vendor/github.com/gregjones/httpcache/httpcache.go - gddo - Git at Google

 // 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).
 //
 package httpcache

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
 	"net/http/httputil"
 	"strings"
 	"sync"
 	"time"
 )

 const (
 	stale = iota
 	fresh
 	transparent
 	// XFromCache is the header added to responses that are returned from the cache
 	XFromCache = "X-From-Cache"
 )

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

 // cacheKey returns the cache key for req.
 func cacheKey(req *http.Request) string {
 	if req.Method == http.MethodGet {
 		return req.URL.String()
 	} else {
 		return req.Method + " " + req.URL.String()
 	}
 }

 // CachedResponse returns the cached http.Response for req if present, and nil
 // otherwise.
 func CachedResponse(c Cache, req *http.Request) (resp *http.Response, err error) {
 	cachedVal, ok := c.Get(cacheKey(req))
 	if !ok {
 		return
 	}

 	b := bytes.NewBuffer(cachedVal)
 	return http.ReadResponse(bufio.NewReader(b), req)
 }

 // MemoryCache is an implemtation of Cache that stores responses in an in-memory map.
 type MemoryCache struct {
 	mu    sync.RWMutex
 	items map[string][]byte
 }

 // Get returns the []byte representation of the response and true if present, false if not
 func (c *MemoryCache) Get(key string) (resp []byte, ok bool) {
 	c.mu.RLock()
 	resp, ok = c.items[key]
 	c.mu.RUnlock()
 	return resp, ok
 }

 // Set saves response resp to the cache with key
 func (c *MemoryCache) Set(key string, resp []byte) {
 	c.mu.Lock()
 	c.items[key] = resp
 	c.mu.Unlock()
 }

 // Delete removes key from the cache
 func (c *MemoryCache) Delete(key string) {
 	c.mu.Lock()
 	delete(c.items, key)
 	c.mu.Unlock()
 }

 // NewMemoryCache returns a new Cache that will store items in an in-memory map
 func NewMemoryCache() *MemoryCache {
 	c := &MemoryCache{items: map[string][]byte{}}
 	return c
 }

 // 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
 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
 }

 // NewTransport returns a new Transport with the
 // provided Cache implementation and MarkCachedResponses set to true
 func NewTransport(c Cache) *Transport {
 	return &Transport{Cache: c, MarkCachedResponses: true}
 }

 // Client returns an *http.Client that caches responses.
 func (t *Transport) Client() *http.Client {
 	return &http.Client{Transport: t}
 }

 // varyMatches will return false unless all of the cached values for the headers listed in Vary
 // match the new request
 func varyMatches(cachedResp *http.Response, req *http.Request) bool {
 	for _, header := range headerAllCommaSepValues(cachedResp.Header, "vary") {
 		header = http.CanonicalHeaderKey(header)
 		if header != "" && req.Header.Get(header) != cachedResp.Header.Get("X-Varied-"+header) {
 			return false
 		}
 	}
 	return true
 }

 // 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.
 func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
 	cacheKey := cacheKey(req)
 	cacheable := (req.Method == "GET" || req.Method == "HEAD") && req.Header.Get("range") == ""
 	var cachedResp *http.Response
 	if cacheable {
 		cachedResp, err = CachedResponse(t.Cache, req)
 	} else {
 		// Need to invalidate an existing value
 		t.Cache.Delete(cacheKey)
 	}

 	transport := t.Transport
 	if transport == nil {
 		transport = http.DefaultTransport
 	}

 	if cacheable && cachedResp != nil && err == nil {
 		if t.MarkCachedResponses {
 			cachedResp.Header.Set(XFromCache, "1")
 		}

 		if varyMatches(cachedResp, req) {
 			// Can only use cached value if the new request doesn't Vary significantly
 			freshness := getFreshness(cachedResp.Header, req.Header)
 			if freshness == fresh {
 				return cachedResp, nil
 			}

