changeset 47393:75e1104f23a2

revlog: use dedicated code for reading sidedata

We are about to introduce a new, dedicated, file to store sidedata. Before doing so, we make sidedata reading go through different code as reading data chunk. This will simplify some of the complexity of the next changesets.

The reading is very simple right now and will need some improvement later to
reuse some of the caching strategy we use for the data file.

Differential Revision: https://phab.mercurial-scm.org/D10785

--- a/mercurial/configitems.py	Thu May 27 04:09:10 2021 +0200
+++ b/mercurial/configitems.py	Thu May 27 04:09:30 2021 +0200
@@ -1161,6 +1161,7 @@
 #   keeping references to the affected revlogs, especially memory-wise when
 #   rewriting sidedata.
 # * introduce a proper solution to reduce the number of filelog related files.
+# * use caching for reading sidedata (similar to what we do for data).
 # * Improvement to consider
 #   - avoid compression header in chunk using the default compression?
 #   - forbid "inline" compression mode entirely?

--- a/mercurial/revlog.py	Thu May 27 04:09:10 2021 +0200
+++ b/mercurial/revlog.py	Thu May 27 04:09:30 2021 +0200
@@ -803,6 +803,10 @@
             with func() as fp:
                 yield fp
 
+    def _sidedatareadfp(self):
+        """file object suitable to read sidedata"""
+        return self._datareadfp()
+
     def tiprev(self):
         return len(self.index) - 1
 
@@ -2068,7 +2072,19 @@
         if sidedata_size == 0:
             return {}
 
-        comp_segment = self._getsegment(sidedata_offset, sidedata_size)
+        # XXX this need caching, as we do for data
+        with self._sidedatareadfp() as sdf:
+            sdf.seek(sidedata_offset)
+            comp_segment = sdf.read(sidedata_size)
+
+            if len(comp_segment) < sidedata_size:
+                filename = self._datafile
+                length = sidedata_size
+                offset = sidedata_offset
+                got = len(comp_segment)
+                m = PARTIAL_READ_MSG % (filename, length, offset, got)
+                raise error.RevlogError(m)
+
         comp = self.index[rev][11]
         if comp == COMP_MODE_PLAIN:
             segment = comp_segment