cachecontrol: HTTP Caching Parser and Interpretation

cachecontrol implements RFC 7234 Hypertext Transfer Protocol (HTTP/1.1): Caching. It does this by parsing the Cache-Control and other headers, providing information about requests and responses -- but cachecontrol does not implement an actual cache backend, just the control plane to make decisions about if a particular response is cachable.

Usage

cachecontrol.CachableResponse returns an array of reasons why a response should not be cached and when it expires. In the case that len(reasons) == 0, the response is cachable according to the RFC. However, some people want non-compliant caches for various business use cases, so each reason is specifically named, so if your cache wants to cache POST requests, it can easily do that, but still be RFC compliant in other situations.

Examples

Can you cache Example.com?

package main

import (
	"github.com/pquerna/cachecontrol"

	"fmt"
	"io/ioutil"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("GET", "http://www.example.com/", nil)

	res, _ := http.DefaultClient.Do(req)
	_, _ = ioutil.ReadAll(res.Body)

	reasons, expires, _ := cachecontrol.CachableResponse(req, res, cachecontrol.Options{})

	fmt.Println("Reasons to not cache: ", reasons)
	fmt.Println("Expiration: ", expires.String())
}

Can I use this in a high performance caching server?

cachecontrol is divided into two packages: cachecontrol with a high level API, and a lower level cacheobject package. Use Object in a high performance use case where you have previously parsed headers containing dates or would like to avoid memory allocations.

package main

import (
	"github.com/pquerna/cachecontrol/cacheobject"

	"fmt"
	"io/ioutil"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("GET", "http://www.example.com/", nil)

	res, _ := http.DefaultClient.Do(req)
	_, _ = ioutil.ReadAll(res.Body)

	reqDir, _ := cacheobject.ParseRequestCacheControl(req.Header.Get("Cache-Control"))

	resDir, _ := cacheobject.ParseResponseCacheControl(res.Header.Get("Cache-Control"))
	expiresHeader, _ := http.ParseTime(res.Header.Get("Expires"))
	dateHeader, _ := http.ParseTime(res.Header.Get("Date"))
	lastModifiedHeader, _ := http.ParseTime(res.Header.Get("Last-Modified"))

	obj := cacheobject.Object{
		RespDirectives:         resDir,
		RespHeaders:            res.Header,
		RespStatusCode:         res.StatusCode,
		RespExpiresHeader:      expiresHeader,
		RespDateHeader:         dateHeader,
		RespLastModifiedHeader: lastModifiedHeader,

		ReqDirectives: reqDir,
		ReqHeaders:    req.Header,
		ReqMethod:     req.Method,

		NowUTC: time.Now().UTC(),
	}
	rv := cacheobject.ObjectResults{}

	cacheobject.CachableObject(&obj, &rv)
	cacheobject.ExpirationObject(&obj, &rv)

	fmt.Println("Errors: ", rv.OutErr)
	fmt.Println("Reasons to not cache: ", rv.OutReasons)
	fmt.Println("Warning headers to add: ", rv.OutWarnings)
	fmt.Println("Expiration: ", rv.OutExpirationTime.String())
}

Improvements, bugs, adding features, and taking cachecontrol new directions!

Please open issues in Github for ideas, bugs, and general thoughts. Pull requests are of course preferred :)

Credits

cachecontrol has recieved significant contributions from:

Paul Querna

License

cachecontrol is licensed under the Apache License, Version 2.0

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