Simplify / rustify implementation of keys_from_bin (#3414)

provider/datagen/Cargo.toml

@@ -78,6 +78,7 @@ toml = "0.5"
 writeable = { version = "0.5.1", path = "../../utils/writeable" }
 zerovec = { version = "0.9.4", path = "../../utils/zerovec", features = ["serde", "yoke"] }
 zip = { version = ">=0.5, <0.7", default-features = false, features = ["deflate"] }
+memchr = "2.5.0"
 
 # Dependencies for "bin" feature
 clap = { version = "4", optional = true, features = ["derive"] }

provider/datagen/src/lib.rs

@@ -123,6 +123,7 @@ use icu_provider::prelude::*;
 use icu_provider_adapters::empty::EmptyDataProvider;
 use icu_provider_adapters::filter::Filterable;
 use icu_provider_fs::export::serializers::AbstractSerializer;
+use memchr::memmem;
 use prelude::*;
 use rayon::prelude::*;
 use std::collections::HashSet;
@@ -256,30 +257,29 @@ pub fn keys_from_file<P: AsRef<Path>>(path: P) -> std::io::Result<Vec<DataKey>>
 /// ```
 pub fn keys_from_bin<P: AsRef<Path>>(path: P) -> std::io::Result<Vec<DataKey>> {
  let file = std::fs::read(path.as_ref())?;
- let mut result = Vec::new();
- let mut i = 0;
- let mut last_start = None;
- while i < file.len() {
- if file[i..].starts_with(icu_provider::leading_tag!().as_bytes()) {
- i += icu_provider::leading_tag!().len();
- last_start = Some(i);
- } else if file[i..].starts_with(icu_provider::trailing_tag!().as_bytes())
- && last_start.is_some()
- {
- if let Some(key) = std::str::from_utf8(&file[last_start.unwrap()..i])
- .ok()
- .and_then(crate::key)
- {
- result.push(key);
- }
- i += icu_provider::trailing_tag!().len();
- last_start = None;
- } else {
- i += 1;
- }
- }
+ let file = file.as_slice();
+
+ const LEADING_TAG: &[u8] = icu_provider::leading_tag!().as_bytes();
+ const TRAILING_TAG: &[u8] = icu_provider::trailing_tag!().as_bytes();
+
+ let trailing_tag = memmem::Finder::new(TRAILING_TAG);
+
+ let mut result: Vec<DataKey> = memmem::find_iter(file, LEADING_TAG)
+ .map(|tag_position| tag_position + LEADING_TAG.len())
+ .map(|key_start| &file[key_start..])
+ .filter_map(move |key_fragment| {
+ trailing_tag
+ .find(key_fragment)
+ .map(|end| &key_fragment[..end])
+ })
+ .map(std::str::from_utf8)
+ .filter_map(Result::ok)
+ .filter_map(crate::key)
+ .collect();
+
  result.sort();
  result.dedup();
+
  Ok(result)
 }