Re: [PATCH] xgethostname: handle long hostnames

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

David Turner wrote:

> If the full hostname doesn't fit in the buffer supplied to
> gethostname, POSIX does not specify whether the buffer will be
> null-terminated, so to be safe, we should do it ourselves.
[...]
> +++ b/wrapper.c
> @@ -655,3 +655,16 @@ void sleep_millisec(int millisec)
>  {
>  	poll(NULL, 0, millisec);
>  }
> +
> +int xgethostname(char *buf, size_t len)
> +{
> +	/*
> +	 * If the full hostname doesn't fit in buf, POSIX does not
> +	 * specify whether the buffer will be null-terminated, so to
> +	 * be safe, do it ourselves.
> +	 */
> +	int ret = gethostname(buf, len);
> +	if (!ret)
> +		buf[len - 1] = 0;
> +	return ret;

I wonder if after null-terminating we would want to report this as
an error, instead of silently using a truncated result.  I.e. something
like

> +	if (!ret)
> +		buf[len - 1] = 0;
> +	if (strlen(buf) >= len - 1) {
> +		errno = ENAMETOOLONG;
> +		return -1;
> +	}

(or EINVAL --- either is equally descriptive).

Also POSIX requires that hostnames are <= 255 bytes.  Maybe we can
force the buffer to be large enough.

Thoughts?
Jonathan