 			if freshness == stale {
 				var req2 *http.Request
 				// Add validators if caller hasn't already done so
 				etag := cachedResp.Header.Get("etag")
 				if etag != "" && req.Header.Get("etag") == "" {
 					req2 = cloneRequest(req)
 					req2.Header.Set("if-none-match", etag)
 				}
 				lastModified := cachedResp.Header.Get("last-modified")
 				if lastModified != "" && req.Header.Get("last-modified") == "" {
 					if req2 == nil {
 						req2 = cloneRequest(req)
 					}
 					req2.Header.Set("if-modified-since", lastModified)
 				}
 				if req2 != nil {
 					req = req2
 				}
 			}
 		}

 		resp, err = transport.RoundTrip(req)
 		if err == nil && req.Method == "GET" && resp.StatusCode == http.StatusNotModified {
 			// Replace the 304 response with the one from cache, but update with some new headers
 			endToEndHeaders := getEndToEndHeaders(resp.Header)
 			for _, header := range endToEndHeaders {
 				cachedResp.Header[header] = resp.Header[header]
 			}
 			cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
 			cachedResp.StatusCode = http.StatusOK

 			resp = cachedResp
 		} else if (err != nil || (cachedResp != nil && resp.StatusCode >= 500)) &&
 			req.Method == "GET" && canStaleOnError(cachedResp.Header, req.Header) {
 			// In case of transport failure and stale-if-error activated, returns cached content
 			// when available
 			cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
 			cachedResp.StatusCode = http.StatusOK
 			return cachedResp, nil
 		} else {
 			if err != nil || resp.StatusCode != http.StatusOK {
 				t.Cache.Delete(cacheKey)
 			}
 			if err != nil {
 				return nil, err
 			}
 		}
 	} else {
 		reqCacheControl := parseCacheControl(req.Header)
 		if _, ok := reqCacheControl["only-if-cached"]; ok {
 			resp = newGatewayTimeoutResponse(req)
 		} else {
 			resp, err = transport.RoundTrip(req)
 			if err != nil {
 				return nil, err
 			}
 		}
 	}

 	if cacheable && canStore(parseCacheControl(req.Header), parseCacheControl(resp.Header)) {
 		for _, varyKey := range headerAllCommaSepValues(resp.Header, "vary") {
 			varyKey = http.CanonicalHeaderKey(varyKey)
 			fakeHeader := "X-Varied-" + varyKey
 			reqValue := req.Header.Get(varyKey)
 			if reqValue != "" {
 				resp.Header.Set(fakeHeader, reqValue)
 			}
 		}
 		switch req.Method {
 		case "GET":
 			// Delay caching until EOF is reached.
 			resp.Body = &cachingReadCloser{
 				R: resp.Body,
 				OnEOF: func(r io.Reader) {
 					resp := *resp
 					resp.Body = ioutil.NopCloser(r)
 					respBytes, err := httputil.DumpResponse(&resp, true)
 					if err == nil {
 						t.Cache.Set(cacheKey, respBytes)
 					}
 				},
 			}
 		default:
 			respBytes, err := httputil.DumpResponse(resp, true)
 			if err == nil {
 				t.Cache.Set(cacheKey, respBytes)
 			}
 		}
 	} else {
 		t.Cache.Delete(cacheKey)
 	}
 	return resp, nil
 }

 // ErrNoDateHeader indicates that the HTTP headers contained no Date header.
 var ErrNoDateHeader = errors.New("no Date header")

 // Date parses and returns the value of the Date header.
 func Date(respHeaders http.Header) (date time.Time, err error) {
 	dateHeader := respHeaders.Get("date")
 	if dateHeader == "" {
 		err = ErrNoDateHeader
 		return
 	}

 	return time.Parse(time.RFC1123, dateHeader)
 }

 type realClock struct{}

 func (c *realClock) since(d time.Time) time.Duration {
 	return time.Since(d)
 }

 type timer interface {
 	since(d time.Time) time.Duration
 }

 var clock timer = &realClock{}

 // getFreshness will return one of fresh/stale/transparent based on the cache-control
 // values of the request and the response
 //
 // fresh indicates the response can be returned
 // stale indicates that the response needs validating before it is returned
 // transparent indicates the response should not be used to fulfil the request
 //
 // Because this is only a private cache, 'public' and 'private' in cache-control aren't
 // signficant. Similarly, smax-age isn't used.
 func getFreshness(respHeaders, reqHeaders http.Header) (freshness int) {
 	respCacheControl := parseCacheControl(respHeaders)
 	reqCacheControl := parseCacheControl(reqHeaders)
 	if _, ok := reqCacheControl["no-cache"]; ok {
 		return transparent
 	}
 	if _, ok := respCacheControl["no-cache"]; ok {
 		return stale
 	}
 	if _, ok := reqCacheControl["only-if-cached"]; ok {
 		return fresh
 	}

