I can't figure out why an empty string turns out to be 506 bytes long.
So what happens is that I print a string to screen like this:
fmt.Printf("The last element '%s' ", messages[1])
and I get:
The last element ''
But then, when I print its length:
fmt.Printf("The last element len is '%s' ", len(messages[len(messages) - 1]))
I get:
The last element len is '%!s(int=506)'
I don't get it. Does anyone know what is happening?
I left the entire program here (it's pretty small). To pass input to this program just do:
printf "asti||" | netcat localhost 7777
Here is the program itself:
package main
import (
"fmt"
"net"
"os"
"strings"
)
func main() {
end_of_message_terminator := "||"
beginning_of_next_message := ""
request := make([]byte, 512)
service_port := ":7777"
tcpAddr, err := net.ResolveTCPAddr("tcp4", service_port)
checkError(err)
listener, err := net.ListenTCP("tcp", tcpAddr)
checkError(err)
response_port := ":8887"
tcpAddr_res, err := net.ResolveTCPAddr("tcp4", response_port)
checkError(err)
response_writer, err := net.ListenTCP("tcp", tcpAddr_res)
for {
conn, err := listener.Accept()
if err != nil {
continue
}
read_len, err := conn.Read(request)
if read_len == 0 {
continue
}
request_string := string(request)
fmt.Printf("Request String %s\\END", request_string)
messages := strings.Split(request_string, end_of_message_terminator)
fmt.Printf("%q
", messages)
messages[0] = beginning_of_next_message + messages[0]
fmt.Printf("%s
", messages[0])
fmt.Printf("The last element '%s'
", messages[1])
fmt.Printf("The last element '%s'
", messages[len(messages) - 1])
fmt.Printf("The last element len is '%s'
", len(messages[len(messages) - 1]))
fmt.Printf("The last element is equal to empty string? %s
", messages[len(messages) - 1] == "")
if messages[len(messages) - 1] != "" {
beginning_of_next_message = messages[len(messages) - 1]
messages[len(messages) - 1] = ""
fmt.Printf("was here 00
")
}
if len(messages) == 1 {
continue
}
conn.Close()
}
}
func checkError(err error) {
if err != nil {
fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
os.Exit(1)
}
}
The program is working with the entire request, not the portion filled in by Read. Change the line
request_string := string(request)
to
request_string := string(request[:read_len])
to fix this issue.
A better fix is to use bufio.Scanner to scan for message terminators.
func scanTerminator(data []byte, atEOF bool) (advance int, token []byte, err error) {
if atEOF && len(data) == 0 {
return 0, nil, nil
}
if i := bytes.Index(data, []byte("||")); i >= 0 {
return i + 2, data[:i], nil
}
if atEOF {
return len(data), data, nil
}
return 0, nil, nil
}
func main() {
...
for {
conn, err := listener.Accept()
if err != nil {
// handle error
}
s := bufio.NewScanner(conn)
s.Split(scanTerminator)
for s.Scan() {
message := s.Text()
// process message
}
if s.Err() != nil {
// handle error
}
}
}