bugfix: ngx.re.gmatch might loop infinitely when the pattern matches an empty string. thanks Lance Li and xingxing for tracking this issue down.

Author: agentzh

src/ngx_http_lua_regex.c

@@ -944,7 +944,11 @@ ngx_http_lua_ngx_re_gmatch_iterator(lua_State *L)
     }
 
     offset = cap[1];
-    if (offset == (ssize_t) subj.len) {
+    if (offset == cap[0]) {
+        offset++;
+    }
+
+    if (offset >= (ssize_t) subj.len) {
         offset = -1;
 
         if (!(ctx->flags & NGX_LUA_RE_COMPILE_ONCE)) {

t/035-gmatch.t

@@ -486,3 +486,27 @@ sr failed: 500
 --- error_log
 attempt to use ngx.re.gmatch iterator in a request that did not create it
 
+
+
+=== TEST 20: gmatch (empty matched string)
+--- config
+    location /re {
+        content_by_lua '
+            for m in ngx.re.gmatch("hello", "a|") do
+                if m then
+                    ngx.say("matched: [", m[0], "]")
+                else
+                    ngx.say("not matched: ", m)
+                end
+            end
+        ';
+    }
+--- request
+    GET /re
+--- response_body
+matched: []
+matched: []
+matched: []
+matched: []
+matched: []
+