handle Android timezones

better handle fallback for unsupported os

make paths const

Cargo.toml

@@ -24,7 +24,7 @@ default = ["clock", "std", "oldtime"]
 alloc = []
 libc = []
 std = []
-clock = ["std", "winapi"]
+clock = ["std", "winapi", "iana-time-zone"]
 oldtime = ["time"]
 wasmbind = [] # TODO: empty feature to avoid breaking change in 0.4.20, can be removed later
 unstable-locales = ["pure-rust-locales", "alloc"]
@@ -40,6 +40,7 @@ serde = { version = "1.0.99", default-features = false, optional = true }
 pure-rust-locales = { version = "0.5.2", optional = true }
 criterion = { version = "0.3", optional = true }
 rkyv = {version = "0.7", optional = true}
+iana-time-zone = { version = "0.1.41", optional = true }
 
 [target.'cfg(all(target_arch = "wasm32", not(any(target_os = "emscripten", target_os = "wasi"))))'.dependencies]
 wasm-bindgen = { version = "0.2" }

src/offset/local/tz_info/timezone.rs

@@ -89,7 +89,7 @@ impl TimeZone {
     /// Construct a time zone from the contents of a time zone file
     ///
     /// Parse TZif data as described in [RFC 8536](https://datatracker.ietf.org/doc/html/rfc8536).
-    pub(super) fn from_tz_data(bytes: &[u8]) -> Result<Self, Error> {
+    pub(crate) fn from_tz_data(bytes: &[u8]) -> Result<Self, Error> {
         parser::parse(bytes)
     }
 

src/offset/local/unix.rs

@@ -57,6 +57,7 @@ impl Default for Source {
                 },
                 Err(_) => {
                     // as above, now() should be a better default than some constant
+                    // TODO: see if we can improve caching in the case where the fallback is a valid timezone
                     Source::LocalTime { mtime: SystemTime::now(), last_checked: SystemTime::now() }
                 }
             },
@@ -95,11 +96,32 @@ struct Cache {
     source: Source,
 }
 
+#[cfg(target_os = "android")]
+const TZDB_LOCATION: &str = " /system/usr/share/zoneinfo";
+
+#[cfg(not(target_os = "android"))]
+const TZDB_LOCATION: &str = "/usr/share/zoneinfo";
+
+#[cfg(any(target_os = "emscripten", target_os = "wasi", target_os = "solaris"))]
+fn get_fallback_timezone() -> Option<TimeZone> {
+    TimeZone::utc()
+}
+
+#[cfg(not(any(target_os = "emscripten", target_os = "wasi", target_os = "solaris")))]
+fn get_fallback_timezone() -> Option<TimeZone> {
+    let tz_name = iana_time_zone::get_timezone().ok()?;
+    let bytes = fs::read(format!("{TZDB_LOCATION}/{tz_name}")).ok()?;
+    TimeZone::from_tz_data(&bytes).ok()
+}
+
 impl Default for Cache {
     fn default() -> Cache {
         // default to UTC if no local timezone can be found
         Cache {
-            zone: TimeZone::local().unwrap_or_else(|_| TimeZone::utc()),
+            zone: TimeZone::local()
+                .ok()
+                .or_else(get_fallback_timezone)
+                .unwrap_or_else(TimeZone::utc),
             source: Source::default(),
         }
     }