Reading Data from Socket Golang

Question

I'm trying to read data from a telnet session in golang. I wrote the following functions in an attempt to accomplish this.

Initially I was having an issue where I was reading from a socket with no data so it would lock and never return. BufferSocketData is my attempt to work around this issue as I can't know if there is data to read. The idea is it will wait 1 second before determining there is not data in the socket and return an empty string.

GetData seems to work the first time there is new data in the buffer, but beyond that it gets no new data. I'm sure this has something to do with my use of goroutines and channels, I'm new to go and I'm sure I'm not using them correctly.

Any ideas as to why my subsequent reads return no data?

/*
ReadDataFromSocket - Attempts to read any data in the socket.
*/
func ReadDataFromSocket(sock io.Reader, c chan string) {
    var recvData = make([]byte, 1024)
    var numBytes, _ = sock.Read(recvData)
    c <- string(recvData[:numBytes])
}

/*
BufferSocketData - Read information from the socket and store it in the buffer.
*/
func (tn *TelnetLib) BufferSocketData(inp chan string, out chan string) {
    var data string
    var timeout int64 = 1000 // 1 second timeout.
    var start = utils.GetTimestamp()

    for utils.GetTimestamp()-start < timeout {
        select {
        case data = <-inp:
        default:
        }
        if data != "" {
            break
        }
    }
    out <- data
}

/*
GetData - Start goroutines to get and buffer data.
*/
func (tn *TelnetLib) GetData() {
    var sockCh = make(chan string)
    var buffCh = make(chan string)

    go ReadDataFromSocket(tn.Conn, sockCh)
    go tn.BufferSocketData(sockCh, buffCh)

    var data = <-buffCh

    if data != "" {
        tn.Buffer += data
    }
}

Please let me know if you need any additional information.

score 2 · Accepted Answer · 2018-06-26 15:27:44Z

2

Use SetReadDeadline to read data with a time limit:

func (tn *TelnetLib) GetData() {
    tn.Conn.SetReadDeadline(time.Second)
    recvData := make([]byte, 1024)
    n, err := tn.Conn.Read(recvData)
    if n > 0 {
       // do something with recvData[:n]
    }
    if e, ok := err.(interface{ Timeout() bool }); ok && e.Timeout() {
        // handle timeout
    } else if err != nil {
       // handle error
    }
}

Note that a single call Read may not read all data sent by the peer. You may want to accumulate data by calling Read in a loop or call io.ReadFull.

edited Jun 26, 2018 at 15:27

answered Jun 26, 2018 at 15:17

user5728991

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4 Comments

jhall1990 Over a year ago

This works perfectly. I have another function that attempts reads until a regex match is made or a timeout occurs so GetData performing a single read is exactly what I need. Thanks!

jhall1990 Over a year ago

You wouldn't happen to know how to do something similar with an SSH session object would you?

user5728991 Over a year ago

A different approach is required for an SSH session object. Ask a new question about that.

jhall1990 Over a year ago

Wrote a new question here

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