PureBasic

HTTP GET -- Read Response from Stream

Demonstrates how to send an HTTP GET for a web page, and then read the response from a Stream. The purpose is to fulfill a situation such as the following: "I have a URL and just want the <head> </head> portion of the HTML. This would avoid having to download a potentially enormous web page just to get at header information, such as the <styles>."

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IncludeFile "CkTask.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkRest.pb"
IncludeFile "CkStream.pb"
IncludeFile "CkUrl.pb"

Procedure ChilkatExample()

    success.i = 0

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    rest.i = CkRest::ckCreate()
    If rest.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; In this example, we'll get the web page at http://www.nytimes.com/pages/business/index.html
    ; The domain is "www.nytimes.com", and the path is "/pages/business/index.html"

    ; If we have only the full URL to begin with, it can be loaded into the Chilkat URL object to
    ; access the parts:
    url.i = CkUrl::ckCreate()
    If url.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkUrl::ckParseUrl(url,"http://www.nytimes.com/pages/business/index.html")

    bAutoReconnect.i = 1
    success = CkRest::ckConnect(rest,CkUrl::ckHost(url),CkUrl::ckPort(url),CkUrl::ckSsl(url),bAutoReconnect)

    ; Send the GET request (This sends the GET request, but does not read the response.)
    success = CkRest::ckSendReqNoBody(rest,"GET",CkUrl::ckPath(url))
    If success <> 1
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkUrl::ckDispose(url)
        ProcedureReturn
    EndIf

    ; Read the response header.
    responseStatusCode.i = CkRest::ckReadResponseHeader(rest)
    If responseStatusCode < 0
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkUrl::ckDispose(url)
        ProcedureReturn
    EndIf

    Debug "Response status code = " + Str(responseStatusCode)

    ; We expect a 200 response status.
    If responseStatusCode <> 200

        ; If the response status code is not 200, we could check for a redirect status code and 
        ; then follow it, read the entire response (as shown here), or just call rest.Disconnect
        errResponse.s = CkRest::ckReadRespBodyString(rest)
        If CkRest::ckLastMethodSuccess(rest) <> 1
            Debug CkRest::ckLastErrorText(rest)
        Else
            Debug errResponse
        EndIf

        CkRest::ckDispose(rest)
        CkUrl::ckDispose(url)
        ProcedureReturn
    EndIf

    bodyStream.i = CkStream::ckCreate()
    If bodyStream.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Set a 10 second read timeout for the stream. 
    ; (Give up if no data arrives within 10 seconds after calling a read method.)
    CkStream::setCkReadTimeoutMs(bodyStream, 10000)

    ; Create a background thread task to read the response body (which feeds
    ; it to the bodyStream object.)
    readResponseBodyTask.i = CkRest::ckReadRespBodyStreamAsync(rest,bodyStream,1)

    ; Start the task. 
    success = CkTask::ckRun(readResponseBodyTask)

    ; Read the HTTP response body until the "</head>" is seen, or until
    ; the end-of-stream is reached.

    sbBody.i = CkStringBuilder::ckCreate()
    If sbBody.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    exitLoop.i = 0
    While Not exitLoop AND (CkStream::ckEndOfStream(bodyStream) <> 1)

        bodyText.s = CkStream::ckReadString(bodyStream)
        If CkStream::ckLastMethodSuccess(bodyStream) = 1
            CkStringBuilder::ckAppend(sbBody,bodyText)
            If CkStringBuilder::ckContains(sbBody,"</head>",0)
                exitLoop = 1
            EndIf

        Else
            exitLoop = 1
        EndIf

    Wend

    ; Cancel the remainder of the task...
    CkTask::ckCancel(readResponseBodyTask)

    CkTask::ckDispose(readResponseBodyTask)

    ; Ensure we're disconnected from the server.
    maxWaitMs.i = 50
    CkRest::ckDisconnect(rest,maxWaitMs)

    Debug "----"
    Debug CkStringBuilder::ckGetAsString(sbBody)
    Debug "----"
    Debug "Successfully received the body up to the desired point."


    CkRest::ckDispose(rest)
    CkUrl::ckDispose(url)
    CkStream::ckDispose(bodyStream)
    CkStringBuilder::ckDispose(sbBody)


    ProcedureReturn
EndProcedure