More disciplined use of 'errno'

Set errno to zero before calling any function where we may use its
errno, and check errno for zero before using it (as functions may not
set it even in error). The code assumes that no function will put
garbage on errno (although ISO C allows that): If any function during an
operation set errno, and the operation result in an error, assume that
errno has something to say.

1 files changed, 12 insertions, 4 deletions

diff --git a/lauxlib.c b/lauxlib.c
index fec834d3..d742fd27 100644
--- a/lauxlib.c
+++ b/lauxlib.c
@@ -249,11 +249,13 @@ LUALIB_API int luaL_fileresult (lua_State *L, int stat, const char *fname) {
     return 1;
   }
   else {
+    const char *msg;
     luaL_pushfail(L);
+    msg = (en != 0) ? strerror(en) : "(no extra info)";
     if (fname)
-      lua_pushfstring(L, "%s: %s", fname, strerror(en));
+      lua_pushfstring(L, "%s: %s", fname, msg);
     else
-      lua_pushstring(L, strerror(en));
+      lua_pushstring(L, msg);
     lua_pushinteger(L, en);
     return 3;
   }
@@ -750,9 +752,12 @@ static const char *getF (lua_State *L, void *ud, size_t *size) {
 
 
 static int errfile (lua_State *L, const char *what, int fnameindex) {
-  const char *serr = strerror(errno);
+  int err = errno;
   const char *filename = lua_tostring(L, fnameindex) + 1;
-  lua_pushfstring(L, "cannot %s %s: %s", what, filename, serr);
+  if (err != 0)
+    lua_pushfstring(L, "cannot %s %s: %s", what, filename, strerror(err));
+  else
+    lua_pushfstring(L, "cannot %s %s", what, filename);
   lua_remove(L, fnameindex);
   return LUA_ERRFILE;
 }
@@ -805,6 +810,7 @@ LUALIB_API int luaL_loadfilex (lua_State *L, const char *filename,
   }
   else {
     lua_pushfstring(L, "@%s", filename);
+    errno = 0;
     lf.f = fopen(filename, "r");
     if (lf.f == NULL) return errfile(L, "open", fnameindex);
   }
@@ -814,6 +820,7 @@ LUALIB_API int luaL_loadfilex (lua_State *L, const char *filename,
   if (c == LUA_SIGNATURE[0]) {  /* binary file? */
     lf.n = 0;  /* remove possible newline */
     if (filename) {  /* "real" file? */
+      errno = 0;
       lf.f = freopen(filename, "rb", lf.f);  /* reopen in binary mode */
       if (lf.f == NULL) return errfile(L, "reopen", fnameindex);
       skipcomment(lf.f, &c);  /* re-read initial portion */
@@ -823,6 +830,7 @@ LUALIB_API int luaL_loadfilex (lua_State *L, const char *filename,
     lf.buff[lf.n++] = c;  /* 'c' is the first character of the stream */
   status = lua_load(L, getF, &lf, lua_tostring(L, -1), mode);
   readstatus = ferror(lf.f);
+  errno = 0;  /* no useful error number until here */
   if (filename) fclose(lf.f);  /* close file (even in case of errors) */
   if (readstatus) {
     lua_settop(L, fnameindex);  /* ignore results from 'lua_load' */