From a6f3e61d7070a195a87128974ed916b3a4bc2602 Mon Sep 17 00:00:00 2001
From: John Thacker <johnthacker@gmail.com>
Date: Wed, 11 Oct 2023 09:07:41 -0400
Subject: [PATCH] wsutil: Add a reverse mempbrk function

---
 packaging/debian/libwsutil0.symbols |  1 +
 wsutil/ws_mempbrk.c                 | 15 +++++++++++++++
 wsutil/ws_mempbrk.h                 |  5 +++++
 3 files changed, 21 insertions(+)

diff --git a/packaging/debian/libwsutil0.symbols b/packaging/debian/libwsutil0.symbols
index 07aa526dd9..f3aab23b3e 100644
--- a/packaging/debian/libwsutil0.symbols
+++ b/packaging/debian/libwsutil0.symbols
@@ -491,6 +491,7 @@ libwsutil.so.0 libwsutil0 #MINVER#
  ws_mempbrk_compile@Base 1.99.4
  ws_mempbrk_exec@Base 1.99.4
  ws_memrchr@Base 4.3.0rc0
+ ws_memrpbrk_exec@Base 4.3.0rc0
  ws_optarg@Base 3.5.1
  ws_opterr@Base 3.5.1
  ws_optind@Base 3.5.1
diff --git a/wsutil/ws_mempbrk.c b/wsutil/ws_mempbrk.c
index f3f99b7167..55334242f8 100644
--- a/wsutil/ws_mempbrk.c
+++ b/wsutil/ws_mempbrk.c
@@ -72,6 +72,21 @@ ws_mempbrk_exec(const uint8_t* haystack, size_t haystacklen, const ws_mempbrk_pa
     return ws_mempbrk_portable_exec(haystack, haystacklen, pattern, found_needle);
 }
 
+WS_DLL_PUBLIC const uint8_t *
+ws_memrpbrk_exec(const uint8_t* haystack, size_t haystacklen, const ws_mempbrk_pattern* pattern, unsigned char *found_needle)
+{
+    const uint8_t *haystack_end = haystack + haystacklen;
+
+    while (haystack_end > haystack) {
+        if (pattern->patt[*(--haystack_end)]) {
+            if (found_needle)
+                *found_needle = *haystack_end;
+            return haystack_end;
+        }
+    }
+
+    return NULL;
+}
 
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
diff --git a/wsutil/ws_mempbrk.h b/wsutil/ws_mempbrk.h
index 7aff505f81..210fdfcedf 100644
--- a/wsutil/ws_mempbrk.h
+++ b/wsutil/ws_mempbrk.h
@@ -34,4 +34,9 @@ WS_DLL_PUBLIC void ws_mempbrk_compile(ws_mempbrk_pattern* pattern, const char *n
  */
 WS_DLL_PUBLIC const uint8_t *ws_mempbrk_exec(const uint8_t* haystack, size_t haystacklen, const ws_mempbrk_pattern* pattern, unsigned char *found_needle);
 
+/** Scan for the needles specified by the compiled pattern, starting at the
+ * end of the haystack and working backwards.
+ */
+WS_DLL_PUBLIC const uint8_t *ws_memrpbrk_exec(const uint8_t* haystack, size_t haystacklen, const ws_mempbrk_pattern* pattern, unsigned char *found_needle);
+
 #endif /* __WS_MEMPBRK_H__ */