晋太元中，武陵人捕鱼为业。缘溪行，忘路之远近。忽逢桃花林，夹岸数百步，中无杂树，芳草鲜美，落英缤纷。渔人甚异之，复前行，欲穷其林。 　　林尽水源，便得一山，山有小口，仿佛若有光。便舍船，从口入。初极狭，才通人。复行数十步，豁然开朗。土地平旷，屋舍俨然，有良田、美池、桑竹之属。阡陌交通，鸡犬相闻。其中往来种作，男女衣着，悉如外人。黄发垂髫，并怡然自乐。 　　见渔人，乃大惊，问所从来。具答之。便要还家，设酒杀鸡作食。村中闻有此人，咸来问讯。自云先世避秦时乱，率妻子邑人来此绝境，不复出焉，遂与外人间隔。问今是何世，乃不知有汉，无论魏晋。此人一一为具言所闻，皆叹惋。余人各复延至其家，皆出酒食。停数日，辞去。此中人语云：“不足为外人道也。”(间隔 一作：隔绝) 　　既出，得其船，便扶向路，处处志之。及郡下，诣太守，说如此。太守即遣人随其往，寻向所志，遂迷，不复得路。 　　南阳刘子骥，高尚士也，闻之，欣然规往。未果，寻病终。后遂无问津者。 sh-3ll

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Current File : //lib/node_modules/npm/node_modules/cacache/get.js
'use strict'

const BB = require('bluebird')

const figgyPudding = require('figgy-pudding')
const fs = require('fs')
const index = require('./lib/entry-index')
const memo = require('./lib/memoization')
const pipe = require('mississippi').pipe
const pipeline = require('mississippi').pipeline
const read = require('./lib/content/read')
const through = require('mississippi').through

const GetOpts = figgyPudding({
  integrity: {},
  memoize: {},
  size: {}
})

module.exports = function get (cache, key, opts) {
  return getData(false, cache, key, opts)
}
module.exports.byDigest = function getByDigest (cache, digest, opts) {
  return getData(true, cache, digest, opts)
}
function getData (byDigest, cache, key, opts) {
  opts = GetOpts(opts)
  const memoized = (
    byDigest
      ? memo.get.byDigest(cache, key, opts)
      : memo.get(cache, key, opts)
  )
  if (memoized && opts.memoize !== false) {
    return BB.resolve(byDigest ? memoized : {
      metadata: memoized.entry.metadata,
      data: memoized.data,
      integrity: memoized.entry.integrity,
      size: memoized.entry.size
    })
  }
  return (
    byDigest ? BB.resolve(null) : index.find(cache, key, opts)
  ).then(entry => {
    if (!entry && !byDigest) {
      throw new index.NotFoundError(cache, key)
    }
    return read(cache, byDigest ? key : entry.integrity, {
      integrity: opts.integrity,
      size: opts.size
    }).then(data => byDigest ? data : {
      metadata: entry.metadata,
      data: data,
      size: entry.size,
      integrity: entry.integrity
    }).then(res => {
      if (opts.memoize && byDigest) {
        memo.put.byDigest(cache, key, res, opts)
      } else if (opts.memoize) {
        memo.put(cache, entry, res.data, opts)
      }
      return res
    })
  })
}

module.exports.sync = function get (cache, key, opts) {
  return getDataSync(false, cache, key, opts)
}
module.exports.sync.byDigest = function getByDigest (cache, digest, opts) {
  return getDataSync(true, cache, digest, opts)
}
function getDataSync (byDigest, cache, key, opts) {
  opts = GetOpts(opts)
  const memoized = (
    byDigest
      ? memo.get.byDigest(cache, key, opts)
      : memo.get(cache, key, opts)
  )
  if (memoized && opts.memoize !== false) {
    return byDigest ? memoized : {
      metadata: memoized.entry.metadata,
      data: memoized.data,
      integrity: memoized.entry.integrity,
      size: memoized.entry.size
    }
  }
  const entry = !byDigest && index.find.sync(cache, key, opts)
  if (!entry && !byDigest) {
    throw new index.NotFoundError(cache, key)
  }
  const data = read.sync(
    cache,
    byDigest ? key : entry.integrity,
    {
      integrity: opts.integrity,
      size: opts.size
    }
  )
  const res = byDigest
    ? data
    : {
      metadata: entry.metadata,
      data: data,
      size: entry.size,
      integrity: entry.integrity
    }
  if (opts.memoize && byDigest) {
    memo.put.byDigest(cache, key, res, opts)
  } else if (opts.memoize) {
    memo.put(cache, entry, res.data, opts)
  }
  return res
}

