InfluxDB is a scalable database optimized for storage of time series, real-time application metrics, operations monitoring events, etc, written in Go.
Data is stored in .tsm files, which are kept pretty simple conceptually. Each .tsm file contains a header and footer, which stores offset to an index. Index is used to find a data block for a requested time boundary.
This page hosts a formal specification of InfluxDB TSM file using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.