Close file handle for simple HTTP reads.

If a client requested a single byte range which was less than
the filesize, then the file handle was never explicitly closed.

When the TCP connection was closed, all open file handles on the
bridge are automatically closed too.  Hence, it seems like this is
a moot point - a transient "leak".  However, we have observed some
clients (particularly: CVMFS) that hold open TCP connections for
hours or days, resulting in the "leak" of a file handle per read
operation.  In some cases, the number of file handles leaked was in
the tens-of-thousands.

In addition to the obvious memory issues, this was observable in the
f-stream monitoring as the near-simultaneous closing of 10k file handles
caused UDP buffer overflows and dropped monitoring packets.

src/XrdHttp/XrdHttpReq.cc

@@ -302,6 +302,7 @@ int XrdHttpReq::parseRWOp(char *str) {
       len_ok += len;
       rwOps_split.push_back(nfo);
     }
+    length += len_ok;
 
 
   }
@@ -984,7 +985,7 @@ int XrdHttpReq::ProcessHTTPReq() {
         {
 
           if ( ((reqstate == 3) && (rwOps.size() > 1)) ||
-            (writtenbytes >= filesize) ) {
+            (writtenbytes >= length) ) {
 
             // Close() if this was a readv or we have finished, otherwise read the next chunk
 
@@ -1677,6 +1678,12 @@ int XrdHttpReq::PostProcessHTTPReq(bool final_) {
                        &filesize,
                        &fileflags,
                        &filemodtime);
+
+                // We will default the response size specified by the headers; if that
+                // wasn't given, use the file size.
+                if (!length) {
+                    length = filesize;
+                }
               }
               else
                 TRACEI(REQ, "Can't find the stat information for '" << resource << "' Internal error?");
@@ -1716,6 +1723,12 @@ int XrdHttpReq::PostProcessHTTPReq(bool final_) {
                         &filesize,
                         &fileflags,
                         &filemodtime);
+
+                  // As above: if the client specified a response size, we use that.
+                  // Otherwise, utilize the filesize
+                  if (!length) {
+                    length = filesize;
+                  }
                 }
                 else
                   TRACEI(ALL, "GET returned no STAT information. Internal error?");

src/XrdHttp/XrdHttpReq.hh

@@ -187,7 +187,7 @@ public:
   std::vector<ReadWriteOp> rwOps_split;
 
   bool keepalive;
-  long long length;
+  long long length;  // Total size from client for PUT; total length of response TO client for GET.
   int depth;
   bool sendcontinue;