test/fuzz: fix rpc, secret_connection and pex tests (#6190)

* test/fuzz: fix rpc, secret_connection and pex tests

- ignore empty data in rpc
- provide correct IP in pex
- spawn a goroutine for Write and do multiple Read(s)

* test/fuzz: fix init in pex test

* test/fuzz: assign NewServeMux to global var

* test/fuzz: only try to Unmarshal if blob is not empty

* run fuzz tests for PRs which modify fuzz tests themselves

* test/fuzz: move MakeSwitch into init

test/fuzz/rpc/jsonrpc/server/handler.go

@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"os"
 
 	"github.com/tendermint/tendermint/libs/log"
 	rs "github.com/tendermint/tendermint/rpc/jsonrpc/server"
@@ -18,13 +19,16 @@ var rpcFuncMap = map[string]*rs.RPCFunc{
 var mux *http.ServeMux
 
 func init() {
-	mux := http.NewServeMux()
-	buf := new(bytes.Buffer)
-	lgr := log.NewTMLogger(buf)
+	mux = http.NewServeMux()
+	lgr := log.NewTMLogger(log.NewSyncWriter(os.Stdout))
 	rs.RegisterRPCFuncs(mux, rpcFuncMap, lgr)
 }
 
 func Fuzz(data []byte) int {
+	if len(data) == 0 {
+		return -1
+	}
+
 	req, _ := http.NewRequest("POST", "http://localhost/", bytes.NewReader(data))
 	rec := httptest.NewRecorder()
 	mux.ServeHTTP(rec, req)
@@ -36,9 +40,11 @@ func Fuzz(data []byte) int {
 	if err := res.Body.Close(); err != nil {
 		panic(err)
 	}
-	recv := new(types.RPCResponse)
-	if err := json.Unmarshal(blob, recv); err != nil {
-		panic(err)
+	if len(blob) > 0 {
+		recv := new(types.RPCResponse)
+		if err := json.Unmarshal(blob, recv); err != nil {
+			panic(err)
+		}
 	}
 	return 1
 }