(DataFlex) HTTP Download in Parallel with Simultaneous Range Requests

Demonstrates how to download a large file with parallel simultaneous requests, where each request downloads a segment (range) of the remote file.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-win32.pkg

Procedure Test
    Handle hoHttp
    Boolean iSuccess
    String sUrl
    Variant vResp
    Handle hoResp
    Integer iRemoteFileSize
    Integer iChunkSize
1    Handle hoHttp1
2    Handle hoHttp2
3    Handle hoHttp3
4    Handle hoHttp4
    Handle hoSbRange
    Integer iNumReplaced
    Variant vTask1
    Handle hoTask1
    Variant vTask2
    Handle hoTask2
    Variant vTask3
    Handle hoTask3
    Variant vTask4
    Handle hoTask4
    Integer iNumLive
    Integer iNumErrors
    Handle hoFac
    Boolean iBSame
    String sTemp1
    Boolean bTemp1

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

    Get Create (RefClass(cComChilkatHttp)) To hoHttp
    If (Not(IsComObjectCreated(hoHttp))) Begin
        Send CreateComObject of hoHttp
    End

    // First get the size of the file to be downloaded.
    Move "https://www.chilkatsoft.com/hamlet.xml" To sUrl

    Get ComGetHead Of hoHttp sUrl To vResp
    If (IsComObject(vResp)) Begin
        Get Create (RefClass(cComChilkatHttpResponse)) To hoResp
        Set pvComObject Of hoResp To vResp
    End
    Get ComLastMethodSuccess Of hoHttp To bTemp1
    If (bTemp1 = False) Begin
        Get ComLastErrorText Of hoHttp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComContentLength Of hoResp To iRemoteFileSize
    Send Destroy of hoResp

    Showln "Downloading " iRemoteFileSize " bytes..."

    // Let's download in 4 chunks.
    // (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
    Move (iRemoteFileSize / 4) To iChunkSize

    // The Range header is used to download a range from a resource
    // Range: bytes=<range-start>-<range-end>
    // or
    // Range: bytes=<range-start>-

    // We're writing code this way for clarity..
    Get Create (RefClass(cComChilkatHttp)) To hoHttp1
    If (Not(IsComObjectCreated(hoHttp1))) Begin
        Send CreateComObject of hoHttp1
    End
    Get Create (RefClass(cComChilkatHttp)) To hoHttp2
    If (Not(IsComObjectCreated(hoHttp2))) Begin
        Send CreateComObject of hoHttp2
    End
    Get Create (RefClass(cComChilkatHttp)) To hoHttp3
    If (Not(IsComObjectCreated(hoHttp3))) Begin
        Send CreateComObject of hoHttp3
    End
    Get Create (RefClass(cComChilkatHttp)) To hoHttp4
    If (Not(IsComObjectCreated(hoHttp4))) Begin
        Send CreateComObject of hoHttp4
    End

    Get Create (RefClass(cComChilkatStringBuilder)) To hoSbRange
    If (Not(IsComObjectCreated(hoSbRange))) Begin
        Send CreateComObject of hoSbRange
    End
    Get ComSetString Of hoSbRange "bytes=<range-start>-<range-end>" To iSuccess
    Get ComReplaceI Of hoSbRange "<range-start>" 0 To iNumReplaced
    Get ComReplaceI Of hoSbRange "<range-end>" (iChunkSize - 1) To iNumReplaced
    Get ComGetAsString Of hoSbRange To sTemp1
    Showln sTemp1
    Get ComGetAsString Of hoSbRange To sTemp1
    Send ComSetRequestHeader To hoHttp1 "Range" sTemp1

    Get ComSetString Of hoSbRange "bytes=<range-start>-<range-end>" To iSuccess
    Get ComReplaceI Of hoSbRange "<range-start>" iChunkSize To iNumReplaced
    Get ComReplaceI Of hoSbRange "<range-end>" (2 * iChunkSize - 1) To iNumReplaced
    Get ComGetAsString Of hoSbRange To sTemp1
    Showln sTemp1
    Get ComGetAsString Of hoSbRange To sTemp1
    Send ComSetRequestHeader To hoHttp2 "Range" sTemp1

    Get ComSetString Of hoSbRange "bytes=<range-start>-<range-end>" To iSuccess
    Get ComReplaceI Of hoSbRange "<range-start>" (2 * iChunkSize) To iNumReplaced
    Get ComReplaceI Of hoSbRange "<range-end>" (3 * iChunkSize - 1) To iNumReplaced
    Get ComGetAsString Of hoSbRange To sTemp1
    Showln sTemp1
    Get ComGetAsString Of hoSbRange To sTemp1
    Send ComSetRequestHeader To hoHttp3 "Range" sTemp1

