From bb6e2c4f4cae46a3875bb97d418f9f602aa95449 Mon Sep 17 00:00:00 2001
From: Razvan Dimescu <ssaricu@gmail.com>
Date: Fri, 10 Apr 2026 02:05:18 +0300
Subject: [PATCH] test: cover label cap and empty-label rollback; trim doc
 comments

Closes coverage gaps left by PR #54:

- write_rejects_label_over_63_bytes: pins the incremental 63-byte cap
  inside write_qname's inner loop (boundary at 63 vs 64).
- write_skips_empty_labels: pins the rollback branch (pos = len_pos)
  triggered by leading or consecutive dots.

Doc comments tightened:

- write_qname: drop the streaming-impl walkthrough and the escape-grammar
  restatement (already documented on read_qname).
- name_to_wire: drop the implementation explanation; keep the
  post-escape lowercasing rationale, which pins behavior a future
  refactor could silently break.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/buffer.rs | 32 +++++++++++++++++++++++++-------
 src/dnssec.rs | 10 +++-------
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/src/buffer.rs b/src/buffer.rs
index 2308813..4e954c9 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -180,13 +180,7 @@ impl BytePacketBuffer {
     }
 
     /// Write a qname in wire format, parsing RFC 1035 §5.1 text escapes.
-    ///
-    /// Dots are label separators unless escaped as `\.`. `\\` yields a literal
-    /// backslash, and `\DDD` (three decimal digits) yields an arbitrary byte.
-    ///
-    /// Streams directly into the buffer by reserving a length byte, writing
-    /// the label body, then backpatching the length. Zero intermediate
-    /// allocations on the common path.
+    /// See `read_qname` for the escape grammar.
     pub fn write_qname(&mut self, qname: &str) -> Result<()> {
         if qname.is_empty() || qname == "." {
             self.write_u8(0)?;
@@ -368,6 +362,19 @@ mod tests {
         assert_eq!(&buf.buf[..buf.pos], b"\x04\x00foo\x03com\x00");
     }
 
+    #[test]
+    fn write_skips_empty_labels() {
+        // Leading dot — first (empty) label is rolled back.
+        let mut buf = BytePacketBuffer::new();
+        buf.write_qname(".foo.com").unwrap();
+        assert_eq!(&buf.buf[..buf.pos], b"\x03foo\x03com\x00");
+
+        // Consecutive dots — middle empty label is rolled back.
+        let mut buf = BytePacketBuffer::new();
+        buf.write_qname("foo..com").unwrap();
+        assert_eq!(&buf.buf[..buf.pos], b"\x03foo\x03com\x00");
+    }
+
     #[test]
     fn write_rejects_out_of_range_decimal_escape() {
         let mut buf = BytePacketBuffer::new();
@@ -386,6 +393,17 @@ mod tests {
         assert!(buf.write_qname("\\1").is_err());
     }
 
+    #[test]
+    fn write_rejects_label_over_63_bytes() {
+        // 64 bytes exceeds the wire-format label cap.
+        let mut buf = BytePacketBuffer::new();
+        assert!(buf.write_qname(&"a".repeat(64)).is_err());
+
+        // 63 bytes is the maximum permitted label length.
+        let mut buf = BytePacketBuffer::new();
+        assert!(buf.write_qname(&"a".repeat(63)).is_ok());
+    }
+
     #[test]
     fn roundtrip_preserves_dot_in_label() {
         assert_eq!(write_then_read("exa\\.mple.com"), "exa\\.mple.com");
diff --git a/src/dnssec.rs b/src/dnssec.rs
index 8da1e6c..8614810 100644
--- a/src/dnssec.rs
+++ b/src/dnssec.rs
@@ -722,14 +722,10 @@ pub fn verify_ds(ds: &DnsRecord, dnskey: &DnsRecord, owner: &str) -> bool {
 // -- Canonical wire format --
 
 /// Encode a DNS name in canonical wire form per RFC 4034 §6.2:
-/// uncompressed, with all ASCII letters lowercased.
+/// uncompressed, with ASCII letters lowercased.
 ///
-/// Label parsing and RFC 1035 §5.1 escape handling live in
-/// `BytePacketBuffer::write_qname`; this function then walks the emitted
-/// wire bytes once to lowercase label bodies (length bytes stay untouched).
-/// Lowercasing has to happen post-escape-resolution because a decimal
-/// escape like `\065` yields `'A'`, which canonical form must convert
-/// to `'a'`.
+/// Lowercasing happens *after* escape resolution because `\065` yields
+/// `'A'`, which canonical form must convert to `'a'`.
 pub fn name_to_wire(name: &str) -> Vec<u8> {
     let mut buf = BytePacketBuffer::new();
     buf.write_qname(name)