1 stable release
1.0.0 | Jul 1, 2022 |
---|
#1034 in WebAssembly
89 downloads per month
16KB
100 lines
wasm-bindgen-file-reader
This crate implements a wrapper around a web_sys::File
that implements Read
and Seek
. This is useful when you have a Rust crate that expects a generic reader and want to use it in WebAssembly without loading the entire file into memory and using a std::io::Cursor
.
Note: this only works in a web worker context because it uses the synchronous FileReaderSync interface.
Installation
Add to Cargo.toml:
wasm-bindgen-file-reader = "1"
Usage
See the demo for more information.
Rust code:
use wasm_bindgen_file_reader::WebSysFile;
use std::io::Read;
use std::io::Seek;
use std::io::SeekFrom;
/// Read one byte from the file at a given offset.
#[wasm_bindgen]
pub fn read_at_offset_sync(file: web_sys::File, offset: u64) -> u8 {
let mut wf = WebSysFile::new(file);
// Now we can seek as if this was a real file
wf.seek(SeekFrom::Start(offset))
.expect("failed to seek to offset");
// Use 1-byte buffer because we only want to read one byte
let mut buf = [0];
// The Read API works as with real files
wf.read_exact(&mut buf).expect("failed to read bytes");
buf[0]
}
Javascript code (index.html):
let myWorker = new Worker("worker.js");
document.getElementById("filepicker").addEventListener(
"change",
function() {
let file = this.files[0];
myWorker.postMessage({ file: file, offset: 0 });
myWorker.onmessage = function(e) {
console.log("First byte of file is: ", e.data);
};
},
false
);
Javascript code (worker.js):
onmessage = async function(e) {
let wasm_bindgen_file_reader_test = await Rust.wasm_bindgen_file_reader_test;
let workerResult = wasm_bindgen_file_reader_test.read_at_offset_sync(
e.data.file,
e.data.offset,
);
postMessage(workerResult);
};
Dependencies
~6.5–8.5MB
~171K SLoC