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(C#) HTTP Download in Parallel with Simultaneous Range RequestsDemonstrates how to download a large file with parallel simultaneous requests, where each request downloads a segment (range) of the remote file.
// 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)); |
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