(MFC) Streaming Download Large File to the Local Filesystem

Downloads a large file in a streaming fashion to the local filesystem.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkRest.h>
#include <CkAuthAzureStorage.h>
#include <CkStream.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // Azure File Service Example: Downloads a large file to the local filesystem using a Chilkat stream.
    // See:  https://docs.microsoft.com/en-us/rest/api/storageservices/get-file

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

    CkRest rest;

    // Connect to the Azure Storage Blob Service
    bool bTls = true;
    int port = 443;
    bool bAutoReconnect = true;
    // In this example, the storage account name is "chilkat".
    bool success = rest.Connect("chilkat.file.core.windows.net",port,bTls,bAutoReconnect);
    if (success != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Provide Azure Cloud credentials for the REST calls.
    CkAuthAzureStorage azAuth;
    azAuth.put_AccessKey("AZURE_ACCESS_KEY");
    // The account name used here should match the 1st part of the domain passed in the call to Connect (above).
    azAuth.put_Account("chilkat");
    azAuth.put_Scheme("SharedKey");
    azAuth.put_Service("File");
    // This causes the "x-ms-version: 2020-08-04" header to be automatically added.
    azAuth.put_XMsVersion("2020-08-04");
    success = rest.SetAuthAzureStorage(azAuth);

    // Note: The application does not need to explicitly set the following
    // headers: x-ms-date, Authorization.  These headers
    // are automatically set by Chilkat.

    // When streaming a download to the local filesystem or directed elsewhere,
    // the complete HTTP GET operation must be broken into parts.
    // For example, an HTTP GET consists of sending the request, followed by reading the response header,
    // and then finally the response body.  We'll want to read the response header, and then based
    // on the information received (such as success or failure), either read the response body
    // as an error message, or as the file data.

    // Send the HTTP GET request to download the file.
    // The share is named "pip".
    success = rest.SendReqNoBody("GET","/pip/somethingBig.zip");
    if (success != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Read the response header.
    int responseStatusCode = rest.ReadResponseHeader();
    if (responseStatusCode < 0) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    strOut.append("Response status code = ");
    strOut.appendInt(responseStatusCode);
    strOut.append("\r\n");

    // We expect a 200 response status if the file data is coming.
    // Otherwise, we'll get a string response body with an error message(or no response body).
    if (responseStatusCode == 200) {

        CkStream bodyStream;

        // The stream's sink will be a file.
        bodyStream.put_SinkFile("qa_output/somethingBig.zip");

        // Read the response body to the stream.  Given that we've
        // set the stream's sink to a file, it will stream directly
        // to the file.
        success = rest.ReadRespBodyStream(bodyStream,true);
        if (success != true) {
            strOut.append(rest.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        strOut.append("Successfully received the large file.");
        strOut.append("\r\n");

    }
    else {
        const char *errResponse = rest.readRespBodyString();
        if (rest.get_LastMethodSuccess() != true) {
            strOut.append(rest.lastErrorText());
            strOut.append("\r\n");
        }
        else {
            strOut.append(errResponse);
            strOut.append("\r\n");
        }

    }



    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }