httpcache

README

httpcache

A Transport for Go's http.Client that will cache responses according to the HTTP RFC

Package httpcache provides a http.RoundTripper implementation that works as a mostly RFC-compliant cache for http responses.

It is only suitable for use as a 'private' cache (i.e. for a web-browser or an API-client and not for a shared proxy).

Documentation: http://godoc.org/github.com/gregjones/httpcache

License: MIT (see LICENSE.txt)

Cache backends

• The built-in 'memory' cache stores responses in an in-memory map.
• https://github.com/gregjones/httpcache/diskcache provides a filesystem-backed cache using the diskv library.
• https://github.com/gregjones/httpcache/memcache provides memcache implementations, for both App Engine and 'normal' memcache servers
• https://github.com/sourcegraph/s3cache uses Amazon S3 for storage.

Documentation

Overview

Package httpcache provides a http.RoundTripper implementation that works as a mostly RFC-compliant cache for http responses.

It is only suitable for use as a 'private' cache (i.e. for a web-browser or an API-client and not for a shared proxy).

'max-stale' set on a request is not currently respected. (max-age and min-fresh both are.)

Index

• Constants
• Variables
• func CachedResponse(c Cache, req *http.Request) (resp *http.Response, err error)
• func Date(respHeaders http.Header) (date time.Time, err error)
• type Cache
• type MemoryCache
  • func NewMemoryCache() *MemoryCache
  • func (c *MemoryCache) Delete(key string)
  • func (c *MemoryCache) Get(key string) (resp []byte, ok bool)
  • func (c *MemoryCache) Set(key string, resp []byte)
• type Transport
  • func NewMemoryCacheTransport() *Transport
  • func NewTransport(c Cache) *Transport
  • func (t *Transport) Client() *http.Client
  • func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error)

Constants

const (

	// XFromCache is the header added to responses that are returned from the cache
	XFromCache = "X-From-Cache"
)

Variables

var ErrNoDateHeader = errors.New("no Date header")

ErrNoDateHeader indicates that the HTTP headers contained no Date header.

Functions

func CachedResponse

func CachedResponse(c Cache, req *http.Request) (resp *http.Response, err error)

CachedResponse returns the cached http.Response for req if present, and nil otherwise.

func Date

func Date(respHeaders http.Header) (date time.Time, err error)

Date parses and returns the value of the Date header.

Types

type Cache

type Cache interface {
	// Get returns the []byte representation of a cached response and a bool
	// set to true if the value isn't empty
	Get(key string) (responseBytes []byte, ok bool)
	// Set stores the []byte representation of a response against a key
	Set(key string, responseBytes []byte)
	// Delete removes the value associated with the key
	Delete(key string)
}

A Cache interface is used by the Transport to store and retrieve responses.

type MemoryCache

type MemoryCache struct {
	// contains filtered or unexported fields
}

MemoryCache is an implemtation of Cache that stores responses in an in-memory map.

func NewMemoryCache

func NewMemoryCache() *MemoryCache

NewMemoryCache returns a new Cache that will store items in an in-memory map

func (*MemoryCache) Delete

func (c *MemoryCache) Delete(key string)

Delete removes key from the cache

func (*MemoryCache) Get

func (c *MemoryCache) Get(key string) (resp []byte, ok bool)

Get returns the []byte representation of the response and true if present, false if not

func (*MemoryCache) Set

func (c *MemoryCache) Set(key string, resp []byte)

Set saves response resp to the cache with key

type Transport

type Transport struct {
	// The RoundTripper interface actually used to make requests
	// If nil, http.DefaultTransport is used
	Transport http.RoundTripper
	Cache     Cache
	// If true, responses returned from the cache will be given an extra header, X-From-Cache
	MarkCachedResponses bool
}

Transport is an implementation of http.RoundTripper that will return values from a cache where possible (avoiding a network request) and will additionally add validators (etag/if-modified-since) to repeated requests allowing servers to return 304 / Not Modified

func NewMemoryCacheTransport

func NewMemoryCacheTransport() *Transport

NewMemoryCacheTransport returns a new Transport using the in-memory cache implementation

func NewTransport

func NewTransport(c Cache) *Transport

NewTransport returns a new Transport with the provided Cache implementation and MarkCachedResponses set to true

func (*Transport) Client

func (t *Transport) Client() *http.Client

Client returns an *http.Client that caches responses.

func (*Transport) RoundTrip

func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error)

RoundTrip takes a Request and returns a Response

If there is a fresh Response already in cache, then it will be returned without connecting to the server.

If there is a stale Response, then any validators it contains will be set on the new request to give the server a chance to respond with NotModified. If this happens, then the cached Response will be returned.