Somewhat reasonable error-handling

README.md

@@ -52,7 +52,7 @@ Thus, with a connection and a way of communication, the server will send a filei
 - **VERY** slow; FIXED - [ ]   
 - **VERY** expensive on resources; FIXED - [ ]
 - If `MAXFILEDATASIZE` is bigger than appr. 1024 - the packets on the other end will not be unmarshalled due to error ??; FIXED - [ ]
-- Lack of proper error-handling; FIXED - [ ]
+- Lack of proper error-handling; somewhat FIXED - [x]
 - Lack of information about the process of transferring (ETA, lost packets, etc.); FIXED - [ ]
 - No way to verify if the transferred file is not corrupted; FIXED - [ ]
 - No encryption; FIXED - [ ] 

client/client.go

@@ -139,10 +139,11 @@ func (c *Client) WritePieceOfFile(filePacket protocol.Packet) error {
 // Listens in an endless loop; reads incoming packages and puts them into channel
 func (c *Client) ReceivePackets() {
 	for {
-		incomingPacket := protocol.ReadFromConn(c.Connection)
-		isvalid, _ := protocol.IsValidPacket(incomingPacket)
-		if !isvalid {
-			continue
+		incomingPacket, err := protocol.ReadFromConn(c.Connection)
+		if err != nil {
+			// in current implementation there is no way to receive a working file even if only one packet is missing
+			fmt.Printf("Error reading a packet: %s\nExiting...", err)
+			os.Exit(-1)
 		}
 		c.IncomingPackets <- incomingPacket
 	}

protocol/protocol.go

@@ -34,39 +34,40 @@ type Packet struct {
 }
 
 // converts valid packet bytes into `Packet` struct
-func ReadPacketBytes(packetBytes []byte) Packet {
-	// makes sure that the packet is ALWAYS less or equal to the maximum packet size
-	// this allows not to use any client or server checks
-
-	//fmt.Println("READING packet: ", string(packetBytes))
-
+func ReadPacketBytes(packetBytes []byte) (Packet, error) {
 	var packet Packet
 	err := json.Unmarshal(packetBytes, &packet)
 	if err != nil {
-		fmt.Printf("Could not unmarshal the packet: %s\n", err)
-		return Packet{}
+		return Packet{}, fmt.Errorf("could not unmarshal packet bytes: %s", err)
 	}
-	return packet
+	return packet, nil
 }
 
 // Converts `Packet` struct into []byte
-func EncodePacket(packet Packet) []byte {
+func EncodePacket(packet Packet) ([]byte, error) {
 	packetBytes, err := json.Marshal(packet)
 	if err != nil {
-		return []byte("")
+		return nil, fmt.Errorf("could not marshal packet bytes: %s", err)
 	}
-	return packetBytes
+	return packetBytes, nil
 }
 
 // Measures the packet length
-func MeasurePacket(packet Packet) uint64 {
-	packetBytes := EncodePacket(packet)
-	return uint64(len(packetBytes))
+func MeasurePacket(packet Packet) (uint64, error) {
+	packetBytes, err := EncodePacket(packet)
+	if err != nil {
+		return 0, fmt.Errorf("could not measure the packet: %s", err)
+	}
+	return uint64(len(packetBytes)), nil
 }
 
 // Checks if given packet is valid, returns a boolean and an explanation message
 func IsValidPacket(packet Packet) (bool, string) {
-	if MeasurePacket(packet) > uint64(MAXPACKETSIZE) {
+	packetSize, err := MeasurePacket(packet)
+	if err != nil {
+		return false, "Measurement error"
+	}
+	if packetSize > uint64(MAXPACKETSIZE) {
 		return false, "Exceeded MAXPACKETSIZE"
 	}
 	if len(packet.FileData) > MAXFILEDATASIZE {
@@ -74,7 +75,7 @@ func IsValidPacket(packet Packet) (bool, string) {
 	}
 
 	if strings.TrimSpace(string(packet.Header)) == "" {
-		return false, "Blank header"
+		return false, "Empty header"
 	}
 	return true, ""
 }
@@ -87,38 +88,42 @@ func SendPacket(connection net.Conn, packet Packet) error {
 		return fmt.Errorf("this packet is invalid !: %v; The error: %v", packet, msg)
 	}
 
-	packetSize := MeasurePacket(packet)
+	packetSize, err := MeasurePacket(packet)
+	if err != nil {
+		return err
+	}
 
 	// write packetsize between delimeters (ie: |727|{"HEADER":"PING"...})
 	connection.Write([]byte(fmt.Sprintf("%s%d%s", PACKETSIZEDELIMETER, packetSize, PACKETSIZEDELIMETER)))
 
-	// write an actual packet
-	connection.Write(EncodePacket(packet))
+	// write the packet itself
+	packetBytes, err := EncodePacket(packet)
+	if err != nil {
+		return fmt.Errorf("could not send a packet: %s", err)
+	}
+	connection.Write(packetBytes)
 
-	//fmt.Println("Sending packet: ", string(EncodePacket(packet)), "  Length: ", packetSize)
 	return nil
 }
 
