Handle prometheus post query cache correctly (#590)

* 1. Handle prometheus post query cache correctly
2. Support request content type is application JSON with charset

Signed-off-by: xiaoqing <xiaoqingnb@gmail.com>

* fix compile issues

Signed-off-by: James Ranson <james@ranson.org>

* fix typo

Signed-off-by: James Ranson <james@ranson.org>

---------

Signed-off-by: xiaoqing <xiaoqingnb@gmail.com>
Signed-off-by: James Ranson <james@ranson.org>
Co-authored-by: James Ranson <james@ranson.org>

pkg/proxy/engines/key.go

@@ -95,12 +95,12 @@ func (pr *proxyRequest) DeriveCacheKey(extra string) string {
 	}
 
 	if methods.HasBody(r.Method) && pc.CacheKeyFormFields != nil && len(pc.CacheKeyFormFields) > 0 {
-		ct := r.Header.Get(headers.NameContentType)
+		ct := strings.ToLower(r.Header.Get(headers.NameContentType))
 		if ct == headers.ValueXFormURLEncoded ||
-			strings.HasPrefix(ct, headers.ValueMultipartFormData) || ct == headers.ValueApplicationJSON {
+			strings.HasPrefix(ct, headers.ValueMultipartFormData) || strings.HasPrefix(ct, headers.ValueApplicationJSON) {
 			if strings.HasPrefix(ct, headers.ValueMultipartFormData) {
 				pr.ParseMultipartForm(1024 * 1024)
-			} else if ct == headers.ValueApplicationJSON {
+			} else if strings.HasPrefix(ct, headers.ValueApplicationJSON) {
 				var document map[string]interface{}
 				err := json.Unmarshal(b, &document)
 				if err == nil {

pkg/proxy/params/params.go

@@ -97,6 +97,10 @@ func GetRequestValues(r *http.Request) (url.Values, string, bool) {
 		r.Body.Close()
 		r.Body = io.NopCloser(bytes.NewReader(b))
 		s = string(b)
+		isBody = true
+		if strings.HasPrefix(strings.ToLower(r.Header.Get(headers.NameContentType)), headers.ValueApplicationJSON) {
+			return v, s, isBody
+		}
 		if vs, err := url.ParseQuery(s); err == nil && isQueryBody(r) {
 			for vsk := range vs {
 				for _, vsv := range vs[vsk] {
@@ -108,7 +112,6 @@ func GetRequestValues(r *http.Request) (url.Values, string, bool) {
 				}
 			}
 		}
-		isBody = true
 	}
 	return v, s, isBody
 }