String {
match file_reader.result() {
Some(value) => match value {
FileReaderResult::String(value) => value,
_ => String::from("not a text"),
}
None => String::from("empty")
}
}
fn main() {
stdweb::initialize();
stdweb::event_loop();
}
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