 	date, err := Date(respHeaders)
 	if err != nil {
 		return stale
 	}
 	currentAge := clock.since(date)

 	var lifetime time.Duration
 	var zeroDuration time.Duration

 	// If a response includes both an Expires header and a max-age directive,
 	// the max-age directive overrides the Expires header, even if the Expires header is more restrictive.
 	if maxAge, ok := respCacheControl["max-age"]; ok {
 		lifetime, err = time.ParseDuration(maxAge + "s")
 		if err != nil {
 			lifetime = zeroDuration
 		}
 	} else {
 		expiresHeader := respHeaders.Get("Expires")
 		if expiresHeader != "" {
 			expires, err := time.Parse(time.RFC1123, expiresHeader)
 			if err != nil {
 				lifetime = zeroDuration
 			} else {
 				lifetime = expires.Sub(date)
 			}
 		}
 	}

 	if maxAge, ok := reqCacheControl["max-age"]; ok {
 		// the client is willing to accept a response whose age is no greater than the specified time in seconds
 		lifetime, err = time.ParseDuration(maxAge + "s")
 		if err != nil {
 			lifetime = zeroDuration
 		}
 	}
 	if minfresh, ok := reqCacheControl["min-fresh"]; ok {
 		//  the client wants a response that will still be fresh for at least the specified number of seconds.
 		minfreshDuration, err := time.ParseDuration(minfresh + "s")
 		if err == nil {
 			currentAge = time.Duration(currentAge + minfreshDuration)
 		}
 	}

 	if maxstale, ok := reqCacheControl["max-stale"]; ok {
 		// Indicates that the client is willing to accept a response that has exceeded its expiration time.
 		// If max-stale is assigned a value, then the client is willing to accept a response that has exceeded
 		// its expiration time by no more than the specified number of seconds.
 		// If no value is assigned to max-stale, then the client is willing to accept a stale response of any age.
 		//
 		// Responses served only because of a max-stale value are supposed to have a Warning header added to them,
 		// but that seems like a  hassle, and is it actually useful? If so, then there needs to be a different
 		// return-value available here.
 		if maxstale == "" {
 			return fresh
 		}
 		maxstaleDuration, err := time.ParseDuration(maxstale + "s")
 		if err == nil {
 			currentAge = time.Duration(currentAge - maxstaleDuration)
 		}
 	}

 	if lifetime > currentAge {
 		return fresh
 	}

 	return stale
 }

 // Returns true if either the request or the response includes the stale-if-error
 // cache control extension: https://tools.ietf.org/html/rfc5861
 func canStaleOnError(respHeaders, reqHeaders http.Header) bool {
 	respCacheControl := parseCacheControl(respHeaders)
 	reqCacheControl := parseCacheControl(reqHeaders)

 	var err error
 	lifetime := time.Duration(-1)

 	if staleMaxAge, ok := respCacheControl["stale-if-error"]; ok {
 		if staleMaxAge != "" {
 			lifetime, err = time.ParseDuration(staleMaxAge + "s")
 			if err != nil {
 				return false
 			}
 		} else {
 			return true
 		}
 	}
 	if staleMaxAge, ok := reqCacheControl["stale-if-error"]; ok {
 		if staleMaxAge != "" {
 			lifetime, err = time.ParseDuration(staleMaxAge + "s")
 			if err != nil {
 				return false
 			}
 		} else {
 			return true
 		}
 	}

 	if lifetime >= 0 {
 		date, err := Date(respHeaders)
 		if err != nil {
 			return false
 		}
 		currentAge := clock.since(date)
 		if lifetime > currentAge {
 			return true
 		}
 	}