-// Reads a packet from a connection by retrieving the packet length. Only once
-// ASSUMING THAT THE PACKETS ARE SENT BY `SendPacket` method !!!!
-func ReadFromConn(connection net.Conn) Packet {
-	var gotPacketSize bool = false
+// Reads a packet from given connection.
+// ASSUMING THAT THE PACKETS ARE SENT BY `SendPacket` function !!!!
+func ReadFromConn(connection net.Conn) (Packet, error) {
+	var err error
 	var delimeterCounter int = 0
-
-	var packetSizeStr string = ""
+	var packetSizeStrBuffer string = ""
 	var packetSize int = 0
+
 	for {
-		// still need to get a packetsize
-		if !gotPacketSize {
 		// reading byte-by-byte
 		buffer := make([]byte, 1)
-			connection.Read(buffer)
+		connection.Read(buffer) // no fixed time limit, so no need to check for an error
 
 		// found a delimeter
 		if string(buffer) == PACKETSIZEDELIMETER {
 			delimeterCounter++
 
-				// the first delimeter is found, skipping the rest of the code
+			// the first delimeter has been found, skipping the rest of the loop
 			if delimeterCounter == 1 {
 				continue
 			}
@@ -126,30 +131,34 @@ func ReadFromConn(connection net.Conn) Packet {
 
 		// found the first delimeter, skip was performed, now reading an actual packetsize
 		if delimeterCounter == 1 {
-				packetSizeStr += string(buffer)
+			// adding a character of the packet size to the `string buffer`; ie: | <- read, reading now -> 1 23|PACKET_HERE
+			packetSizeStrBuffer += string(buffer)
+
 		} else if delimeterCounter == 2 {
 			// found the last delimeter, thus already read the whole packetsize
-				packetSize, _ = strconv.Atoi(packetSizeStr)
-				gotPacketSize = true
+			// converting from string to int
+			packetSize, err = strconv.Atoi(packetSizeStrBuffer)
+			if err != nil {
+				return Packet{}, fmt.Errorf("could not convert packet size into integer: %s", err)
+			}
+			// packet size has been found, breaking from the loop
+			break
 		}
-			// skipping the rest of the code because we don`t know the packet size yet
-			continue
 	}
-		// have a packetsize, now reading the whole packet
 
-		//fmt.Println("Got a packetsize!: ", packetSize)
+	// have a packetsize, now reading the whole packet
 	packetBuffer := make([]byte, packetSize)
 	connection.Read(packetBuffer)
 
-		packet := ReadPacketBytes(packetBuffer)
-
-		isvalid, _ := IsValidPacket(packet)
-		if isvalid {
-			return packet
+	packet, err := ReadPacketBytes(packetBuffer)
+	if err != nil {
+		return Packet{}, err
 	}
 
-		break
+	isvalid, msg := IsValidPacket(packet)
+	if isvalid {
+		return packet, nil
 	}
 
-	return Packet{}
+	return Packet{}, fmt.Errorf("received an invalid packet. Reason: %s", msg)
 }

server/server.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"os"
 
 	"github.com/Unbewohnte/FTU/protocol"
 )
@@ -19,7 +20,7 @@ func GetLocalIP() (string, error) {
 
 	localAddr := conn.LocalAddr().(*net.UDPAddr)
 
-	return string(localAddr.IP), nil
+	return localAddr.IP.String(), nil
 }
 
 // gets a remote ip. Borrowed from StackOverflow, thank you, whoever I brought it from
@@ -100,15 +101,14 @@ func (s *Server) Disconnect() {
 }
 
 // Accepts one connection
-func (s *Server) WaitForConnection() error {
+func (s *Server) WaitForConnection() {
 	connection, err := s.Listener.Accept()
 	if err != nil {
-		return fmt.Errorf("could not accept a connection: %s", err)
+		fmt.Printf("Could not accept a connection: %s", err)
+		os.Exit(-1)
 	}
 	s.Connection = connection
 	fmt.Println("New connection from ", s.Connection.RemoteAddr())
-
-	return nil
 }
 
 // Closes the listener. Used only when there is still no connection from `AcceptConnections`
@@ -174,10 +174,11 @@ func (s *Server) SendPiece() error {
 // Listens in an endless loop; reads incoming packages and puts them into channel
 func (s *Server) ReceivePackets() {
 	for {
-		incomingPacket := protocol.ReadFromConn(s.Connection)
-		isvalid, _ := protocol.IsValidPacket(incomingPacket)
-		if !isvalid {
-			continue
+		incomingPacket, err := protocol.ReadFromConn(s.Connection)
+		if err != nil {
+			// in current implementation there is no way to receive a working file even if only one packet is missing
+			fmt.Printf("Error reading a packet: %s\nExiting...", err)
+			os.Exit(-1)
 		}
 		s.IncomingPackets <- incomingPacket
 	}
@@ -226,7 +227,8 @@ func (s *Server) MainLoop() {
 			}
 			err := s.SendPiece()
 			if err != nil {
-				fmt.Println(err)
+				fmt.Printf("Could not send a piece of file: %s", err)
+				os.Exit(-1)
 			}
 
 		case protocol.HeaderDisconnecting: