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//! Logic was mainly ported from https://android.googlesource.com/platform/libcore/+/jb-mr2-release/luni/src/main/java/libcore/util/ZoneInfoDB.java
use core::{cmp::Ordering, convert::TryInto};
use std::{
fs::File,
io::{self, ErrorKind, Read, Seek, SeekFrom},
};
// The database uses 32-bit (4 byte) integers.
const TZ_INT_SIZE: usize = 4;
// The first 12 bytes contain a special version string.
const MAGIC_SIZE: usize = 12;
const HEADER_SIZE: usize = MAGIC_SIZE + 3 * TZ_INT_SIZE;
// The database reserves 40 bytes for each id.
const TZ_NAME_SIZE: usize = 40;
const INDEX_ENTRY_SIZE: usize = TZ_NAME_SIZE + 3 * TZ_INT_SIZE;
const TZDATA_LOCATIONS: [TzdataLocation; 2] = [
TzdataLocation {
env_var: "ANDROID_DATA",
path: "/misc/zoneinfo/",
},
TzdataLocation {
env_var: "ANDROID_ROOT",
path: "/usr/share/zoneinfo/",
},
];
#[derive(Debug)]
struct TzdataLocation {
env_var: &'static str,
path: &'static str,
}
#[derive(Debug, Clone, Copy)]
struct Header {
index_offset: usize,
data_offset: usize,
_zonetab_offset: usize,
}
#[derive(Debug)]
struct Index(Vec<u8>);
#[derive(Debug, Clone, Copy)]
struct IndexEntry<'a> {
_name: &'a [u8],
offset: usize,
length: usize,
_raw_utc_offset: usize,
}
pub(super) fn find_file() -> Result<File, io::Error> {
for location in &TZDATA_LOCATIONS {
if let Ok(env_value) = std::env::var(location.env_var) {
if let Ok(file) = File::open(format!("{}{}tzdata", env_value, location.path)) {
return Ok(file);
}
}
}
Err(io::Error::from(io::ErrorKind::NotFound))
}
pub(super) fn find_tz_data_in_file(
mut file: impl Read + Seek,
tz_name: &str,
) -> Result<Vec<u8>, io::Error> {
let header = Header::new(&mut file)?;
let index = Index::new(&mut file, header)?;
if let Some(entry) = index.find_entry(tz_name) {
file.seek(SeekFrom::Start((entry.offset + header.data_offset) as u64))?;
let mut tz_data = vec![0u8; entry.length];
file.read_exact(&mut tz_data)?;
Ok(tz_data)
} else {
Err(io::Error::from(ErrorKind::NotFound))
}
}
impl Header {
fn new(mut file: impl Read + Seek) -> Result<Self, io::Error> {
let mut buf = [0; HEADER_SIZE];
file.read_exact(&mut buf)?;
if !buf.starts_with(b"tzdata") || buf[MAGIC_SIZE - 1] != 0u8 {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
"invalid magic number",
));
}
Ok(Self {
index_offset: parse_tz_int(&buf, MAGIC_SIZE) as usize,
data_offset: parse_tz_int(&buf, MAGIC_SIZE + TZ_INT_SIZE) as usize,
_zonetab_offset: parse_tz_int(&buf, MAGIC_SIZE + 2 * TZ_INT_SIZE) as usize,
})
}
}
impl Index {
fn new(mut file: impl Read + Seek, header: Header) -> Result<Self, io::Error> {
file.seek(SeekFrom::Start(header.index_offset as u64))?;
let size = header.data_offset - header.index_offset;
let mut bytes = vec![0; size];
file.read_exact(&mut bytes)?;
Ok(Self(bytes))
}
fn find_entry(&self, name: &str) -> Option<IndexEntry> {
let name_bytes = name.as_bytes();
let name_len = name_bytes.len();
if name_len > TZ_NAME_SIZE {
return None;
}
let zeros = [0u8; TZ_NAME_SIZE];
let cmp = |chunk: &&[u8]| -> Ordering {
// tz names always have TZ_NAME_SIZE bytes and are right-padded with 0s
// so we check that a chunk starts with `name` and the remaining bytes are 0
chunk[..name_len]
.cmp(name_bytes)
.then_with(|| chunk[name_len..TZ_NAME_SIZE].cmp(&zeros[name_len..]))
};
let chunks: Vec<_> = self.0.chunks_exact(INDEX_ENTRY_SIZE).collect();
chunks
.binary_search_by(cmp)
.map(|idx| IndexEntry::new(chunks[idx]))
.ok()
}
}
impl<'a> IndexEntry<'a> {
fn new(bytes: &'a [u8]) -> Self {
Self {
_name: bytes[..TZ_NAME_SIZE]
.splitn(2, |&b| b == 0u8)
.next()
.unwrap(),
offset: parse_tz_int(bytes, TZ_NAME_SIZE) as usize,
length: parse_tz_int(bytes, TZ_NAME_SIZE + TZ_INT_SIZE) as usize,
_raw_utc_offset: parse_tz_int(bytes, TZ_NAME_SIZE + 2 * TZ_INT_SIZE) as usize,
}
}
}
/// Panics if slice does not contain [TZ_INT_SIZE] bytes beginning at start.
fn parse_tz_int(slice: &[u8], start: usize) -> u32 {
u32::from_be_bytes(slice[start..start + TZ_INT_SIZE].try_into().unwrap())
}
#[cfg(test)]
mod test {
use super::*;
use std::fs::File;
use std::io::Cursor;
#[test]
fn parse() {
let mut archive = File::open("tests/resources/tzdata.zip").unwrap();
let mut zip = zip::ZipArchive::new(&mut archive).unwrap();
let mut file = zip.by_index(0).unwrap();
let mut data = Vec::new();
file.read_to_end(&mut data).unwrap();
let cursor = Cursor::new(data);
let tz = find_tz_data_in_file(cursor, "Europe/Kiev").unwrap();
assert!(tz.starts_with(b"TZif2"));
}
}
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