 	return false
 }

 func getEndToEndHeaders(respHeaders http.Header) []string {
 	// These headers are always hop-by-hop
 	hopByHopHeaders := map[string]struct{}{
 		"Connection":          struct{}{},
 		"Keep-Alive":          struct{}{},
 		"Proxy-Authenticate":  struct{}{},
 		"Proxy-Authorization": struct{}{},
 		"Te":                struct{}{},
 		"Trailers":          struct{}{},
 		"Transfer-Encoding": struct{}{},
 		"Upgrade":           struct{}{},
 	}

 	for _, extra := range strings.Split(respHeaders.Get("connection"), ",") {
 		// any header listed in connection, if present, is also considered hop-by-hop
 		if strings.Trim(extra, " ") != "" {
 			hopByHopHeaders[http.CanonicalHeaderKey(extra)] = struct{}{}
 		}
 	}
 	endToEndHeaders := []string{}
 	for respHeader, _ := range respHeaders {
 		if _, ok := hopByHopHeaders[respHeader]; !ok {
 			endToEndHeaders = append(endToEndHeaders, respHeader)
 		}
 	}
 	return endToEndHeaders
 }

 func canStore(reqCacheControl, respCacheControl cacheControl) (canStore bool) {
 	if _, ok := respCacheControl["no-store"]; ok {
 		return false
 	}
 	if _, ok := reqCacheControl["no-store"]; ok {
 		return false
 	}
 	return true
 }

 func newGatewayTimeoutResponse(req *http.Request) *http.Response {
 	var braw bytes.Buffer
 	braw.WriteString("HTTP/1.1 504 Gateway Timeout\r\n\r\n")
 	resp, err := http.ReadResponse(bufio.NewReader(&braw), req)
 	if err != nil {
 		panic(err)
 	}
 	return resp
 }

 // cloneRequest returns a clone of the provided *http.Request.
 // The clone is a shallow copy of the struct and its Header map.
 // (This function copyright goauth2 authors: https://code.google.com/p/goauth2)
 func cloneRequest(r *http.Request) *http.Request {
 	// shallow copy of the struct
 	r2 := new(http.Request)
 	*r2 = *r
 	// deep copy of the Header
 	r2.Header = make(http.Header)
 	for k, s := range r.Header {
 		r2.Header[k] = s
 	}
 	return r2
 }

 type cacheControl map[string]string

 func parseCacheControl(headers http.Header) cacheControl {
 	cc := cacheControl{}
 	ccHeader := headers.Get("Cache-Control")
 	for _, part := range strings.Split(ccHeader, ",") {
 		part = strings.Trim(part, " ")
 		if part == "" {
 			continue
 		}
 		if strings.ContainsRune(part, '=') {
 			keyval := strings.Split(part, "=")
 			cc[strings.Trim(keyval[0], " ")] = strings.Trim(keyval[1], ",")
 		} else {
 			cc[part] = ""
 		}
 	}
 	return cc
 }

 // headerAllCommaSepValues returns all comma-separated values (each
 // with whitespace trimmed) for header name in headers. According to
 // Section 4.2 of the HTTP/1.1 spec
 // (http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2),
 // values from multiple occurrences of a header should be concatenated, if
 // the header's value is a comma-separated list.
 func headerAllCommaSepValues(headers http.Header, name string) []string {
 	var vals []string
 	for _, val := range headers[http.CanonicalHeaderKey(name)] {
 		fields := strings.Split(val, ",")
 		for i, f := range fields {
 			fields[i] = strings.TrimSpace(f)
 		}
 		vals = append(vals, fields...)
 	}
 	return vals
 }

 // cachingReadCloser is a wrapper around ReadCloser R that calls OnEOF
 // handler with a full copy of the content read from R when EOF is
 // reached.
 type cachingReadCloser struct {
 	// Underlying ReadCloser.
 	R io.ReadCloser
 	// OnEOF is called with a copy of the content of R when EOF is reached.
 	OnEOF func(io.Reader)

 	buf bytes.Buffer // buf stores a copy of the content of R.
 }

 // Read reads the next len(p) bytes from R or until R is drained. The
 // return value n is the number of bytes read. If R has no data to
 // return, err is io.EOF and OnEOF is called with a full copy of what
 // has been read so far.
 func (r *cachingReadCloser) Read(p []byte) (n int, err error) {
 	n, err = r.R.Read(p)
 	r.buf.Write(p[:n])
 	if err == io.EOF {
 		r.OnEOF(bytes.NewReader(r.buf.Bytes()))
 	}
 	return n, err
 }

 func (r *cachingReadCloser) Close() error {
 	return r.R.Close()
 }

 // NewMemoryCacheTransport returns a new Transport using the in-memory cache implementation
 func NewMemoryCacheTransport() *Transport {
 	c := NewMemoryCache()
 	t := NewTransport(c)
 	return t
 }
	// 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).
	//
	package httpcache

