ReceiveString Returns Only the Immediately Available Data

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Demonstrates that Socket.ReceiveString returns only the text immediately available and not the entire response. The example connects to chilkatsoft.com over TLS and requests big_helloWorld.txt, a large text file of roughly 74,000 lines. A single ReceiveString call returns just the first portion of the response, and the example reports how many characters were received compared with the total size given by the response Content-Length header.

func chilkatTest() {
    var success: Bool = false

    let socket = CkoSocket()!

    //  Connect to chilkatsoft.com over TLS.
    var bTls: Bool = true
    var maxWaitMs: Int = 5000
    success = socket.connect(hostname: "chilkatsoft.com", port: 443, ssl: bTls, maxWaitMs: maxWaitMs)
    if success == false {
        print("\(socket.lastErrorText!)")
        return
    }

    socket.stringCharset = "utf-8"

    //  Send an HTTP GET request for big_helloWorld.txt, a large text file of roughly 74,000 lines of
    //  "Hello World!".  This uses a minimal HTTP request only to exercise ReceiveString against a public
    //  server -- for real HTTP work, use the Chilkat Http, Rest, or HttpCurl classes instead.
    var httpReq: String? = "GET /big_helloWorld.txt HTTP/1.1\r\nHost: chilkatsoft.com\r\nConnection: close\r\n\r\n"
    success = socket.sendString(str: httpReq)
    if success == false {
        print("\(socket.lastErrorText!)")
        return
    }

    //  Call ReceiveString a single time.  It returns only the text that is immediately available --
    //  typically just the first network packet -- and does NOT wait for the entire response to arrive.
    var responseText: String? = socket.receiveString()
    if socket.lastMethodSuccess == false {
        print("\(socket.lastErrorText!)")
        return
    }

    //  Load the received text into a StringBuilder so its length can be measured and the Content-Length
    //  header extracted.  The Content-Length header gives the total size, in bytes, of the response body.
    let sb = CkoStringBuilder()!
    sb.append(value: responseText)
    var contentLength: String? = sb.getBetween(beginMark: "Content-Length: ", endMark: "\r\n")
    if sb.lastMethodSuccess == false {
        print("\(sb.lastErrorText!)")
        return
    }

    //  Compare what this single ReceiveString returned against the full size of the expected response.
    //  The received amount is only a small fraction of the total.
    print("Characters received so far (headers + partial body): \(sb.length.intValue)")
    print("Expected response body size (Content-Length): \(contentLength!) bytes")

    //  A single ReceiveString call returns whatever is currently available, so it cannot indicate whether
    //  the full response has arrived.  This makes it difficult to know when a response is complete: the
    //  application must either know how many bytes to expect (for example from a Content-Length header or
    //  an application-defined length prefix) and keep receiving until that many bytes are collected, or
    //  keep receiving until the peer closes the connection.

}