feat: restful -> grpc gateway (#2155)

* Revert "chore: remove unimplemented gateway (#2139)"

This reverts commit d70e73ec66.

* feat: working gateway

* feat: use mr to make it faster

* feat: working gateway

* chore: add comments

* feat: support protoset besides reflection

* feat: support zrpc client conf

* docs: update readme

* feat: support grpc-metadata- header to gateway- header conversion

* chore: add docs

gateway/requestparser.go

@@ -0,0 +1,43 @@
+package gateway
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+
+	"github.com/fullstorydev/grpcurl"
+	"github.com/golang/protobuf/jsonpb"
+	"github.com/zeromicro/go-zero/rest/pathvar"
+)
+
+func newRequestParser(r *http.Request, resolver jsonpb.AnyResolver) (grpcurl.RequestParser, error) {
+	vars := pathvar.Vars(r)
+	if len(vars) == 0 {
+		return grpcurl.NewJSONRequestParser(r.Body, resolver), nil
+	}
+
+	if r.ContentLength == 0 {
+		var buf bytes.Buffer
+		if err := json.NewEncoder(&buf).Encode(vars); err != nil {
+			return nil, err
+		}
+
+		return grpcurl.NewJSONRequestParser(&buf, resolver), nil
+	}
+
+	m := make(map[string]interface{})
+	if err := json.NewDecoder(r.Body).Decode(&m); err != nil {
+		return nil, err
+	}
+
+	for k, v := range vars {
+		m[k] = v
+	}
+
+	var buf bytes.Buffer
+	if err := json.NewEncoder(&buf).Encode(m); err != nil {
+		return nil, err
+	}
+
+	return grpcurl.NewJSONRequestParser(&buf, resolver), nil
+}