[PATCH 2/2] lua: fix error handling in getpwall and getgrall

[Alexander Turenko]

This commit fixes app-tap/pwd.test.lua test. It seems that the problem
appears after updating to glibc-2.28.

Related to #3766.
---
 src/lua/pwd.lua | 43 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/src/lua/pwd.lua b/src/lua/pwd.lua
index 8f17951df..0a6b73395 100644
--- a/src/lua/pwd.lua
+++ b/src/lua/pwd.lua
@@ -158,22 +158,52 @@ local function getpw(uid)
     return user
 end
 
+-- It seems glibc developers threat POSIX in the following way.
+-- {set,get,end}pwent() and {set,get,end}grent() functions can set
+-- errno to non-zero value that is not listed in the standard in
+-- case of success. Errno should be checked after get{pw,gr}ent
+-- only when it returns a non-NULL value.
+--
+-- https://sourceware.org/bugzilla/show_bug.cgi?id=1969
+-- https://sourceware.org/bugzilla/show_bug.cgi?id=23737
+
+local pwent_grent_errno_list = {
+    errno.EINTR,
+    errno.EIO,
+    errno.EMFILE,
+    errno.ENFILE,
+}
+
+local function is_pwent_grent_errno(e)
+    for _, v in ipairs(pwent_grent_errno_list) do
+        if e == v then
+            return true
+        end
+    end
+    return false
+end
+
 local function getpwall()
     errno(0)
     ffi.C.setpwent()
-    if errno() ~= 0 then
+    if is_pwent_grent_errno(errno()) then
         return nil
     end
     local pws = {}
     while true do
+        errno(0)
         local pw = ffi.C.getpwent()
         if pw == nil then
+            if is_pwent_grent_errno(errno()) then
+                return nil
+            end
             break
         end
         table.insert(pws, getpw(pw.pw_uid))
     end
+    errno(0)
     ffi.C.endpwent()
-    if errno() ~= 0 then
+    if is_pwent_grent_errno(errno()) then
         return nil
     end
     return pws
@@ -182,19 +212,24 @@ end
 local function getgrall()
     errno(0)
     ffi.C.setgrent()
-    if errno() ~= 0 then
+    if is_pwent_grent_errno(errno()) then
         return nil
     end
     local grs = {}
     while true do
+        errno(0)
         local gr = ffi.C.getgrent()
         if gr == nil then
+            if is_pwent_grent_errno(errno()) then
+                return nil
+            end
             break
         end
         table.insert(grs, getpw(gr.gr_gid))
     end
+    errno(0)
     ffi.C.endgrent()
-    if errno() ~= 0 then
+    if is_pwent_grent_errno(errno()) then
         return nil
     end
     return grs
-- 
2.19.2