From d7d933e8a458949043c0ab713e95fb0b6359ba79 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20S=C3=A1=20de=20Mello?= <codasm@pm.me>
Date: Thu, 20 Aug 2026 08:19:02 +0100
Subject: [PATCH] Fix Token::from_encoded accepting a double tilde as valid

The escaped-tilde branch set `escaped = true` unconditionally, so a
`~` following an already-open escape (e.g. the second `~` in "~~0")
was treated as re-opening the escape instead of being rejected. This
let safe code build a PointerBuf via Token::from_encoded that
Pointer::parse then refused on the same bytes.

Fixes #128
---
 CHANGELOG.md |  8 ++++++++
 src/token.rs | 12 +++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a3daeb..6331e79 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+-   Fixed `Token::from_encoded` accepting a `~` immediately followed by
+    another `~` (e.g. `"~~0"`) as valid, letting safe code build a
+    `PointerBuf` that `Pointer::parse` then rejected on the same bytes. A `~`
+    must now always be followed by `0` or `1`. Resolves
+    [#128](https://github.com/chanced/jsonptr/issues/128).
+
 ## [0.8.1] 2026-07-26
 
 ### Added
diff --git a/src/token.rs b/src/token.rs
index 5d68f34..5aeb0cb 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -85,7 +85,7 @@ impl<'a> Token<'a> {
                         source: InvalidEncoding::Slash,
                     })
                 }
-                ENC_PREFIX => {
+                ENC_PREFIX if !escaped => {
                     escaped = true;
                 }
                 TILDE_ENC | SLASH_ENC if escaped => {
@@ -575,6 +575,16 @@ mod tests {
                 source: InvalidEncoding::Tilde
             }
         );
+        // https://github.com/chanced/jsonptr/issues/128
+        let err = Token::from_encoded("~~0").unwrap_err();
+        assert_eq!(
+            err,
+            EncodingError {
+                offset: 1,
+                source: InvalidEncoding::Tilde
+            }
+        );
+
         let sub = String::from("a~");
         let err = Token::from_encoded(&sub).unwrap_err();
         let labels: Vec<_> = err.labels(&sub).unwrap().collect();