fix substraction overflow

Cargo.toml

@@ -2,7 +2,7 @@
 name = "nettext"
 description = "A text-based data format for cryptographic network protocols"
 authors = ["Alex Auvolat <alex@adnab.me>"]
-version = "0.3.2"
+version = "0.3.3"
 edition = "2021"
 license = "AGPL-3.0"
 readme = "README.md"

src/switch64.rs

@@ -32,7 +32,10 @@ pub fn encode(bytes: &[u8], allow_whitespace: bool) -> Vec<u8> {
         // We stop at the first position where we find three consecutive
         // characters to encode as-is
         let mut b64end = bytes.len();
-        for i in pos..bytes.len() - 3 {
+        for i in pos..bytes.len() {
+            if i + 3 > bytes.len() {
+                break;
+            }
             if bytes[i..i + 3]
                 .iter()
                 .all(|c| is_valid_plaintext_char(*c, allow_whitespace))