(.NET Core C#) 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.

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

Chilkat.Http http = new Chilkat.Http();
bool success;

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

Chilkat.HttpResponse resp = http.GetHead(url);
if (http.LastMethodSuccess == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

int remoteFileSize = (int) resp.ContentLength;

Debug.WriteLine("Downloading " + Convert.ToString(remoteFileSize) + " bytes...");

// Let's download in 4 chunks.
// (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
int 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..
Chilkat.Http http1 = new Chilkat.Http();
Chilkat.Http http2 = new Chilkat.Http();
Chilkat.Http http3 = new Chilkat.Http();
Chilkat.Http http4 = new Chilkat.Http();

Chilkat.StringBuilder sbRange = new Chilkat.StringBuilder();
sbRange.SetString("bytes=<range-start>-<range-end>");
int numReplaced = sbRange.ReplaceI("<range-start>",0);
numReplaced = sbRange.ReplaceI("<range-end>",chunkSize - 1);
Debug.WriteLine(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);
Debug.WriteLine(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);
Debug.WriteLine(sbRange.GetAsString());
http3.SetRequestHeader("Range",sbRange.GetAsString());

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

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

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

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

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

// Wait for the downloads to complete.
int 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.
int numErrors = 0;
if (task1.GetResultBool() == false) {
    Debug.WriteLine(task1.ResultErrorText);
    numErrors = numErrors + 1;
}

if (task2.GetResultBool() == false) {
    Debug.WriteLine(task2.ResultErrorText);
    numErrors = numErrors + 1;
}

if (task3.GetResultBool() == false) {
    Debug.WriteLine(task3.ResultErrorText);
    numErrors = numErrors + 1;
}

if (task4.GetResultBool() == false) {
    Debug.WriteLine(task4.ResultErrorText);
    numErrors = numErrors + 1;
}

if (numErrors > 0) {

    return;
}

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

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

// Compare files.
bool bSame = fac.FileContentsEqual("qa_output/hamlet.xml","qa_output/hamletRegular.xml");
Debug.WriteLine("bSame = " + Convert.ToString(bSame));