Support ohos tzdata since oh35

Author: MirageLyu

src/offset/local/tz_info/parser.rs

@@ -247,6 +247,21 @@ impl<'a> Cursor<'a> {
         Ok(u32::from_be_bytes(buf))
     }
 
+    #[cfg(target_env = "ohos")]
+    pub(crate) fn seek_after(&mut self, offset: usize) -> Result<usize, io::Error> {
+        if offset < self.read_count {
+            return Err(io::Error::from(ErrorKind::UnexpectedEof));
+        }
+        match self.remaining.get((offset - self.read_count)..) {
+            Some(remaining) => {
+                self.remaining = remaining;
+                self.read_count = offset;
+                Ok(offset)
+            }
+            _ => Err(io::Error::from(ErrorKind::UnexpectedEof)),
+        }
+    }
+
     /// Read exactly `count` bytes, reducing remaining data and incrementing read count
     pub(crate) fn read_exact(&mut self, count: usize) -> Result<&'a [u8], io::Error> {
         match (self.remaining.get(..count), self.remaining.get(count..)) {

src/offset/local/tz_info/timezone.rs

@@ -8,6 +8,9 @@ use std::{cmp::Ordering, fmt, str};
 use super::rule::{AlternateTime, TransitionRule};
 use super::{parser, Error, DAYS_PER_WEEK, SECONDS_PER_DAY};
 
+#[cfg(target_env = "ohos")]
+use crate::offset::local::tz_info::parser::Cursor;
+
 /// Time zone
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub(crate) struct TimeZone {
@@ -50,6 +53,12 @@ impl TimeZone {
             }
         }
 
+        // ohos merge all file into tzdata since ver35
+        #[cfg(target_env = "ohos")]
+        {
+            return Self::from_tz_data(&find_ohos_tz_data(tz_string)?);
+        }
+
         let mut chars = tz_string.chars();
         if chars.next() == Some(':') {
             return Self::from_file(&mut find_tz_file(chars.as_str())?);
@@ -629,6 +638,58 @@ fn find_tz_file(path: impl AsRef<Path>) -> Result<File, Error> {
     }
 }
 
+#[cfg(target_env = "ohos")]
+fn from_tzdata_bytes(bytes: &mut Vec<u8>, tz_string: &str) -> Result<Vec<u8>, Error> {
+    const VERSION_SIZE: usize = 12;
+    const OFFSET_SIZE: usize = 4;
+    const INDEX_CHUNK_SIZE: usize = 48;
+    const ZONENAME_SIZE: usize = 40;
+
+    let mut cursor = Cursor::new(&bytes);
+    // version head
+    let _ = cursor.read_exact(VERSION_SIZE)?;
+    let index_offset_offset = cursor.read_be_u32()?;
+    let data_offset_offset = cursor.read_be_u32()?;
+    // final offset
+    let _ = cursor.read_be_u32()?;
+
+    cursor.seek_after(index_offset_offset as usize)?;
+    let mut idx = index_offset_offset;
+    while idx < data_offset_offset {
+        let index_buf = cursor.read_exact(ZONENAME_SIZE)?;
+        let offset = cursor.read_be_u32()?;
+        let length = cursor.read_be_u32()?;
+        let zone_name = str::from_utf8(index_buf)?.trim_end_matches('\0');
+        if zone_name != tz_string {
+            idx += INDEX_CHUNK_SIZE as u32;
+            continue;
+        }
+        cursor.seek_after((data_offset_offset + offset) as usize)?;
+        return match cursor.read_exact(length as usize) {
+            Ok(result) => Ok(result.to_vec()),
+            Err(_err) => Err(Error::InvalidTzFile("invalid ohos tzdata chunk")),
+        };
+    }
+
+    Err(Error::InvalidTzString("cannot find tz string within tzdata"))
+}
+
+#[cfg(target_env = "ohos")]
+fn from_tzdata_file(file: &mut File, tz_string: &str) -> Result<Vec<u8>, Error> {
+    let mut bytes = Vec::new();
+    file.read_to_end(&mut bytes)?;
+    from_tzdata_bytes(&mut bytes, tz_string)
+}
+
+#[cfg(target_env = "ohos")]
+fn find_ohos_tz_data(tz_string: &str) -> Result<Vec<u8>, Error> {
+    const TZDATA_PATH: &str = "/system/etc/zoneinfo/tzdata";
+    match File::open(TZDATA_PATH) {
+        Ok(mut file) => from_tzdata_file(&mut file, tz_string),
+        Err(err) => Err(err.into()),
+    }
+}
+
 // Possible system timezone directories
 #[cfg(unix)]
 const ZONE_INFO_DIRECTORIES: [&str; 4] =