Steps towards encryption

- Added certstore and retrieval of the local trust root.
- Major work on keeping the context between calls to the milter.
- Added a context for an email in processing
- Added Husk specific errors

src/crypto.rs

@@ -0,0 +1,47 @@
+//
+// Husk milter
+//
+// cryptographic functions
+//
+
+use anyhow;
+use sequoia_openpgp::parse::Parse;
+use sequoia_openpgp::{Fingerprint, Cert};
+use sequoia_openpgp::cert::raw::RawCertParser;
+use sequoia_cert_store::CertStore;
+use crate::types::errors::HuskError;
+
+pub fn get_local_trust_root(cert_store: &CertStore) -> anyhow::Result<Cert> {
+
+    let root = cert_store.certd()
+        .and_then(|certd| {
+            match certd.certd().get(sequoia_cert_store::store::openpgp_cert_d::TRUST_ROOT) {
+                Ok(Some((_tag, bytes))) => Some(bytes),
+                Ok(None) => None,
+                Err(_) => None
+            }
+        })
+        .and_then(|bytes| {
+            match RawCertParser::from_bytes(&bytes[..]) {
+                Ok(mut parser) => {
+                    match parser.next() {
+                        Some(Ok(cert)) => {
+                            match Cert::from_bytes(cert.as_bytes()) {
+                                Ok(c) => Some(c),
+                                Err(_) => None,
+                            }
+                        },
+                        Some(Err(_))
+                        | None => None
+                    }
+                },
+                Err(_) => None,
+            }
+        });
+
+    match root {
+        Some(r) => Ok(r),
+        None => Err(HuskError::NoLocalTrustRoot.into())
+    }
+
+}