ReceiveSb Returns Only the Immediately Available Data

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Demonstrates that Socket.ReceiveSb returns only the data 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 ReceiveSb 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 = False

Dim socket As New Chilkat.Socket

'  Connect to chilkatsoft.com over TLS.
Dim bTls As Boolean = True
Dim maxWaitMs As Integer = 5000
success = socket.Connect("chilkatsoft.com",443,bTls,maxWaitMs)
If (success = False) Then
    Debug.WriteLine(socket.LastErrorText)
    Exit Sub
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 ReceiveSb against a public
'  server -- for real HTTP work, use the Chilkat Http, Rest, or HttpCurl classes instead.
Dim httpReq As String = "GET /big_helloWorld.txt HTTP/1.1" & vbCrLf & "Host: chilkatsoft.com" & vbCrLf & "Connection: close" & vbCrLf & vbCrLf
success = socket.SendString(httpReq)
If (success = False) Then
    Debug.WriteLine(socket.LastErrorText)
    Exit Sub
End If


'  Call ReceiveSb a single time.  It returns only the bytes that are immediately available --
'  typically just the first network packet -- and does NOT wait for the entire response to arrive.
Dim sb As New Chilkat.StringBuilder
success = socket.ReceiveSb(sb)
If (success = False) Then
    Debug.WriteLine(socket.LastErrorText)
    Exit Sub
End If


'  The response begins with HTTP headers.  The Content-Length header gives the total size, in bytes,
'  of the response body.
Dim contentLength As String = sb.GetBetween("Content-Length: ",vbCrLf)
If (sb.LastMethodSuccess = False) Then
    Debug.WriteLine(sb.LastErrorText)
    Exit Sub
End If


'  Compare what this single ReceiveSb returned against the full size of the expected response.  The
'  received amount is only a small fraction of the total.
Debug.WriteLine("Characters received so far (headers + partial body): " & sb.Length)
Debug.WriteLine("Expected response body size (Content-Length): " & contentLength & " bytes")

'  A single ReceiveSb 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.