1 files changed, 106 insertions, 0 deletions
diff --git a/ext/node/ops/buffer.rs b/ext/node/ops/buffer.rs
index 74a011ab8..01f878ec1 100644
--- a/ext/node/ops/buffer.rs
+++ b/ext/node/ops/buffer.rs
@@ -1,5 +1,7 @@
 // Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
 
+use deno_core::anyhow::anyhow;
+use deno_core::anyhow::Result;
 use deno_core::op2;
 
 #[op2(fast)]
@@ -11,3 +13,107 @@ pub fn op_is_ascii(#[buffer] buf: &[u8]) -> bool {
 pub fn op_is_utf8(#[buffer] buf: &[u8]) -> bool {
   std::str::from_utf8(buf).is_ok()
 }
+
+#[op2]
+#[buffer]
+pub fn op_transcode(
+  #[buffer] source: &[u8],
+  #[string] from_encoding: &str,
+  #[string] to_encoding: &str,
+) -> Result<Vec<u8>> {
+  match (from_encoding, to_encoding) {
+    ("utf8", "ascii") => Ok(utf8_to_ascii(source)),
+    ("utf8", "latin1") => Ok(utf8_to_latin1(source)),
+    ("utf8", "utf16le") => utf8_to_utf16le(source),
+    ("utf16le", "utf8") => utf16le_to_utf8(source),
+    ("latin1", "utf16le") | ("ascii", "utf16le") => {
+      Ok(latin1_ascii_to_utf16le(source))
+    }
+    (from, to) => Err(anyhow!("Unable to transcode Buffer {from}->{to}")),
+  }
+}
+
+fn latin1_ascii_to_utf16le(source: &[u8]) -> Vec<u8> {
+  let mut result = Vec::with_capacity(source.len() * 2);
+  for &byte in source {
+    result.push(byte);
+    result.push(0);
+  }
+  result
+}
+
+fn utf16le_to_utf8(source: &[u8]) -> Result<Vec<u8>> {
+  let ucs2_vec: Vec<u16> = source
+    .chunks(2)
+    .map(|chunk| u16::from_le_bytes([chunk[0], chunk[1]]))
+    .collect();
+  String::from_utf16(&ucs2_vec)
+    .map(|utf8_string| utf8_string.into_bytes())
+    .map_err(|e| anyhow!("Invalid UTF-16 sequence: {}", e))
+}
+
+fn utf8_to_utf16le(source: &[u8]) -> Result<Vec<u8>> {
+  let utf8_string = std::str::from_utf8(source)?;
+  let ucs2_vec: Vec<u16> = utf8_string.encode_utf16().collect();
+  let bytes: Vec<u8> = ucs2_vec.iter().flat_map(|&x| x.to_le_bytes()).collect();
+  Ok(bytes)
+}
+
+fn utf8_to_latin1(source: &[u8]) -> Vec<u8> {
+  let mut latin1_bytes = Vec::with_capacity(source.len());
+  let mut i = 0;
+  while i < source.len() {
+    match source[i] {
+      byte if byte <= 0x7F => {
+        // ASCII character
+        latin1_bytes.push(byte);
+        i += 1;
+      }
+      byte if (0xC2..=0xDF).contains(&byte) && i + 1 < source.len() => {
+        // 2-byte UTF-8 sequence
+        let codepoint =
+          ((byte as u16 & 0x1F) << 6) | (source[i + 1] as u16 & 0x3F);
+        latin1_bytes.push(if codepoint <= 0xFF {
+          codepoint as u8
+        } else {
+          b'?'
+        });
+        i += 2;
+      }
+      _ => {
+        // 3-byte or 4-byte UTF-8 sequence, or invalid UTF-8
+        latin1_bytes.push(b'?');
+        // Skip to the next valid UTF-8 start byte
+        i += 1;
+        while i < source.len() && (source[i] & 0xC0) == 0x80 {
+          i += 1;
+        }
+      }
+    }
+  }
+  latin1_bytes
+}
+
+fn utf8_to_ascii(source: &[u8]) -> Vec<u8> {
+  let mut ascii_bytes = Vec::with_capacity(source.len());
+  let mut i = 0;
+  while i < source.len() {
+    match source[i] {
+      byte if byte <= 0x7F => {
+        // ASCII character
+        ascii_bytes.push(byte);
+        i += 1;
+      }
+      _ => {
+        // Non-ASCII character
+        ascii_bytes.push(b'?');
+        // Skip to the next valid UTF-8 start byte
+        i += 1;
+        while i < source.len() && (source[i] & 0xC0) == 0x80 {
+          i += 1;
+        }
+      }
+    }
+  }
+  ascii_bytes
+}