TCP client / server file transfer in Go - tcp

Question

I'm new to Go and I'm having troubles debugging this client / server file transfer code. When I request a 719kb png file from the server, I get the 719kb.. but not perfectly, the png when I open it isn't completely displayed (some is cut off. Where am I going wrong here?
// CLIENT ///
package main
import (
"bufio"
"bytes"
"fmt"
"io"
"log"
"net"
"os"
"strings"
)
const BUFFER_SIZE = 1024
func main() {
//get port and ip address to dial
if len(os.Args) != 3 {
fmt.Println("useage example: tcpClient 127.0.0.1 7005")
return
}
var ip string = os.Args[1]
var port string = os.Args[2]
connection, err := net.Dial("tcp", ip+":"+port)
if err != nil {
fmt.Println("There was an error making a connection")
}
//read from
reader := bufio.NewReader(os.Stdin)
fmt.Print("Please enter 'get <filename>' or 'send <filename>' to transfer files to the server\n\n")
inputFromUser, _ := reader.ReadString('\n')
arrayOfCommands := strings.Split(inputFromUser, " ")
if arrayOfCommands[0] == "get" {
getFileFromServer(arrayOfCommands[1], connection)
} else if arrayOfCommands[0] == "send" {
sendFileToServer(arrayOfCommands[1], connection)
} else {
fmt.Println("Bad Command")
}
}
func sendFileToServer(fileName string, connection net.Conn) {
var currentByte int64 = 0
fmt.Println("send to client")
fileBuffer := make([]byte, BUFFER_SIZE)
var err error
//file to read
file, err := os.Open(strings.TrimSpace(fileName)) // For read access.
if err != nil {
connection.Write([]byte("-1"))
log.Fatal(err)
}
connection.Write([]byte("send " + fileName))
//read file until there is an error
for err == nil || err != io.EOF {
_, err = file.ReadAt(fileBuffer, currentByte)
currentByte += BUFFER_SIZE
fmt.Println(fileBuffer)
connection.Write(fileBuffer)
}
file.Close()
connection.Close()
}
func getFileFromServer(fileName string, connection net.Conn) {
var currentByte int64 = 0
fileBuffer := make([]byte, BUFFER_SIZE)
var err error
file, err := os.Create(strings.TrimSpace(fileName))
if err != nil {
log.Fatal(err)
}
connection.Write([]byte("get " + fileName))
for {
connection.Read(fileBuffer)
cleanedFileBuffer := bytes.Trim(fileBuffer, "\x00")
_, err = file.WriteAt(cleanedFileBuffer, currentByte)
currentByte += BUFFER_SIZE
if err == io.EOF {
break
}
}
file.Close()
return
}
// END CLIENT //
// SERVER //
package main
import (
"bytes"
"fmt"
"io"
"log"
"net"
"os"
"strings"
)
const BUFFER_SIZE = 1024
const PORT = "7005"
func main() {
fmt.Println("start listening")
server, error := net.Listen("tcp", "localhost:"+PORT)
if error != nil {
fmt.Println("There was an error starting the server" + error.Error())
return
}
//infinate loop
for {
connection, error := server.Accept()
if error != nil {
fmt.Println("There was am error with the connection" + error.Error())
return
}
fmt.Println("connected")
//handle the connection, on it's own thread, per connection
go connectionHandler(connection)
}
}
func connectionHandler(connection net.Conn) {
buffer := make([]byte, BUFFER_SIZE)
_, error := connection.Read(buffer)
if error != nil {
fmt.Println("There is an error reading from connection", error.Error())
return
}
fmt.Println("command recieved: " + string(buffer))
//loop until disconntect
cleanedBuffer := bytes.Trim(buffer, "\x00")
cleanedInputCommandString := strings.TrimSpace(string(cleanedBuffer))
arrayOfCommands := strings.Split(cleanedInputCommandString, " ")
fmt.Println(arrayOfCommands[0])
if arrayOfCommands[0] == "get" {
sendFileToClient(arrayOfCommands[1], connection)
} else if arrayOfCommands[0] == "send" {
fmt.Println("getting a file")
getFileFromClient(arrayOfCommands[1], connection)
} else {
_, error = connection.Write([]byte("bad command"))
}
}
func sendFileToClient(fileName string, connection net.Conn) {
var currentByte int64 = 0
fmt.Println("send to client")
fileBuffer := make([]byte, BUFFER_SIZE)
//file to read
file, err := os.Open(strings.TrimSpace(fileName)) // For read access.
if err != nil {
log.Fatal(err)
}
var err2 error
//read file until there is an error
for {
_, err2 = file.ReadAt(fileBuffer, currentByte)
currentByte += BUFFER_SIZE
fmt.Println(fileBuffer)
connection.Write(fileBuffer)
if err2 == io.EOF {
break
}
}
file.Close()
return
}
func getFileFromClient(fileName string, connection net.Conn) {
var currentByte int64 = 0
fileBuffer := make([]byte, BUFFER_SIZE)
var err error
file, err := os.Create(strings.TrimSpace(fileName))
if err != nil {
log.Fatal(err)
}
connection.Write([]byte("get " + fileName))
for err == nil || err != io.EOF {
connection.Read(fileBuffer)
cleanedFileBuffer := bytes.Trim(fileBuffer, "\x00")
_, err = file.WriteAt(cleanedFileBuffer, currentByte)
if len(string(fileBuffer)) != len(string(cleanedFileBuffer)) {
break
}
currentByte += BUFFER_SIZE
}
connection.Close()
file.Close()
return
}
// END SERVER //

Answer 1

You need to account for the number of bytes returned from ReadAt, otherwise the last fileBuffer you send will have extra garbage bytes.
Example:
n, err := file.ReadAt(fileBuffer, currentByte)
connection.Write(fileBuffer[:n])
Also bytes.Trim(fileBuffer, "\x00") will destroy almost any binary file since usually they use null bytes to fill space.
Also the proper way of doing this is just using io.Copy:
file, err := os.Open(strings.TrimSpace(fileName)) // For read access.
if err != nil {
log.Fatal(err)
}
defer file.Close() // make sure to close the file even if we panic.
n, err = io.Copy(connection, file)
if err != nil {
log.Fatal(err)
}
fmt.Println(n, "bytes sent")