Match the public and private APIs for content reading (#386)

`wnfs` changes:
- Made the length param optional and renamed the offset param to match the public side.
- Copied the doc test from the public side to the private side.
- Made it so that `PrivateFile.get_content` uses its `read_at` method.
- Added `PublicFile.get_content` to reflect the private side.
- Made `PrivateFile.read_at` take `byte_offset` as `u64` instead of `usize`

`wnfs-wasm` changes:
- Added `PrivateFile.read_at`
- Made it so that `PrivateFile.get_content` uses its `read_at` method.
- Added `PublicFile.get_content`
- Adjusted tests to use new and changed methods.

---

* refactor: (wnfs) make PrivateFile.read_at's length param an option to reflect the public side

* refactor: `get_content` should use `read_at` and add `get_content` to `PublicFile`

* feat: (wnfs-wasm) add `read_at` to `PrivateFile` and add `get_content` to `PublicFile`

* refactor: (wnfs) use u64 type for block indexes

* fix: (wnfs-wasm) adjust to new `read_at` `byte_offset` param type

* Apply suggestions from code review

Co-authored-by: Philipp Krüger <philipp.krueger1@gmail.com>
Signed-off-by: Steven Vandevelde <steven.vandevelde@hey.com>

* refactor: make `offset` a `u64` in `can_read_section_of_file`

* fix: remove unstable let expression

---------

Signed-off-by: Steven Vandevelde <steven.vandevelde@hey.com>
Co-authored-by: Philipp Krüger <philipp.krueger1@gmail.com>

wnfs-wasm/src/fs/private/file.rs

@@ -9,7 +9,7 @@ use crate::{
     value,
 };
 use chrono::{DateTime, Utc};
-use js_sys::{Date, Promise, Uint8Array};
+use js_sys::{Date, Number, Promise, Uint8Array};
 use std::rc::Rc;
 use wasm_bindgen::{prelude::wasm_bindgen, JsValue};
 use wasm_bindgen_futures::future_to_promise;
@@ -86,23 +86,40 @@ impl PrivateFile {
     /// Gets the entire content of a file.
     #[wasm_bindgen(js_name = "getContent")]
     pub fn get_content(&self, forest: &PrivateForest, store: BlockStore) -> JsResult<Promise> {
+        self.read_at(value!(0).into(), None, forest, store)
+    }
+
+    /// Gets the metadata of this file.
+    pub fn metadata(&self) -> JsResult<JsValue> {
+        JsMetadata(self.0.get_metadata()).try_into()
+    }
+
+    /// Gets the content of the file at given offset & with an optional byte limit.
+    #[wasm_bindgen(js_name = "readAt")]
+    pub fn read_at(
+        &self,
+        byte_offset: Number,
+        limit: Option<Number>,
+        forest: &PrivateForest,
+        store: BlockStore,
+    ) -> JsResult<Promise> {
         let file = Rc::clone(&self.0);
         let store = ForeignBlockStore(store);
         let forest = Rc::clone(&forest.0);
 
+        let byte_offset = f64::from(byte_offset) as u64;
+        let limit = limit.map(|lim| f64::from(lim) as usize);
+
         Ok(future_to_promise(async move {
-            let content = file
-                .get_content(&forest, &store)
+            let result = file
+                .read_at(byte_offset, limit, &forest, &store)
                 .await
-                .map_err(error("Cannot get content of file"))?;
+                .map_err(error("Cannot read file"))?;
 
-            Ok(value!(Uint8Array::from(content.as_slice())))
-        }))
-    }
+            let uint8array = Uint8Array::from(result.as_ref());
 
-    /// Gets the metadata of this file.
-    pub fn metadata(&self) -> JsResult<JsValue> {
-        JsMetadata(self.0.get_metadata()).try_into()
+            Ok(value!(uint8array))
+        }))
     }
 
     /// Gets a unique id for node.

wnfs-wasm/src/fs/public/file.rs

@@ -89,6 +89,12 @@ impl PublicFile {
         arr
     }
 
+    /// Gets the entire content of a file.
+    #[wasm_bindgen(js_name = "getContent")]
+    pub fn get_content(&self, store: BlockStore) -> JsResult<Promise> {
+        self.read_at(value!(0).into(), None, store)
+    }
+
     /// Gets the metadata of this file.
     pub fn metadata(&self) -> JsResult<JsValue> {
         JsMetadata(self.0.get_metadata()).try_into()