python-systemd: Reader return special fields and _Reader changes

Changes to _Reader make it match closer to C API, by removing `get_next`
and `get_previous`. A `get_all` method added, which returns dictionary
of fields using C API SD_JOURNAL_FOREACH_DATA macro, which can be used
in conjunction with `next`.

_Reader `get`, `next`, `get_{realtime,monotonic,cursor}` and new
`previous` methods are made private. This is so the traversal and
getting of journal fields can be made transparent in the python
interface.

Reader now solely implements `get_next` and `get_previous`, returning a
standard dictionary (future: other mapping types?) with all standard and
special fields through the converters. This makes the output the same as
journalctl json/export format output.

Iterator methods also moved to Reader, as they do not function as intend
with changes to _Reader.

These changes also mean that more optimised journal interfaces can be
made more easily from _Reader, by avoiding getting of unrequired fields
by using the `_get` method, and avoiding field conversions.

1 files changed, 42 insertions, 3 deletions

diff --git a/systemd/journal.py b/systemd/journal.py
index 48f57ac..6c740b0 100644
--- a/systemd/journal.py
+++ b/systemd/journal.py
@@ -176,6 +176,25 @@ class Reader(_Reader):
                 result[key] = self._convert_field(key, value)
         return result
 
+    def __iter__(self):
+        """Part of iterator protocol.
+        Returns self.
+        """
+        return self
+
+    if _sys.version_info >= (3,):
+        def __next__(self):
+            """Part of iterator protocol.
+            Returns self.get_next().
+            """
+            return self.get_next()
+    else:
+        def next(self):
+            """Part of iterator protocol.
+            Returns self.get_next().
+            """
+            return self.get_next()
+
     def add_match(self, *args, **kwargs):
         """Add one or more matches to the filter journal log entries.
         All matches of different field are combined in a logical AND,
@@ -190,15 +209,35 @@ class Reader(_Reader):
             super(Reader, self).add_match(arg)
 
     def get_next(self, skip=1):
-        """Return the next log entry as a dictionary of fields.
+        """Return the next log entry as a mapping type, currently
+        a standard dictionary of fields.
 
         Optional skip value will return the `skip`\-th log entry.
 
         Entries will be processed with converters specified during
         Reader creation.
         """
-        return self._convert_entry(
-            super(Reader, self).get_next(skip))
+        if super(Reader, self)._next(skip):
+            entry = super(Reader, self)._get_all()
+            if entry:
+                entry['__REALTIME_TIMESTAMP'] =  self._get_realtime()
+                entry['__MONOTONIC_TIMESTAMP']  = self._get_monotonic()
+                entry['__CURSOR']  = self._get_cursor()
+                return self._convert_entry(entry)
+        return dict()
+
+    def get_previous(self, skip=1):
+        """Return the previous log entry as a mapping type,
+        currently a standard dictionary of fields.
+
+        Optional skip value will return the -`skip`\-th log entry.
+
+        Entries will be processed with converters specified during
+        Reader creation.
+
+        Equivilent to get_next(-skip).
+        """
+        return self.get_next(-skip)
 
     def query_unique(self, field):
         """Return unique values appearing in the journal for given `field`.