Converting a Gmail API Message into an OpenPop Mime message

Question

Is it possible to convert a Gmail API Message into an OpenPop Mime Message?

Currently, I have:

List<Message> messagesList = new List<Message>();
List<string> rawMessagesList = new List<string>();
foreach(Message m in messages)
{
    Message m2 = service.Users.Messages.Get("me", m.Id).Execute();
    string m3 = service.Users.Messages.Get("me", m.Id).Execute().Raw;
    messagesList.Add(m2);
    rawMessagesList.Add(m3);
} 

string rMessage = rawMessagesList[0];
byte[] byteMessage = Encoding.ASCII.GetBytes(rMessage);

OpenPop.Mime.Message openPopMessage = new OpenPop.Mime.Message(byteMessage);
string newStringMessage = FindPlainTextInMessage(openPopMessage);
Console.Read();

Unfortunately, all it returns is nothing, because the raw request returns as null. Is there a scope requirement, or some other reason why gmail is not returning the raw message?

Answer 1

To obtain the Raw string, you need to specify the Raw format in your GetRequest.

var emailRequest = svc.Users.Messages.Get("userId", "id");
emailRequest.Format = UsersResource.MessagesResource.GetRequest.FormatEnum.Raw;

var rawString = emailRequest.Execute().Raw;

At this point, rawString is a base64url encoded string. You have to convert it to a normal string before encoding to bytes (see https://datatracker.ietf.org/doc/html/draft-ietf-jose-json-web-signature-08#appendix-C):

private static byte[] Base64UrlDecode(string arg)
{
    // Convert from base64url string to base64 string
    string s = arg;
    s = s.Replace('-', '+').Replace('_', '/');
    switch(s.Length % 4)
    {
        case 0:
            break;              // No pad chars in this case
        case 2:
            s += "==";
            break;              // Two pad chars
        case 3:
            s += "=";
            break;              // One pad char
        default:
            throw new Exception("Illegal base64url string!");
    }

    return Convert.FromBase64String(s);
}

You can then use the result of Base64UrlDecode to create the OpenPop MIME message.