tasks: squash out CRs in task logs to avoid huge transfers

Reloading an existing update task page was taking an extremely long time
to fetch down the task log and then pegging the client CPU such that the
browser gave a warning. Digging into it, logs from a Clear Linux update
task can be of the order of 500MB in size (with all of the line
refreshing using CRs that happens during downloads), causing (a) the
transfer to take a long time and (b) the JS code that updates the log
text box to be extremely busy. If we're loading the entire log from
scratch (as we are when we refresh the page) rather than just getting an
update since the last poll, we don't need any of those line refreshes -
so squash them out before returning the data.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

layerindex/views.py

@@ -6,6 +6,7 @@
 
 import os
 import sys
+import re
 from datetime import datetime
 from itertools import islice
 from pkg_resources import parse_version
@@ -1564,10 +1565,12 @@ def task_log_view(request, task_id):
         raise Http404
     try:
         f.seek(start)
-        # We need to escape this or else things that look like tags in the output
-        # will be interpreted as such by the browser
         datastr = f.read()
         origlen = len(datastr)
+        # Squash out CRs *within* the string (CRs at the start preserved)
+        datastr = re.sub(b'\n[^\n]+\r', b'\n', datastr)
+        # We need to escape this or else things that look like tags in the output
+        # will be interpreted as such by the browser
         data = escape(datastr)
         response = HttpResponse(data)
         try: