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capnp.nim

Cap'n Proto bindings for Nim

WARNING: the project is not actively maintained

capnp.nim is a Nim implementation of Cap'n Proto serialization scheme and RPC protocol.

The serialization layer is production ready. The RPC layers is also fairly well tested, enough to be useful, but not the whole protocol is implemented.

The main user of this library is MetaContainer.

Installing

Use nimble to install capnp.nim:

nimble install capnp

Create symlink to canpnc binary result (capnp compiler expects capnpc-nim binary, but Nimble is unable to produce binary name that contains -):

ln -s ~/.nimble/bin/capnpc ~/.nimble/bin/capnpc-nim

Generating wrapping code

capnp.nim can generate Nim types (with some metadata) from .capnp file. The resulting objects use native Nim datatypes like seq or strings (this means that this implementation, unlike C++ one, doesn't have O(1) deserialization time).

capnp compile -onim your-protocol-file.capnp > you-output-file.nim

Using the library

import persondef, capnp
# unpack the raw serialized data
let p: Person = newUnpackerFlat(packed).unpackStruct(0, Person)
# and pack again
let packed2 = packStruct(p)

Debugging options

Define the following symbols during compilation (e.g -d:caprpcTraceMessages):

  • caprpcTraceMessages - print all messages sent by RPC system
  • caprpcTraceLifetime - print info about release messages, useful while debugging cross-machine leaks
  • caprpcPrintExceptions - print exceptions raised inside called methods (server)