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/http/httputil"
	"strings"
	"sync"
	"time"
	)

	const (
	stale = iota
	fresh
	transparent
	// XFromCache is the header added to responses that are returned from the cache
	XFromCache = "X-From-Cache"
	)

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

	// cacheKey returns the cache key for req.
	func cacheKey(req *http.Request) string {
	if req.Method == http.MethodGet {
	return req.URL.String()
	} else {
	return req.Method + " " + req.URL.String()
	}
	}

	// CachedResponse returns the cached http.Response for req if present, and nil
	// otherwise.
	func CachedResponse(c Cache, req http.Request) (resp http.Response, err error) {
	cachedVal, ok := c.Get(cacheKey(req))
	if !ok {
	return
	}

	b := bytes.NewBuffer(cachedVal)
	return http.ReadResponse(bufio.NewReader(b), req)
	}

	// MemoryCache is an implemtation of Cache that stores responses in an in-memory map.
	type MemoryCache struct {
	mu sync.RWMutex
	items map[string][]byte
	}

	// Get returns the []byte representation of the response and true if present, false if not
	func (c *MemoryCache) Get(key string) (resp []byte, ok bool) {
	c.mu.RLock()
	resp, ok = c.items[key]
	c.mu.RUnlock()
	return resp, ok
	}

	// Set saves response resp to the cache with key
	func (c *MemoryCache) Set(key string, resp []byte) {
	c.mu.Lock()
	c.items[key] = resp
	c.mu.Unlock()
	}

	// Delete removes key from the cache
	func (c *MemoryCache) Delete(key string) {
	c.mu.Lock()
	delete(c.items, key)
	c.mu.Unlock()
	}

	// NewMemoryCache returns a new Cache that will store items in an in-memory map
	func NewMemoryCache() *MemoryCache {
	c := &MemoryCache{items: map[string][]byte{}}
	return c
	}

	// 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
	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
	}

	// NewTransport returns a new Transport with the
	// provided Cache implementation and MarkCachedResponses set to true
	func NewTransport(c Cache) *Transport {
	return &Transport{Cache: c, MarkCachedResponses: true}
	}

	// Client returns an *http.Client that caches responses.
	func (t Transport) Client() http.Client {
	return &http.Client{Transport: t}
	}

	// varyMatches will return false unless all of the cached values for the headers listed in Vary
	// match the new request
	func varyMatches(cachedResp http.Response, req http.Request) bool {
	for _, header := range headerAllCommaSepValues(cachedResp.Header, "vary") {
	header = http.CanonicalHeaderKey(header)
	if header != "" && req.Header.Get(header) != cachedResp.Header.Get("X-Varied-"+header) {
	return false
	}
	}
	return true
	}

	// 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.
	func (t Transport) RoundTrip(req http.Request) (resp *http.Response, err error) {
	cacheKey := cacheKey(req)
	cacheable := (req.Method == "GET" \|\| req.Method == "HEAD") && req.Header.Get("range") == ""
	var cachedResp *http.Response
	if cacheable {
	cachedResp, err = CachedResponse(t.Cache, req)
	} else {
	// Need to invalidate an existing value
	t.Cache.Delete(cacheKey)
	}

	transport := t.Transport
	if transport == nil {
	transport = http.DefaultTransport
	}

	if cacheable && cachedResp != nil && err == nil {
	if t.MarkCachedResponses {
	cachedResp.Header.Set(XFromCache, "1")
	}

	if varyMatches(cachedResp, req) {
	// Can only use cached value if the new request doesn't Vary significantly
	freshness := getFreshness(cachedResp.Header, req.Header)
	if freshness == fresh {
	return cachedResp, nil
	}

