code review 4530079: mail: new package.

src/pkg/mail/message.go

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-/*
-Package mail implements parsing of mail messages according to RFC 5322.
-
-TODO(dsymonds): Message formatting.
-*/
+// Package mail implements parsing of mail messages according to RFC 5322.
 package mail
 
 import (
         "bufio"
         "io"
         "net/textproto"
         "os"
+        "time"
 )
 
 // A Message represents a parsed mail message.
 type Message struct {
-        Header textproto.MIMEHeader
-
-        Body io.Reader
+        Header Header
+        Body   io.Reader
 }
 
-// ReadMessage reads and parses a message from b.
+// ReadMessage reads a message from r.
+// The headers are parsed, and the body of the message will be reading from r.
 func ReadMessage(r io.Reader) (msg *Message, err os.Error) {
         tp := textproto.NewReader(bufio.NewReader(r))
 
-        msg = new(Message)
-
-        msg.Header, err = tp.ReadMIMEHeader()
+        hdr, err := tp.ReadMIMEHeader()
         if err != nil {
                 return nil, err
         }
 
-        // Body is the remainder.
-        msg.Body = tp.R
-
-        return msg, nil
+        return &Message{
+                Header: Header(hdr),
+                Body:   tp.R,
+        }, nil
 }
 
-// TODO(dsymonds): Parsers for specific headers such as Date, To, etc.
+// Layouts suitable for passing to time.Parse.
+// These are tried in order.
+var dateLayouts []string
+
+func init() {
+        // Generate layouts based on RFC 5322, section 3.3.
+
+        dows := [...]string{"", "Mon, "}     // day-of-week
+        days := [...]string{"2", "02"}       // day = 1*2DIGIT
+        years := [...]string{"2006", "06"}   // year = 4*DIGIT / 2*DIGIT
+        seconds := [...]string{":05", ""}    // second
+        zones := [...]string{"-0700", "MST"} // zone = (("+" / "-") 4DIGIT) / "GMT" / ...
+
+        for _, dow := range dows {
+                for _, day := range days {
+                        for _, year := range years {
+                                for _, second := range seconds {
+                                        for _, zone := range zones {
+                                                s := dow + day + " Jan " + year + " 15:04" + second + " " + zone
+                                                dateLayouts = append(dateLayouts, s)
+                                        }
+                                }
+                        }
+                }
+        }
+}
+
+func parseDate(date string) (*time.Time, os.Error) {
+        for _, layout := range dateLayouts {
+                t, err := time.Parse(layout, date)
+                if err == nil {
+                        return t, nil
+                }
+        }
+        return nil, os.ErrorString("mail: header could not be parsed")
+}
+
+// TODO(dsymonds): Parsers for more specific headers such as To, From, etc.
+
+// A Header represents the key-value pairs in a mail message header.
+type Header map[string][]string
+
+// Get gets the first value associated with the given key.
+// If there are no values associated with the key, Get returns "".
+func (h Header) Get(key string) string {
+        return textproto.MIMEHeader(h).Get(key)
+}
+
+var ErrHeaderNotPresent = os.ErrorString("mail: header not in message")
+
+// Date parses the Date header field.
+func (h Header) Date() (*time.Time, os.Error) {
+        hdr := h.Get("Date")
+        if hdr == "" {
+                return nil, ErrHeaderNotPresent
+        }
+        return parseDate(hdr)
+}