Fix up is binary & sync_lib docs & tests

backend/sync_lib/src/lib.rs

@@ -6,53 +6,57 @@ use wasm_bindgen::prelude::*;
 
 pub mod errors;
 
+/// Encode binary data for easy transport over HTTP. Inverse of
+/// `base64_to_bytes`.
 #[wasm_bindgen(js_name = bytesToBase64)]
 pub fn bytes_to_base64(input: &[u8]) -> String { STANDARD_NO_PAD.encode(input) }
 
-#[wasm_bindgen(js_name = stringToBase64)]
-pub fn string_to_base64(input: &str) -> String { bytes_to_base64(input.as_bytes()) }
-
+/// Inverse of `bytes_to_base64`.
 #[wasm_bindgen(js_name = base64ToBytes)]
 pub fn base64_to_bytes(input: &str) -> Result<Vec<u8>, SyncLibError> {
     STANDARD_NO_PAD.decode(input).map_err(SyncLibError::from)
 }
 
-#[wasm_bindgen(js_name = base64ToString)]
-pub fn base64_to_string(input: &str) -> Result<String, SyncLibError> {
-    let bytes = base64_to_bytes(input)?;
-    String::from_utf8(bytes).map_err(SyncLibError::from)
-}
-
+/// Merge two documents with a common parent. Relies on `reconcile::reconcile`
+/// for texts and returns the right document as-is if either of the updated
+/// documents is binary.
 #[wasm_bindgen]
-pub fn merge(parent: &[u8], left: &[u8], right: &[u8]) -> Result<Vec<u8>, SyncLibError> {
-    Ok(if is_binary(right) {
+pub fn merge(parent: &[u8], left: &[u8], right: &[u8]) -> Vec<u8> {
+    if is_binary(parent) || is_binary(left) || is_binary(right) {
         right.to_vec()
     } else {
         reconcile::reconcile(
-            str::from_utf8(parent).map_err(SyncLibError::from)?,
-            str::from_utf8(left).map_err(SyncLibError::from)?,
-            str::from_utf8(right).map_err(SyncLibError::from)?,
+            str::from_utf8(parent).expect("parent must be valid UTF-8 because it's not binary"),
+            str::from_utf8(left).expect("left must be valid UTF-8 because it's not binary"),
+            str::from_utf8(right).expect("right must be valid UTF-8 because it's not binary"),
         )
         .into_bytes()
-    })
+    }
 }
 
+/// WASM wrapper around `reconcile::reconcile` for text merging.
 #[wasm_bindgen(js_name = mergeText)]
 pub fn merge_text(parent: &str, left: &str, right: &str) -> String {
     reconcile::reconcile(parent, left, right)
 }
 
+/// Heuristically determine if the given data is a binary or a text file's
+/// content.
 #[wasm_bindgen(js_name = isBinary)]
-pub fn is_binary(data: &[u8]) -> bool { std::str::from_utf8(data).is_ok() }
+pub fn is_binary(data: &[u8]) -> bool {
+    if data.iter().any(|&b| b == 0) {
+        // Even though the NUL character is valid in UTF-8, it's highly suspicious in
+        // human-readable text.
+        return true;
+    }
 
+    std::str::from_utf8(data).is_err()
+}
+
+/// Set up panic hook for better error messages in the browser console.
 #[cfg(feature = "console_error_panic_hook")]
 #[wasm_bindgen(js_name = setPanicHook)]
 pub fn set_panic_hook() {
-    // When the `console_error_panic_hook` feature is enabled, we can call the
-    // `set_panic_hook` function at least once during initialization, and then
-    // we will get better error messages if our code ever panics.
-    //
-    // For more details see
     // https://github.com/rustwasm/console_error_panic_hook#readme
     console_error_panic_hook::set_once();
 }