Sending Attachments Using iOS Gmail API

Understanding the iOS Gmail API and Sending Attachments with Email

In this article, we will delve into the world of iOS development and explore how to send emails using the Gmail API. Specifically, we will focus on sending attachments with email.

Introduction

The Gmail API is a powerful tool for developers who want to integrate email functionality into their apps. With its robust features and user-friendly interface, it’s no wonder why many developers choose to use the Gmail API in their iOS applications.

However, one of the most common challenges developers face when working with the Gmail API is sending attachments. In this article, we will explore the different approaches to sending attachments using the Gmail API on iOS.

Background

Before we dive into the code, it’s essential to understand the basics of how the Gmail API works. The Gmail API allows users to send and receive emails programmatically. To do this, developers need to authenticate with the Gmail API using OAuth 2.0 and then use the API’s GTLQueryGmail class to send and receive emails.

The Problem

In our case, we’re trying to send an email with attachments. However, when we try to upload the attachment data using GTLUploadParameters, we get a 501 error. This is because the Gmail API requires us to use a specific format for sending attachments.

The Solution

To solve this problem, we need to modify our code to follow the Gmail API’s guidelines for sending attachments. Specifically, we need to create a string that represents the email message in the correct format.

Creating the Email Message String

The email message string should look something like this:

Content-Type: multipart/mixed; boundary="project"
Date: Fri, 08 Jul 2016 14:25:32 +0800
From: <[email@domain.com](mailto:[email@domain.com])>
To: <[email@domain.com](mailto:[email@domain.com])>
Subject: Sample Subject

--project
Content-Type: text/plain; charset="UTF-8"
Sample body

--project
Content-Type: image/png; name="SampleImage1.jpg"
Content-Transfer-Encoding: base64

<Image data>

--project
Content-Type: image/png; name="SampleImage2.jpg"
Content-Transfer-Encoding: base64

<Image data>

--project--

As you can see, the email message string consists of several parts:

Content-Type: multipart/mixed; boundary="project": This specifies that the email is a multipart message with multiple parts.
Date: Fri, 08 Jul 2016 14:25:32 +0800: This sets the date and time of the email.
From: <[email@domain.com](mailto:[email@domain.com])>: This specifies the sender’s email address.
To: <[email@domain.com](mailto:[email@domain.com])>: This specifies the recipient’s email address.
Subject: Sample Subject: This sets the subject of the email.
The two --project lines separate the different parts of the email message.

Modifying Our Code

To send an email with attachments using the Gmail API, we need to modify our code to create this string and then use it to send the email.

- (void)sendEmailWithAttachments {
    // Create a new email message string
    NSString *rawMessage = @"";

    if (arrFilenames.count > 0) {

        rawMessage = [[[[[[[rawMessage stringByAppendingString:@"Content-Type: multipart/mixed; boundary=\"project\"\r\n"]stringByAppendingString:@"Date: Fri, 08 Jul 2016 14:25:32 +0800\r\n"]stringByAppendingString:@"From: <[email@domain.com](mailto:[email@domain.com])>\r\n"]stringByAppendingString:@"To: <[email@domain.com](mailto:[email@domain.com])>\r\n"]stringByAppendingString:@"Subject: Sample Subject\r\n"]stringByAppendingString:@"\n--project\r\n"];

        rawMessage = [[rawMessage stringByAppendingString:@"Content-Type: text/plain; charset=\"UTF-8\"\r\n"]stringByAppendingString:@"Sample body\r\n"];
        
        for (NSString *filename in arrFilenames) {
            NSData *pngData = UIImagePNGRepresentation([Utilities getImageFromFolder:FOLDER_UPLOADS filename:filename]);
            NSString *pngString = [NSString stringWithFormat:@"%@\r\n",GTLEncodeBase64(pngData)];
            rawMessage = [rawMessage stringByAppendingString:[NSString stringWithFormat:@"Content-Type: image/png; name=\"%@\"\r\n" ,filename]];
            rawMessage = [rawMessage stringByAppendingString:@"Content-Transfer-Encoding: base64\r\n"];
            rawMessage = [rawMessage stringByAppendingString:pngString];
        }

        rawMessage = [rawMessage stringByAppendingString:@"\r\n--project--"];

    }else{

        rawMessage = [[[[[rawMessage stringByAppendingString:@"Content-Type: text/plain; charset=\"UTF-8\"\r\n"]stringByAppendingString:@"Sample body\r\n"]stringByAppendingString:@"\n"]stringByAppendingString:@"\r\n--project--"];
    }

    // Set the email message string as the payload for the request
    request=[NSMutableData data];
    [request appendData:[NSData dataWithData:[rawMessage dataUsingEncoding:NSUTF8StringEncoding]]];

    // Create a new request to send the email
    NSURL *url = [[NSURL URLWithString:@"https://www.googleapis.com/gmail/v1/users/me/messages"] absoluteURL];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    request.HTTPMethod = @"POST";
    request.HTTPBody = request;
    
    // Add the authentication headers to the request
    NSString *authToken = [[NSUserDefaults standardUserDefaults] stringForKey:@"authToken"];
    [request setValue:authToken forHTTPHeaderField:@"Authorization"];

    // Send the request and get the response
    NSURLResponse *response = [NSURLRequest requestWithURL:url].response;
    NSData *responseData = [NSData dataWithContentsOfResponseData:response.data];
}

Conclusion

In this example, we modified our code to follow the Gmail API’s guidelines for sending attachments. We created a string that represents the email message in the correct format and then used it to send the email.

By following these steps, you should be able to send an email with attachments using the Gmail API.

Last modified on 2023-06-30