    Get ComSetString Of hoSbRange "bytes=<range-start>-" To iSuccess
    Get ComReplaceI Of hoSbRange "<range-start>" (3 * iChunkSize) To iNumReplaced
    Get ComGetAsString Of hoSbRange To sTemp1
    Showln sTemp1
    Get ComGetAsString Of hoSbRange To sTemp1
    Send ComSetRequestHeader To hoHttp4 "Range" sTemp1

    // Start each range download
    Get ComDownloadAsync Of hoHttp1 sUrl "qa_output/chunk1.dat" To vTask1
    If (IsComObject(vTask1)) Begin
        Get Create (RefClass(cComChilkatTask)) To hoTask1
        Set pvComObject Of hoTask1 To vTask1
    End
    Get ComRun Of hoTask1 To iSuccess

    Get ComDownloadAsync Of hoHttp2 sUrl "qa_output/chunk2.dat" To vTask2
    If (IsComObject(vTask2)) Begin
        Get Create (RefClass(cComChilkatTask)) To hoTask2
        Set pvComObject Of hoTask2 To vTask2
    End
    Get ComRun Of hoTask2 To iSuccess

    Get ComDownloadAsync Of hoHttp3 sUrl "qa_output/chunk3.dat" To vTask3
    If (IsComObject(vTask3)) Begin
        Get Create (RefClass(cComChilkatTask)) To hoTask3
        Set pvComObject Of hoTask3 To vTask3
    End
    Get ComRun Of hoTask3 To iSuccess

    Get ComDownloadAsync Of hoHttp4 sUrl "qa_output/chunk4.dat" To vTask4
    If (IsComObject(vTask4)) Begin
        Get Create (RefClass(cComChilkatTask)) To hoTask4
        Set pvComObject Of hoTask4 To vTask4
    End
    Get ComRun Of hoTask4 To iSuccess

    // Wait for the downloads to complete.
    Move 4 To iNumLive
    While (iNumLive > 0)
        Move 0 To iNumLive
        Get ComLive Of hoTask1 To bTemp1
        If (bTemp1 = True) Begin
            Move (iNumLive + 1) To iNumLive
        End

        Get ComLive Of hoTask2 To bTemp1
        If (bTemp1 = True) Begin
            Move (iNumLive + 1) To iNumLive
        End

        Get ComLive Of hoTask3 To bTemp1
        If (bTemp1 = True) Begin
            Move (iNumLive + 1) To iNumLive
        End

        Get ComLive Of hoTask4 To bTemp1
        If (bTemp1 = True) Begin
            Move (iNumLive + 1) To iNumLive
        End

        If (iNumLive > 0) Begin
            // SleepMs is a convenience method to cause the caller to sleep for N millisec.
            // It does not cause the given task to sleep..
            Send ComSleepMs To hoTask1 10
        End

    Loop

    // All should be downloaded now..
    // Examine the result of each Download.
    Move 0 To iNumErrors
    Get ComGetResultBool Of hoTask1 To bTemp1
    If (bTemp1 = False) Begin
        Get ComResultErrorText Of hoTask1 To sTemp1
        Showln sTemp1
        Move (iNumErrors + 1) To iNumErrors
    End

    Get ComGetResultBool Of hoTask2 To bTemp1
    If (bTemp1 = False) Begin
        Get ComResultErrorText Of hoTask2 To sTemp1
        Showln sTemp1
        Move (iNumErrors + 1) To iNumErrors
    End

    Get ComGetResultBool Of hoTask3 To bTemp1
    If (bTemp1 = False) Begin
        Get ComResultErrorText Of hoTask3 To sTemp1
        Showln sTemp1
        Move (iNumErrors + 1) To iNumErrors
    End

    Get ComGetResultBool Of hoTask4 To bTemp1
    If (bTemp1 = False) Begin
        Get ComResultErrorText Of hoTask4 To sTemp1
        Showln sTemp1
        Move (iNumErrors + 1) To iNumErrors
    End

    If (iNumErrors > 0) Begin
        Send Destroy of hoTask1
        Send Destroy of hoTask2
        Send Destroy of hoTask3
        Send Destroy of hoTask4
        Procedure_Return
    End

    // All downloads were successful.
    // Compose the file from the parts.
    Get Create (RefClass(cComCkFileAccess)) To hoFac
    If (Not(IsComObjectCreated(hoFac))) Begin
        Send CreateComObject of hoFac
    End
    Get ComReassembleFile Of hoFac "qa_output" "chunk" "dat" "qa_output/hamlet.xml" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoFac To sTemp1
        Showln sTemp1
    End
    Else Begin
        Showln "Success."
    End

    Send Destroy of hoTask1
    Send Destroy of hoTask2
    Send Destroy of hoTask3
    Send Destroy of hoTask4

    // Let's download in the regular way, and then compare files..
    Get ComDownload Of hoHttp sUrl "qa_output/hamletRegular.xml" To iSuccess

    // Compare files.
    Get ComFileContentsEqual Of hoFac "qa_output/hamlet.xml" "qa_output/hamletRegular.xml" To iBSame
    Showln "bSame = " iBSame


End_Procedure