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iterator.js
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iterator.js
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const Buffer = require('warp-isomorphic').Buffer;
const leb128 = require('leb128').unsigned;
const wasm2json = require('./wasm2json.js');
const Pipe = require('buffer-pipe');
const SECTIONS = [
'custom',
'type',
'import',
'function',
'table',
'memory',
'global',
'export',
'start',
'element',
'code',
'data',
];
/**
* The Module Iterator allows for iteration over a webassembly module's sections.
* A section is wrapped in a section class. A section class instance allows you
* append entries to a given section
*/
module.exports = class ModuleIterator {
/**
* param {Buffer} wasm - a webassembly binary
*/
constructor(wasm) {
this._wasm = wasm;
this._sections = [];
this._modified = false;
}
/**
* if the orignal wasm module was modified then this will return the modified
* wasm module
*/
get wasm() {
if (this._modified) {
this._wasm = Buffer.concat(this._sections.concat(this._pipe.buffer));
this._modified = false;
}
return this._wasm;
}
/**
* Iterates through the module's sections
* return {Iterator.<Section>}
*/
*[Symbol.iterator]() {
this._pipe = new Pipe(this._wasm);
this._sections = [this._pipe.read(8)];
while (!this._pipe.end) {
const start = this._pipe.bytesRead;
const sectionType = this._pipe.read(1)[0];
const size = Number(leb128.read(this._pipe));
const body = this._pipe.read(size);
const end = this._pipe.bytesRead;
const section = this._wasm.slice(start, end);
const index = this._sections.push(section) - 1;
yield new Section(sectionType, body, this, index);
}
}
_update(index, data) {
this._modified = true;
this._sections[index] = data;
}
};
/**
* The section class is always internal created by the Module class. And return
* through the Module's iternator
*/
class Section {
constructor(sectionType, section, it, index) {
this._it = it;
this._index = index;
this.type = SECTIONS[sectionType];
this._type = sectionType;
this._section = section;
const pipe = new Pipe(section);
if (this.type !== 'custom') {
this.count = Number(leb128.read(pipe));
}
this._body = pipe.buffer;
}
/**
* Parses the section and return the JSON repesentation of it
* returns {Object}
*/
toJSON() {
return wasm2json.sectionParsers[this.type](new Pipe(this._section));
}
/**
* Appends an array of entries to this section. NOTE: this will modify the
* parent wasm module.
* @param {Arrayy.<Buffer>} entries
*/
appendEntries(entries) {
this.count += entries.length;
this._body = Buffer.concat([this._body].concat(entries));
const bodyAndCount = Buffer.concat([leb128.encode(this.count), this._body]);
// encode length has save modifed section
this._it._update(
this._index,
Buffer.concat([
Buffer.from([this._type]),
leb128.encode(bodyAndCount.length),
bodyAndCount,
])
);
}
}