httpcache/roundtripper.go at master · bartventer/httpcache · GitHub

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// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

// Package httpcache provides an implementation of http.RoundTripper that adds

// transparent HTTP response caching according to RFC 9111 (HTTP Caching).

// The main entry point is [NewTransport], which returns an [http.RoundTripper] for use with [http.Client].

// httpcache supports the required standard HTTP caching directives, as well as extension directives such as

// stale-while-revalidate, stale-if-error and immutable.

// Example usage:

// package main

// import (

// "log/slog"

// "net/http"

// "time"

// "github.com/bartventer/httpcache"

// // Register a cache backend by importing the package

// _ "github.com/bartventer/httpcache/store/fscache"

// )

// func main() {

// dsn := "fscache://?appname=myapp" // Example DSN for the file system cache backend

// client := &http.Client{

// Transport: httpcache.NewTransport(

// dsn,

// httpcache.WithSWRTimeout(10*time.Second),

// httpcache.WithLogger(slog.Default()),

// ),

// }

package httpcache

import (

"cmp"

"context"

"errors"

"iter"

"log/slog"

"net/http"

"time"

"github.com/bartventer/httpcache/internal"

"github.com/bartventer/httpcache/store"

"github.com/bartventer/httpcache/store/driver"

)

const (

DefaultSWRTimeout = 5 * time.Second

CacheStatusHeader = internal.CacheStatusHeader

)

// transport is an implementation of [http.RoundTripper] that caches HTTP responses

// according to the HTTP caching rules defined in RFC 9111.

type transport struct {

// Configurable options

cache internal.ResponseCache // Cache for storing and retrieving responses

upstream http.RoundTripper // Underlying round tripper for upstream/origin requests

swrTimeout time.Duration // Timeout for Stale-While-Revalidate requests

logger *internal.Logger // Logger for debug output, if needed

// Internal details

rmc internal.RequestMethodChecker // Checks if HTTP request methods are understood

vm internal.VaryMatcher // Matches Vary headers to determine cache validity

uk internal.URLKeyer // Generates unique cache keys for requests

fc internal.FreshnessCalculator // Calculates the freshness of cached responses

ce internal.CacheabilityEvaluator // Evaluates if a response is cacheable

siep internal.StaleIfErrorPolicy // Handles stale-if-error caching policies

ci internal.CacheInvalidator // Invalidates cache entries based on conditions

rs internal.ResponseStorer // Stores HTTP responses in the cache

vrh internal.ValidationResponseHandler // Processes validation responses for revalidation

clock internal.Clock // Provides time-related operations, can be mocked for testing

}

// ErrOpenCache is used as the panic value when the cache cannot be opened.

// You may recover from this panic if you wish to handle the situation gracefully.

// Example usage:

// defer func() {

// if r := recover(); r != nil {

// if err, ok := r.(error); ok && errors.Is(err, ErrOpenCache) {

// // Handle the error gracefully, e.g., log it or return a default transport

// log.Println("Failed to open cache:", err)

// client := &http.Client{

// Transport: http.DefaultTransport, // Fallback to default transport

// }

// // Use the fallback client as needed

// _ = client

// } else {

// // Re-panic if it's not the expected error

// panic(r)

// }

// }()

var ErrOpenCache = errors.New("httpcache: failed to open cache")

// NewTransport returns an [http.RoundTripper] that caches HTTP responses using

// the specified cache backend.

// The dsn parameter follows the format documented in [store.Open].

// Configuration is done via functional options like [WithUpstream] and

// [WithSWRTimeout].

// Panics with [ErrOpenCache] if the cache backend cannot be opened.

func NewTransport(dsn string, options ...Option) http.RoundTripper {

cache, err := store.Open(dsn)

if err != nil {

panic(ErrOpenCache)

}

return newTransport(cache, options...)

}

func newTransport(conn driver.Conn, options ...Option) http.RoundTripper {

rt := &transport{

cache: internal.NewResponseCache(conn),

rmc: internal.NewRequestMethodChecker(),

vm: internal.NewVaryMatcher(internal.NewHeaderValueNormalizer()),

uk: internal.NewURLKeyer(),

ce: internal.NewCacheabilityEvaluator(),

clock: internal.NewClock(),

}

for _, opt := range options {

opt.apply(rt)

}

rt.upstream = cmp.Or(rt.upstream, http.DefaultTransport)

rt.swrTimeout = cmp.Or(max(rt.swrTimeout, 0), DefaultSWRTimeout)

if rt.logger == nil {

rt.logger = internal.NewLogger(slog.DiscardHandler)

}

rt.fc = internal.NewFreshnessCalculator(rt.clock)

rt.ci = internal.NewCacheInvalidator(rt.cache, rt.uk)

rt.siep = internal.NewStaleIfErrorPolicy(rt.clock)

rt.rs = internal.NewResponseStorer(

rt.cache,

internal.NewVaryHeaderNormalizer(),

internal.NewVaryKeyer(),

)

rt.vrh = internal.NewValidationResponseHandler(

rt.logger,

rt.clock,

rt.ci,

rt.ce,

rt.siep,

rt.rs,

)

return rt

}

// NewClient returns a new [http.Client], configured with a transport that

// caches HTTP responses, using the specified cache backend DSN.

