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

6 files changed, 120 insertions, 86 deletions

diff --git a/lib/multi.c b/lib/multi.c
index e1325f029..8e4091687 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -1801,9 +1801,17 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
         result = Curl_speedcheck(data, now);
 
       if(( (data->set.max_send_speed == 0) ||
-           (data->progress.ulspeed < data->set.max_send_speed))  &&
+           (Curl_pgrsLimitWaitTime(data->progress.uploaded,
+                                   data->progress.ul_limit_size,
+                                   data->set.max_send_speed,
+                                   data->progress.ul_limit_start,
+                                   now) <= 0))  &&
          ( (data->set.max_recv_speed == 0) ||
-           (data->progress.dlspeed < data->set.max_recv_speed)))
+           (Curl_pgrsLimitWaitTime(data->progress.downloaded,
+                                   data->progress.dl_limit_size,
+                                   data->set.max_recv_speed,
+                                   data->progress.dl_limit_start,
+                                   now) <= 0)))
         multistate(data, CURLM_STATE_PERFORM);
       break;
 
@@ -1814,35 +1822,31 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
       bool comeback = FALSE;
 
       /* check if over send speed */
-      if((data->set.max_send_speed > 0) &&
-         (data->progress.ulspeed > data->set.max_send_speed)) {
-        int buffersize;
-
-        multistate(data, CURLM_STATE_TOOFAST);
-
-        /* calculate upload rate-limitation timeout. */
-        buffersize = (int)(data->set.buffer_size ?
-                           data->set.buffer_size : BUFSIZE);
-        timeout_ms = Curl_sleep_time(data->set.max_send_speed,
-                                     data->progress.ulspeed, buffersize);
-        Curl_expire_latest(data, timeout_ms);
-        break;
+      if(data->set.max_send_speed > 0) {
+        timeout_ms = Curl_pgrsLimitWaitTime(data->progress.uploaded,
+                                            data->progress.ul_limit_size,
+                                            data->set.max_send_speed,
+                                            data->progress.ul_limit_start,
+                                            now);
+        if(timeout_ms > 0) {
+          multistate(data, CURLM_STATE_TOOFAST);
+          Curl_expire_latest(data, timeout_ms);
+          break;
+        }
       }
 
       /* check if over recv speed */
-      if((data->set.max_recv_speed > 0) &&
-         (data->progress.dlspeed > data->set.max_recv_speed)) {
-        int buffersize;
-
-        multistate(data, CURLM_STATE_TOOFAST);
-
-        /* Calculate download rate-limitation timeout. */
-        buffersize = (int)(data->set.buffer_size ?
-                           data->set.buffer_size : BUFSIZE);
-        timeout_ms = Curl_sleep_time(data->set.max_recv_speed,
-                                     data->progress.dlspeed, buffersize);
-        Curl_expire_latest(data, timeout_ms);
-        break;
+      if(data->set.max_recv_speed > 0) {
+        timeout_ms = Curl_pgrsLimitWaitTime(data->progress.downloaded,
+                                            data->progress.dl_limit_size,
+                                            data->set.max_recv_speed,
+                                            data->progress.dl_limit_start,
+                                            now);
+        if(timeout_ms > 0) {
+          multistate(data, CURLM_STATE_TOOFAST);
+          Curl_expire_latest(data, timeout_ms);
+          break;
+        }
       }
 
       /* read/write data if it is ready to do so */
diff --git a/lib/progress.c b/lib/progress.c
index 760ca1cc3..0f67ef250 100644
--- a/lib/progress.c
+++ b/lib/progress.c
@@ -216,18 +216,93 @@ void Curl_pgrsStartNow(struct Curl_easy *data)
 {
   data->progress.speeder_c = 0; /* reset the progress meter display */
   data->progress.start = Curl_tvnow();
+  data->progress.ul_limit_start.tv_sec = 0;
+  data->progress.ul_limit_start.tv_usec = 0;
+  data->progress.dl_limit_start.tv_sec = 0;
+  data->progress.dl_limit_start.tv_usec = 0;
   /* clear all bits except HIDE and HEADERS_OUT */
   data->progress.flags &= PGRS_HIDE|PGRS_HEADERS_OUT;
 }
 
+/*
+ * This is used to handle speed limits, calculating how much milliseconds we
+ * need to wait until we're back under the speed limit, if needed.
+ *
+ * The way it works is by having a "starting point" (time & amount of data
+ * transfered by then) used in the speed computation, to be used instead of the
+ * start of the transfer.
+ * This starting point is regularly moved as transfer goes on, to keep getting
+ * accurate values (instead of average over the entire tranfer).
+ *
+ * This function takes the current amount of data transfered, the amount at the
+ * starting point, the limit (in bytes/s), the time of the starting point and
+ * the current time.
+ *
+ * Returns -1 if no waiting is needed (not enough data transfered since
+ * starting point yet), 0 when no waiting is needed but the starting point
+ * should be reset (to current), or the number of milliseconds to wait to get
+ * back under the speed limit.
+ */
+long Curl_pgrsLimitWaitTime(curl_off_t cursize,
+                            curl_off_t startsize,
+                            curl_off_t limit,
+                            struct timeval start,
+                            struct timeval now)
+{
+    curl_off_t size = cursize - startsize;
+    long minimum, actual;
+
+    /* we don't have a starting point yet -- return 0 so it gets (re)set */
+    if(start.tv_sec == 0 && start.tv_usec == 0)
+        return 0;
+
+    /* not enough data yet */
+    if(size < limit)
+      return -1;
+
+    minimum = (long) (CURL_OFF_T_C(1000) * size / limit);
+    actual = Curl_tvdiff(now, start);
+
+    if(actual < minimum)
+      return minimum - actual;
+    else
+      return 0;
+}
+
 void Curl_pgrsSetDownloadCounter(struct Curl_easy *data, curl_off_t size)
 {
+  struct timeval now = Curl_tvnow();
+
   data->progress.downloaded = size;
+
+  /* download speed limit */
+  if((data->set.max_recv_speed > 0) &&
+     (Curl_pgrsLimitWaitTime(data->progress.downloaded,
+                             data->progress.dl_limit_size,
+                             data->set.max_recv_speed,
+                             data->progress.dl_limit_start,
+                             now) == 0)) {
+    data->progress.dl_limit_start = now;
+    data->progress.dl_limit_size = size;
+  }
 }
 
