net/http: added ParseTime function.

Parses a time header value into a time.Time according to rfc2616 sec 3.3.

R=golang-dev, dave, rsc, r
CC=bradfitz, golang-dev
https://golang.org/cl/6344046

src/pkg/net/http/header.go

@@ -9,6 +9,7 @@ import (
 	"net/textproto"
 	"sort"
 	"strings"
+	"time"
 )
 
 // A Header represents the key-value pairs in an HTTP header.
@@ -53,6 +54,25 @@ func (h Header) Write(w io.Writer) error {
 	return h.WriteSubset(w, nil)
 }
 
+var timeFormats = []string{
+	TimeFormat,
+	time.RFC850,
+	time.ANSIC,
+}
+
+// ParseTime parses a time header (such as the Date: header),
+// trying each of the three formats allowed by HTTP/1.1:
+// TimeFormat, time.RFC850, and time.ANSIC.
+func ParseTime(text string) (t time.Time, err error) {
+	for _, layout := range timeFormats {
+		t, err = time.Parse(layout, text)
+		if err == nil {
+			return
+		}
+	}
+	return
+}
+
 var headerNewlineToSpace = strings.NewReplacer("\n", " ", "\r", " ")
 
 type writeStringer interface {

src/pkg/net/http/header_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"runtime"
 	"testing"
+	"time"
 )
 
 var headerWriteTests = []struct {
@@ -99,6 +100,38 @@ func TestHeaderWrite(t *testing.T) {
 	}
 }
 
+var parseTimeTests = []struct {
+	h   Header
+	err bool
+}{
+	{Header{"Date": {""}}, true},
+	{Header{"Date": {"invalid"}}, true},
+	{Header{"Date": {"1994-11-06T08:49:37Z00:00"}}, true},
+	{Header{"Date": {"Sun, 06 Nov 1994 08:49:37 GMT"}}, false},
+	{Header{"Date": {"Sunday, 06-Nov-94 08:49:37 GMT"}}, false},
+	{Header{"Date": {"Sun Nov  6 08:49:37 1994"}}, false},
+}
+
+func TestParseTime(t *testing.T) {
+	expect := time.Date(1994, 11, 6, 8, 49, 37, 0, time.UTC)
+	for i, test := range parseTimeTests {
+		d, err := ParseTime(test.h.Get("Date"))
+		if err != nil {
+			if !test.err {
+				t.Errorf("#%d:\n got err: %v", i, err)
+			}
+			continue
+		}
+		if test.err {
+			t.Errorf("#%d:\n  should err", i)
+			continue
+		}
+		if !expect.Equal(d) {
+			t.Errorf("#%d:\n got: %v\nwant: %v", i, d, expect)
+		}
+	}
+}
+
 type hasTokenTest struct {
 	header string
 	token  string