better error handling in c&w

cmd/magneticod/dht/mainline/codec.go

@@ -8,6 +8,7 @@ package mainline
 import (
 	"encoding/binary"
 	"fmt"
+	"github.com/pkg/errors"
 	"net"
 
 	"github.com/anacrolix/missinggo/iter"
@@ -251,10 +252,10 @@ func (e *Error) UnmarshalBencode(b []byte) (err error) {
 
 	matches := result[0][1:]
 	if _, err := fmt.Sscanf(string(matches[0]), "%d", &code); err != nil {
-		return fmt.Errorf("could not parse the error code: %s", err.Error())
+		return errors.Wrap(err, "could not parse error code")
 	}
 	if _, err := fmt.Sscanf(string(matches[1]), "%d", &msgLen); err != nil {
-		return fmt.Errorf("could not parse the error message length: %s", err.Error())
+		return errors.Wrap(err, "could not parse error msg length")
 	}
 
 	if len(matches[2]) != msgLen {

cmd/magneticow/handlers.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"encoding/hex"
+	"fmt"
+	"github.com/pkg/errors"
 	"net/http"
 	"strings"
 	"time"
@@ -14,73 +16,67 @@ import (
 func rootHandler(w http.ResponseWriter, r *http.Request) {
 	nTorrents, err := database.GetNumberOfTorrents()
 	if err != nil {
-		panic(err.Error())
+		handlerError(errors.Wrap(err, "GetNumberOfTorrents"), w)
+		return
 	}
 
-	err = templates["homepage"].Execute(w, struct {
+	_ = templates["homepage"].Execute(w, struct {
 		NTorrents uint
 	}{
 		NTorrents: nTorrents,
 	})
-	if err != nil {
-		panic(err.Error())
-	}
 }
 
-// TODO: we might as well move torrents.html into static...
 func torrentsHandler(w http.ResponseWriter, r *http.Request) {
 	data := mustAsset("templates/torrents.html")
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	// Cache static resources for a day
 	w.Header().Set("Cache-Control", "max-age=86400")
-	w.Write(data)
+	_, _ = w.Write(data)
 }
 
 func torrentsInfohashHandler(w http.ResponseWriter, r *http.Request) {
 	infoHash, err := hex.DecodeString(mux.Vars(r)["infohash"])
 	if err != nil {
-		panic(err.Error())
+		handlerError(errors.Wrap(err, "cannot decode infohash"), w)
+		return
 	}
 
 	torrent, err := database.GetTorrent(infoHash)
 	if err != nil {
-		panic(err.Error())
+		handlerError(errors.Wrap(err, "cannot get torrent"), w)
+		return
 	}
 	if torrent == nil {
-		w.WriteHeader(404)
-		w.Write([]byte("torrent not found!"))
+		respondError(w, http.StatusNotFound, "torrent not found!")
 		return
 	}
 
 	files, err := database.GetFiles(infoHash)
 	if err != nil {
-		panic(err.Error())
+		handlerError(errors.Wrap(err, "could not get files"), w)
+		return
 	}
 	if files == nil {
-		w.WriteHeader(500)
-		w.Write([]byte("files not found what!!!"))
+		handlerError(fmt.Errorf("could not get files"), w)
 		return
 	}
 
-	err = templates["torrent"].Execute(w, struct {
+	_ = templates["torrent"].Execute(w, struct {
 		T *persistence.TorrentMetadata
 		F []persistence.File
 	}{
 		T: torrent,
 		F: files,
 	})
-	if err != nil {
-		panic("error while executing template!")
-	}
 }
 
-// TODO: we might as well move statistics.html into static...
 func statisticsHandler(w http.ResponseWriter, r *http.Request) {
 	data := mustAsset("templates/statistics.html")
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	// Cache static resources for a day
 	w.Header().Set("Cache-Control", "max-age=86400")
-	w.Write(data)
+	_, _ = w.Write(data)
 }
 
 func feedHandler(w http.ResponseWriter, r *http.Request) {
@@ -111,32 +107,24 @@ func feedHandler(w http.ResponseWriter, r *http.Request) {
 		nil,
 	)
 	if err != nil {
-		respondError(w, 400, err.Error())
+		handlerError(errors.Wrap(err, "query torrent"), w)
 		return
 	}
 
