confused about ngx_write_file

[Ruslan Ermilov]

On Mon, Nov 20, 2017 at 02:59:39AM -0500, hook wrote:
> Hi 
>     I'm writing some module with using ngx_write_file.  I found file's
> offset is incorrect, in this case:
>     ```
>     u_char  av = 0x01 | 0x04;
>     // file cur offset -> 4096;
>     ngx_write_file(file, &av, 1, 4)
>     ```
>     file->offset would be 4097, but real offset is 4096.

file->offset is only used for sequential read/write.  For other
cases, its value is undefined.

>     I'm confused with the codes :
> 192 ssize_t
> 193 ngx_write_file(ngx_file_t *file, u_char *buf, size_t size, off_t
> offset)
> 194 {
> ........
> 221
> 222         file->offset += n;
> 223         written += n;
> 224
> 225         if ((size_t) n == size) {
> 226             return written;
> 227         }
> 228
> 229         offset += n;
> 230         size -= n;
> 231     }
> 
>      should it be:
> 222         written += n;
> 223         offset += n;
> 224
> 225         if (offset > file->offset) {
> 226             file->offset = offset;
> 227         }
> 228
> 229         if ((size_t) n == size) {
> 230             return written;
> 231         }
> 232
> 233         size -= n;
> 234     }
> 
> 
> Thanks!
> 
> Posted at Nginx Forum: https://forum.nginx.org/read.php?2,277386,277386#msg-277386
> 
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-- 
Ruslan Ermilov
Assume stupidity not malice