fix(runtime): lossy utf8 readTextFile (#14456)

cli/tests/unit/files_test.ts

@@ -791,3 +791,19 @@ Deno.test(
     assertEquals(res, "hello world!");
   },
 );
+
+Deno.test(
+  { permissions: { read: true, write: true } },
+  async function readTextFileNonUtf8() {
+    const path = await Deno.makeTempFile();
+    const file = await Deno.open(path, { write: true });
+    await file.write(new TextEncoder().encode("hello "));
+    await file.write(new Uint8Array([0xC0]));
+    file.close();
+
+    const res = await Deno.readTextFile(path);
+    const resSync = Deno.readTextFileSync(path);
+    assertEquals(res, resSync);
+    assertEquals(res, "hello \uFFFD");
+  },
+);

runtime/ops/fs.rs

@@ -21,6 +21,7 @@ use deno_crypto::rand::Rng;
 use log::debug;
 use serde::Deserialize;
 use serde::Serialize;
+use std::borrow::Cow;
 use std::cell::RefCell;
 use std::convert::From;
 use std::env::{current_dir, set_current_dir, temp_dir};
@@ -2032,7 +2033,7 @@ fn op_readfile_text_sync(
   let permissions = state.borrow_mut::<Permissions>();
   let path = Path::new(&path);
   permissions.read.check(path)?;
-  Ok(std::fs::read_to_string(path)?)
+  Ok(string_from_utf8_lossy(std::fs::read(path)?))
 }
 
 #[op]
@@ -2075,7 +2076,7 @@ async fn op_readfile_text_async(
   }
   let fut = tokio::task::spawn_blocking(move || {
     let path = Path::new(&path);
-    Ok(String::from_utf8(std::fs::read(path)?)?)
+    Ok(string_from_utf8_lossy(std::fs::read(path)?))
   });
   if let Some(cancel_rid) = cancel_rid {
     let cancel_handle = state
@@ -2088,3 +2089,14 @@ async fn op_readfile_text_async(
   }
   fut.await?
 }
+
+// Like String::from_utf8_lossy but operates on owned values
+fn string_from_utf8_lossy(buf: Vec<u8>) -> String {
+  match String::from_utf8_lossy(&buf) {
+    // buf contained non-utf8 chars than have been patched
+    Cow::Owned(s) => s,
+    // SAFETY: if Borrowed then the buf only contains utf8 chars,
+    // we do this instead of .into_owned() to avoid copying the input buf
+    Cow::Borrowed(_) => unsafe { String::from_utf8_unchecked(buf) },
+  }
+}