Fix go env panic when failed at loading plugin (#1031)

Fix go env panic when failed at loading plugin to make it easier for troubleshooting.

environments/go/server.go

@@ -2,13 +2,15 @@ package main
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
+	"log"
 	"net/http"
 	"os"
 	"path/filepath"
 	"plugin"
 
+	"github.com/pkg/errors"
+
 	"github.com/fission/fission/environments/go/context"
 )
 
@@ -37,47 +39,47 @@ type (
 
 var userFunc http.HandlerFunc
 
-func loadPlugin(codePath, entrypoint string) http.HandlerFunc {
+func loadPlugin(codePath, entrypoint string) (http.HandlerFunc, error) {
 
 	// if codepath's a directory, load the file inside it
 	info, err := os.Stat(codePath)
 	if err != nil {
-		panic(err)
+		return nil, errors.Wrap(err, "error checking plugin path")
 	}
 	if info.IsDir() {
 		files, err := ioutil.ReadDir(codePath)
 		if err != nil {
-			panic(err)
+			return nil, errors.Wrap(err, "error reading directory")
 		}
 		if len(files) == 0 {
-			panic("No files to load")
+			return nil, errors.New("No files to load")
 		}
 		fi := files[0]
 		codePath = filepath.Join(codePath, fi.Name())
 	}
 
-	fmt.Printf("loading plugin from %v\n", codePath)
+	log.Printf("loading plugin from %v\n", codePath)
 	p, err := plugin.Open(codePath)
 	if err != nil {
-		panic(err)
+		return nil, errors.Wrap(err, "error loading plugin")
 	}
 	sym, err := p.Lookup(entrypoint)
 	if err != nil {
-		panic("Entry point not found")
+		return nil, errors.Wrap(err, "entry point not found")
 	}
 
 	switch h := sym.(type) {
 	case *http.Handler:
-		return (*h).ServeHTTP
+		return (*h).ServeHTTP, nil
 	case *http.HandlerFunc:
-		return *h
+		return *h, nil
 	case func(http.ResponseWriter, *http.Request):
-		return h
+		return h, nil
 	case func(context.Context, http.ResponseWriter, *http.Request):
 		return func(w http.ResponseWriter, r *http.Request) {
 			c := context.New()
 			h(c, w, r)
-		}
+		}, nil
 	default:
 		panic("Entry point not found: bad type")
 	}
@@ -94,16 +96,28 @@ func specializeHandler(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		if os.IsNotExist(err) {
 			w.WriteHeader(http.StatusNotFound)
+			log.Printf(err.Error())
 			w.Write([]byte(CODE_PATH + ": not found"))
 			return
 		} else {
-			panic(err)
+			err = errors.Wrap(err, "unknown error")
+			log.Printf(err.Error())
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
 		}
 	}
 
-	fmt.Println("Specializing ...")
-	userFunc = loadPlugin(CODE_PATH, "Handler")
-	fmt.Println("Done")
+	log.Println("Specializing ...")
+	userFunc, err = loadPlugin(CODE_PATH, "Handler")
+	if err != nil {
+		err = errors.Wrap(err, "error specializing function")
+		log.Printf(err.Error())
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte(err.Error()))
+		return
+	}
+	log.Println("Done")
 }
 
 func specializeHandlerV2(w http.ResponseWriter, r *http.Request) {
@@ -115,6 +129,7 @@ func specializeHandlerV2(w http.ResponseWriter, r *http.Request) {
 
 	body, err := ioutil.ReadAll(r.Body)
 	if err != nil {
+		log.Println(err.Error())
 		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}
@@ -129,16 +144,28 @@ func specializeHandlerV2(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		if os.IsNotExist(err) {
 			w.WriteHeader(http.StatusNotFound)
+			log.Printf(err.Error())
 			w.Write([]byte(CODE_PATH + ": not found"))
 			return
 		} else {
-			panic(err)
+			err = errors.Wrap(err, "unknown error")
+			log.Printf(err.Error())
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
 		}
 	}
 
-	fmt.Println("Specializing ...")
-	userFunc = loadPlugin(loadreq.FilePath, loadreq.FunctionName)
-	fmt.Println("Done")
+	log.Println("Specializing ...")
+	userFunc, err = loadPlugin(loadreq.FilePath, loadreq.FunctionName)
+	if err != nil {
+		err = errors.Wrap(err, "error specializing function")
+		log.Printf(err.Error())
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte(err.Error()))
+		return
+	}
+	log.Println("Done")
 }
 
 func readinessProbeHandler(w http.ResponseWriter, r *http.Request) {
@@ -160,6 +187,6 @@ func main() {
 		userFunc(w, r)
 	})
 
-	fmt.Println("Listening on 8888 ...")
+	log.Println("Listening on 8888 ...")
 	http.ListenAndServe(":8888", nil)
 }