hameg-hmo: Avoid getting stuck upon SCPI timeouts.

Correctly set the length of the buffer used to hold the SCPI response
from the device containing the binary acquisition data.

If a timeout occurs, truncate the buffer and send the partial response
from the device instead of getting stuck on timeouts!

Thanks to Stefan Brüns for reviewing the first version of this patch
and spotting out a serious problem with it.

This fixes bug #1323.

diff --git a/src/scpi/scpi.c b/src/scpi/scpi.c
index 31f82a3f912351c2bc653bb66dfed90f6e61a6db..2477cf2323971c314880c3bc235732fd076c0af3 100644 (file)
--- a/src/scpi/scpi.c
+++ b/src/scpi/scpi.c
@@ -961,6 +961,7 @@ SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
 {
        int ret;
        GString* response;
+       gsize oldlen;
        char buf[10];
        long llen;
        long datalen;
@@ -990,14 +991,14 @@ SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
        *scpi_response = NULL;
 
        /* Get (the first chunk of) the response. */
-       while (response->len < 2) {
+       do {
                ret = scpi_read_response(scpi, response, timeout);
                if (ret < 0) {
                        g_mutex_unlock(&scpi->scpi_mutex);
                        g_string_free(response, TRUE);
                        return ret;
                }
-       }
+       } while (response->len < 2);
 
        /*
         * SCPI protocol data blocks are preceeded with a length spec.
@@ -1044,25 +1045,33 @@ SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
        g_string_erase(response, 0, 2 + llen);
 
        /*
-        * If the initially assumed length does not cover the data block
-        * length, then re-allocate the buffer size to the now known
-        * length, and keep reading more chunks of response data.
+        * Re-allocate the buffer size to the now known length
+        * and keep reading more chunks of response data.
         */
-       if (response->len < (unsigned long)(datalen)) {
-               int oldlen = response->len;
-               g_string_set_size(response, datalen);
-               g_string_set_size(response, oldlen);
-       }
-
-       while (response->len < (unsigned long)(datalen)) {
-               ret = scpi_read_response(scpi, response, timeout);
-               if (ret < 0) {
-                       g_mutex_unlock(&scpi->scpi_mutex);
-                       g_string_free(response, TRUE);
-                       return ret;
-               }
-               if (ret > 0)
-                       timeout = g_get_monotonic_time() + scpi->read_timeout_us;
+       oldlen = response->len;
+       g_string_set_size(response, datalen);
+       g_string_set_size(response, oldlen);
+
+       if (oldlen < (unsigned long)(datalen)) {
+               do {
+                       oldlen = response->len;
+                       ret = scpi_read_response(scpi, response, timeout);
+
+                       /* On timeout truncate the buffer and send the partial response
+                        * instead of getting stuck on timeouts...
+                        */
+                       if (ret == SR_ERR_TIMEOUT) {
+                               datalen = oldlen;
+                               break;
+                       }
+                       if (ret < 0) {
+                               g_mutex_unlock(&scpi->scpi_mutex);
+                               g_string_free(response, TRUE);
+                               return ret;
+                       }
+                       if (ret > 0)
+                               timeout = g_get_monotonic_time() + scpi->read_timeout_us;
+               } while (response->len < (unsigned long)(datalen));
        }
 
        g_mutex_unlock(&scpi->scpi_mutex);