Node.js

HTTP Download in Parallel with Simultaneous Range Requests

See more HTTP Examples

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

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

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

    var http = new chilkat.Http();

    // First get the size of the file to be downloaded.
    var url = "https://www.chilkatsoft.com/hamlet.xml";

    var resp = new chilkat.HttpResponse();
    success = http.HttpNoBody("HEAD",url,resp);
    if (success == false) {
        console.log(http.LastErrorText);
        return;
    }

    var remoteFileSize = resp.ContentLength;

    console.log("Downloading " + remoteFileSize + " bytes...");

    // Let's download in 4 chunks.
    // (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
    var chunkSize = remoteFileSize / 4;

    // 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..
    var http1 = new chilkat.Http();
    var http2 = new chilkat.Http();
    var http3 = new chilkat.Http();
    var http4 = new chilkat.Http();

    var sbRange = new chilkat.StringBuilder();
    sbRange.SetString("bytes=<range-start>-<range-end>");
    var numReplaced = sbRange.ReplaceI("<range-start>",0);
    numReplaced = sbRange.ReplaceI("<range-end>",chunkSize - 1);
    console.log(sbRange.GetAsString());
    http1.SetRequestHeader("Range",sbRange.GetAsString());

    sbRange.SetString("bytes=<range-start>-<range-end>");
    numReplaced = sbRange.ReplaceI("<range-start>",chunkSize);
    numReplaced = sbRange.ReplaceI("<range-end>",2 * chunkSize - 1);
    console.log(sbRange.GetAsString());
    http2.SetRequestHeader("Range",sbRange.GetAsString());

    sbRange.SetString("bytes=<range-start>-<range-end>");
    numReplaced = sbRange.ReplaceI("<range-start>",2 * chunkSize);
    numReplaced = sbRange.ReplaceI("<range-end>",3 * chunkSize - 1);
    console.log(sbRange.GetAsString());
    http3.SetRequestHeader("Range",sbRange.GetAsString());

    sbRange.SetString("bytes=<range-start>-");
    numReplaced = sbRange.ReplaceI("<range-start>",3 * chunkSize);
    console.log(sbRange.GetAsString());
    http4.SetRequestHeader("Range",sbRange.GetAsString());

    // Start each range download
    // task1: Task
    var task1 = http1.DownloadAsync(url,"qa_output/chunk1.dat");
    task1.Run();

    // task2: Task
    var task2 = http2.DownloadAsync(url,"qa_output/chunk2.dat");
    task2.Run();

    // task3: Task
    var task3 = http3.DownloadAsync(url,"qa_output/chunk3.dat");
    task3.Run();

    // task4: Task
    var task4 = http4.DownloadAsync(url,"qa_output/chunk4.dat");
    task4.Run();

    // Wait for the downloads to complete.
    var numLive = 4;
    while (numLive > 0) {
        numLive = 0;
        if (task1.Live == true) {
            numLive = numLive+1;
        }

        if (task2.Live == true) {
            numLive = numLive+1;
        }

        if (task3.Live == true) {
            numLive = numLive+1;
        }

        if (task4.Live == true) {
            numLive = numLive+1;
        }

        if (numLive > 0) {
            // SleepMs is a convenience method to cause the caller to sleep for N millisec.
            // It does not cause the given task to sleep..
            task1.SleepMs(10);
        }

    }

    // All should be downloaded now..
    // Examine the result of each Download.
    var numErrors = 0;
    if (task1.GetResultBool() == false) {
        console.log(task1.ResultErrorText);
        numErrors = numErrors+1;
    }

    if (task2.GetResultBool() == false) {
        console.log(task2.ResultErrorText);
        numErrors = numErrors+1;
    }

    if (task3.GetResultBool() == false) {
        console.log(task3.ResultErrorText);
        numErrors = numErrors+1;
    }

    if (task4.GetResultBool() == false) {
        console.log(task4.ResultErrorText);
        numErrors = numErrors+1;
    }

    if (numErrors > 0) {

        return;
    }

    // All downloads were successful.
    // Compose the file from the parts.
    var fac = new chilkat.FileAccess();
    success = fac.ReassembleFile("qa_output","chunk","dat","qa_output/hamlet.xml");
    if (success == false) {
        console.log(fac.LastErrorText);
    }
    else {
        console.log("Success.");
    }

    // Let's download in the regular way, and then compare files..
    success = http.Download(url,"qa_output/hamletRegular.xml");

    // Compare files.
    var bSame = fac.FileContentsEqual("qa_output/hamlet.xml","qa_output/hamletRegular.xml");
    console.log("bSame = " + bSame);

}

chilkatExample();