I'm trying to pull out the subject and body of an email with .Net. It seems to go OK except for the text/html MessagePart. I'm not sure of the encoding etc - has anybody got this working OK? It errors for me when trying to convert.
Here is the raw string for the text/html Body Data
"PGRpdiBkaXI9Imx0ciI-dGV4dCBpbiBoZXJlPGJyPjwvZGl2Pg0K"
which throws an error.
"The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters."
Here is the code:
UsersResource.MessagesResource.GetRequest gr = gs.Users.Messages.Get(userEmail, TextBox1.Text);
gr.Format = UsersResource.MessagesResource.GetRequest.FormatEnum.Full;
Message m = gr.Execute();
foreach (MessagePart p in m.Payload.Parts)
{
if (p.MimeType == "text/html")
{
try
{
byte[] data = Convert.FromBase64String(p.Body.Data);
string decodedString = Encoding.UTF8.GetString(data);
Response.Write(decodedString);
}
catch (Exception ex) { }
}
}
I'm getting the decoding wrong???
Thanks for your help.
The body data appears to be base64url-encoded, not base64-encoded. The difference is the use of - and _, instead of + and /, in the encoding’s alphabet of 64 characters. One solution is to replace all - and _ characters with + and / respectively, before calling FromBase64String.
See https://www.rfc-editor.org/rfc/rfc4648#section-5
Here is the code I ended up using:
foreach (MessagePart p in m.Payload.Parts)
{
if (p.MimeType == "text/html")
{
byte[] data = FromBase64ForUrlString(p.Body.Data);
string decodedString = Encoding.UTF8.GetString(data);
Response.Write(decodedString);
}
}
....
public static byte[] FromBase64ForUrlString(string base64ForUrlInput)
{
int padChars = (base64ForUrlInput.Length % 4) == 0 ? 0 : (4 - (base64ForUrlInput.Length % 4));
StringBuilder result = new StringBuilder(base64ForUrlInput, base64ForUrlInput.Length + padChars);
result.Append(String.Empty.PadRight(padChars, '='));
result.Replace('-', '+');
result.Replace('_', '/');
return Convert.FromBase64String(result.ToString());
}
Good article http://www.codeproject.com/Tips/76650/Base-base-url-base-url-and-z-base-encoding
On this page https://developers.google.com/gmail/api/v1/reference/users/messages/attachments/get
you can find that there is a .NET example with this code for decoding:
// Converting from RFC 4648 base64-encoding
// see http://en.wikipedia.org/wiki/Base64#Implementations_and_history
String attachData = attachPart.Data.Replace('-', '+');
attachData = attachData.Replace('_', '/');
byte[] data = Convert.FromBase64String(attachData);
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