From b124215679be30c8c0bb13b5796064b932d19589 Mon Sep 17 00:00:00 2001
From: Takumi2008 <cclark@mailgun.com>
Date: Thu, 4 Nov 2021 20:41:41 -0500
Subject: [PATCH] support parsing month before day

---
 clock/rfc822.go      | 242 ++++++++++++-------------------------------
 clock/rfc822_test.go |   8 +-
 2 files changed, 74 insertions(+), 176 deletions(-)

diff --git a/clock/rfc822.go b/clock/rfc822.go
index cb84062a..664941d5 100644
--- a/clock/rfc822.go
+++ b/clock/rfc822.go
@@ -2,8 +2,67 @@ package clock
 
 import (
 	"strconv"
+	"time"
 )
 
+var datetimeLayouts = [48]string{
+	// Day first month 2nd abbreviated.
+	"Mon, 2 Jan 2006 15:04:05 MST",
+	"Mon, 2 Jan 2006 15:04:05 -0700",
+	"Mon, 2 Jan 2006 15:04:05 -0700 (MST)",
+	"2 Jan 2006 15:04:05 MST",
+	"2 Jan 2006 15:04:05 -0700",
+	"2 Jan 2006 15:04:05 -0700 (MST)",
+	"Mon, 2 Jan 2006 15:04 MST",
+	"Mon, 2 Jan 2006 15:04 -0700",
+	"Mon, 2 Jan 2006 15:04 -0700 (MST)",
+	"2 Jan 2006 15:04 MST",
+	"2 Jan 2006 15:04 -0700",
+	"2 Jan 2006 15:04 -0700 (MST)",
+
+	// Month first day 2nd abbreviated.
+	"Mon, Jan 2 2006 15:04:05 MST",
+	"Mon, Jan 2 2006 15:04:05 -0700",
+	"Mon, Jan 2 2006 15:04:05 -0700 (MST)",
+	"Jan 2 2006 15:04:05 MST",
+	"Jan 2 2006 15:04:05 -0700",
+	"Jan 2 2006 15:04:05 -0700 (MST)",
+	"Mon, Jan 2 2006 15:04 MST",
+	"Mon, Jan 2 2006 15:04 -0700",
+	"Mon, Jan 2 2006 15:04 -0700 (MST)",
+	"Jan 2 2006 15:04 MST",
+	"Jan 2 2006 15:04 -0700",
+	"Jan 2 2006 15:04 -0700 (MST)",
+
+	// Day first month 2nd not abbreviated.
+	"Mon, 2 January 2006 15:04:05 MST",
+	"Mon, 2 January 2006 15:04:05 -0700",
+	"Mon, 2 January 2006 15:04:05 -0700 (MST)",
+	"2 January 2006 15:04:05 MST",
+	"2 January 2006 15:04:05 -0700",
+	"2 January 2006 15:04:05 -0700 (MST)",
+	"Mon, 2 January 2006 15:04 MST",
+	"Mon, 2 January 2006 15:04 -0700",
+	"Mon, 2 January 2006 15:04 -0700 (MST)",
+	"2 January 2006 15:04 MST",
+	"2 January 2006 15:04 -0700",
+	"2 January 2006 15:04 -0700 (MST)",
+
+	// Month first day 2nd not abbreviated.
+	"Mon, January 2 2006 15:04:05 MST",
+	"Mon, January 2 2006 15:04:05 -0700",
+	"Mon, January 2 2006 15:04:05 -0700 (MST)",
+	"January 2 2006 15:04:05 MST",
+	"January 2 2006 15:04:05 -0700",
+	"January 2 2006 15:04:05 -0700 (MST)",
+	"Mon, January 2 2006 15:04 MST",
+	"Mon, January 2 2006 15:04 -0700",
+	"Mon, January 2 2006 15:04 -0700 (MST)",
+	"January 2 2006 15:04 MST",
+	"January 2 2006 15:04 -0700",
+	"January 2 2006 15:04 -0700 (MST)",
+}
+
 // Allows seamless JSON encoding/decoding of rfc822 formatted timestamps.
 // https://www.ietf.org/rfc/rfc822.txt section 5.
 type RFC822Time struct {
@@ -18,180 +77,15 @@ func NewRFC822Time(t Time) RFC822Time {
 
