feat: Implement LDAP bind/whoami

vendor/dn_escape/src/lib.rs

@@ -0,0 +1,69 @@
+// CODE DEVELOPED BY THE LDAP3 PROJECT, UNDER MIT LICENSE.
+
+use std::borrow::Cow;
+
+/// Escape an attribute value in a relative distinguished name (RDN).
+///
+/// When a literal string is used to represent an attribute value in an RDN,
+/// some of its characters might need to be escaped according to the rules
+/// of [RFC 4514](https://tools.ietf.org/html/rfc4514).
+///
+/// The function is named `dn_escape()` instead of `rdn_escape()` because of
+/// a long-standing association of its intended use with the handling of DNs.
+///
+/// The argument, `val`, can be owned or borrowed. The function doesn't
+/// allocate the return value unless there's need to escape the input.
+pub fn dn_escape<'a, S: Into<Cow<'a, str>>>(val: S) -> Cow<'a, str> {
+    #[inline]
+    fn always_escape(c: u8) -> bool {
+        c == b'"'
+            || c == b'+'
+            || c == b','
+            || c == b';'
+            || c == b'<'
+            || c == b'='
+            || c == b'>'
+            || c == b'\\'
+            || c == 0
+    }
+
+    #[inline]
+    fn escape_leading(c: u8) -> bool {
+        c == b' ' || c == b'#'
+    }
+
+    #[inline]
+    fn escape_trailing(c: u8) -> bool {
+        c == b' '
+    }
+
+    #[inline]
+    fn xdigit(c: u8) -> u8 {
+        c + if c < 10 { b'0' } else { b'a' - 10 }
+    }
+
+    let val = val.into();
+    let mut output = None;
+    for (i, &c) in val.as_bytes().iter().enumerate() {
+        if always_escape(c)
+            || i == 0 && escape_leading(c)
+            || i + 1 == val.len() && escape_trailing(c)
+        {
+            if output.is_none() {
+                output = Some(Vec::with_capacity(val.len() + 12)); // guess: up to 4 escaped chars
+                output.as_mut().unwrap().extend(val[..i].as_bytes());
+            }
+            let output = output.as_mut().unwrap();
+            output.push(b'\\');
+            output.push(xdigit(c >> 4));
+            output.push(xdigit(c & 0xF));
+        } else if let Some(ref mut output) = output {
+            output.push(c);
+        }
+    }
+    if let Some(output) = output {
+        Cow::Owned(String::from_utf8(output).expect("dn escaped"))
+    } else {
+        val
+    }
+}