Cap'n Proto

Cap'n Proto serialization/RPC system - core tools and C++ library (by capnproto)

Cap'n Proto Alternatives

Similar projects and alternatives to Cap'n Proto

NOTE: The number of mentions on this list indicates mentions on common posts plus user suggested alternatives. Hence, a higher number means a better Cap'n Proto alternative or higher similarity.

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Cap'n Proto reviews and mentions

Posts with mentions or reviews of Cap'n Proto. We have used some of these posts to build our list of alternatives and similar projects. The last one was on 2024-06-03.
  • The Simdjson Library
    4 projects | | 3 Jun 2024
  • Demystifying the Protobuf Wire Format
    4 projects | | 17 May 2024
    To be fair, if that's what you need ProtoBuf isn't the only option. Cap'n Proto[1], JSON Schema[2], or any other well supported message-definition language could probably achieve that as well, each with their own positives and negatives.



  • Mysterious Moving Pointers
    1 project | | 14 Apr 2024
    Yeah I pretty much only use my own alternate container implementations (from KJ[0]), which avoid these footguns, but the result is everyone complains our project is written in Kenton-Language rather than C++ and there's no Stack Overflow for it and we can't hire engineers who know how to write it... oops.


  • Show HN: Comprehensive inter-process communication (IPC) toolkit in modern C++
    2 projects | | 9 Apr 2024
    - may massively reduce the latency involved.

    Those sharing Cap'n Proto-encoded data may have particular interest. Cap'n Proto ( is fantastic at its core task - in-place serialization with zero-copy - and we wanted to make the IPC (inter-process communication) involving capnp-serialized messages be zero-copy, end-to-end.

    That said, we paid equal attention to other varieties of payload; it's not limited to capnp-encoded messages. For example there is painless (<-- I hope!) zero-copy transmission of arbitrary combinations of STL-compliant native C++ data structures.

    To help determine whether Flow-IPC is relevant to you we wrote an intro blog post. It works through an example, summarizes the available features, and has some performance results.

    Of course there's nothing wrong with going straight to the GitHub link and getting into the README and docs.

    Currently Flow-IPC is for Linux. (macOS/ARM64 and Windows support could follow soon, depending on demand/contributions.)

  • Condvars and atomics do not mix
    1 project | | 24 Mar 2024
    FWIW, my C++ toolkit library, KJ, does the same thing.[0]

    But presumably you could still write a condition predicate which looks at things which aren't actually part of the mutex-wrapped structure? Or does is the Rust type system able to enforce that the callback can only consider the mutex-wrapped value and values that are constant over the lifetime of the wait? (You need the latter e.g. if you are waiting for the mutex-wrapped value to compare equal to some local variable...)


  • Cap'n'Proto: infinitely faster than Protobuf
    1 project | | 26 Feb 2024
  • I don’t understand zero copy
    2 projects | /r/rust | 7 Dec 2023
    The second one is to encode data in such a way that you can read it and operate on it directly from the buffer. You write data in a layout that is the same, or easily transformed as types in memory. To do that you usually need to encode with a known schema, only Sized types to efficiently compute fields locations as offsets in the buffer, and you usually represent pointers as offset into the encode. You can look at capnproto protocol for instance
  • OpenTF Renames Itself to OpenTofu
    5 projects | | 20 Sep 2023
    Worked well for Cap'n Proto (the cerealization protocol)!
  • A Critique of the Cap'n Proto Schema Language
    3 projects | | 20 Aug 2023
    With all due respect, you read completely wrong.

    * The very first use case for which Cap'n Proto was designed was to be the protocol that used to talk between sandbox and supervisor -- an explicitly adversarial security scenario.

    * The documentation explicitly calls out how implementations should manage resource exhaustion problems like deep recursion depth (stack overflow risk).

    * The implementation has been fuzz-tested multiple ways, including as part of Google's oss-fuzz.

    * When there are security bugs, I issue advisories like this:

    * The primary aim of the entire project is to be a Capability-Based Security RPC protocol.

  • Cap'n Proto: serialization/RPC system – core tools and C++ library
    1 project | | 28 Jul 2023
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