 // ParseRFC822Time parses an RFC822 time string.
 func ParseRFC822Time(s string) (Time, error) {
-	t, err := parseRFC822TimeAbreviated(s)
-	if err == nil {
-		return t, err
-	}
-	if _, ok := err.(*ParseError); !ok {
-		return Time{}, err
-	}
-	if t, err = parseRFC822Time(s); err == nil {
-		return t, err
-	}
-	if _, ok := err.(*ParseError); !ok {
-		return Time{}, err
-	}
-	if t, err = parseRFC822TimeAbreviatedNoSeconds(s); err == nil {
-		return t, err
-	}
-	if _, ok := err.(*ParseError); !ok {
-		return Time{}, err
-	}
-	return parseRFC822TimeNoSeconds(s)
-}
-
-// parseRFC822TimeAbbreviated attempts to parse a an RFC822 time with the month abbreviated.
-func parseRFC822TimeAbreviated(s string) (Time, error) {
-	t, err := Parse("Mon, 2 Jan 2006 15:04:05 MST", s)
-	if err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "MST" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 Jan 2006 15:04:05 -0700", s); err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 Jan 2006 15:04:05 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "Mon" {
-		return Time{}, err
-	}
-	if t, err = Parse("2 Jan 2006 15:04:05 MST", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "MST" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 Jan 2006 15:04:05 -0700", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 Jan 2006 15:04:05 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	return Time{}, err
-}
-
-func parseRFC822TimeAbreviatedNoSeconds(s string) (Time, error) {
-	t, err := Parse("Mon, 2 Jan 2006 15:04 MST", s)
-	if err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "MST" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 Jan 2006 15:04 -0700", s); err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 Jan 2006 15:04 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "Mon" {
-		return Time{}, err
-	}
-	if t, err = Parse("2 Jan 2006 15:04 MST", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "MST" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 Jan 2006 15:04 -0700", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 Jan 2006 15:04 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	return Time{}, err
-}
-
-// parseRFC822Time attempts to parse an RFC822 time with the full month name.
-func parseRFC822Time(s string) (Time, error) {
-	t, err := Parse("Mon, 2 January 2006 15:04:05 MST", s)
-	if err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "MST" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 January 2006 15:04:05 -0700", s); err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 January 2006 15:04:05 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "Mon" {
-		return Time{}, err
-	}
-	if t, err = Parse("2 January 2006 15:04:05 MST", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "MST" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 January 2006 15:04:05 -0700", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 January 2006 15:04:05 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	return Time{}, err
-}
-
-func parseRFC822TimeNoSeconds(s string) (Time, error) {
-	t, err := Parse("Mon, 2 January 2006 15:04 MST", s)
-	if err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "MST" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 January 2006 15:04 -0700", s); err == nil {
-		return t, nil
-	}
-	if parseErr, ok := err.(*ParseError); !ok || (parseErr.LayoutElem != "" && parseErr.LayoutElem != "Mon") {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("Mon, 2 January 2006 15:04 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "Mon" {
-		return Time{}, err
-	}
-	if t, err = Parse("2 January 2006 15:04 MST", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "MST" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 January 2006 15:04 -0700", s); err == nil {
-		return t, err
-	}
-	if parseErr, ok := err.(*ParseError); !ok || parseErr.LayoutElem != "" {
-		return Time{}, parseErr
-	}
-	if t, err = Parse("2 January 2006 15:04 -0700 (MST)", s); err == nil {
-		return t, err
-	}
-	return Time{}, err
+	var t time.Time
+	var err error
+	for _, layout := range datetimeLayouts {
+		t, err = Parse(layout, s)
+		if err == nil {
+			return t, err
+		}
+	}
+	return t, err
 }
 
 // NewRFC822Time creates RFC822Time from a Unix timestamp (seconds from Epoch).
diff --git a/clock/rfc822_test.go b/clock/rfc822_test.go
index 6b97e1f0..d83d6bfa 100644
--- a/clock/rfc822_test.go
+++ b/clock/rfc822_test.go
@@ -137,10 +137,10 @@ func TestRFC822UnmarshalingError(t *testing.T) {
 		outError  string
 	}{{
 		inEncoded: `{"ts": "Thu, 29 Aug 2019 11:20:07"}`,
-		outError:  `parsing time "Thu, 29 Aug 2019 11:20:07" as "Mon, 2 January 2006 15:04 MST": cannot parse "Aug 2019 11:20:07" as "January"`,
+		outError:  `parsing time "Thu, 29 Aug 2019 11:20:07" as "January 2 2006 15:04 -0700 (MST)": cannot parse "Thu, 29 Aug 2019 11:20:07" as "January"`,
 	}, {
 		inEncoded: `{"ts": "foo"}`,
-		outError:  `parsing time "foo" as "2 January 2006 15:04 MST": cannot parse "foo" as "2"`,
+		outError:  `parsing time "foo" as "January 2 2006 15:04 -0700 (MST)": cannot parse "foo" as "January"`,
 	}, {
 		inEncoded: `{"ts": 42}`,
 		outError:  "invalid syntax",
@@ -170,6 +170,8 @@ func TestParseRFC822Time(t *testing.T) {
 		{"2 June 2021 17:06:41 GMT"},
 		{"2 June 2021 17:06:41 -0700"},
 		{"2 June 2021 17:06:41 -0700 (MST)"},
+		{"Wed, Nov 03 2021 17:48:06 CST"},
+		{"Wed, November 03 2021 17:48:06 CST"},
 
 		// Timestamps without seconds.
 		{"Sun, 31 Oct 2021 12:10 -5000"},
@@ -186,6 +188,8 @@ func TestParseRFC822Time(t *testing.T) {
 		{"2 June 2021 17:06 GMT"},
 		{"2 June 2021 17:06 -0700"},
 		{"2 June 2021 17:06 -0700 (MST)"},
+		{"Wed, Nov 03 2021 17:48 CST"},
+		{"Wed, November 03 2021 17:48 CST"},
 	} {
 		t.Run(tt.rfc822Time, func(t *testing.T) {
 			_, err := ParseRFC822Time(tt.rfc822Time)