Add documentation and make load safe

lib/runtime-core/src/cache.rs

@@ -29,16 +29,34 @@ pub enum Error {
     InvalidatedCache,
 }
 
+impl From<io::Error> for Error {
+    fn from(io_err: io::Error) -> Self {
+        Error::IoError(io_err)
+    }
+}
+
+/// The hash of a wasm module.
+/// 
+/// Used as a key when loading and storing modules in a [`Cache`].
+/// 
+/// [`Cache`]: trait.Cache.html
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct WasmHash([u8; 32]);
 
 impl WasmHash {
+    /// Hash a wasm module.
+    /// 
+    /// # Note: 
+    /// This does no verification that the supplied data
+    /// is, in fact, a wasm module.
     pub fn generate(wasm: &[u8]) -> Self {
         let mut array = [0u8; 32];
         array.copy_from_slice(Sha256::digest(wasm).as_slice());
         WasmHash(array)
     }
 
+    /// Create the hexadecimal representation of the
+    /// stored hash.
     pub fn encode(self) -> String {
         hex::encode(self.0)
     }
@@ -183,10 +201,13 @@ impl SerializedCache {
     }
 }
 
+/// A generic cache for storing and loading compiled wasm modules.
+/// 
+/// The `wasmer-runtime` supplies a naive `FileSystemCache` api.
 pub trait Cache {
     type LoadError;
     type StoreError;
 
-    unsafe fn load(&self, key: WasmHash) -> Result<Module, Self::LoadError>;
+    fn load(&self, key: WasmHash) -> Result<Module, Self::LoadError>;
     fn store(&mut self, module: Module) -> Result<WasmHash, Self::StoreError>;
 }

lib/runtime/src/cache.rs

@@ -91,12 +91,42 @@ use wasmer_runtime_core::cache::{Error as CacheError, SerializedCache};
 //     }
 // }
 
-pub struct FSCache {
+/// Representation of a directory that contains compiled wasm artifacts.
+///
+/// The `FileSystemCache` type implements the [`Cache`] trait, which allows it to be used
+/// generically when some sort of cache is required.
+///
+/// [`Cache`]: trait.Cache.html
+///
+/// # Usage:
+///
+/// ```rust
+/// use wasmer_runtime::cache::{Cache, FileSystemCache};
+///
+/// # use wasmer_runtime::{Module, error::CacheError};
+/// fn store_and_load_module(module: Module) -> Result<Module, CacheError> {
+///     // Create a new file system cache.
+///     // This is unsafe because we can't ensure that the artifact wasn't
+///     // corrupted or tampered with.
+///     let mut fs_cache = unsafe { FileSystemCache::new("some/directory/goes/here")? };
+///     // Store a module into the cache.
+///     // The returned `key` is equivalent to `module.info().wasm_hash`.
+///     let key = fs_cache.store(module)?;
+///     // Load the module back from the cache with the `key`.
+///     fs_cache.load(key)
+/// }
+/// ```
+pub struct FileSystemCache {
     path: PathBuf,
 }
 
-impl FSCache {
+impl FileSystemCache {
-    pub fn open<P: Into<PathBuf>>(path: P) -> io::Result<FSCache> {
+    /// Construct a new `FileSystemCache` around the specified directory.
+    ///
+    /// # Note:
+    /// This method is unsafe because there's no way to ensure the artifacts
+    /// stored in this cache haven't been corrupted or tampered with.
+    pub unsafe fn new<P: Into<PathBuf>>(path: P) -> io::Result<Self> {
         let path: PathBuf = path.into();
 
         if path.exists() {
@@ -129,17 +159,17 @@ impl FSCache {
     }
 }
 
-impl Cache for FSCache {
+impl Cache for FileSystemCache {
     type LoadError = CacheError;
     type StoreError = CacheError;
 
-    unsafe fn load(&self, key: WasmHash) -> Result<Module, CacheError> {
+    fn load(&self, key: WasmHash) -> Result<Module, CacheError> {
         let filename = key.encode();
         let mut new_path_buf = self.path.clone();
         new_path_buf.push(filename);
 
         let serialized_cache = SerializedCache::open(new_path_buf)?;
-        wasmer_runtime_core::load_cache_with(serialized_cache, super::default_compiler())
+        unsafe { wasmer_runtime_core::load_cache_with(serialized_cache, super::default_compiler()) }
     }
 
     fn store(&mut self, module: Module) -> Result<WasmHash, CacheError> {