net/mail: make address parsing (more) public

Code for parsing email addresses was already partially part of the public API with "func (Header) AddressList".  This CL adds a trivial implementation for two public methods to parse address and lists from a string. With tests.

R=dsymonds
CC=golang-dev
https://golang.org/cl/5676067

src/pkg/net/mail/message.go

@@ -127,7 +127,7 @@ func (h Header) AddressList(key string) ([]*Address, error) {
 	if hdr == "" {
 		return nil, ErrHeaderNotPresent
 	}
-	return newAddrParser(hdr).parseAddressList()
+	return ParseAddressList(hdr)
 }
 
 // Address represents a single mail address.
@@ -138,6 +138,16 @@ type Address struct {
 	Address string // user@domain
 }
 
+// Parses a single RFC 5322 address, e.g. "Barry Gibbs <bg@example.com>"
+func ParseAddress(address string) (*Address, error) {
+	return newAddrParser(address).parseAddress()
+}
+
+// ParseAddressList parses the given string as a list of addresses.
+func ParseAddressList(list string) ([]*Address, error) {
+	return newAddrParser(list).parseAddressList()
+}
+
 // String formats the address as a valid RFC 5322 address.
 // If the address's name contains non-ASCII characters
 // the name will be rendered according to RFC 2047.

src/pkg/net/mail/message_test.go

@@ -227,13 +227,24 @@ func TestAddressParsing(t *testing.T) {
 		},
 	}
 	for _, test := range tests {
-		addrs, err := newAddrParser(test.addrsStr).parseAddressList()
+		if len(test.exp) == 1 {
+			addr, err := ParseAddress(test.addrsStr)
 			if err != nil {
-			t.Errorf("Failed parsing %q: %v", test.addrsStr, err)
+				t.Errorf("Failed parsing (single) %q: %v", test.addrsStr, err)
+				continue
+			}
+			if !reflect.DeepEqual([]*Address{addr}, test.exp) {
+				t.Errorf("Parse (single) of %q: got %+v, want %+v", test.addrsStr, addr, test.exp)
+			}
+		}
+
+		addrs, err := ParseAddressList(test.addrsStr)
+		if err != nil {
+			t.Errorf("Failed parsing (list) %q: %v", test.addrsStr, err)
 			continue
 		}
 		if !reflect.DeepEqual(addrs, test.exp) {
-			t.Errorf("Parse of %q: got %+v, want %+v", test.addrsStr, addrs, test.exp)
+			t.Errorf("Parse (list) of %q: got %+v, want %+v", test.addrsStr, addrs, test.exp)
 		}
 	}
 }