(Objective-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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#import <CkoHttp.h>
#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoJsonObject.h>
#import <CkoBinData.h>

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

CkoHttp *http = [[CkoHttp alloc] init];
BOOL success;

http.AuthToken = @"ACCESS_TOKEN";
http.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".
NSString *attachmentId = @"ANGjdJ-oy3aCuZISJKLAhUdaEksCEklbAPyMaWzFgqOMGbPCRkgwgeu_Kttd99C17OBTHROkDZGekibTKWXGfscB5ww7fw4E65_V1dQ-jHhb2TD1Cdm58-BbNw2iDxzptco8iILPiSnLLfFn5Ps7nsRcxHaGTt3r0yqFKCuIYNnPK1vM04BXI_cfzo-HnI4I3tD6oHNHOGVQrL01MdShFQjPELPUjXM8z1qs7Kom-QyvV1iOldUN-66UuhynsmDX-CMM5TIdB-8KD_lmdhf-0DqG8JnCA20XpXyfqwS8XFkPA-t-QSjb7SdkHQFtQ4lz2PcBREFzZ2eI5j0l0Y_dQHRPYTeMwkVl1yl4MfFT4C4iso3VSF-eqaIjiFCbXKCFNyeEIW5WFsv189dhlSqU";

NSString *messageId = @"1712bc1dc22da2a2";

[http SetUrlVar: @"messageId" value: messageId];
[http SetUrlVar: @"attachmentId" value: attachmentId];

NSString *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=="
// }

NSString *outputFilePath = @"qa_output/helloWorld.pdf";

// Download into a StringBuilder.
CkoStringBuilder *sbJson = [[CkoStringBuilder alloc] init];
success = [http DownloadSb: url charset: @"utf-8" sb: sbJson];
if (success == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

if ([http.LastStatus intValue] != 200) {
    // Something failed.
    // the JSON contains an error message.
    NSLog(@"%@",[sbJson GetAsString]);
    return;
}

// Load into a Chilkat JSON object.
CkoJsonObject *json = [[CkoJsonObject alloc] init];
success = [json LoadSb: sbJson];

// Extract the base64url data into a BinData.
CkoBinData *bd = [[CkoBinData alloc] init];
success = [json BytesOf: @"data" encoding: @"base64url" bd: bd];

// Save the data to a file.
success = [bd WriteFile: @"qa_output/helloWorld.pdf"];

NSLog(@"%@",@"Success.");