Simplified quick_abort_pct code and improved its docs

CONTRIBUTORS

@@ -470,6 +470,7 @@ Thank you!
     Sergey Merzlikin <[email protected]>
     Sergio Durigan Junior <[email protected]>
     Sergio Rabellino <[email protected]>
+    Shailesh Vashishth <[email protected]>
     Shigechika Aikawa <[email protected]>
     Shmaya Frankel <[email protected]>
     Silamael <[email protected]>

doc/release-notes/release-7.sgml.in

@@ -194,6 +194,20 @@ This section gives an account of those changes in three categories:
 	<tag>external_acl_type</tag>
 	<p>Removed <em>%IDENT</em> format code with Ident protocol support.
 
+	<tag>quick_abort_pct</tag>
+	<p>Instead of ignoring <em>quick_abort_pct</em> settings that would,
+	together with other conditions, abort a pending download of a 99-byte or
+	smaller response, Squid now honors <em>quick_abort_pct</em> for all
+	response sizes. Most Squids are not going to be affected by this change
+	because default quick_abort_min settings (16KB) prevent aborts of 99-byte
+	responses even before <em>quick_abort_pct</em> is checked.
+	<p>Due to conversion from integer to floating point math, this change may
+	affect responses larger than 99 bytes as well, but these effects ought to
+	be limited to cases where the decision is based on a tiny difference (e.g.,
+	receiving 1% more bytes would have triggered full download). In most such
+	cases, the decision could probably go either way due to response header
+	size fluctuations anyway.
+
 </descrip>
 
 <sect1>Removed directives<label id="removeddirectives">

src/cf.data.pre

@@ -6626,16 +6626,14 @@ TYPE: int
 DEFAULT: 95
 LOC: Config.quickAbort.pct
 DOC_START
-	The cache by default continues downloading aborted requests
-	which are almost completed (less than 16 KB remaining). This
-	may be undesirable on slow (e.g. SLIP) links and/or very busy
-	caches.  Impatient users may tie up file descriptors and
-	bandwidth by repeatedly requesting and immediately aborting
-	downloads.
-
-	When the user aborts a request, Squid will check the
-	quick_abort values to the amount of data transferred until
-	then.
+	Continuing to download a cachable response after its request is aborted is
+	going to waste resources if the received response is not requested again.
+	On the other hand, aborting an in-progress download may effectively waste
+	(already spent) resources if the received cachable response is requested
+	again. Such waste is especially noticeable when, for example, impatient
+	users repeatedly request and then abort slow downloads. To balance these
+	trade-offs when a request is aborted during response download, Squid may
+	check quick_abort_* directives to decide whether to finish the retrieval:
 
 	If the transfer has less than 'quick_abort_min' KB remaining,
 	it will finish the retrieval.
@@ -6652,6 +6650,10 @@ DOC_START
 
 	If you want retrievals to always continue if they are being
 	cached set 'quick_abort_min' to '-1 KB'.
+
+	Many other conditions affect Squid decision to abort or continue download.
+	For example, Squid continues to download responses that feed other
+	requests but aborts responses with unknown body length.
 DOC_END
 
 NAME: read_ahead_gap

src/store_client.cc

@@ -984,13 +984,7 @@ CheckQuickAbortIsReasonable(StoreEntry * entry)
         return true;
     }
 
-    // XXX: This is absurd! TODO: For positives, "a/(b/c) > d" is "a*c > b*d".
-    if (expectlen < 100) {
-        debugs(90, 3, "quick-abort? NO avoid FPE");
-        return false;
-    }
-
-    if ((curlen / (expectlen / 100)) > (Config.quickAbort.pct)) {
+    if (curlen > expectlen*(Config.quickAbort.pct/100.0)) {
         debugs(90, 3, "quick-abort? NO past point of no return");
         return false;
     }