One log file is a prologue followed by a suite of blocks.

All values in headers and prologue are saved in little endian byte format. The data itself is marshalled in the Typelib marshalling format, i.e. in an endian-specific format. Use typelib to swap the endianness if needed.

Prologue (12 bytes)

Offset    Size      Field description
+0        7         Magic field, currently "POCOSIM" (see Logging::FORMAT_MAGIC)
+7        4         Format version (currently 2, see Logging::FORMAT_VERSION)
+11       1         Endianness (1 = big, 0 = little)

General block header (8 bytes)

Offset    Size      Field description
+0        1         Block type (see "Block types" below)
+1        1         Padding
+2        2         Stream index
+4        4         Payload size

Block types

StreamBlockType = 1

these blocks declare a new stream. There are two stream types: control and
data, and the actual stream type is determined in the block payload. See below
for the two stream declaration format.

DataBlockType = 2

A sample in an already declared data stream

ControlBlockType = 3

A sample in an already declared control stream

Note that control streams are currently unused.

Data stream declaration block

Offset    Size      Field description
+0        1         Block type   (= 1 for stream declaration block)
+1        1         Padding
+2        2         Stream index
+4        4         Payload size (variable)
+8        1         Stream type (= 1 for data streams)
+9        4         stream name size
+13       -         stream name
-         4         stream type name size
-         -         stream type name
-         4         type registry size
-         -         type registry marshalled in Typelib's XML format

Data block

Offset    Size      Field description
+0        1         Block type   (= 2 for data block)
+1        1         Padding
+2        2         Stream index
+4        4         Payload size (variable)
+8        4         real time (sec)
+12       4         real time (usec)
+16       4         logical time (sec)
+20       4         logical time (usec)
+24       4         data size
+25       1         block flags
+26       data_size data

The only bit used in the block flags is the first one. If set, the payload is compressed using gzip compression. Otherwise, it is not compressed.

Control stream declaration block

Offset    Size      Field description
+0        1         Block type   (= 1 for stream declaration block)
+1        1         Padding
+2        2         Stream index
+4        4         Payload size (= 1)
+8        1         Stream type (= 2 for control streams)