mirror of
https://github.com/ClusterCockpit/cc-backend
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125 lines
3.4 KiB
Go
125 lines
3.4 KiB
Go
// Copyright (C) 2022 NHR@FAU, University Erlangen-Nuremberg.
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// All rights reserved.
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// Use of this source code is governed by a MIT-style
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// license that can be found in the LICENSE file.
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package lrucache
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import (
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"bytes"
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"net/http"
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"strconv"
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"time"
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)
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// HttpHandler is can be used as HTTP Middleware in order to cache requests,
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// for example static assets. By default, the request's raw URI is used as key and nothing else.
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// Results with a status code other than 200 are cached with a TTL of zero seconds,
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// so basically re-fetched as soon as the current fetch is done and a new request
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// for that URI is done.
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type HttpHandler struct {
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cache *Cache
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fetcher http.Handler
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defaultTTL time.Duration
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// Allows overriding the way the cache key is extracted
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// from the http request. The defailt is to use the RequestURI.
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CacheKey func(*http.Request) string
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}
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var _ http.Handler = (*HttpHandler)(nil)
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type cachedResponseWriter struct {
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w http.ResponseWriter
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statusCode int
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buf bytes.Buffer
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}
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type cachedResponse struct {
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headers http.Header
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statusCode int
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data []byte
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fetched time.Time
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}
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var _ http.ResponseWriter = (*cachedResponseWriter)(nil)
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func (crw *cachedResponseWriter) Header() http.Header {
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return crw.w.Header()
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}
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func (crw *cachedResponseWriter) Write(bytes []byte) (int, error) {
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return crw.buf.Write(bytes)
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}
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func (crw *cachedResponseWriter) WriteHeader(statusCode int) {
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crw.statusCode = statusCode
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}
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// Returns a new caching HttpHandler. If no entry in the cache is found or it was too old, `fetcher` is called with
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// a modified http.ResponseWriter and the response is stored in the cache. If `fetcher` sets the "Expires" header,
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// the ttl is set appropriately (otherwise, the default ttl passed as argument here is used).
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// `maxmemory` should be in the unit bytes.
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func NewHttpHandler(maxmemory int, ttl time.Duration, fetcher http.Handler) *HttpHandler {
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return &HttpHandler{
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cache: New(maxmemory),
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defaultTTL: ttl,
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fetcher: fetcher,
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CacheKey: func(r *http.Request) string {
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return r.RequestURI
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},
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}
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}
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// gorilla/mux style middleware:
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func NewMiddleware(maxmemory int, ttl time.Duration) func(http.Handler) http.Handler {
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return func(next http.Handler) http.Handler {
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return NewHttpHandler(maxmemory, ttl, next)
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}
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}
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// Tries to serve a response to r from cache or calls next and stores the response to the cache for the next time.
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func (h *HttpHandler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
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if r.Method != http.MethodGet {
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h.ServeHTTP(rw, r)
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return
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}
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cr := h.cache.Get(h.CacheKey(r), func() (interface{}, time.Duration, int) {
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crw := &cachedResponseWriter{
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w: rw,
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statusCode: 200,
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buf: bytes.Buffer{},
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}
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h.fetcher.ServeHTTP(crw, r)
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cr := &cachedResponse{
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headers: rw.Header().Clone(),
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statusCode: crw.statusCode,
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data: crw.buf.Bytes(),
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fetched: time.Now(),
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}
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cr.headers.Set("Content-Length", strconv.Itoa(len(cr.data)))
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ttl := h.defaultTTL
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if cr.statusCode != http.StatusOK {
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ttl = 0
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} else if cr.headers.Get("Expires") != "" {
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if expires, err := http.ParseTime(cr.headers.Get("Expires")); err == nil {
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ttl = time.Until(expires)
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}
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}
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return cr, ttl, len(cr.data)
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}).(*cachedResponse)
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for key, val := range cr.headers {
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rw.Header()[key] = val
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}
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cr.headers.Set("Age", strconv.Itoa(int(time.Since(cr.fetched).Seconds())))
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rw.WriteHeader(cr.statusCode)
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rw.Write(cr.data)
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}
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