// See [NewTransport] for details on the DSN and available options.

func NewClient(dsn string, options ...Option) *http.Client {

return &http.Client{Transport: NewTransport(dsn, options...)}

}

var _ http.RoundTripper = (*transport)(nil)

func (r *transport) RoundTrip(req *http.Request) (*http.Response, error) {

urlKey := r.uk.URLKey(req.URL)

if !r.rmc.IsRequestMethodUnderstood(req) {

return r.handleUnrecognizedMethod(req, urlKey)

}

refs, err := r.cache.GetRefs(urlKey)

if err != nil || len(refs) == 0 {

return r.handleCacheMiss(req, urlKey, nil, -1)

}

refIndex, found := r.vm.VaryHeadersMatch(refs, req.Header)

if !found {

return r.handleCacheMiss(req, urlKey, refs, -1)

}

entry, err := r.cache.Get(refs[refIndex].ResponseID, req)

if err != nil {

r.logger.LogCacheError(

"Error retrieving cache entry; possible corruption.",

err,

req,

urlKey,

internal.MiscFunc(func() internal.Misc {

return internal.Misc{Refs: refs, RefIndex: refIndex}

}),

)

return r.handleCacheMiss(req, urlKey, refs, refIndex)

}

return r.handleCacheHit(req, entry, urlKey, refs, refIndex)

}

func (r *transport) handleUnrecognizedMethod(

req *http.Request,

urlKey string,

) (*http.Response, error) {

if !internal.IsUnsafeMethod(req.Method) {

resp, err := r.upstream.RoundTrip(req)

if err != nil {

return nil, err

}

internal.CacheStatusBypass.ApplyTo(resp.Header)

r.logger.LogCacheBypass(

"Bypass; unrecognized (safe) method, served from upstream.",

req,

urlKey,

nil,

)

return resp, nil

}

resp, err := r.upstream.RoundTrip(req)

if err != nil {

return nil, err

}

if internal.IsNonErrorStatus(resp.StatusCode) {

refs, _ := r.cache.GetRefs(urlKey)

r.ci.InvalidateCache(req.URL, resp.Header, refs, urlKey)

}

internal.CacheStatusBypass.ApplyTo(resp.Header)

r.logger.LogCacheBypass(

"Bypass; unrecognized (unsafe) method, served from upstream.",

req,

urlKey,

nil,

)

return resp, nil

}

func (r *transport) handleCacheMiss(

req *http.Request,

urlKey string,

refs internal.ResponseRefs,

refIndex int,

) (*http.Response, error) {

ccReq := internal.ParseCCRequestDirectives(req.Header)

if ccReq.OnlyIfCached() {

r.logger.LogCacheMiss(

req,

urlKey,

internal.MiscFunc(func() internal.Misc {

return internal.Misc{

CCReq: ccReq,

Refs: refs,

RefIndex: refIndex,

}

}),

)

return make504Response(req)

}

resp, start, end, err := r.roundTripTimed(req)

if err != nil {

return nil, err

}

ccResp := internal.ParseCCResponseDirectives(resp.Header)

if r.ce.CanStoreResponse(resp, ccReq, ccResp) {

_ = r.rs.StoreResponse(req, resp, urlKey, refs, start, end, refIndex)

}

internal.CacheStatusMiss.ApplyTo(resp.Header)

r.logger.LogCacheMiss(req, urlKey, internal.MiscFunc(func() internal.Misc {

return internal.Misc{

CCReq: ccReq,

CCResp: ccResp,

Refs: refs,

RefIndex: refIndex,

}

}))

return resp, nil

}

//nolint:cyclop // The complexity of this function is justified by the need to handle multiple caching scenarios according to RFC 9111.

func (r *transport) handleCacheHit(

req *http.Request,

stored *internal.Response,

urlKey string,

refs internal.ResponseRefs,

refIndex int,

) (*http.Response, error) {

ccReq := internal.ParseCCRequestDirectives(req.Header)

ccResp := internal.ParseCCResponseDirectives(stored.Data.Header)

freshness := r.fc.CalculateFreshness(stored, ccReq, ccResp)

respNoCacheFieldsRaw, hasRespNoCache := ccResp.NoCache()

respNoCacheFieldsSeq, isRespNoCacheQualified := respNoCacheFieldsRaw.Value()

// RFC 8246: If response is fresh and immutable, always serve from cache unless request has no-cache

if !freshness.IsStale && ccResp.Immutable() && !ccReq.NoCache() {

return r.serveFromCache(

req,

urlKey,

stored,

freshness,

isRespNoCacheQualified,

respNoCacheFieldsSeq,

)

