speed caps: not based on average speeds anymore

Speed limits (from CURLOPT_MAX_RECV_SPEED_LARGE &
CURLOPT_MAX_SEND_SPEED_LARGE) were applied simply by comparing limits
with the cumulative average speed of the entire transfer; While this
might work at times with good/constant connections, in other cases it
can result to the limits simply being "ignored" for more than "short
bursts" (as told in man page).

Consider a download that goes on much slower than the limit for some
time (because bandwidth is used elsewhere, server is slow, whatever the
reason), then once things get better, curl would simply ignore the limit
up until the average speed (since the beginning of the transfer) reached
the limit.  This could prove the limit useless to effectively avoid
using the entire bandwidth (at least for quite some time).

So instead, we now use a "moving starting point" as reference, and every
time at least as much as the limit as been transferred, we can reset
this starting point to the current position. This gets a good limiting
effect that applies to the "current speed" with instant reactivity (in
case of sudden speed burst).

Closes #971

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/urldata.h b/lib/urldata.h
index 1f4d2551e..3ac050b53 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1173,6 +1173,14 @@ struct Progress {
   struct timeval t_startsingle;
   struct timeval t_startop;
   struct timeval t_acceptdata;
+
+  /* upload speed limit */
+  struct timeval ul_limit_start;
+  curl_off_t ul_limit_size;
+  /* download speed limit */
+  struct timeval dl_limit_start;
+  curl_off_t dl_limit_size;
+
 #define CURR_TIME (5+1) /* 6 entries for 5 seconds */
 
   curl_off_t speeder[ CURR_TIME ];