Correct TXT sort order on unlikely edge cases

[dnssec-prover] / src / rr.rs

diff --git a/src/rr.rs b/src/rr.rs
index 14826e3d1e00c53c76b691e4c06ef9ed762dd791..41c0ee2df8d13ff8dcd6de0f667db01d3e9fe805 100644 (file)
--- a/src/rr.rs
+++ b/src/rr.rs
@@ -7,7 +7,7 @@ use alloc::vec::Vec;
 use alloc::string::String;
 use alloc::borrow::ToOwned;
 
-use core::cmp::Ordering;
+use core::cmp::{self, Ordering};
 
 use crate::ser::*;
 
@@ -171,8 +171,18 @@ pub struct Txt {
 impl PartialOrd for Txt {
        fn partial_cmp(&self, o: &Txt) -> Option<Ordering> {
                Some(self.name.cmp(&o.name)
-                       .then_with(|| self.data.len().cmp(&o.data.len()))
-                       .then_with(|| self.data.cmp(&o.data)))
+                       .then_with(|| {
+                               // Compare in wire encoding form, i.e. compare in 255-byte chunks
+                               for i in 1..(self.data.len() / 255) + 2 {
+                                       let start = (i - 1)*255;
+                                       let self_len = cmp::min(i * 255, self.data.len());
+                                       let o_len = cmp::min(i * 255, o.data.len());
+                                       let slice_cmp = self_len.cmp(&o_len)
+                                               .then_with(|| self.data[start..self_len].cmp(&o.data[start..o_len]));
+                                       if !slice_cmp.is_eq() { return slice_cmp; }
+                               }
+                               Ordering::Equal
+                       }))
        }
 }
 impl StaticRecord for Txt {