	if freshness == stale {
	var req2 *http.Request
	// Add validators if caller hasn't already done so
	etag := cachedResp.Header.Get("etag")
	if etag != "" && req.Header.Get("etag") == "" {
	req2 = cloneRequest(req)
	req2.Header.Set("if-none-match", etag)
	}
	lastModified := cachedResp.Header.Get("last-modified")
	if lastModified != "" && req.Header.Get("last-modified") == "" {
	if req2 == nil {
	req2 = cloneRequest(req)
	}
	req2.Header.Set("if-modified-since", lastModified)
	}
	if req2 != nil {
	req = req2
	}
	}
	}

	resp, err = transport.RoundTrip(req)
	if err == nil && req.Method == "GET" && resp.StatusCode == http.StatusNotModified {
	// Replace the 304 response with the one from cache, but update with some new headers
	endToEndHeaders := getEndToEndHeaders(resp.Header)
	for _, header := range endToEndHeaders {
	cachedResp.Header[header] = resp.Header[header]
	}
	cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
	cachedResp.StatusCode = http.StatusOK

	resp = cachedResp
	} else if (err != nil \|\| (cachedResp != nil && resp.StatusCode >= 500)) &&
	req.Method == "GET" && canStaleOnError(cachedResp.Header, req.Header) {
	// In case of transport failure and stale-if-error activated, returns cached content
	// when available
	cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
	cachedResp.StatusCode = http.StatusOK
	return cachedResp, nil
	} else {
	if err != nil \|\| resp.StatusCode != http.StatusOK {
	t.Cache.Delete(cacheKey)
	}
	if err != nil {
	return nil, err
	}
	}
	} else {
	reqCacheControl := parseCacheControl(req.Header)
	if _, ok := reqCacheControl["only-if-cached"]; ok {
	resp = newGatewayTimeoutResponse(req)
	} else {
	resp, err = transport.RoundTrip(req)
	if err != nil {
	return nil, err
	}
	}
	}

	if cacheable && canStore(parseCacheControl(req.Header), parseCacheControl(resp.Header)) {
	for _, varyKey := range headerAllCommaSepValues(resp.Header, "vary") {
	varyKey = http.CanonicalHeaderKey(varyKey)
	fakeHeader := "X-Varied-" + varyKey
	reqValue := req.Header.Get(varyKey)
	if reqValue != "" {
	resp.Header.Set(fakeHeader, reqValue)
	}
	}
	switch req.Method {
	case "GET":
	// Delay caching until EOF is reached.
	resp.Body = &cachingReadCloser{
	R: resp.Body,
	OnEOF: func(r io.Reader) {
	resp := *resp
	resp.Body = ioutil.NopCloser(r)
	respBytes, err := httputil.DumpResponse(&resp, true)
	if err == nil {
	t.Cache.Set(cacheKey, respBytes)
	}
	},
	}
	default:
	respBytes, err := httputil.DumpResponse(resp, true)
	if err == nil {
	t.Cache.Set(cacheKey, respBytes)
	}
	}
	} else {
	t.Cache.Delete(cacheKey)
	}
	return resp, nil
	}

	// ErrNoDateHeader indicates that the HTTP headers contained no Date header.
	var ErrNoDateHeader = errors.New("no Date header")

	// Date parses and returns the value of the Date header.
	func Date(respHeaders http.Header) (date time.Time, err error) {
	dateHeader := respHeaders.Get("date")
	if dateHeader == "" {
	err = ErrNoDateHeader
	return
	}

	return time.Parse(time.RFC1123, dateHeader)
	}

	type realClock struct{}

	func (c *realClock) since(d time.Time) time.Duration {
	return time.Since(d)
	}

	type timer interface {
	since(d time.Time) time.Duration
	}

	var clock timer = &realClock{}

	// getFreshness will return one of fresh/stale/transparent based on the cache-control
	// values of the request and the response
	//
	// fresh indicates the response can be returned
	// stale indicates that the response needs validating before it is returned
	// transparent indicates the response should not be used to fulfil the request
	//
	// Because this is only a private cache, 'public' and 'private' in cache-control aren't
	// signficant. Similarly, smax-age isn't used.
	func getFreshness(respHeaders, reqHeaders http.Header) (freshness int) {
	respCacheControl := parseCacheControl(respHeaders)
	reqCacheControl := parseCacheControl(reqHeaders)
	if _, ok := reqCacheControl["no-cache"]; ok {
	return transparent
	}
	if _, ok := respCacheControl["no-cache"]; ok {
	return stale
	}
	if _, ok := reqCacheControl["only-if-cached"]; ok {
	return fresh
	}

