1 files changed, 94 insertions, 0 deletions
diff --git a/cli/text_encoding.rs b/cli/text_encoding.rs
new file mode 100644
index 000000000..9d8e5bcc9
--- /dev/null
+++ b/cli/text_encoding.rs
@@ -0,0 +1,94 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+use encoding_rs::*;
+use std::{
+  borrow::Cow,
+  io::{Error, ErrorKind},
+};
+
+/// Attempts to detect the character encoding of the provided bytes.
+///
+/// Supports UTF-8, UTF-16 Little Endian and UTF-16 Big Endian.
+pub fn detect_charset(bytes: &'_ [u8]) -> &'static str {
+  const UTF16_LE_BOM: &[u8] = b"\xFF\xFE";
+  const UTF16_BE_BOM: &[u8] = b"\xFE\xFF";
+
+  if bytes.starts_with(UTF16_LE_BOM) {
+    "utf-16le"
+  } else if bytes.starts_with(UTF16_BE_BOM) {
+    "utf-16be"
+  } else {
+    // Assume everything else is utf-8
+    "utf-8"
+  }
+}
+
+/// Attempts to convert the provided bytes to a UTF-8 string.
+///
+/// Supports all encodings supported by the encoding_rs crate, which includes
+/// all encodings specified in the WHATWG Encoding Standard, and only those
+/// encodings (see: https://encoding.spec.whatwg.org/).
+pub fn convert_to_utf8<'a>(
+  bytes: &'a [u8],
+  charset: &'_ str,
+) -> Result<Cow<'a, str>, Error> {
+  match Encoding::for_label(charset.as_bytes()) {
+    Some(encoding) => encoding
+      .decode_without_bom_handling_and_without_replacement(bytes)
+      .ok_or_else(|| ErrorKind::InvalidData.into()),
+    None => Err(Error::new(
+      ErrorKind::InvalidInput,
+      format!("Unsupported charset: {}", charset),
+    )),
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  fn test_detection(test_data: &[u8], expected_charset: &str) {
+    let detected_charset = detect_charset(test_data);
+    assert_eq!(
+      expected_charset.to_lowercase(),
+      detected_charset.to_lowercase()
+    );
+  }
+
+  #[test]
+  fn test_detection_utf8_no_bom() {
+    let test_data = "Hello UTF-8 it is \u{23F0} for Deno!"
+      .to_owned()
+      .into_bytes();
+    test_detection(&test_data, "utf-8");
+  }
+
+  #[test]
+  fn test_detection_utf16_little_endian() {
+    let test_data = b"\xFF\xFEHello UTF-16LE".to_owned().to_vec();
+    test_detection(&test_data, "utf-16le");
+  }
+
+  #[test]
+  fn test_detection_utf16_big_endian() {
+    let test_data = b"\xFE\xFFHello UTF-16BE".to_owned().to_vec();
+    test_detection(&test_data, "utf-16be");
+  }
+
+  #[test]
+  fn test_decoding_unsupported_charset() {
+    let test_data = Vec::new();
+    let result = convert_to_utf8(&test_data, "utf-32le");
+    assert!(result.is_err());
+    let err = result.expect_err("Err expected");
+    assert!(err.kind() == ErrorKind::InvalidInput);
+  }
+
+  #[test]
+  fn test_decoding_invalid_utf8() {
+    let test_data = b"\xFE\xFE\xFF\xFF".to_vec();
+    let result = convert_to_utf8(&test_data, "utf-8");
+    assert!(result.is_err());
+    let err = result.expect_err("Err expected");
+    assert!(err.kind() == ErrorKind::InvalidData);
+  }
+}