All articles tagged #rust-nom

I've been working on my new Rust side-project for several months now, and I've got some learnings to share. The project is called pq - it's a command-line tool to parse and query log files as time series. It comes with its own domain-specific language that is highly influenced by PromQL. A typical pq usage may look like this:

tail -f /var/log/nginx/access.log | pq '
/...some fancy regex.../
| map {
    .0 as ip,
    .1:ts,
    .2 as method,
    .3:str as status_code,
    .4 as content_len
  }
| select topk(
      10,
      sum(
          count_over_time(
              __line__{method="GET", status_code="200"}[1s]
          )
      ) by (ip)
  )
| to_json
'

pq has many components, including various log parsing strategies and a pretty sophisticated query execution engine. But surprisingly or not, about half of the time I've put into this project so far was dedicated to writing the parser of the pq's own query language. To be honest, when I was starting the project, I didn't see that coming...

Luckily, writing a parser in Rust was mostly a pleasant experience, thanks to a crate concisely named nom. Although learning how to write parsers with nom wasn't completely seamless. So here is my journey.

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