Make plugin binary patch safe

I was attempting to build a conda package for openresty at work. Conda lets you install pre-compiled binary packages to user selected prefixes. For binaries, it patches the installed binaries to replace the hard coded old prefixes with new ones padded with a bunch of \x0.

This didn't work for my case because of the use of lua_pushliteral() which allows you to send null characters as part of the string. So at the end (after bin-patching), the package.path and package.cpath become:
<hard-coded-default-patched-for-new-prefix>\x0\x0...\x0<whatever-path-was-before>
and then the old path gets ignored by lua.

The following patch fixes this problem, but I am not sure if it is the right fix.

From cef7b49268e320df9130146455d3f99b71fe74dd Mon Sep 17 00:00:00 2001
From: Nehal J Wani <nehaljw.kkd1@gmail.com>
Date: Sat, 4 Apr 2020 10:36:15 -0400
Subject: [PATCH] Use LUA_DEFAULT_PATH and LUA_DEFAULT_CPATH in a bin patch
 safe manner

Change-Id: I09ae467182dc1b171778e296da9beda293b9e28e
---
 ngx_lua-0.10.15/src/ngx_http_lua_util.c        | 4 ++--
 ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/ngx_lua-0.10.15/src/ngx_http_lua_util.c b/ngx_lua-0.10.15/src/ngx_http_lua_util.c
index 88e9986..4e1e0c4 100644
--- a/ngx_lua-0.10.15/src/ngx_http_lua_util.c
+++ b/ngx_lua-0.10.15/src/ngx_http_lua_util.c
@@ -267,7 +267,7 @@ ngx_http_lua_new_state(lua_State *parent_vm, ngx_cycle_t *cycle,
                        "lua prepending default package.path with %s",
                        LUA_DEFAULT_PATH);

-        lua_pushliteral(L, LUA_DEFAULT_PATH ";"); /* package default */
+        lua_pushstring(L, LUA_DEFAULT_PATH ";"); /* package default */
         lua_getfield(L, -2, "path"); /* package default old */
         old_path = lua_tolstring(L, -1, &old_path_len);
         lua_concat(L, 2); /* package new */
@@ -280,7 +280,7 @@ ngx_http_lua_new_state(lua_State *parent_vm, ngx_cycle_t *cycle,
                        "lua prepending default package.cpath with %s",
                        LUA_DEFAULT_CPATH);

-        lua_pushliteral(L, LUA_DEFAULT_CPATH ";"); /* package default */
+        lua_pushstring(L, LUA_DEFAULT_CPATH ";"); /* package default */
         lua_getfield(L, -2, "cpath"); /* package default old */
         old_cpath = lua_tolstring(L, -1, &old_cpath_len);
         lua_concat(L, 2); /* package new */
diff --git a/ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c b/ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c
index 463938b..2d8deaa 100644
--- a/ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c
+++ b/ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c
@@ -249,7 +249,7 @@ ngx_stream_lua_new_state(lua_State *parent_vm, ngx_cycle_t *cycle,
                        "lua prepending default package.path with %s",
                        LUA_DEFAULT_PATH);

-        lua_pushliteral(L, LUA_DEFAULT_PATH ";"); /* package default */
+        lua_pushstring(L, LUA_DEFAULT_PATH ";"); /* package default */
         lua_getfield(L, -2, "path"); /* package default old */
         old_path = lua_tolstring(L, -1, &old_path_len);
         lua_concat(L, 2); /* package new */
@@ -262,7 +262,7 @@ ngx_stream_lua_new_state(lua_State *parent_vm, ngx_cycle_t *cycle,
                        "lua prepending default package.cpath with %s",
                        LUA_DEFAULT_CPATH);

-        lua_pushliteral(L, LUA_DEFAULT_CPATH ";"); /* package default */
+        lua_pushstring(L, LUA_DEFAULT_CPATH ";"); /* package default */
         lua_getfield(L, -2, "cpath"); /* package default old */
         old_cpath = lua_tolstring(L, -1, &old_cpath_len);
         lua_concat(L, 2); /* package new */
--
2.17.1

Review ngx_lua-0.10.15/src/ngx_http_lua_util.c and ngx_stream_lua-0.0.7/src/ngx_stream_lua_util.c, focusing on the ngx_*_lua_new_state functions where LUA_DEFAULT_PATH and LUA_DEFAULT_CPATH are pushed. Reproduce the prefix-patching scenario described in the issue and verify that package.path and package.cpath retain the existing path after patching. Done means confirming the safe behavior in both HTTP and stream implementations.