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// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
//! This example shows you how to define ops in Rust and then call them from
//! JavaScript.
use anyhow::anyhow;
use deno_core::json_op_sync;
use deno_core::JsRuntime;
use deno_core::Op;
use serde_json::Value;
use std::io::Write;
fn main() {
// Initialize a runtime instance
let mut runtime = JsRuntime::new(Default::default());
// The first thing we do is define two ops. They will be used to show how to
// pass data to Rust and back to JavaScript.
//
// The first one is used to print data to stdout, because by default the
// JavaScript console functions are just stubs (they don't do anything).
//
// The second one just transforms some input and returns it to JavaScript.
// Register the op for outputting bytes to stdout.
// It can be invoked with Deno.core.dispatch and the id this method returns
// or Deno.core.dispatchByName and the name provided.
runtime.register_op(
"op_print",
// The op_fn callback takes a state object OpState
// and a vector of ZeroCopyBuf's, which are mutable references
// to ArrayBuffer's in JavaScript.
|_state, zero_copy| {
let mut out = std::io::stdout();
// Write the contents of every buffer to stdout
for buf in zero_copy {
out.write_all(&buf).unwrap();
}
Op::Sync(Box::new([])) // No meaningful result
},
);
// Register the JSON op for summing a number array.
// A JSON op is just an op where the first ZeroCopyBuf is a serialized JSON
// value, the return value is also a serialized JSON value. It can be invoked
// with Deno.core.jsonOpSync and the name.
runtime.register_op(
"op_sum",
// The json_op_sync function automatically deserializes
// the first ZeroCopyBuf and serializes the return value
// to reduce boilerplate
json_op_sync(|_state, json: Vec<f64>, zero_copy| {
// We check that we only got the JSON value.
if !zero_copy.is_empty() {
Err(anyhow!("Expected exactly one argument"))
} else {
// And if we did, do our actual task
let sum = json.iter().fold(0.0, |a, v| a + v);
// Finally we return a JSON value
Ok(Value::from(sum))
}
}),
);
// Now we see how to invoke the ops we just defined. The runtime automatically
// contains a Deno.core object with several functions for interacting with it.
// You can find its definition in core.js.
runtime.execute(
"<init>",
r#"
// First we initialize the ops cache.
// This maps op names to their id's.
Deno.core.ops();
// Then we define a print function that uses
// our op_print op to display the stringified argument.
const _newline = new Uint8Array([10]);
function print(value) {
Deno.core.dispatchByName('op_print', Deno.core.encode(value.toString()), _newline);
}
// Finally we register the error class used by op_sum
// so that it throws the correct class.
Deno.core.registerErrorClass('Error', Error);
"#,
).unwrap();
// Now we can finally use this in an example.
runtime
.execute(
"<usage>",
r#"
const arr = [1, 2, 3];
print("The sum of");
print(arr);
print("is");
print(Deno.core.jsonOpSync('op_sum', arr));
// And incorrect usage
try {
print(Deno.core.jsonOpSync('op_sum', 0));
} catch(e) {
print('Exception:');
print(e);
}
"#,
)
.unwrap();
}
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