module.exports.stream = getStream
function getStream (cache, key, opts) {
  opts = GetOpts(opts)
  let stream = through()
  const memoized = memo.get(cache, key, opts)
  if (memoized && opts.memoize !== false) {
    stream.on('newListener', function (ev, cb) {
      ev === 'metadata' && cb(memoized.entry.metadata)
      ev === 'integrity' && cb(memoized.entry.integrity)
      ev === 'size' && cb(memoized.entry.size)
    })
    stream.write(memoized.data, () => stream.end())
    return stream
  }
  index.find(cache, key).then(entry => {
    if (!entry) {
      return stream.emit(
        'error', new index.NotFoundError(cache, key)
      )
    }
    let memoStream
    if (opts.memoize) {
      let memoData = []
      let memoLength = 0
      memoStream = through((c, en, cb) => {
        memoData && memoData.push(c)
        memoLength += c.length
        cb(null, c, en)
      }, cb => {
        memoData && memo.put(cache, entry, Buffer.concat(memoData, memoLength), opts)
        cb()
      })
    } else {
      memoStream = through()
    }
    stream.emit('metadata', entry.metadata)
    stream.emit('integrity', entry.integrity)
    stream.emit('size', entry.size)
    stream.on('newListener', function (ev, cb) {
      ev === 'metadata' && cb(entry.metadata)
      ev === 'integrity' && cb(entry.integrity)
      ev === 'size' && cb(entry.size)
    })
    pipe(
      read.readStream(cache, entry.integrity, opts.concat({
        size: opts.size == null ? entry.size : opts.size
      })),
      memoStream,
      stream
    )
  }).catch(err => stream.emit('error', err))
  return stream
}

module.exports.stream.byDigest = getStreamDigest
function getStreamDigest (cache, integrity, opts) {
  opts = GetOpts(opts)
  const memoized = memo.get.byDigest(cache, integrity, opts)
  if (memoized && opts.memoize !== false) {
    const stream = through()
    stream.write(memoized, () => stream.end())
    return stream
  } else {
    let stream = read.readStream(cache, integrity, opts)
    if (opts.memoize) {
      let memoData = []
      let memoLength = 0
      const memoStream = through((c, en, cb) => {
        memoData && memoData.push(c)
        memoLength += c.length
        cb(null, c, en)
      }, cb => {
        memoData && memo.put.byDigest(
          cache,
          integrity,
          Buffer.concat(memoData, memoLength),
          opts
        )
        cb()
      })
      stream = pipeline(stream, memoStream)
    }
    return stream
  }
}

module.exports.info = info
function info (cache, key, opts) {
  opts = GetOpts(opts)
  const memoized = memo.get(cache, key, opts)
  if (memoized && opts.memoize !== false) {
    return BB.resolve(memoized.entry)
  } else {
    return index.find(cache, key)
  }
}

module.exports.hasContent = read.hasContent

module.exports.copy = function cp (cache, key, dest, opts) {
  return copy(false, cache, key, dest, opts)
}
module.exports.copy.byDigest = function cpDigest (cache, digest, dest, opts) {
  return copy(true, cache, digest, dest, opts)
}
function copy (byDigest, cache, key, dest, opts) {
  opts = GetOpts(opts)
  if (read.copy) {
    return (
      byDigest ? BB.resolve(null) : index.find(cache, key, opts)
    ).then(entry => {
      if (!entry && !byDigest) {
        throw new index.NotFoundError(cache, key)
      }
      return read.copy(
        cache, byDigest ? key : entry.integrity, dest, opts
      ).then(() => byDigest ? key : {
        metadata: entry.metadata,
        size: entry.size,
        integrity: entry.integrity
      })
    })
  } else {
    return getData(byDigest, cache, key, opts).then(res => {
      return fs.writeFileAsync(dest, byDigest ? res : res.data)
        .then(() => byDigest ? key : {
          metadata: res.metadata,
          size: res.size,
          integrity: res.integrity
        })
    })
  }
}