Check for encryption

- collect body of incoming mail.
- check if incoming mail is already encrypted - dont touch it if it is.
- check if recipients of that mail can encrypt.

src/crypto.rs

@@ -7,9 +7,10 @@
 use std::sync::Arc;
 
 use anyhow;
-use sequoia_openpgp::parse::Parse;
+use bytes::Bytes;
+use sequoia_openpgp::parse::{PacketParser, PacketParserResult, Parse};
 use sequoia_openpgp::policy::StandardPolicy;
-use sequoia_openpgp::{Fingerprint, Cert};
+use sequoia_openpgp::{Fingerprint, Cert, Packet};
 use sequoia_openpgp::cert::raw::RawCertParser;
 use sequoia_cert_store::{Store, CertStore, LazyCert};
 use sequoia_wot::{self as wot};
@@ -55,7 +56,7 @@ pub fn get_local_trust_root(cert_store: &CertStore) -> anyhow::Result<Cert> {
 
 }
 
-pub fn get_certificates<'hc>(context: &HuskContext<'hc>, email: &str) 
+pub fn get_certificates<'hc>(context: &HuskContext<'hc>, email: &str)
     -> Vec<Arc<LazyCert<'hc>>> {
 
     let cert_store = &context.cert_store;
@@ -125,3 +126,31 @@ pub fn get_introducers<'c>(cert_store: &CertStore<'c>, policy: &StandardPolicy,
 
     result
 }
+
+pub fn is_encrypted(body: &Bytes) -> bool {
+
+    let mut ppr = match PacketParser::from_bytes(body) {
+        Ok(pp) => pp,
+        Err(_) => return false, // no OpenPGP artifacts
+    };
+
+    let mut encrypted: bool = false;
+
+    while let PacketParserResult::Some(pp) = ppr {
+        if let Packet::SEIP(_) = pp.packet {
+            encrypted = true;
+        }
+
+        // parse the whole message, don't stop at first SEIP
+        ppr = match pp.recurse() {
+            Ok((_, next_ppr)) => next_ppr,
+            Err(_) => return false, // broken artifact -> not encrypted
+        }
+    }
+    if let PacketParserResult::EOF(eof) = ppr {
+        if eof.is_message().is_ok() && encrypted  {
+            return true;
+        }
+    }
+    false
+}