Re: [PATCH 03/18] gathdlc: add mechansim to detect '+++' escape sequence

[Denis Kenzior <denkenz@gmail.com>]

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Hi Guillaume,

On 03/25/2011 10:25 AM, Guillaume Zajac wrote:
> ---
>  gatchat/gathdlc.c |  114 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 114 insertions(+), 0 deletions(-)
> 
> diff --git a/gatchat/gathdlc.c b/gatchat/gathdlc.c
> index 7c45454..21e4533 100644
> --- a/gatchat/gathdlc.c
> +++ b/gatchat/gathdlc.c
> @@ -50,6 +50,13 @@
>  
>  #define HDLC_FCS(fcs, c) crc_ccitt_byte(fcs, c)
>  
> +/* Amount of fiftieths of second to detect '+++'.
> + * Range is 0 to 0xff.
> + */
> +#define ESC_TIME 	0x32

Where is this coming from?  Is this supposed to be controlled by an
S-register?  If so, you might want to use a proper variable for this.

> +
> +#define GUARD_TIMEOUTS	1000	/* Pause time before and after '+++' sequence */
> +

This seems redundant to the ESC_TIME timeout...

>  struct _GAtHDLC {
>  	gint ref_count;
>  	GAtIO *io;
> @@ -68,6 +75,12 @@ struct _GAtHDLC {
>  	gboolean in_read_handler;
>  	gboolean destroyed;
>  	gboolean no_carrier_detect;
> +	GAtSuspendFunc suspend_func;
> +	gpointer suspend_data;
> +	guint cmpt;
> +	guint suspend_timeout;
> +	guint pause_timeout;

You never clean up these g_sources (e.g. in the case where GAtHDLC is
forcefully removed).  This is a big no no in a library, you must clean
up after yourself in all cases.

I would also replace the suspend_timeout with a GTimer directly.

> +	gboolean paused;
>  };
>  
>  static void hdlc_record(int fd, gboolean in, guint8 *data, guint16 length)
> @@ -130,6 +143,47 @@ guint32 g_at_hdlc_get_recv_accm(GAtHDLC *hdlc)
>  	return hdlc->recv_accm;
>  }
>  
> +void g_at_hdlc_set_suspend_function(GAtHDLC *hdlc, GAtSuspendFunc func,
> +							gpointer user_data)
> +{
> +	if (hdlc == NULL)
> +		return;
> +
> +	hdlc->suspend_func = func;
> +	hdlc->suspend_data = user_data;
> +}
> +
> +static gboolean paused_timeout_cb(gpointer user_data)
> +{
> +	GAtHDLC *hdlc = user_data;
> +
> +	hdlc->paused = TRUE;
> +
> +	return FALSE;
> +}
> +
> +static gboolean susp_timeout_cb(gpointer user_data)
> +{
> +	GAtHDLC *hdlc = user_data;
> +
> +	hdlc->cmpt = 0;
> +
> +	return FALSE;
> +}
> +
> +static gboolean hdlc_suspend(gpointer user_data)
> +{
> +	GAtHDLC *hdlc = user_data;
> +
> +	g_at_io_set_write_handler(hdlc->io, NULL, NULL);
> +	g_at_io_set_read_handler(hdlc->io, NULL, NULL);
> +
> +	if (hdlc->suspend_func)
> +		hdlc->suspend_func(hdlc->suspend_data);
> +
> +	return FALSE;
> +}
> +
>  static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
>  {
>  	GAtHDLC *hdlc = user_data;
> @@ -142,6 +196,13 @@ static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
>  
>  	hdlc->in_read_handler = TRUE;
>  
> +	/*
> +	 * We delete the the paused_timeout_cb or hdlc_suspend as soons as
> +	 * we read a data.
> +	 */
> +	if (hdlc->pause_timeout > 0)
> +		g_source_remove(hdlc->pause_timeout);
> +
>  	while (pos < len) {
>  		/*
>  		 * We try to detect NO CARRIER conditions here.  We
> @@ -153,6 +214,21 @@ static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
>  				hdlc->decode_offset == 0 && *buf == '\r')
>  			break;
>  
> +		/*
> +		 * If there was no character for 1 second we try to detect
> +		 * the '+' character to suspend data call if 3 '+' are
> +		 * detected in less than 20 * ESC_TIME milliseconds.
> +		 */
> +		if (*buf == '+' && hdlc->paused) {
> +			if (hdlc->cmpt == 0)
> +				hdlc->suspend_timeout = g_timeout_add (20 * ESC_TIME,
> +							susp_timeout_cb, hdlc);
> +			hdlc->cmpt++;
> +		} else {
> +			hdlc->cmpt = 0;
> +			hdlc->paused = FALSE;
> +		}
> +
>  		if (hdlc->decode_escape == TRUE) {
>  			unsigned char val = *buf ^ HDLC_TRANS;
>  
> @@ -190,6 +266,9 @@ static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
>  		}
>  	}
>  
> +	if (hdlc->cmpt == 3)
> +		goto suspend;
> +
>  out:
>  	ring_buffer_drain(rbuf, pos);
>  
> @@ -197,6 +276,37 @@ out:
>  
>  	if (hdlc->destroyed)
>  		g_free(hdlc);
> +
> +	/*
> +	 * If there were no data pause for GUARD_TIMEOUTS ms,
> +	 * we try again to check it.
> +	 */
> +	if (!hdlc->paused)
> +		hdlc->pause_timeout = g_timeout_add (GUARD_TIMEOUTS,
> +							paused_timeout_cb,
> +							hdlc);
> +
> +	return;
> +
> +suspend:
> +	/*
> +	 * If the suspend timeout still exists,
> +	 * delete it.
> +	 */
> +	if (hdlc->suspend_timeout > 0)
> +		g_source_remove(hdlc->suspend_timeout);
> +
> +	/*
> +	 * Restart the counter and reset the ring buffer.
> +	 */
> +	hdlc->cmpt = 0;
> +	ring_buffer_reset(rbuf);

This sounds like a really bad idea.  What are you trying to accomplish here?

> +
> +	/*
> +	 * Wait for another pause of GUARD_TIMEOUTS ms before returning to command mode.
> +	 */
> +	hdlc->paused = FALSE;
> +	hdlc->pause_timeout = g_timeout_add (GUARD_TIMEOUTS, hdlc_suspend, hdlc);
>  }
>  
>  GAtHDLC *g_at_hdlc_new_from_io(GAtIO *io)
> @@ -245,6 +355,10 @@ GAtHDLC *g_at_hdlc_new_from_io(GAtIO *io)
>  	hdlc->io = g_at_io_ref(io);
>  	g_at_io_set_read_handler(hdlc->io, new_bytes, hdlc);
>  
> +	hdlc->cmpt = 0;
> +
> +	hdlc->paused = FALSE;
> +

In general it isn't necessary to initialize variables to zero since we
use g_try_new0 which zeros the structure already.

>  	return hdlc;
>  
>  error:

Regards,
-Denis