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 fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

success = 0

set socket = CreateObject("Chilkat.Socket")

'  Connect to chilkatsoft.com over TLS.
bTls = 1
maxWaitMs = 5000
success = socket.Connect("chilkatsoft.com",443,bTls,maxWaitMs)
If (success = 0) Then
    outFile.WriteLine(socket.LastErrorText)
    WScript.Quit
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.
httpReq = "GET /big_helloWorld.txt HTTP/1.1" & vbCrLf & "Host: chilkatsoft.com" & vbCrLf & "Connection: close" & vbCrLf & vbCrLf
success = socket.SendString(httpReq)
If (success = 0) Then
    outFile.WriteLine(socket.LastErrorText)
    WScript.Quit
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.
responseText = socket.ReceiveString()
If (socket.LastMethodSuccess = 0) Then
    outFile.WriteLine(socket.LastErrorText)
    WScript.Quit
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.
set sb = CreateObject("Chilkat.StringBuilder")
success = sb.Append(responseText)
contentLength = sb.GetBetween("Content-Length: ",vbCrLf)
If (sb.LastMethodSuccess = 0) Then
    outFile.WriteLine(sb.LastErrorText)
    WScript.Quit
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.
outFile.WriteLine("Characters received so far (headers + partial body): " & sb.Length)
outFile.WriteLine("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.

outFile.Close