feat(runtime): implement custom logging handler that print function name (ChainSafe#1825)

* implement custom logging handler that print function name

* move log handler to runtime package

Author: edwardmack

lib/runtime/log_handler.go

@@ -0,0 +1,34 @@
+// Copyright 2019 ChainSafe Systems (ON) Corp.
+// This file is part of gossamer.
+//
+// The gossamer library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The gossamer library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the gossamer library. If not, see <http://www.gnu.org/licenses/>.
+
+package runtime
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+
+	log "github.com/ChainSafe/log15"
+)
+
+// CustomFileHandler returns a Handler that adds the name of the calling function to the context with key "func"
+//  and the line number and file of the calling function to the context with key "caller".
+func CustomFileHandler(h log.Handler) log.Handler {
+	return log.FuncHandler(func(r *log.Record) error {
+		r.Ctx = append(r.Ctx, "func", strings.TrimLeft(filepath.Ext(r.Call.Frame().Function), "."), "caller", fmt.Sprint(r.Call))
+		return h.Log(r)
+	})
+}

lib/runtime/wasmer/instance.go

@@ -108,7 +108,7 @@ func newInstance(code []byte, cfg *Config) (*Instance, error) {
 	// if cfg.LogLvl set to < 0, then don't change package log level
 	if cfg.LogLvl >= 0 {
 		h := log.StreamHandler(os.Stdout, log.TerminalFormat())
-		h = log.CallerFileHandler(h)
+		h = runtime.CustomFileHandler(h)
 		logger.SetHandler(log.LvlFilterHandler(cfg.LogLvl, h))
 	}