}

if (freshness.IsStale && ccResp.MustRevalidate()) ||

(hasRespNoCache && !isRespNoCacheQualified) { // Unqualified no-cache: must revalidate before serving from cache

goto revalidate

}

if ccReq.OnlyIfCached() || (!freshness.IsStale && !ccReq.NoCache()) {

return r.serveFromCache(

req,

urlKey,

stored,

freshness,

isRespNoCacheQualified,

respNoCacheFieldsSeq,

)

}

if swr, swrValid := ccResp.StaleWhileRevalidate(); freshness.IsStale && swrValid {

age := freshness.Age.Value + r.clock.Since(freshness.Age.Timestamp)

staleFor := age - freshness.UsefulLife

if staleFor >= 0 && staleFor < swr {

return r.handleStaleWhileRevalidate(req, stored, urlKey, freshness, ccReq)

}

revalidate:

req = withConditionalHeaders(req, stored.Data.Header)

resp, start, end, err := r.roundTripTimed(req)

if err != nil {

return nil, err

}

ctx := internal.RevalidationContext{

URLKey: urlKey,

Start: start,

End: end,

CCReq: ccReq,

Stored: stored,

Refs: refs,

RefIndex: refIndex,

Freshness: freshness,

}

return r.vrh.HandleValidationResponse(ctx, req, resp)

}

func (r *transport) serveFromCache(

req *http.Request,

urlKey string,

stored *internal.Response,

freshness *internal.Freshness,

noCacheQualified bool,

noCacheFieldsSeq iter.Seq[string],

) (*http.Response, error) {

if noCacheQualified {

//Qualified no-cache: may serve from cache with fields stripped

for field := range noCacheFieldsSeq {

stored.Data.Header.Del(field)

}

internal.SetAgeHeader(stored.Data, r.clock, freshness.Age)

internal.CacheStatusHit.ApplyTo(stored.Data.Header)

r.logger.LogCacheHit(req, urlKey, internal.MiscFunc(func() internal.Misc {

return internal.Misc{

Stored: stored,

Freshness: freshness,

}

}))

return stored.Data, nil

}

// handleStaleWhileRevalidate serves a stale cached response immediately and triggers

// background revalidation in a separate goroutine (RFC 5861, §3).

func (r *transport) handleStaleWhileRevalidate(

req *http.Request,

stored *internal.Response,

urlKey string,

freshness *internal.Freshness,

ccReq internal.CCRequestDirectives,

) (*http.Response, error) {

req2 := req.Clone(req.Context())

req2 = withConditionalHeaders(req2, stored.Data.Header)

// Background revalidation is "best effort"; it is not guaranteed to complete

// if the program exits before the goroutine finishes. This design choice was

// made to keep the API simple and avoid requiring explicit shutdown coordination.

// Open a discussion at github.com/bartventer/httpcache/issues if your use case requires

// guaranteed completion.

go r.backgroundRevalidate(req2, stored, urlKey, freshness, ccReq)

internal.CacheStatusStale.ApplyTo(stored.Data.Header)

r.logger.LogCacheStaleRevalidate(req, urlKey, internal.MiscFunc(func() internal.Misc {

return internal.Misc{

CCReq: ccReq,

Stored: stored,

Freshness: freshness,

}

}))

return stored.Data, nil

}

func (r *transport) backgroundRevalidate(

req *http.Request,

stored *internal.Response,

urlKey string,

freshness *internal.Freshness,

ccReq internal.CCRequestDirectives,

) {

ctx, cancel := context.WithTimeout(req.Context(), r.swrTimeout)

defer cancel()

req = req.WithContext(ctx)

errc := make(chan error, 1)

go func() {

defer close(errc)

//nolint:bodyclose // The response is not used, so we don't need to close it.

resp, start, end, err := r.roundTripTimed(req)

if err != nil {

errc <- err

return

}

select {

case <-req.Context().Done():

errc <- req.Context().Err()

return

default:

}

revalCtx := internal.RevalidationContext{

URLKey: urlKey,

Start: start,

End: end,

CCReq: ccReq,

Stored: stored,

Freshness: freshness,

}

//nolint:bodyclose // The response is not used, so we don't need to close it.

_, err = r.vrh.HandleValidationResponse(revalCtx, req, resp)

errc <- err

}()

select {

case <-ctx.Done():

case <-errc:

}

func (r *transport) roundTripTimed(

req *http.Request,

) (resp *http.Response, start, end time.Time, err error) {

start = r.clock.Now()

resp, err = r.upstream.RoundTrip(req)

end = r.clock.Now()

if resp != nil {

_ = internal.FixDateHeader(resp.Header, end)

}

return

}

httpcache/roundtripper.go at master · bartventer/httpcache · GitHub

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