Go io string to int Atoi invalid argument - websocket

Question

I'm trying to parse a string from WebSockets connection in Go language. I'm implementing both sides of the connection, so the specification of data format is depending only on me.
As this is a simple app (generally for learning purposes), I've come up with ActionId Data, where ActionId is a uint8. BackendHandler is a handler for every request in WebSocket Connection.
Platform information
kuba:~$ echo {$GOARCH,$GOOS,`6g -V`}
amd64 linux 6g version release.r60.3 9516
code:
const ( // Specifies ActionId's
SabPause = iota
)
func BackendHandler(ws *websocket.Conn) {
buf := make([]byte, 512)
_, err := ws.Read(buf)
if err != nil { panic(err.String()) }
str := string(buf)
tmp, _ := strconv.Atoi(str[:0])
data := str[2:]
fmt.Println(tmp, data)
switch tmp {
case SabPause:
// Here I get `parsing "2": invalid argument`
// when passing "0 2" to websocket connection
minutes, ok := strconv.Atoui(data)
if ok != nil {
panic(ok.String())
}
PauseSab(uint8(minutes))
default:
panic("Unmatched input for BackendHandler")
}
}
All the output: (note the Println that I used for inspecting)
0 2
panic: parsing "2": invalid argument [recovered]
panic: runtime error: invalid memory address or nil pointer dereference
I couldn't find the code from which this error is launch, only where the error code is defined (dependent on platform). I'd appreciate general ideas for improving my code, but mainly I just want to solve the conversion problem.
Is this related to my buffer -> string conversion and slice-manipulation(I didn't want to use SplitAfter methods)?
Edit
This code reproduces the problem:
package main
import (
"strconv"
"io/ioutil"
)
func main() {
buf , _ := ioutil.ReadFile("input")
str := string(buf)
_, ok := strconv.Atoui(str[2:])
if ok != nil {
panic(ok.String())
}
}
The file input has to contain 0 2\r\n (depending on the file ending, it may look different on other OSes). This code can be fixed by adding the ending index for reslice, this way:
_, ok := strconv.Atoui(str[2:3])

Answer 1

You didn't provide a small compilable and runnable program to illustrate your problem. Nor did you provide full and meaningful print diagnostic messages.
My best guess is that you have a C-style null-terminated string. For example, simplifying your code,
package main
import (
"fmt"
"strconv"
)
func main() {
buf := make([]byte, 512)
buf = []byte("0 2\x00") // test data
str := string(buf)
tmp, err := strconv.Atoi(str[:0])
if err != nil {
fmt.Println(err)
}
data := str[2:]
fmt.Println("tmp:", tmp)
fmt.Println("str:", len(str), ";", str, ";", []byte(str))
fmt.Println("data", len(data), ";", data, ";", []byte(data))
// Here I get `parsing "2": invalid argument`
// when passing "0 2" to websocket connection
minutes, ok := strconv.Atoui(data)
if ok != nil {
panic(ok.String())
}
_ = minutes
}
Output:
parsing "": invalid argument
tmp: 0
str: 4 ; 0 2 ; [48 32 50 0]
data 2 ; 2 ; [50 0]
panic: parsing "2": invalid argument
runtime.panic+0xac /home/peter/gor/src/pkg/runtime/proc.c:1254
runtime.panic(0x4492c0, 0xf840002460)
main.main+0x603 /home/peter/gopath/src/so/temp.go:24
main.main()
runtime.mainstart+0xf /home/peter/gor/src/pkg/runtime/amd64/asm.s:78
runtime.mainstart()
runtime.goexit /home/peter/gor/src/pkg/runtime/proc.c:246
runtime.goexit()
----- goroutine created by -----
_rt0_amd64+0xc9 /home/peter/gor/src/pkg/runtime/amd64/asm.s:65
If you add my print diagnostic statements to your code, what do you see?
Note that your tmp, _ := strconv.Atoi(str[:0]) statement is probably wrong, since str[:0] is equivalent to str[0:0], which is equivalent to the empty string "".
I suspect that your problem is that you are ignoring the n return value from ws.Read. For example (including diagnostic messages), I would expect,
buf := make([]byte, 512)
buf = buf[:cap(buf)]
n, err := ws.Read(buf)
if err != nil {
panic(err.String())
}
fmt.Println(len(buf), n)
buf = buf[:n]
fmt.Println(len(buf), n)
Also, try using this code to set tmp,
tmp, err := strconv.Atoi(str[:1])
if err != nil {
panic(err.String())
}