(C++) Download GMail Message Attachment by ID

Demonstrates how to download a GMail email attachment by the attachment ID.

For more information, see https://developers.google.com/gmail/api/v1/reference/users/messages/attachments/get

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#include <CkHttp.h>
#include <CkStringBuilder.h>
#include <CkJsonObject.h>
#include <CkBinData.h>

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

    CkHttp http;
    bool success;

    http.put_AuthToken("ACCESS_TOKEN");
    http.put_Accept("application/json");

    // See the following example:  Get GMail Message (format=full)
    // It shows how to download an email by message ID, and it shows how to parse the JSON
    // response which includes attachment names, ids, and other information.

    // This example will assume we already have the attachment id and filename.

    // This is the attachment ID for a file named "helloWorld.pdf".
    const char *attachmentId = "ANGjdJ-oy3aCuZISJKLAhUdaEksCEklbAPyMaWzFgqOMGbPCRkgwgeu_Kttd99C17OBTHROkDZGekibTKWXGfscB5ww7fw4E65_V1dQ-jHhb2TD1Cdm58-BbNw2iDxzptco8iILPiSnLLfFn5Ps7nsRcxHaGTt3r0yqFKCuIYNnPK1vM04BXI_cfzo-HnI4I3tD6oHNHOGVQrL01MdShFQjPELPUjXM8z1qs7Kom-QyvV1iOldUN-66UuhynsmDX-CMM5TIdB-8KD_lmdhf-0DqG8JnCA20XpXyfqwS8XFkPA-t-QSjb7SdkHQFtQ4lz2PcBREFzZ2eI5j0l0Y_dQHRPYTeMwkVl1yl4MfFT4C4iso3VSF-eqaIjiFCbXKCFNyeEIW5WFsv189dhlSqU";

    const char *messageId = "1712bc1dc22da2a2";

    http.SetUrlVar("messageId",messageId);
    http.SetUrlVar("attachmentId",attachmentId);

    const char *url = "https://www.googleapis.com/gmail/v1/users/userId/messages/{$messageId}/attachments/{$attachmentId}";

    // When we download, the response is JSON that contains the attachment data base64url encoded, like this:
    // {
    //  "size": 934,
    //  "data": "JVBERi0xLjM ... CiUlRU9GCg=="
    // }

    const char *outputFilePath = "qa_output/helloWorld.pdf";

    // Download into a StringBuilder.
    CkStringBuilder sbJson;
    success = http.DownloadSb(url,"utf-8",sbJson);
    if (success == false) {
        std::cout << http.lastErrorText() << "\r\n";
        return;
    }

    if (http.get_LastStatus() != 200) {
        // Something failed.
        // the JSON contains an error message.
        std::cout << sbJson.getAsString() << "\r\n";
        return;
    }

    // Load into a Chilkat JSON object.
    CkJsonObject json;
    success = json.LoadSb(sbJson);

    // Extract the base64url data into a BinData.
    CkBinData bd;
    success = json.BytesOf("data","base64url",bd);

    // Save the data to a file.
    success = bd.WriteFile("qa_output/helloWorld.pdf");

    std::cout << "Success." << "\r\n";
    }