From 155c6b9e76e462e1d47ea528ca87f366adccdea3 Mon Sep 17 00:00:00 2001
From: Howard Hinnant <howard.hinnant@gmail.com>
Date: Thu, 12 Sep 2024 15:51:49 +0100
Subject: [PATCH] Bring text parsing into compliance with the tzdata spec *
 Fixes #836

---
 src/tz.cpp | 79 +++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 58 insertions(+), 21 deletions(-)

diff --git a/src/tz.cpp b/src/tz.cpp
index 82e4312..89a08fd 100644
--- a/src/tz.cpp
+++ b/src/tz.cpp
@@ -581,27 +581,57 @@ get_tzdb_list()
     return tz_db;
 }
 
+inline
+static
+char
+tolower(char c)
+{
+    return static_cast<char>(std::tolower(c));
+}
+
+inline
+static
+void
+tolower(std::string& s)
+{
+    for (auto& c : s)
+        c = tolower(c);
+}
+
+inline
 static
 std::string
-parse3(std::istream& in)
+get_alpha_word(std::istream& in)
 {
-    std::string r(3, ' ');
-    ws(in);
-    r[0] = static_cast<char>(in.get());
-    r[1] = static_cast<char>(in.get());
-    r[2] = static_cast<char>(in.get());
-    return r;
+    std::string s;
+    while (!in.eof() && std::isalpha(in.peek()))
+        s.push_back(static_cast<char>(in.get()));
+    return s;
+}
+
+inline
+static
+bool
+is_prefix_of(std::string const& key, std::string const& value)
+{
+    return key.compare(0, key.size(), value, 0, key.size()) == 0;
 }
 
 static
 unsigned
 parse_month(std::istream& in)
 {
-    CONSTDATA char*const month_names[] =
-        {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
-         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
-    auto s = parse3(in);
-    auto m = std::find(std::begin(month_names), std::end(month_names), s) - month_names;
+    static std::string const month_names[] =
+        {"january", "february", "march", "april", "may", "june",
+         "july", "august", "september", "october", "november", "december"};
+    auto s = get_alpha_word(in);
+    tolower(s);
+    auto m = std::find_if(std::begin(month_names), std::end(month_names),
+                 [&s](std::string const& m)
+                 {
+                     return is_prefix_of(s, m);
+                 })
+                  - month_names;
     if (m >= std::end(month_names) - std::begin(month_names))
         throw std::runtime_error("oops: bad month name: " + s);
     return static_cast<unsigned>(++m);
@@ -817,10 +847,16 @@ static
 unsigned
 parse_dow(std::istream& in)
 {
-    CONSTDATA char*const dow_names[] =
-        {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
-    auto s = parse3(in);
-    auto dow = std::find(std::begin(dow_names), std::end(dow_names), s) - dow_names;
+    static std::string const dow_names[] =
+        {"sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday"};
+    auto s = get_alpha_word(in);
+    tolower(s);
+    auto dow = std::find_if(std::begin(dow_names), std::end(dow_names),
+                 [&s](std::string const& dow)
+                 {
+                     return is_prefix_of(s, dow);
+                 })
+                  - dow_names;
     if (dow >= std::end(dow_names) - std::begin(dow_names))
         throw std::runtime_error("oops: bad dow name: " + s);
     return static_cast<unsigned>(dow);
@@ -1081,7 +1117,7 @@ detail::operator>>(std::istream& is, MonthDayTime& x)
         auto m = parse_month(is);
         if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
         {
-            if (is.peek() == 'l')
+            if (tolower(is.peek()) == 'l')
             {
                 for (int i = 0; i < 4; ++i)
                     is.get();
@@ -3642,22 +3678,23 @@ init_tzdb()
                 std::istringstream in(line);
                 std::string word;
                 in >> word;
-                if (word == "Rule")
+                tolower(word);
+                if (is_prefix_of(word, "rule"))
                 {
                     db->rules.push_back(Rule(line));
                     continue_zone = false;
                 }
-                else if (word == "Link")
+                else if (is_prefix_of(word, "link"))
                 {
                     db->links.push_back(time_zone_link(line));
                     continue_zone = false;
                 }
-                else if (word == "Leap")
+                else if (is_prefix_of(word, "leap"))
                 {
                     db->leap_seconds.push_back(leap_second(line, detail::undocumented{}));
                     continue_zone = false;
                 }
-                else if (word == "Zone")
+                else if (is_prefix_of(word, "zone"))
                 {
                     db->zones.push_back(time_zone(line, detail::undocumented{}));
                     continue_zone = true;