Read a BSR file

BSR data files are where all the data transmitted during a session is stored. BSR data files have the file suffix .data and are binary files written in network byte or big-endian order. The first eight bytes of a BSR data file always contains the following signature, which identifies the file as a BSR file: "\x89BSR\r\n\x1a\n".

Following the BSR signature, a BSR file contains “chunks” of data. Each chunk contains the same basic metadata information: length, protocol, chunk type, direction, and a timestamp. The chunk type indicates the expected data payload. The first chunk in a BSR file is the header chunk, and the last chunk in a BSR file is the EOF chunk. The remaining chunks in the file depend on the protocol identified in the BSR header.

The only protocol currently supported for session recording is SSH. Data files for SSH are prefixed with either messages- or requests-, and suffixed with either inbound or outbound to indicate the direction the data came from. Message files contain raw data from an SSH session and contain a header chunk, data chunks, and an EOF chunk. Request files contain a header chunk, SSH request message chunks, and an EOF chunk.

SSH request message chunks follow the SSH connection and channel request definitions. Boundary populates these chunks using a protobuf definition provided here: SSH Chunks.

Boundary session recording playback generates an asciinema from a session channel’s messages-outbound.data file. For more information on finding and viewing BSR data using the asciinema, refer to Find and view recorded sessions.

While Boundary does not currently provide tooling to read other BSR .data files, the BSR definition is available in our community repository, and you can use it to develop external tooling.