About the format type specifiers

[Maxim Dounin]

Hello!

On Tue, Jul 24, 2012 at 03:34:39PM +0800, 姚伟斌 wrote:

> 1. The type of 'ngx_msec_int_t', from the source code, It's defined like this:
> 
> typedef ngx_int_t   ngx_rbtree_key_int_t;
> typedef ngx_rbtree_key_int_t  ngx_msec_int_t;
> 
> So It should be an ngx_int_t.
> 
> In the file of ngx_http_log_module.c, It appears like this:
> 
> static u_char *
> ngx_http_log_request_time(ngx_http_request_t *r, u_char *buf,
>     ngx_http_log_op_t *op)
> {
>     ngx_time_t      *tp;
>     ngx_msec_int_t   ms;
> 
>     tp = ngx_timeofday();
> 
>     ms = (ngx_msec_int_t)
>              ((tp->sec - r->start_sec) * 1000 + (tp->msec - r->start_msec));
>     ms = ngx_max(ms, 0);
> 
>     return ngx_sprintf(buf, "%T.%03M", ms / 1000, ms % 1000);
> }

In case of ngx_msec_int_t it's almost always possible to use %M 
which has identical size, as it's only used for intermediate 
computations and ensured to be non-negative.  (Note the 
ngx_max(ms, 0) call in the code above.)

> 2. The type of '' ngx_gid_t" and "ngx_uid_t", from the source code.
> They are defined like this:
> 
>  typedef uid_t  ngx_uid_t;
>  typedef gid_t  ngx_gid_t;
> 
> And I googled [1][2] about the types of uid_t and gid_t and They seem
> to unsigned integer.

Just a side note: no, POSIX doesn't define signedness of 
uid_t/gid_t.  It only says they should be "integer types", see
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_types.h.html.

> 
> In the file of ngx_process_cycle.c, it appears like this:
> 
>     if (geteuid() == 0) {
>         if (setgid(ccf->group) == -1) {
>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>                           "setgid(%d) failed", ccf->group);
>             /* fatal */
>             exit(2);
>         }
> 
>         if (initgroups(ccf->username, ccf->group) == -1) {
>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>                           "initgroups(%s, %d) failed",
>                           ccf->username, ccf->group);
>         }
> 
>         if (setuid(ccf->user) == -1) {
>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>                           "setuid(%d) failed", ccf->user);
>             /* fatal */
>             exit(2);
>         }
>     }
> 
> I want to know the correct format specifiers with ngx_msec_int_t,
> uid_t and gid_t. I'm a little confused with above codes.

See above for ngx_msec_int_t.  Most safe way to print 
ngx_uint_t/ngx_gid_t is probably to do so with intermediate cast 
to some defined big-enough type.

Strictly speaking the above code isn't correct and might print 
garbage on some platforms.  It probably worth adding explicit 
casts to int.

Maxim Dounin