Add Fetch.internal_date method (#113)

This method gives the parsed internal date from the FETCH answer.

Cargo.toml

@@ -32,6 +32,7 @@ bufstream = "0.1"
 imap-proto = "0.7"
 nom = "4.0"
 base64 = "0.10"
+chrono = "0.4"
 
 [dev-dependencies]
 lettre = "0.9"

src/lib.rs

@@ -62,6 +62,7 @@
 
 extern crate base64;
 extern crate bufstream;
+extern crate chrono;
 extern crate imap_proto;
 extern crate native_tls;
 extern crate nom;

src/types/fetch.rs

@@ -1,6 +1,12 @@
 use super::{Flag, Seq, Uid};
+use chrono::{DateTime, FixedOffset};
 use imap_proto::types::{AttributeValue, Envelope, MessageSection, SectionPath};
 
+/// Format of Date and Time as defined RFC3501.
+/// See `date-time` element in [Formal Syntax](https://tools.ietf.org/html/rfc3501#section-9)
+/// chapter of this RFC.
+const DATE_TIME_FORMAT: &str = "%d-%b-%Y %H:%M:%S %z";
+
 /// An IMAP [`FETCH` response](https://tools.ietf.org/html/rfc3501#section-7.4.2) that contains
 /// data about a particular message. This response occurs as the result of a `FETCH` or `STORE`
 /// command, as well as by unilateral server decision (e.g., flag updates).
@@ -119,4 +125,24 @@ impl Fetch {
             })
             .next()
     }
+
+    /// Extract the `INTERNALDATE` of a `FETCH` response
+    ///
+    /// See [section 2.3.3 of RFC 3501](https://tools.ietf.org/html/rfc3501#section-2.3.3) for
+    /// details.
+    pub fn internal_date(&self) -> Option<DateTime<FixedOffset>> {
+        self.fetch
+            .iter()
+            .filter_map(|av| match av {
+                AttributeValue::InternalDate(date_time) => Some(*date_time),
+                _ => None,
+            })
+            .next()
+            .and_then(
+                |date_time| match DateTime::parse_from_str(date_time, DATE_TIME_FORMAT) {
+                    Ok(date_time) => Some(date_time),
+                    Err(_) => None,
+                },
+            )
+    }
 }

tests/imap_integration.rs

@@ -134,6 +134,8 @@ fn inbox() {
     let to = &e.to.as_ref().unwrap()[0];
     assert_eq!(to.mailbox, Some("inbox"));
     assert_eq!(to.host, Some("localhost"));
+    let date_opt = fetch.internal_date();
+    assert!(date_opt.is_some());
 
     // and let's delete it to clean up
     c.store("1", "+FLAGS (\\Deleted)").unwrap();
@@ -190,6 +192,8 @@ fn inbox_uid() {
     assert_eq!(fetch.uid, Some(uid));
     let e = fetch.envelope().unwrap();
     assert_eq!(e.subject, Some("My first e-mail"));
+    let date_opt = fetch.internal_date();
+    assert!(date_opt.is_some());
 
     // and let's delete it to clean up
     c.uid_store(format!("{}", uid), "+FLAGS (\\Deleted)")