(MFC) Download Binary File to In-Memory Bytes

This example demonstrates how to download the binary content of a file from Google Drive directly into local memory.

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

See Also: Using MFC CString in Chilkat

#include <CkAuthGoogle.h>
#include <CkRest.h>
#include <CkCache.h>
#include <CkStringBuilder.h>
#include <CkByteData.h>
#include <CkFileAccess.h>

void ChilkatSample(void)
    {
    CkString strOut;

    bool success = true;

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

    // This example uses a previously obtained access token having permission for the 
    // Google Drive scope.

    CkAuthGoogle gAuth;
    gAuth.put_AccessToken("GOOGLE-DRIVE-ACCESS-TOKEN");

    CkRest rest;

    // Connect using TLS.
    // A single REST object, once connected, can be used for many Google Drive REST API calls.
    // The auto-reconnect indicates that if the already-established HTTPS connection is closed,
    // then it will be automatically re-established as needed.
    bool bAutoReconnect = true;
    success = rest.Connect("www.googleapis.com",443,true,bAutoReconnect);

    // Provide the authentication credentials (i.e. the access token)
    rest.SetAuthGoogle(gAuth);

    // ------------------------------------------------------------------------------
    // To download a file, we must know the file ID.
    // In a previous example (see Build Local Metadata Cache
    // we built a local cache to make it easy to lookup file IDs given a file path.
    // Let's say we want to download "testFolder/abc/123/penguins.jpg".
    // First we lookup the fileId in the cache.  With the fileId, we can download the file.
    CkCache gdCache;
    gdCache.put_Level(0);
    gdCache.AddRoot("C:/ckCache/googleDrive");

    const char *fileId = gdCache.fetchText("testFolder/abc/123/penguins.jpg");
    if (gdCache.get_LastMethodSuccess() != true) {
        strOut.append("Filepath not found in cache.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // We need to send a GET request like this:
    // GET https://www.googleapis.com/drive/v3/files/fileId?alt=media
    // The fileId is part of the path.
    CkStringBuilder sbPath;
    sbPath.Append("/drive/v3/files/");
    sbPath.Append(fileId);
    rest.AddQueryParam("alt","media");

    // To download to memory, we'll send the request in one call, then receive
    // the response header, and then the response body.
    // If the response header indicates failure or an unexpected response, then the
    // body is not the data we desire.

    // First send the HTTP request.
    success = rest.SendReqNoBody("GET",sbPath.getAsString());
    if (success != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Get the response header.
    int statusCode = rest.ReadResponseHeader();
    if (statusCode != 200) {
        strOut.append("response status code = ");
        strOut.appendInt(rest.get_ResponseStatusCode());
        strOut.append("\r\n");
        strOut.append("response status text = ");
        strOut.append(rest.responseStatusText());
        strOut.append("\r\n");
        strOut.append("response header: ");
        strOut.append(rest.responseHeader());
        strOut.append("\r\n");

        // Read the response body (which should be error text or HTML)
        const char *errResponseBody = rest.readRespBodyString();
        if (rest.get_LastMethodSuccess() == true) {
            strOut.append("response body: ");
            strOut.append(errResponseBody);
            strOut.append("\r\n");
        }

        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Read the response body, which should contain the file data.
    CkByteData jpgBytes;
    success = rest.ReadRespBodyBinary(jpgBytes);
    if (rest.get_LastMethodSuccess() != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Save jpgBytes to a file so we can examine the file to verify that it worked.
    CkFileAccess fac;
    fac.WriteEntireFile("qa_output/penguins_out.jpg",jpgBytes);

    strOut.append("File downloaded.");
    strOut.append("\r\n");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }