Re: [pve-devel] [PATCH proxmox 1/2] notify: smtp: forward original message instead nesting

[Lukas Wagner <l.wagner@proxmox.com>]

Thanks for the review!

On 1/9/24 14:26, Wolfgang Bumiller wrote:
> On Wed, Dec 13, 2023 at 05:42:00PM +0100, Lukas Wagner wrote:
>> For mails forwarded by `proxmox-mail-forward` to an SMTP target, the
>> original message was nested as a 'message/rfc822' message part.
>> Originally this approach was chosen to avoid having to rewrite
>> message headers.
>> Good email-clients, such as Thunderbird can display these inline.
>> Other, more limited clients will show these messages as an attached
>> .eml file, which is not really a good user experience.
>>
>> This patch changes the approach for message forwarding to be more like
>> forwarding mails in a mail client. We create a new message and
>> add the original message body as a body. Additionally, we also copy
>> over all message headers that are relevant to correctly display the
>> original message body (e.g. Content-Type, Content-Transfer-Encoding)
>>
>> Tested with a couple of different email messages (varying in
>> structure, body parts, encoding, etc.) against the following SMTP
>> relays:
>>    - gmail
>>    - outlook
>>    - our own webmail service
>>
>> Originally reported in our community forum:
>> https://forum.proxmox.com/threads/proxmox-mail-forward-sends-mails-as-eml.137710/
>>
>> Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
>> ---
>>
>> Notes:
>>      proxmox-mail-forward needs a bump once this is applied.
>>
>>   proxmox-notify/src/endpoints/smtp.rs | 99 ++++++++++++++++++++++++----
>>   1 file changed, 88 insertions(+), 11 deletions(-)
>>
>> diff --git a/proxmox-notify/src/endpoints/smtp.rs b/proxmox-notify/src/endpoints/smtp.rs
>> index 064c9f9..4b8ff2d 100644
>> --- a/proxmox-notify/src/endpoints/smtp.rs
>> +++ b/proxmox-notify/src/endpoints/smtp.rs
>> @@ -1,8 +1,9 @@
>> +use std::time::Duration;
>> +
>>   use lettre::message::{Mailbox, MultiPart, SinglePart};
>>   use lettre::transport::smtp::client::{Tls, TlsParameters};
>>   use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
>>   use serde::{Deserialize, Serialize};
>> -use std::time::Duration;
>>   
>>   use proxmox_schema::api_types::COMMENT_SCHEMA;
>>   use proxmox_schema::{api, Updater};
>> @@ -231,17 +232,93 @@ impl Endpoint for SmtpEndpoint {
>>               }
>>               #[cfg(feature = "mail-forwarder")]
>>               Content::ForwardedMail { ref raw, title, .. } => {
>> -                email_builder = email_builder.subject(title);
>> +                use lettre::message::header::{ContentTransferEncoding, HeaderName, HeaderValue};
>> +                use lettre::message::Body;
>>   
>> -                // Forwarded messages are embedded inline as 'message/rfc822'
>> -                // this let's us avoid rewriting any headers (e.g. From)
>> -                email_builder
>> -                    .singlepart(
>> -                        SinglePart::builder()
>> -                            .header(ContentType::parse("message/rfc822").unwrap())
>> -                            .body(raw.to_owned()),
>> -                    )
>> -                    .map_err(|err| Error::NotifyFailed(self.name().into(), Box::new(err)))?
>> +                let parsed_message = mail_parser::Message::parse(raw)
>> +                    .ok_or_else(|| Error::Generic("could not parse forwarded email".to_string()))?;
>> +
>> +                let root_part = parsed_message
>> +                    .part(0)
>> +                    .ok_or_else(|| Error::Generic("root message part not present".to_string()))?;
>> +
>> +                let raw_body = parsed_message
>> +                    .raw_message()
>> +                    .get(root_part.offset_body..root_part.offset_end)
>> +                    .ok_or_else(|| Error::Generic("could not get raw body content".to_string()))?;
>> +
>> +                // We assume that the original message content is already properly
>> +                // encoded, thus we add the original message body 'Binary' encoding.
>> +                // This prohibits lettre from trying to re-encode our raw body data.
>> +                // lettre will automatically set the `Content-Transfer-Encoding: binary` header,
>> +                // which we need to remove. The actual transfer encoding is later
>> +                // copied from the original message headers.
>> +                let body =
>> +                    Body::new_with_encoding(raw_body.to_vec(), ContentTransferEncoding::Binary)
>> +                        .map_err(|_| Error::Generic("could not create body".into()))?;
>> +                let mut message = email_builder
>> +                    .subject(title)
>> +                    .body(body)
>> +                    .map_err(|err| Error::NotifyFailed(self.name().into(), Box::new(err)))?;
>> +                message
>> +                    .headers_mut()
>> +                    .remove_raw("Content-Transfer-Encoding");
>> +
>> +                // Copy over all headers that are relevant to display the original body correctly.
>> +                // Unfortunately this is a bit cumbersome, as we use separate crates for mail parsing (mail-parser)
>> +                // and creating/sending mails (lettre).
>> +                // Note: Other MIME-Headers, such as Content-{ID,Description,Disposition} are only used
>> +                // for body-parts in multipart messages, so we can ignore them for the messages headers.
>> +                // Since we send the original raw body, the part-headers will be included any way.
>> +                for header in parsed_message.headers() {
>> +                    let header_name = header.name.as_str();
>> +                    // Email headers are case-insensitive, so convert to lowercase...
>> +                    let value = match header_name.to_lowercase().as_str() {
>> +                        "content-type" => {
>> +                            if let mail_parser::HeaderValue::ContentType(ct) = header.value() {
>> +                                // mail_parser does not give us access to the full decoded and unfolded
>> +                                // header value, so we unfortunately need to reassemble it ourselves.
>> +                                // Meh.
> 
> urgh
> 

urgh indeed...
>> +                                let mut value = ct.ctype().to_string();
>> +                                if let Some(subtype) = ct.subtype() {
>> +                                    value.push('/');
>> +                                    value.push_str(subtype);
>> +                                }
>> +                                if let Some(attributes) = ct.attributes() {
>> +                                    for attribute in attributes {
>> +                                        value.push_str(&format!(
>> +                                            "; {}=\"{}\"",
>> +                                            attribute.0, attribute.1
>> +                                        ));
> 
> should be more efficient to use
> let _ = write!(value, "...");
> instead of `push_str()` on a temporarily allocated (format!()) string.

Right, thanks! Will send a v2.
> 
>> +                                    }
>> +                                }
>> +                                Some(value)
>> +                            } else {
>> +                                None
>> +                            }
>> +                        }
>> +                        "content-transfer-encoding" | "mime-version" => {
>> +                            if let mail_parser::HeaderValue::Text(text) = header.value() {
>> +                                Some(text.to_string())
>> +                            } else {
>> +                                None
>> +                            }
>> +                        }
>> +                        _ => None,
>> +                    };
>> +
>> +                    if let Some(value) = value {
>> +                        match HeaderName::new_from_ascii(header_name.into()) {
>> +                            Ok(name) => {
>> +                                let header = HeaderValue::new(name, value);
>> +                                message.headers_mut().insert_raw(header);
>> +                            }
>> +                            Err(e) => log::error!("could not set header: {e}"),
>> +                        }
>> +                    }
>> +                }
>> +
>> +                message
>>               }
>>           };
>>   
>> -- 
>> 2.39.2

-- 
- Lukas