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

[Alexander Turenko <alexander.turenko@tarantool.org>]

We had discussion with Vladimir and decided to remove errno checks when
a return value does not indicate possibility of an error.

The new patch is at bottom of the email.

WBR, Alexander Turenko.

On Mon, Dec 03, 2018 at 11:33:24AM +0300, Vladimir Davydov wrote:
> On Sun, Dec 02, 2018 at 06:57:32PM +0300, Alexander Turenko wrote:
> > 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.
> 
> s/threat/treat
> 

Removed the comment at all.

> > +-- {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.
> 
> Why do you need to check for specific error codes then?
> 

Discussed it with Vladimir and decided to check only get{pw,gr}ent()
only when they return NULL.

> > +--
> > +-- 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
> 
> According to the manual setpwent never fails in any visible to the user
> way so why check errno here?
> 

It does not stated explicitly in manual pages or POSIX, but it seems to
be in spirit of Unix APIs.

> >          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
> 
> Again, endpwent never fails. May be, remove this check altogether?
> 
> Same concerns setgrent and endgrent.

Done.

> 
> >          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

The new patch
-------------

commit d8a5e29ecfd486a3f998d4a41d8e0bb17463c27d
Author: Alexander Turenko <alexander.turenko@tarantool.org>
Date:   Sun Dec 2 17:58:09 2018 +0300

    lua: fix error handling in getpwall and getgrall
    
    This commit fixes app-tap/pwd.test.lua test. It seems that the problem
    appears after updating to glibc-2.28.
    
    It seems that usual way to handle errors in Unix is to check errno only
    when a return value indicates possibility of an error.
    
    Related to #3766.

diff --git a/src/lua/pwd.lua b/src/lua/pwd.lua
index 8f17951df..b2c8e121f 100644
--- a/src/lua/pwd.lua
+++ b/src/lua/pwd.lua
@@ -159,44 +159,37 @@ local function getpw(uid)
 end
 
 local function getpwall()
-    errno(0)
     ffi.C.setpwent()
-    if errno() ~= 0 then
-        return nil
-    end
     local pws = {}
     while true do
+        errno(0)
         local pw = ffi.C.getpwent()
         if pw == nil then
+            if errno() ~= 0 then
+                return nil
+            end
             break
         end
         table.insert(pws, getpw(pw.pw_uid))
     end
     ffi.C.endpwent()
-    if errno() ~= 0 then
-        return nil
-    end
     return pws
 end
 
 local function getgrall()
-    errno(0)
     ffi.C.setgrent()
-    if errno() ~= 0 then
-        return nil
-    end
     local grs = {}
     while true do
         local gr = ffi.C.getgrent()
         if gr == nil then
+            if errno() ~= 0 then
+                return nil
+            end
             break
         end
         table.insert(grs, getpw(gr.gr_gid))
     end
     ffi.C.endgrent()
-    if errno() ~= 0 then
-        return nil
-    end
     return grs
 end