114 lines
3.1 KiB
JavaScript
114 lines
3.1 KiB
JavaScript
'use strict'
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const assert = require('assert')
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const Joi = require('joi')
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const coalesce = require('./coalesce')
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const serverStartTimeGMTString = new Date().toGMTString()
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const serverStartTimestamp = Date.now()
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const queryParamSchema = Joi.object({
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// Not using nonNegativeInteger because it's not required.
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maxAge: Joi.number()
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.integer()
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.min(0),
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})
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.unknown(true)
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.required()
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function overrideCacheLengthFromQueryParams(queryParams) {
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try {
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const { maxAge: overrideCacheLength } = Joi.attempt(
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queryParams,
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queryParamSchema,
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{ allowUnknown: true }
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)
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return overrideCacheLength
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} catch (e) {
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return undefined
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}
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}
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function coalesceCacheLength({
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cacheHeaderConfig,
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serviceDefaultCacheLengthSeconds,
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serviceOverrideCacheLengthSeconds,
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queryParams,
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}) {
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const { defaultCacheLengthSeconds } = cacheHeaderConfig
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// The config returns a number so this should never happen. But this logic
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// would be completely broken if it did.
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assert(defaultCacheLengthSeconds !== undefined)
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const cacheLength = coalesce(
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serviceDefaultCacheLengthSeconds,
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defaultCacheLengthSeconds
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)
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// Overrides can apply _more_ caching, but not less. Query param overriding
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// can request more overriding than service override, but not less.
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const candidateOverrides = [
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serviceOverrideCacheLengthSeconds,
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overrideCacheLengthFromQueryParams(queryParams),
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].filter(x => x !== undefined)
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return Math.max(cacheLength, ...candidateOverrides)
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}
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function setHeadersForCacheLength(res, cacheLengthSeconds) {
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const now = new Date()
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const nowGMTString = now.toGMTString()
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// Send both Cache-Control max-age and Expires in case the client implements
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// HTTP/1.0 but not HTTP/1.1.
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let cacheControl, expires
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if (cacheLengthSeconds === 0) {
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// Prevent as much downstream caching as possible.
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cacheControl = 'no-cache, no-store, must-revalidate'
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expires = nowGMTString
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} else {
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cacheControl = `max-age=${cacheLengthSeconds}`
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expires = new Date(now.getTime() + cacheLengthSeconds * 1000).toGMTString()
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}
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res.setHeader('Date', nowGMTString)
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res.setHeader('Cache-Control', cacheControl)
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res.setHeader('Expires', expires)
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}
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function setCacheHeaders({
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cacheHeaderConfig,
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serviceDefaultCacheLengthSeconds,
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serviceOverrideCacheLengthSeconds,
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queryParams,
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res,
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}) {
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const cacheLengthSeconds = coalesceCacheLength({
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cacheHeaderConfig,
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serviceDefaultCacheLengthSeconds,
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serviceOverrideCacheLengthSeconds,
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queryParams,
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})
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setHeadersForCacheLength(res, cacheLengthSeconds)
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}
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const staticCacheControlHeader = `max-age=${24 * 3600}` // 1 day.
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function setCacheHeadersForStaticResource(res) {
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res.setHeader('Cache-Control', staticCacheControlHeader)
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res.setHeader('Last-Modified', serverStartTimeGMTString)
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}
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function serverHasBeenUpSinceResourceCached(req) {
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return (
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serverStartTimestamp <= new Date(req.headers['if-modified-since']).getTime()
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)
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}
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module.exports = {
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coalesceCacheLength,
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setCacheHeaders,
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setHeadersForCacheLength,
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setCacheHeadersForStaticResource,
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serverHasBeenUpSinceResourceCached,
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}
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