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.

Dim success As Boolean
success = False

Dim socket As New Chilkat.Socket

//  Connect to chilkatsoft.com over TLS.
Dim bTls As Boolean
bTls = True
Dim maxWaitMs As Int32
maxWaitMs = 5000
success = socket.Connect("chilkatsoft.com",443,bTls,maxWaitMs)
If (success = False) Then
    System.DebugLog(socket.LastErrorText)
    Return
End If

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.
Dim httpReq As String
httpReq = "GET /big_helloWorld.txt HTTP/1.1" + EndOfLine.Windows + "Host: chilkatsoft.com" + EndOfLine.Windows + "Connection: close" + EndOfLine.Windows + EndOfLine.Windows
success = socket.SendString(httpReq)
If (success = False) Then
    System.DebugLog(socket.LastErrorText)
    Return
End If

//  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.
Dim responseText As String
responseText = socket.ReceiveString()
If (socket.LastMethodSuccess = False) Then
    System.DebugLog(socket.LastErrorText)
    Return
End If

//  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.
Dim sb As New Chilkat.StringBuilder
success = sb.Append(responseText)
Dim contentLength As String
contentLength = sb.GetBetween("Content-Length: ",EndOfLine.Windows)
If (sb.LastMethodSuccess = False) Then
    System.DebugLog(sb.LastErrorText)
    Return
End If

//  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.
System.DebugLog("Characters received so far (headers + partial body): " + Str(sb.Length))
System.DebugLog("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.