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seekers.js
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seekers.js
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const varint = require('fast-varint')
const { decode } = require('./decode')
const { STRING, OBJECT, TAG_SIZE, TAG_MASK } = require('./constants')
// buffer -> start -> target -> result
// WeakMap<Buffer, Map<number, Map<string, number>>>
const cache1 = new WeakMap()
// TODO rewrite the seek methods so that there is minimal copies.
function seekKey(buffer, start, target) {
if (start === -1) return -1
const tag = varint.decode(buffer, start)
const type = tag & TAG_MASK
if (type !== OBJECT) return -1
target = Buffer.isBuffer(target) ? target : Buffer.from(target)
const targetLength = target.length
const len = tag >> TAG_SIZE
for (let c = varint.decode.bytes; c < len; ) {
const keyTag = varint.decode(buffer, start + c)
c += varint.decode.bytes
const keyLen = keyTag >> TAG_SIZE
const keyType = keyTag & TAG_MASK
if (keyType === STRING && targetLength === keyLen)
if (
buffer.compare(
target,
0,
targetLength,
start + c,
start + c + targetLength
) === 0
)
return start + c + keyLen
c += keyLen
const valueTag = varint.decode(buffer, start + c)
c += varint.decode.bytes
const valueLen = valueTag >> TAG_SIZE
c += valueLen
}
return -1
}
function createSeekPathSrc(target) {
return (
'"use strict";\n' + //go fast sauce!
target
.map(function (e, i) {
return ' var k' + i + ' = Buffer.from(' + JSON.stringify(e) + ');' //strings only!
})
.join('\n') +
'\n' +
' return function (buffer, start) {\n' +
target
.map(function (_, i) {
return ' start = seekKey(buffer, start, k' + i + ')'
})
.join('\n') +
'\n' +
' return start;\n' +
'}\n'
)
}
function seekKey2(buffer, start, target, targetStart) {
const tag = varint.decode(buffer, start)
const type = tag & TAG_MASK
if (type !== OBJECT) return -1
let c = varint.decode.bytes
const len = tag >> TAG_SIZE
const targetTag = varint.decode(target, targetStart)
const targetLen = (targetTag >> TAG_SIZE) + varint.decode.bytes
for (; c < len; ) {
const keyTag = varint.decode(buffer, start + c)
if (
keyTag === targetTag &&
buffer.compare(
target,
targetStart,
targetLen,
start + c,
start + c + targetLen
) === 0
)
return start + c + targetLen
c += varint.decode.bytes
const keyLen = keyTag >> TAG_SIZE
c += keyLen
const valueTag = varint.decode(buffer, start + c)
c += varint.decode.bytes
const valueLen = valueTag >> TAG_SIZE
c += valueLen
}
return -1
}
function seekKeyCached(buffer, start, target) {
let cache2 = cache1.get(buffer)
if (!cache2) cache1.set(buffer, (cache2 = new Map()))
let cache3 = cache2.get(start)
if (!cache3) cache2.set(start, (cache3 = new Map()))
if (typeof target !== 'string') {
throw new Error('seekKeyCached only supports string target')
}
if (cache3.has(target)) {
return cache3.get(target)
} else {
const result = seekKey(buffer, start, target)
cache3.set(target, result)
return result
}
}
function seekPath(buffer, start, target, targetStart) {
targetStart = targetStart || 0
const ary = decode(target, targetStart)
if (!Array.isArray(ary)) throw new Error('path must be encoded array')
for (let i = 0; i < ary.length; i++) {
var string = ary[i]
start = seekKey(buffer, start, string)
if (start === -1) return -1
}
return start
}
function createSeekPath(target) {
return new Function('seekKey', createSeekPathSrc(target))(seekKey)
}
module.exports = {
seekKey,
seekKey2,
seekKeyCached,
seekPath,
createSeekPathSrc,
createSeekPath,
}