Add a cached fs abstraction (#141)

crates/common/src/cached_fs/mod.rs

@@ -0,0 +1,49 @@
+//! This module implements a cached file system allowing for results to be stored in-memory rather
+//! rather being queried from the file system again.
+
+use std::fs;
+use std::io::{Error, Result};
+use std::path::{Path, PathBuf};
+
+use moka::sync::Cache;
+use once_cell::sync::Lazy;
+
+pub fn read(path: impl AsRef<Path>) -> Result<Vec<u8>> {
+    static READ_CACHE: Lazy<Cache<PathBuf, Vec<u8>>> = Lazy::new(|| Cache::new(10_000));
+
+    let path = path.as_ref().canonicalize()?;
+    match READ_CACHE.get(path.as_path()) {
+        Some(content) => Ok(content),
+        None => {
+            let content = fs::read(path.as_path())?;
+            READ_CACHE.insert(path, content.clone());
+            Ok(content)
+        }
+    }
+}
+
+pub fn read_to_string(path: impl AsRef<Path>) -> Result<String> {
+    let content = read(path)?;
+    String::from_utf8(content).map_err(|_| {
+        Error::new(
+            std::io::ErrorKind::InvalidData,
+            "The contents of the file are not valid UTF8",
+        )
+    })
+}
+
+pub fn read_dir(path: impl AsRef<Path>) -> Result<Box<dyn Iterator<Item = Result<PathBuf>>>> {
+    static READ_DIR_CACHE: Lazy<Cache<PathBuf, Vec<PathBuf>>> = Lazy::new(|| Cache::new(10_000));
+
+    let path = path.as_ref().canonicalize()?;
+    match READ_DIR_CACHE.get(path.as_path()) {
+        Some(entries) => Ok(Box::new(entries.into_iter().map(Ok)) as Box<_>),
+        None => {
+            let entries = fs::read_dir(path.as_path())?
+                .flat_map(|maybe_entry| maybe_entry.map(|entry| entry.path()))
+                .collect();
+            READ_DIR_CACHE.insert(path.clone(), entries);
+            Ok(read_dir(path).unwrap())
+        }
+    }
+}