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libghostty: simplify Wasm allocation API

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Replace a bunch of type-specific Wasm allocation functions with a generic
byte allocator and reusable opaque out-parameters for pointers. This
makes it a lot more ergonomic (relatively) to use the Wasm interface
and removes a dozen or so exports.

This also updates the `ghostty_type_json` `abi` field with a maximum
alignment value that host sides can use to keep every allocation aligned
properly, easily, without hardcoding numbers.

This adds a test to verify this all works as intended and runs in CI.
This commit is contained in:
Mitchell Hashimoto
2026-08-16 12:37:16 -07:00
parent 0ba6250388
commit a8e9b413f1
17 changed files with 481 additions and 243 deletions
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60
example/wasm-key-encode/index.html
View File

@@ -163,6 +163,7 @@
let wasmMemory = null;
let encoderPtr = null;
let lastKeyEvent = null;
let typeLayout = null;
async function loadWasm() {
try {
@@ -184,6 +185,12 @@
wasmInstance = wasmModule.instance;
wasmMemory = wasmInstance.exports.memory;
const jsonPtr = wasmInstance.exports.ghostty_type_json();
const jsonStr = new TextDecoder().decode(
new Uint8Array(wasmMemory.buffer, jsonPtr, wasmMemory.buffer.byteLength - jsonPtr)
).split('\0')[0];
typeLayout = JSON.parse(jsonStr);
return true;
} catch (e) {
@@ -199,6 +206,15 @@
return wasmMemory.buffer;
}
function readUsize(ptr) {
const view = new DataView(getBuffer());
switch (typeLayout.abi.usize_size) {
case 4: return view.getUint32(ptr, true);
case 8: return Number(view.getBigUint64(ptr, true));
default: throw new Error('unsupported size_t width');
}
}
function formatHex(bytes) {
return Array.from(bytes)
.map(b => b.toString(16).padStart(2, '0'))
@@ -415,16 +431,28 @@
function encodeKeyEvent(event) {
if (!encoderPtr) return null;
const usizeSize = typeLayout.abi.usize_size;
let eventPtrPtr = 0;
let eventPtr = 0;
let utf8Ptr = 0;
let utf8Length = 0;
let requiredPtr = 0;
let required = 0;
let bufPtr = 0;
let writtenPtr = 0;
try {
// Create key event
const eventPtrPtr = wasmInstance.exports.ghostty_wasm_alloc_opaque();
eventPtrPtr = wasmInstance.exports.ghostty_wasm_alloc_opaque();
const result = wasmInstance.exports.ghostty_key_event_new(0, eventPtrPtr);
if (result !== 0) {
throw new Error(`ghostty_key_event_new failed with result ${result}`);
}
const eventPtr = new DataView(getBuffer()).getUint32(eventPtrPtr, true);
eventPtr = wasmInstance.exports.ghostty_wasm_take_opaque(eventPtrPtr);
wasmInstance.exports.ghostty_wasm_free_opaque(eventPtrPtr);
eventPtrPtr = 0;
// Get action from radio buttons
const actionRadio = document.querySelector('input[name="action"]:checked');
@@ -458,9 +486,10 @@
// Set UTF-8 text from the key event (the actual character produced)
if (event.key.length === 1) {
const utf8Bytes = new TextEncoder().encode(event.key);
const utf8Ptr = wasmInstance.exports.ghostty_wasm_alloc_u8_array(utf8Bytes.length);
utf8Length = utf8Bytes.length;
utf8Ptr = wasmInstance.exports.ghostty_wasm_alloc(utf8Length);
new Uint8Array(getBuffer()).set(utf8Bytes, utf8Ptr);
wasmInstance.exports.ghostty_key_event_set_utf8(eventPtr, utf8Ptr, utf8Bytes.length);
wasmInstance.exports.ghostty_key_event_set_utf8(eventPtr, utf8Ptr, utf8Length);
}
// Set unshifted codepoint
@@ -470,15 +499,15 @@
}
// Encode the key event
const requiredPtr = wasmInstance.exports.ghostty_wasm_alloc_usize();
requiredPtr = wasmInstance.exports.ghostty_wasm_alloc(usizeSize);
wasmInstance.exports.ghostty_key_encoder_encode(
encoderPtr, eventPtr, 0, 0, requiredPtr
);
const required = new DataView(getBuffer()).getUint32(requiredPtr, true);
required = readUsize(requiredPtr);
const bufPtr = wasmInstance.exports.ghostty_wasm_alloc_u8_array(required);
const writtenPtr = wasmInstance.exports.ghostty_wasm_alloc_usize();
bufPtr = wasmInstance.exports.ghostty_wasm_alloc(required);
writtenPtr = wasmInstance.exports.ghostty_wasm_alloc(usizeSize);
const encodeResult = wasmInstance.exports.ghostty_key_encoder_encode(
encoderPtr, eventPtr, bufPtr, required, writtenPtr
);
@@ -487,7 +516,7 @@
return null; // No encoding for this key
}
const written = new DataView(getBuffer()).getUint32(writtenPtr, true);
const written = readUsize(writtenPtr);
const encoded = new Uint8Array(getBuffer()).slice(bufPtr, bufPtr + written);
return {
@@ -498,6 +527,13 @@
} catch (e) {
console.error('Encoding error:', e);
return null;
} finally {
wasmInstance.exports.ghostty_wasm_free(writtenPtr, usizeSize);
wasmInstance.exports.ghostty_wasm_free(bufPtr, required);
wasmInstance.exports.ghostty_wasm_free(requiredPtr, usizeSize);
wasmInstance.exports.ghostty_wasm_free(utf8Ptr, utf8Length);
wasmInstance.exports.ghostty_key_event_free(eventPtr);
wasmInstance.exports.ghostty_wasm_free_opaque(eventPtrPtr);
}
}
@@ -555,13 +591,14 @@
if (!encoderPtr) return;
const flags = getKittyFlags();
const flagsPtr = wasmInstance.exports.ghostty_wasm_alloc_u8();
const flagsPtr = wasmInstance.exports.ghostty_wasm_alloc(1);
new DataView(getBuffer()).setUint8(flagsPtr, flags);
wasmInstance.exports.ghostty_key_encoder_setopt(
encoderPtr,
5, // GHOSTTY_KEY_ENCODER_OPT_KITTY_FLAGS
flagsPtr
);
wasmInstance.exports.ghostty_wasm_free(flagsPtr, 1);
// Re-encode last key with new flags
reencodeLastKey();
@@ -649,7 +686,8 @@
throw new Error(`ghostty_key_encoder_new failed with result ${result}`);
}
encoderPtr = new DataView(getBuffer()).getUint32(encoderPtrPtr, true);
encoderPtr = wasmInstance.exports.ghostty_wasm_take_opaque(encoderPtrPtr);
wasmInstance.exports.ghostty_wasm_free_opaque(encoderPtrPtr);
// Set kitty flags based on checkboxes
updateEncoderFlags();