From af2da5ac10091b6c2ca96931efe5ceb8454aa771 Mon Sep 17 00:00:00 2001
From: Paul Dicker <pitdicker@gmail.com>
Date: Fri, 19 May 2023 16:24:07 +0200
Subject: [PATCH] Parse invalid single-letter timezones as `-00:00`

---
 src/format/parse.rs | 11 ++++++-----
 src/format/scan.rs  | 27 +++++++++++++--------------
 2 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/src/format/parse.rs b/src/format/parse.rs
index 74bfaf768a..c4e2561500 100644
--- a/src/format/parse.rs
+++ b/src/format/parse.rs
@@ -1296,12 +1296,13 @@ mod tests {
             ("Tue, 20 Jan 2015 17:35:20 PDT", Ok("Tue, 20 Jan 2015 17:35:20 -0700")),
             ("Tue, 20 Jan 2015 17:35:20 PST", Ok("Tue, 20 Jan 2015 17:35:20 -0800")),
             ("Tue, 20 Jan 2015 17:35:20 pst", Ok("Tue, 20 Jan 2015 17:35:20 -0800")),
-            // named single-letter military timezones must fallback to +0000
+            // Z is the only single-letter military timezones that maps to +0000
             ("Tue, 20 Jan 2015 17:35:20 Z", Ok("Tue, 20 Jan 2015 17:35:20 +0000")),
-            ("Tue, 20 Jan 2015 17:35:20 A", Ok("Tue, 20 Jan 2015 17:35:20 +0000")),
-            ("Tue, 20 Jan 2015 17:35:20 a", Ok("Tue, 20 Jan 2015 17:35:20 +0000")),
-            ("Tue, 20 Jan 2015 17:35:20 K", Ok("Tue, 20 Jan 2015 17:35:20 +0000")),
-            ("Tue, 20 Jan 2015 17:35:20 k", Ok("Tue, 20 Jan 2015 17:35:20 +0000")),
+            // other named single-letter military timezones must fallback to -0000
+            ("Tue, 20 Jan 2015 17:35:20 A", Ok("Tue, 20 Jan 2015 17:35:20 -0000")),
+            ("Tue, 20 Jan 2015 17:35:20 a", Ok("Tue, 20 Jan 2015 17:35:20 -0000")),
+            ("Tue, 20 Jan 2015 17:35:20 K", Ok("Tue, 20 Jan 2015 17:35:20 -0000")),
+            ("Tue, 20 Jan 2015 17:35:20 k", Ok("Tue, 20 Jan 2015 17:35:20 -0000")),
             // named single-letter timezone "J" is specifically not valid
             ("Tue, 20 Jan 2015 17:35:20 J", Err(INVALID)),
             ("Tue, 20 Jan 2015 17:35:20 -0890", Err(OUT_OF_RANGE)), // bad offset minutes
diff --git a/src/format/scan.rs b/src/format/scan.rs
index 659308e727..f923f3d21a 100644
--- a/src/format/scan.rs
+++ b/src/format/scan.rs
@@ -356,30 +356,29 @@ pub(super) fn timezone_offset_2822(s: &str) -> ParseResult<(&str, Option<i32>)>
         let name = &s.as_bytes()[..upto];
         let s = &s[upto..];
         let offset_hours = |o| Ok((s, Some(o * 3600)));
-        if equals(name, "gmt") || equals(name, "ut") {
-            offset_hours(0)
+        // RFC 2822 requires support for some named North America timezones, a small subset of all
+        // named timezones.
+        if equals(name, "gmt") || equals(name, "ut") || equals(name, "z") || equals(name, "Z") {
+            return offset_hours(0);
         } else if equals(name, "edt") {
-            offset_hours(-4)
+            return offset_hours(-4);
         } else if equals(name, "est") || equals(name, "cdt") {
-            offset_hours(-5)
+            return offset_hours(-5);
         } else if equals(name, "cst") || equals(name, "mdt") {
-            offset_hours(-6)
+            return offset_hours(-6);
         } else if equals(name, "mst") || equals(name, "pdt") {
-            offset_hours(-7)
+            return offset_hours(-7);
         } else if equals(name, "pst") {
-            offset_hours(-8)
+            return offset_hours(-8);
         } else if name.len() == 1 {
-            match name[0] {
+            if let b'a'..=b'i' | b'k'..=b'y' | b'A'..=b'I' | b'K'..=b'Y' = name[0] {
                 // recommended by RFC 2822: consume but treat it as -0000
-                b'a'..=b'i' | b'k'..=b'z' | b'A'..=b'I' | b'K'..=b'Z' => offset_hours(0),
-                _ => Err(INVALID),
+                return Ok((s, None));
             }
-        } else {
-            Err(INVALID)
         }
+        Err(INVALID)
     } else {
-        let (s_, offset) = timezone_offset_internal(s, |s| Ok(s), false, false)?;
-        Ok((s_, offset))
+        timezone_offset_internal(s, |s| Ok(s), false, false)
     }
 }