Start milestone 3

- Add functionality to query online sources (Keyservers, etc) for
  certificates.
- Use introducers to determine which UserIDs should be fetched from
  online soources. Check certifications before importing certifiactes
  into the local cert store.
- start docker image for local end-to-end testing.

src/types/errors.rs

@@ -18,4 +18,6 @@ pub enum HuskError {
     NoCertStore,
     #[error("No encryption keys found")]
     NoEncryptionKeys,
+    #[error("Error while looking up email {0}: {1}")]
+    KeyLookupError(String, String),
 }

src/types/husk_context.rs

@@ -21,6 +21,7 @@ pub struct HuskContext<'hc> {
     pub cert_store: CertStore<'hc>,
     pub local_trust_root: Cert,
     pub introducers: Vec<Introducer>,
+    pub keyservers: Vec<String>,
     pub mail: MailContext<'hc>,
 }
 
@@ -43,6 +44,7 @@ impl<'hc> HuskContext<'hc> {
             cert_store,
             local_trust_root,
             introducers,
+            keyservers: config.get_keyservers(),
             mail: MailContext::new(),
         })
     }
@@ -55,9 +57,9 @@ impl<'hc> HuskContext<'hc> {
         self.mail = MailContext::new();
     }
 
-    pub fn add_recipient(&mut self, rcpt: String) -> anyhow::Result<()> {
+    pub async fn add_recipient(&mut self, rcpt: String) {
         
-        let certs = crypto::get_certificates(&self, rcpt.as_str());
+        let certs = crypto::get_certificates(&self, rcpt.as_str()).await;
 
         self.mail.add_recipient(rcpt, certs)
     }

src/types/introducer.rs

@@ -29,5 +29,29 @@ impl Introducer {
             false
         }
     }
+
+    pub fn is_introducing(&self, cert: &Cert) -> bool {
+
+        let policy = StandardPolicy::new();
+        let mut result = false;
+
+        let my_keyid = self.cert.keyid();
+
+        if let Ok(vc) = cert.with_policy(&policy, None) {
+            vc.userids()
+                .revoked(false)
+                .for_each(|u| {
+                    u.certifications().for_each(|s| {
+                        if s.signature_alive(None, None).is_ok() {
+                            s.issuers().for_each(|i| {
+                                if i == &my_keyid { result = true; }          
+                            });
+                        }
+                    })
+                });
+        }
+
+        result
+    }
 }
 

src/types/mail_context.rs

@@ -44,13 +44,11 @@ impl<'mc> MailContext<'mc> {
         self.sender = Some(sender);
     }
 
-    pub fn add_recipient(&mut self, rcpt: String, certs: Vec<Arc<LazyCert<'mc>>>) -> anyhow::Result<()> {
+    pub fn add_recipient(&mut self, rcpt: String, certs: Vec<Arc<LazyCert<'mc>>>) {
         let mut recipient: Recipient = rcpt.into();
         recipient.certs = certs;
 
         self.recipients.push(recipient);
-
-        Ok(())
     }
 
     pub fn add_chunk(&mut self, chunk: Bytes) {