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.

LOCAL nSuccess
LOCAL oSocket
LOCAL nBTls
LOCAL nMaxWaitMs
LOCAL cHttpReq
LOCAL cResponseText
LOCAL oSb
LOCAL cContentLength

nSuccess := 0

oSocket := CreateObject("Chilkat.Socket")

//  Connect to chilkatsoft.com over TLS.
nBTls := 1
nMaxWaitMs := 5000
nSuccess := oSocket:Connect("chilkatsoft.com", 443, nBTls, nMaxWaitMs)
IF (nSuccess == 0)
    ? oSocket:LastErrorText
    oSocket:destroy()
    RETURN
ENDIF

oSocket: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.
cHttpReq := "GET /big_helloWorld.txt HTTP/1.1" + Chr(13) + Chr(10) + "Host: chilkatsoft.com" + Chr(13) + Chr(10) + "Connection: close" + Chr(13) + Chr(10) + Chr(13) + Chr(10)
nSuccess := oSocket:SendString(cHttpReq)
IF (nSuccess == 0)
    ? oSocket:LastErrorText
    oSocket:destroy()
    RETURN
ENDIF

//  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.
cResponseText := oSocket:ReceiveString()
IF (oSocket:LastMethodSuccess == 0)
    ? oSocket:LastErrorText
    oSocket:destroy()
    RETURN
ENDIF

//  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.
oSb := CreateObject("Chilkat.StringBuilder")
oSb:Append(cResponseText)
cContentLength := oSb:GetBetween("Content-Length: ", Chr(13) + Chr(10))
IF (oSb:LastMethodSuccess == 0)
    ? oSb:LastErrorText
    oSocket:destroy()
    oSb:destroy()
    RETURN
ENDIF

//  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.
? "Characters received so far (headers + partial body): " + Str(oSb:Length)
? "Expected response body size (Content-Length): " + cContentLength + " 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.

oSocket:destroy()
oSb:destroy()