Misc adjustments

* Add CacheKey option
* Remove redundant nil check
* Optionally allow caching for other HTTP methods than GET and HEAD

httpcache.go

@@ -37,7 +37,16 @@ type Cache interface {
 }
 
 // cacheKey returns the cache key for req.
-func cacheKey(req *http.Request) string {
+func (t *Transport) cacheKey(req *http.Request) string {
+	if t.CacheKey != nil {
+		return t.CacheKey(req)
+	}
+
+	cacheable := (req.Method != http.MethodHead || req.Method == "HEAD") && req.Header.Get("range") == ""
+	if !cacheable {
+		return ""
+	}
+
 	if req.Method == http.MethodGet {
 		return req.URL.String()
 	} else {
@@ -47,8 +56,8 @@ func cacheKey(req *http.Request) 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))
+func (t *Transport) cachedResponse(req *http.Request) (resp *http.Response, err error) {
+	cachedVal, ok := t.Cache.Get(t.cacheKey(req))
 	if !ok {
 		return
 	}
@@ -105,11 +114,15 @@ type Transport struct {
 	// If true, responses returned from the cache will be given an extra header, X-From-Cache
 	MarkCachedResponses bool
 
+	// CacheKey is an optional func that returns the key to use to store the response.
+	// An empty string signals that this request should not be cached.
+	CacheKey func(req *http.Request) string
+
 	// Around is an optional func.
 	// If set, the Transport will call Around at the start of RoundTrip
 	// and defer the returned func until the end of RoundTrip.
 	// Typically used to implement a lock that is held for the duration of the RoundTrip.
-	Around func(key string) func()
+	Around func(req *http.Request, key string) func()
 }
 
 // varyMatches will return false unless all of the cached values for the headers listed in Vary
@@ -133,14 +146,16 @@ func varyMatches(cachedResp *http.Response, req *http.Request) bool {
 // 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)
+	cacheKey := t.cacheKey(req)
 	if f := t.Around; f != nil {
-		defer f(cacheKey)()
+		defer f(req, cacheKey)()
 	}
-	cacheable := (req.Method == "GET" || req.Method == "HEAD") && req.Header.Get("range") == ""
+
+	cacheable := cacheKey != ""
+
 	var cachedResp *http.Response
 	if cacheable {
-		cachedResp, err = cachedResponse(t.Cache, req)
+		cachedResp, err = t.cachedResponse(req)
 	} else {
 		// Need to invalidate an existing value
 		t.Cache.Delete(cacheKey)
@@ -185,15 +200,16 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 		}
 
 		resp, err = transport.RoundTrip(req)
-		if err == nil && req.Method == "GET" && resp.StatusCode == http.StatusNotModified {
+
+		if err == nil && req.Method != http.MethodHead && 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]
 			}
 			resp = cachedResp
-		} else if (err != nil || (cachedResp != nil && resp.StatusCode >= 500)) &&
-			req.Method == "GET" && canStaleOnError(cachedResp.Header, req.Header) {
+		} else if (err != nil || resp.StatusCode >= 500) &&
+			req.Method != http.MethodHead && canStaleOnError(cachedResp.Header, req.Header) {
 			// In case of transport failure and stale-if-error activated, returns cached content
 			// when available
 			return cachedResp, nil
@@ -227,7 +243,12 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 			}
 		}
 		switch req.Method {
-		case "GET":
+		case http.MethodHead:
+			respBytes, err := httputil.DumpResponse(resp, true)
+			if err == nil {
+				t.Cache.Set(cacheKey, respBytes)
+			}
+		default:
 			// Delay caching until EOF is reached.
 			resp.Body = &cachingReadCloser{
 				R: resp.Body,
@@ -240,11 +261,7 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 					}
 				},
 			}
-		default:
-			respBytes, err := httputil.DumpResponse(resp, true)
-			if err == nil {
-				t.Cache.Set(cacheKey, respBytes)
-			}
+
 		}
 	} else {
 		t.Cache.Delete(cacheKey)