'use strict'
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/**
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* Module dependencies.
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*/
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const compressible = require('compressible')
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const isJSON = require('koa-is-json')
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const status = require('statuses')
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const Stream = require('stream')
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const bytes = require('bytes')
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const zlib = require('zlib')
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/**
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* Encoding methods supported.
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*/
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const encodingMethods = {
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gzip: zlib.createGzip,
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deflate: zlib.createDeflate
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}
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/**
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* Regex to match no-transform directive in a cache-control header
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*/
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const NO_TRANSFORM_REGEX = /(?:^|,)\s*?no-transform\s*?(?:,|$)/
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/**
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* Compress middleware.
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*
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* @param {Object} [options]
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* @return {Function}
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* @api public
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*/
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module.exports = (options = {}) => {
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let { filter = compressible, threshold = 1024 } = options
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if (typeof threshold === 'string') threshold = bytes(threshold)
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return async (ctx, next) => {
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ctx.vary('Accept-Encoding')
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await next()
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let { body } = ctx
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if (!body) return
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if (ctx.res.headersSent || !ctx.writable) return
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if (ctx.compress === false) return
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if (ctx.request.method === 'HEAD') return
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if (status.empty[ctx.response.status]) return
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if (ctx.response.get('Content-Encoding')) return
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// forced compression or implied
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if (!(ctx.compress === true || filter(ctx.response.type))) return
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// Don't compress for Cache-Control: no-transform
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// https://tools.ietf.org/html/rfc7234#section-5.2.1.6
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const cacheControl = ctx.response.get('Cache-Control')
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if (cacheControl && NO_TRANSFORM_REGEX.test(cacheControl)) return
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// identity
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const encoding = ctx.acceptsEncodings('gzip', 'deflate', 'identity')
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if (!encoding) ctx.throw(406, 'supported encodings: gzip, deflate, identity')
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if (encoding === 'identity') return
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// json
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if (isJSON(body)) body = ctx.body = JSON.stringify(body)
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// threshold
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if (threshold && ctx.response.length < threshold) return
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ctx.set('Content-Encoding', encoding)
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ctx.res.removeHeader('Content-Length')
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const stream = ctx.body = encodingMethods[encoding](options)
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if (body instanceof Stream) {
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body.pipe(stream)
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} else {
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stream.end(body)
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}
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}
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}
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