 	// It is much more convenient to write the XML deceleration manually*, and then process the XML
-	// template using template/html and send, then to use encoding/xml.
+	// template using template/html and send, than to use encoding/xml.
 	//
 	// *: https://github.com/golang/go/issues/3133
 	//
 	// TODO: maybe do it properly, even if it's inconvenient?
-
-	_, err = w.Write([]byte(`<?xml version="1.0" encoding="utf-8" standalone="yes"?>`))
-	if err != nil {
-		panic(err.Error())
-	}
-
-	err = templates["feed"].Execute(w, struct {
+	_, _ = w.Write([]byte(`<?xml version="1.0" encoding="utf-8" standalone="yes"?>`))
+	_ = templates["feed"].Execute(w, struct {
 		Title    string
 		Torrents []persistence.TorrentMetadata
 	}{
 		Title:    title,
 		Torrents: torrents,
 	})
-	if err != nil {
-		panic(err.Error())
-	}
 }
 
 func staticHandler(w http.ResponseWriter, r *http.Request) {
@@ -155,5 +143,5 @@ func staticHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", contentType)
 	// Cache static resources for a day
 	w.Header().Set("Cache-Control", "max-age=86400")
-	w.Write(data)
+	_, _ = w.Write(data)
 }

cmd/magneticow/main.go

@@ -5,9 +5,9 @@ import (
 	"bytes"
 	"encoding/hex"
 	"fmt"
+	"github.com/pkg/errors"
 	"html/template"
 	"io"
-	"log"
 	"net/http"
 	"os"
 	"os/signal"
@@ -156,7 +156,7 @@ func main() {
 	var err error
 	database, err = persistence.MakeDatabase(opts.Database, logger)
 	if err != nil {
-		panic(err.Error())
+		zap.L().Fatal("could not access to database", zap.Error(err))
 	}
 
 	decoder.IgnoreUnknownKeys(false)
@@ -178,7 +178,8 @@ func respondError(w http.ResponseWriter, statusCode int, format string, a ...int
 func mustAsset(name string) []byte {
 	data, err := Asset(name)
 	if err != nil {
-		log.Panicf("Could NOT access the requested resource `%s`: %s (please inform us, this is a BUG!)", name, err.Error())
+		zap.L().Panic("Could NOT access the requested resource! THIS IS A BUG, PLEASE REPORT",
+			zap.String("name", name), zap.Error(err))
 	}
 	return data
 }
@@ -250,7 +251,7 @@ func loadCred(cred string) error {
 			if err == io.EOF {
 				break
 			}
-			return fmt.Errorf("error while reading line %d: %s", lineno, err.Error())
+			return errors.Wrapf(err, "while reading line %d", lineno)
 		}
 
 		line = line[:len(line)-1] // strip '\n'
@@ -316,7 +317,5 @@ func BasicAuth(handler http.HandlerFunc, realm string) http.HandlerFunc {
 func authenticate(w http.ResponseWriter, realm string) {
 	w.Header().Set("WWW-Authenticate", `Basic realm="`+realm+`"`)
 	w.WriteHeader(401)
-	if _, err := w.Write([]byte("Unauthorised.\n")); err != nil {
-		panic(err.Error())
-	}
+	_, _ = w.Write([]byte("Unauthorised.\n"))
 }

cmd/magneticow/util.go

@@ -0,0 +1,8 @@
+package main
+
+import "net/http"
+
+func handlerError(err error, w http.ResponseWriter) {
+	w.WriteHeader(http.StatusInternalServerError)
+	_, _ = w.Write([]byte(err.Error()))
+}