 void Curl_pgrsSetUploadCounter(struct Curl_easy *data, curl_off_t size)
 {
+  struct timeval now = Curl_tvnow();
+
   data->progress.uploaded = size;
+
+  /* upload speed limit */
+  if((data->set.max_send_speed > 0) &&
+     (Curl_pgrsLimitWaitTime(data->progress.uploaded,
+                             data->progress.ul_limit_size,
+                             data->set.max_send_speed,
+                             data->progress.ul_limit_start,
+                             now) == 0)) {
+    data->progress.ul_limit_start = now;
+    data->progress.ul_limit_size = size;
+  }
 }
 
 void Curl_pgrsSetDownloadSize(struct Curl_easy *data, curl_off_t size)
diff --git a/lib/progress.h b/lib/progress.h
index a77b7ce59..155ff04fe 100644
--- a/lib/progress.h
+++ b/lib/progress.h
@@ -49,7 +49,11 @@ void Curl_pgrsSetUploadCounter(struct Curl_easy *data, curl_off_t size);
 int Curl_pgrsUpdate(struct connectdata *);
 void Curl_pgrsResetTimesSizes(struct Curl_easy *data);
 void Curl_pgrsTime(struct Curl_easy *data, timerid timer);
-
+long Curl_pgrsLimitWaitTime(curl_off_t cursize,
+                            curl_off_t startsize,
+                            curl_off_t limit,
+                            struct timeval start,
+                            struct timeval now);
 
 /* Don't show progress for sizes smaller than: */
 #define LEAST_SIZE_PROGRESS BUFSIZE
diff --git a/lib/transfer.c b/lib/transfer.c
index e4a2835f8..5d5ee6be0 100644
--- a/lib/transfer.c
+++ b/lib/transfer.c
@@ -1264,60 +1264,6 @@ int Curl_single_getsock(const struct connectdata *conn,
   return bitmap;
 }
 
-/*
- * Determine optimum sleep time based on configured rate, current rate,
- * and packet size.
- * Returns value in milliseconds.
- *
- * The basic idea is to adjust the desired rate up/down in this method
- * based on whether we are running too slow or too fast.  Then, calculate
- * how many milliseconds to wait for the next packet to achieve this new
- * rate.
- */
-long Curl_sleep_time(curl_off_t rate_bps, curl_off_t cur_rate_bps,
-                             int pkt_size)
-{
-  curl_off_t min_sleep = 0;
-  curl_off_t rv = 0;
-
-  if(rate_bps == 0)
-    return 0;
-
-  /* If running faster than about .1% of the desired speed, slow
-   * us down a bit.  Use shift instead of division as the 0.1%
-   * cutoff is arbitrary anyway.
-   */
-  if(cur_rate_bps > (rate_bps + (rate_bps >> 10))) {
-    /* running too fast, decrease target rate by 1/64th of rate */
-    rate_bps -= rate_bps >> 6;
-    min_sleep = 1;
-  }
-  else if(cur_rate_bps < (rate_bps - (rate_bps >> 10))) {
-    /* running too slow, increase target rate by 1/64th of rate */
-    rate_bps += rate_bps >> 6;
-  }
-
-  /* Determine number of milliseconds to wait until we do
-   * the next packet at the adjusted rate.  We should wait
-   * longer when using larger packets, for instance.
-   */
-  rv = ((curl_off_t)(pkt_size * 1000) / rate_bps);
-
-  /* Catch rounding errors and always slow down at least 1ms if
-   * we are running too fast.
-   */
-  if(rv < min_sleep)
-    rv = min_sleep;
-
-  /* Bound value to fit in 'long' on 32-bit platform.  That's
-   * plenty long enough anyway!
-   */
-  if(rv > 0x7fffffff)
-    rv = 0x7fffffff;
-
-  return (long)rv;
-}
-
 /* Curl_init_CONNECT() gets called each time the handle switches to CONNECT
    which means this gets called once for each subsequent redirect etc */
 void Curl_init_CONNECT(struct Curl_easy *data)
diff --git a/lib/transfer.h b/lib/transfer.h
index 0058f8c86..518967260 100644
--- a/lib/transfer.h
+++ b/lib/transfer.h
@@ -64,8 +64,5 @@ Curl_setup_transfer (struct connectdata *data,
                curl_off_t *writecountp /* return number of bytes written */
 );
 
-long Curl_sleep_time(curl_off_t rate_bps, curl_off_t cur_rate_bps,
-                     int pkt_size);
-
 #endif /* HEADER_CURL_TRANSFER_H */
 
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 ];