	date, err := Date(respHeaders)
	if err != nil {
	return stale
	}
	currentAge := clock.since(date)

	var lifetime time.Duration
	var zeroDuration time.Duration

	// If a response includes both an Expires header and a max-age directive,
	// the max-age directive overrides the Expires header, even if the Expires header is more restrictive.
	if maxAge, ok := respCacheControl["max-age"]; ok {
	lifetime, err = time.ParseDuration(maxAge + "s")
	if err != nil {
	lifetime = zeroDuration
	}
	} else {
	expiresHeader := respHeaders.Get("Expires")
	if expiresHeader != "" {
	expires, err := time.Parse(time.RFC1123, expiresHeader)
	if err != nil {
	lifetime = zeroDuration
	} else {
	lifetime = expires.Sub(date)
	}
	}
	}

	if maxAge, ok := reqCacheControl["max-age"]; ok {
	// the client is willing to accept a response whose age is no greater than the specified time in seconds
	lifetime, err = time.ParseDuration(maxAge + "s")
	if err != nil {
	lifetime = zeroDuration
	}
	}
	if minfresh, ok := reqCacheControl["min-fresh"]; ok {
	// the client wants a response that will still be fresh for at least the specified number of seconds.
	minfreshDuration, err := time.ParseDuration(minfresh + "s")
	if err == nil {
	currentAge = time.Duration(currentAge + minfreshDuration)
	}
	}

	if maxstale, ok := reqCacheControl["max-stale"]; ok {
	// Indicates that the client is willing to accept a response that has exceeded its expiration time.
	// If max-stale is assigned a value, then the client is willing to accept a response that has exceeded
	// its expiration time by no more than the specified number of seconds.
	// If no value is assigned to max-stale, then the client is willing to accept a stale response of any age.
	//
	// Responses served only because of a max-stale value are supposed to have a Warning header added to them,
	// but that seems like a hassle, and is it actually useful? If so, then there needs to be a different
	// return-value available here.
	if maxstale == "" {
	return fresh
	}
	maxstaleDuration, err := time.ParseDuration(maxstale + "s")
	if err == nil {
	currentAge = time.Duration(currentAge - maxstaleDuration)
	}
	}

	if lifetime > currentAge {
	return fresh
	}

	return stale
	}

	// Returns true if either the request or the response includes the stale-if-error
	// cache control extension: https://tools.ietf.org/html/rfc5861
	func canStaleOnError(respHeaders, reqHeaders http.Header) bool {
	respCacheControl := parseCacheControl(respHeaders)
	reqCacheControl := parseCacheControl(reqHeaders)

	var err error
	lifetime := time.Duration(-1)

	if staleMaxAge, ok := respCacheControl["stale-if-error"]; ok {
	if staleMaxAge != "" {
	lifetime, err = time.ParseDuration(staleMaxAge + "s")
	if err != nil {
	return false
	}
	} else {
	return true
	}
	}
	if staleMaxAge, ok := reqCacheControl["stale-if-error"]; ok {
	if staleMaxAge != "" {
	lifetime, err = time.ParseDuration(staleMaxAge + "s")
	if err != nil {
	return false
	}
	} else {
	return true
	}
	}

	if lifetime >= 0 {
	date, err := Date(respHeaders)
	if err != nil {
	return false
	}
	currentAge := clock.since(date)
	if lifetime > currentAge {
	return true
	}
	}

	return false
	}

	func getEndToEndHeaders(respHeaders http.Header) []string {
	// These headers are always hop-by-hop
	hopByHopHeaders := map[string]struct{}{
	"Connection": struct{}{},
	"Keep-Alive": struct{}{},
	"Proxy-Authenticate": struct{}{},
	"Proxy-Authorization": struct{}{},
	"Te": struct{}{},
	"Trailers": struct{}{},
	"Transfer-Encoding": struct{}{},
	"Upgrade": struct{}{},
	}

