From 95b5e8c90811faea610304431a01a0d9131f3a3d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Puel?= <andrepuel@gmail.com>
Date: Sun, 4 Jul 2021 21:47:35 -0300
Subject: [PATCH] Fixes the CRC32 calculation for FINGERPRINT

Added a golden-standard unit test for fingerprint calculation. The hardcoded expected value on the unit test was calculated using boost's C++ implementation of CRC32. This code was fixed by using CRC_32_ISO_HDLC algorithm on CRC calculation.
---
 crates/stun/src/fingerprint.rs                |  4 ++--
 .../stun/src/fingerprint/fingerprint_test.rs  | 21 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/crates/stun/src/fingerprint.rs b/crates/stun/src/fingerprint.rs
index 8b6816612..d3e39a0d3 100644
--- a/crates/stun/src/fingerprint.rs
+++ b/crates/stun/src/fingerprint.rs
@@ -6,7 +6,7 @@ use crate::checks::*;
 use crate::message::*;
 
 use anyhow::Result;
-use crc::{Crc, CRC_32_ISCSI};
+use crc::{Crc, CRC_32_ISO_HDLC};
 
 // FingerprintAttr represents FINGERPRINT attribute.
 //
@@ -31,7 +31,7 @@ const FINGERPRINT_SIZE: usize = 4; // 32 bit
 // the 32-bit value 0x5354554e (the XOR helps in cases where an
 // application packet is also using CRC-32 in it).
 pub fn fingerprint_value(b: &[u8]) -> u32 {
-    let checksum = Crc::<u32>::new(&CRC_32_ISCSI).checksum(b);
+    let checksum = Crc::<u32>::new(&CRC_32_ISO_HDLC).checksum(b);
     checksum ^ FINGERPRINT_XOR_VALUE // XOR
 }
 
diff --git a/crates/stun/src/fingerprint/fingerprint_test.rs b/crates/stun/src/fingerprint/fingerprint_test.rs
index 3ca879016..d3472b27a 100644
--- a/crates/stun/src/fingerprint/fingerprint_test.rs
+++ b/crates/stun/src/fingerprint/fingerprint_test.rs
@@ -3,6 +3,27 @@ use crate::textattrs::TextAttribute;
 
 use crate::attributes::ATTR_SOFTWARE;
 
+#[test]
+fn fingerprint_uses_crc_32_iso_hdlc() -> Result<()> {
+    let mut m = Message::new();
+
+    let a = TextAttribute {
+        attr: ATTR_SOFTWARE,
+        text: "software".to_owned(),
+    };
+    a.add_to(&mut m)?;
+    m.write_header();
+
+    FINGERPRINT.add_to(&mut m)?;
+    m.write_header();
+
+    assert_eq!(&m.raw[0..m.raw.len()-8], b"\x00\x00\x00\x14\x21\x12\xA4\x42\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x22\x00\x08\x73\x6F\x66\x74\x77\x61\x72\x65");
+
+    assert_eq!(m.raw[m.raw.len() - 4..], [0xe4, 0x4c, 0x33, 0xd9]);
+
+    Ok(())
+}
+
 #[test]
 fn test_fingerprint_check() -> Result<()> {
     let mut m = Message::new();