From b7c5b4e13c7c0de42a11c1b6ff291ac4a00d4f26 Mon Sep 17 00:00:00 2001
From: Daniel Sharifi <daniel.sharifi@dfinity.org>
Date: Fri, 24 Jan 2025 17:15:08 +0100
Subject: [PATCH] feat: add const try_from_str constructor to DnsName type.

---
 src/server_name.rs | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/server_name.rs b/src/server_name.rs
index ced1554..997a226 100644
--- a/src/server_name.rs
+++ b/src/server_name.rs
@@ -204,6 +204,14 @@ impl<'a> DnsName<'a> {
             Err(_) => Err(s),
         }
     }
+
+    /// Produces a borrowed [`DnsName`] from a borrowed [`str`].
+    pub const fn try_from_str(s: &str) -> Result<DnsName<'_>, InvalidDnsNameError> {
+        match validate(s.as_bytes()) {
+            Ok(_) => Ok(DnsName(DnsNameInner::Borrowed(s))),
+            Err(_) => Err(InvalidDnsNameError),
+        }
+    }
 }
 
 #[cfg(feature = "alloc")]
@@ -300,7 +308,7 @@ impl fmt::Display for InvalidDnsNameError {
 #[cfg(feature = "std")]
 impl StdError for InvalidDnsNameError {}
 
-fn validate(input: &[u8]) -> Result<(), InvalidDnsNameError> {
+const fn validate(input: &[u8]) -> Result<(), InvalidDnsNameError> {
     enum State {
         Start,
         Next,
@@ -323,7 +331,9 @@ fn validate(input: &[u8]) -> Result<(), InvalidDnsNameError> {
         return Err(InvalidDnsNameError);
     }
 
-    for ch in input {
+    let mut character_index = 0;
+    while character_index < input.len() {
+        let ch = input[character_index];
         state = match (state, ch) {
             (Start | Next | NextAfterNumericOnly | Hyphen { .. }, b'.') => {
                 return Err(InvalidDnsNameError)
@@ -349,6 +359,7 @@ fn validate(input: &[u8]) -> Result<(), InvalidDnsNameError> {
             ) => Subsequent { len: len + 1 },
             _ => return Err(InvalidDnsNameError),
         };
+        character_index += 1;
     }
 
     if matches!(