	for _, extra := range strings.Split(respHeaders.Get("connection"), ",") {
	// any header listed in connection, if present, is also considered hop-by-hop
	if strings.Trim(extra, " ") != "" {
	hopByHopHeaders[http.CanonicalHeaderKey(extra)] = struct{}{}
	}
	}
	endToEndHeaders := []string{}
	for respHeader, _ := range respHeaders {
	if _, ok := hopByHopHeaders[respHeader]; !ok {
	endToEndHeaders = append(endToEndHeaders, respHeader)
	}
	}
	return endToEndHeaders
	}

	func canStore(reqCacheControl, respCacheControl cacheControl) (canStore bool) {
	if _, ok := respCacheControl["no-store"]; ok {
	return false
	}
	if _, ok := reqCacheControl["no-store"]; ok {
	return false
	}
	return true
	}

	func newGatewayTimeoutResponse(req http.Request) http.Response {
	var braw bytes.Buffer
	braw.WriteString("HTTP/1.1 504 Gateway Timeout\r\n\r\n")
	resp, err := http.ReadResponse(bufio.NewReader(&braw), req)
	if err != nil {
	panic(err)
	}
	return resp
	}

	// cloneRequest returns a clone of the provided *http.Request.
	// The clone is a shallow copy of the struct and its Header map.
	// (This function copyright goauth2 authors: https://code.google.com/p/goauth2)
	func cloneRequest(r http.Request) http.Request {
	// shallow copy of the struct
	r2 := new(http.Request)
	r2 = r
	// deep copy of the Header
	r2.Header = make(http.Header)
	for k, s := range r.Header {
	r2.Header[k] = s
	}
	return r2
	}

	type cacheControl map[string]string

	func parseCacheControl(headers http.Header) cacheControl {
	cc := cacheControl{}
	ccHeader := headers.Get("Cache-Control")
	for _, part := range strings.Split(ccHeader, ",") {
	part = strings.Trim(part, " ")
	if part == "" {
	continue
	}
	if strings.ContainsRune(part, '=') {
	keyval := strings.Split(part, "=")
	cc[strings.Trim(keyval[0], " ")] = strings.Trim(keyval[1], ",")
	} else {
	cc[part] = ""
	}
	}
	return cc
	}

	// headerAllCommaSepValues returns all comma-separated values (each
	// with whitespace trimmed) for header name in headers. According to
	// Section 4.2 of the HTTP/1.1 spec
	// (http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2),
	// values from multiple occurrences of a header should be concatenated, if
	// the header's value is a comma-separated list.
	func headerAllCommaSepValues(headers http.Header, name string) []string {
	var vals []string
	for _, val := range headers[http.CanonicalHeaderKey(name)] {
	fields := strings.Split(val, ",")
	for i, f := range fields {
	fields[i] = strings.TrimSpace(f)
	}
	vals = append(vals, fields...)
	}
	return vals
	}

	// cachingReadCloser is a wrapper around ReadCloser R that calls OnEOF
	// handler with a full copy of the content read from R when EOF is
	// reached.
	type cachingReadCloser struct {
	// Underlying ReadCloser.
	R io.ReadCloser
	// OnEOF is called with a copy of the content of R when EOF is reached.
	OnEOF func(io.Reader)

	buf bytes.Buffer // buf stores a copy of the content of R.
	}

	// Read reads the next len(p) bytes from R or until R is drained. The
	// return value n is the number of bytes read. If R has no data to
	// return, err is io.EOF and OnEOF is called with a full copy of what
	// has been read so far.
	func (r *cachingReadCloser) Read(p []byte) (n int, err error) {
	n, err = r.R.Read(p)
	r.buf.Write(p[:n])
	if err == io.EOF {
	r.OnEOF(bytes.NewReader(r.buf.Bytes()))
	}
	return n, err
	}

	func (r *cachingReadCloser) Close() error {
	return r.R.Close()
	}

	// NewMemoryCacheTransport returns a new Transport using the in-memory cache implementation
	func NewMemoryCacheTransport() *Transport {
	c := NewMemoryCache()
	t := NewTransport(c)
	return t
	}