1 files changed, 39 insertions, 0 deletions
diff --git a/python/skytools/gzlog.py b/python/skytools/gzlog.py
new file mode 100644
index 00000000..558e2813
--- /dev/null
+++ b/python/skytools/gzlog.py
@@ -0,0 +1,39 @@
+
+"""Atomic append of gzipped data.
+
+The point is - if several gzip streams are concated, they
+are read back as one whose stream.
+"""
+
+import gzip
+from cStringIO import StringIO
+
+__all__ = ['gzip_append']
+
+#
+# gzip storage
+#
+def gzip_append(filename, data, level = 6):
+    """Append a block of data to file with safety checks."""
+
+    # compress data
+    buf = StringIO()
+    g = gzip.GzipFile(fileobj = buf, compresslevel = level, mode = "w")
+    g.write(data)
+    g.close()
+    zdata = buf.getvalue()
+    
+    # append, safely
+    f = open(filename, "a+", 0)
+    f.seek(0, 2)
+    pos = f.tell()
+    try:
+        f.write(zdata)
+        f.close()
+    except Exception, ex:
+        # rollback on error
+        f.seek(pos, 0)
+        f.truncate()
+        f.close()
+        raise ex
+