Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

CloudEvents Expression Language

See original GitHub issue

I want to propose to start a new effort to develop an expression language to filter CloudEvents.


One of the main drivers is the ability to have more powerful filtering capabilities in the subscription API, where the existing filter dialect basic is not powerful enough for most of production use cases. I foresee an eventual application of such language in the Discovery API and the Workflow spec.

Expected outcome

Our goal is to develop a spec for an expression language tailored for CloudEvents. Some goals of this language are, but not limited to, the following features:

  • Total functional programming language, hence the termination of the evaluation of the expression is always guaranteed
  • Type system conform to the CloudEvents type system
  • Boolean operators (and/or/nor/xor)
  • Comparison operators on the types provided by the type system
  • Regex
  • Function invocation semantics + basic built-ins (e.g. type assertions/casting,

It’s out of the scope of the effort to develop a generic expression language, hence the input of the expression will always be a CloudEvent.


  • We could help the implementers providing the antlr grammar for it.
  • We should implement this language in our sdks (I’m willing to help for java, golang, rust).
  • I would prefer to exclude payload filtering from the initial efforts, since I consider it a complex argument (It comes to my mind problems like payload too big, supporting different content types, …)
  • We don’t want anything particularly fancy regarding the syntax, so my feeling is that we should a C-like syntax or similar, something familiar for cloud developers out there

Issue Analytics

  • State:closed
  • Created 3 years ago
  • Reactions:2
  • Comments:15 (11 by maintainers)

github_iconTop GitHub Comments

slinkydevelopercommented, Dec 1, 2020

I managed to sketch some ideas and I wrote them down in a doc. It’s not a spec, it’s not formal, It’s more a braindump with all the ideas I have for this language:

loopingzcommented, Nov 20, 2020

One of the concerns we heard in the past, was resources intensive filtering, it is pretty common on regexp. As you might not have control over who is calling your subscription API we need to find a way to limit its impact

Read more comments on GitHub >

github_iconTop Results From Across the Web

CloudEvents SQL Expression Language - HackMD
CloudEvents SQL expressions (also known as CESQL) allow matching of CloudEvent attributes against complex expressions that lean on the syntax of Structured ...
Read more >
CloudEvents format - HTTP protocol binding | Eventarc
CloudEvents ( is a specification for describing event data in a common way. The specification is under the Cloud Native Computing ...
Read more >
[Eventing] CloudEvents SQL - Google Groups
I just want to let you know that in the CloudEvents community Lionel and I are working on a fancy new SQL-like expression...
Read more >
Cloud Events - Object Partners
Exploring the CloudEvents Landscape. ... Cel defines an expression language for matching cloud events and operating on them.
Read more >
Connecting Clusters - TriggerMesh
Broker is the temporary storage for CloudEvents. ... A PingSource produces periodic events based on a cron expression.
Read more >

github_iconTop Related Medium Post

No results found

github_iconTop Related StackOverflow Question

No results found

github_iconTroubleshoot Live Code

Lightrun enables developers to add logs, metrics and snapshots to live code - no restarts or redeploys required.
Start Free

github_iconTop Related Reddit Thread

No results found

github_iconTop Related Hackernoon Post

No results found

github_iconTop Related Tweet

No results found

github_iconTop Related Post

No results found

github_iconTop Related Hashnode Post

No results found