libjq-go

CGO bindings for jq with cache for compiled programs and ready-to-use static builds of libjq.

No dependencies in go.mod! 👍

Usage

import (
  "fmt"
  . "github.com/flant/libjq-go" // import Jq() shortcut
)

func main() {
	// 1. Run one jq program with one input.
	res, err = Jq().Program(".foo").Run(`{"foo":"bar"}`)

	// 2. Use directory with jq modules.
	res, err = Jq().WithLibPath("./jq_lib").
		Program(`....`).
		Run(`...`)
	
	// 3. Use program text as a key for a cache.
	for _, data := range inputJsons {
		res, err = Jq().Program(".foo").Cached().Run(data)
		// Do something with result ...
	}
	
	// 4. Explicitly precompile jq expression to speed up processing of multiple inputs.
	prg, err := Jq().Program(".foo").Precompile()
	for _, data := range inputJsons {
		res, err = prg.Run(data)
		// Do something with result ...
	}
	
	// 5. It is safe to use Jq() from multiple go-routines.
	//    Note however that programs are executed synchronously.
	go func() {
		res, err = Jq().Program(".foo").Run(`{"foo":"bar"}`)
	}()
	go func() {
		res, err = Jq().Program(".foo").Cached().Run(`{"foo":"bar"}`)
	}()
}

The full code is available in example.go.

Build

1. Local build

The recommended and fastest way to build your program with libjq-go is to use prebuilt libjq static libraries, available in Releases. See local-build example for inspiration.

wget https://github.com/flant/libjq-go/releases/download/jq-b6be13d5-0/libjq-glibc-amd64.tgz
tar zxf libjq-glibc-amd64.tgz
CGO_ENABLED=1 \
CGO_CFLAGS="-I./libjq/include" \
CGO_LDFLAGS="-L./libjq/lib" \
go build example.go

Also, you can use libjq in a form of dynamic library available in your OS or build static library from jq sources. Either way, read below about jq sources and performance issues.

MacOS with brewed jq

brew install jq
CGO_ENABLED=1 go build example.go

2. Docker build

The recommended way for docker build is to use static libjq from flant/jq image available on hub.docker.com.

FROM flant/jq:b6be13d5-musl as libjq

FROM golang:1.15-alpine as builder
...
COPY --from=libjq /libjq /app/libjq/
...
RUN ... go build example.go

# Final image
FROM alpine:3.12
COPY --from=builder ...

Full source is available in simple example.

If prebuilt libjq is not an option, you can build static libjq in a separate image and then copy libjq to 'go builder' image. See this approach in a Dockerfile of flant/shell-operator project.

3. Static build

Go can produce static binaries with CGO enabled. You should use static build of libjq and add -ldflags to go build command.

FROM flant/jq:b6be13d5-musl as libjq

FROM golang:1.15-alpine as builder
...
COPY --from=libjq /libjq /app/libjq/
...
RUN CGO_ENABLED=1 ... \
    go build \
    -ldflags="-linkmode external -extldflags '-static' -s -w" \
    example.go

# Final image
FROM alpine:3.12
COPY --from=builder ...

See docker-static-build example.

Notes

jq source compatibility and jq 1.6 performance

TL;DR

If your program works as a cli filter for one jq expression (like jq command itself) you can use any commit from stedolan/jq.
If your program works as a server and process many jq expressions, consider use b6be13d5 commit and prebuilt libjq assets.

Long story:

This library was tested with jq-1.5, jq-1.6 and with some commits from master branch. The submodule jq in this repository points to unreleased commit stedolan/jq@b6be13d5.

Which commit should you choose? Take these considerations into account:

jq-1.5 works good, but it lucks new features.
jq-1.6 turns out to be slow, see: stedolan/jq#2069 and flant/libjq-go#10.
latest master have problem with fromjson and tonumber stedolan/jq#2091.
stedolan/jq@b6be13d5 is a commit that has features of v1.6 and a good performance and correctly handles errors in fromjson.

Go compatibility

libjq-go is known to work with Go 1.11 and later versions.

prebuilt libjq

For faster builds we publish prebuilt libjq static libraries (and jq command) in flant/jq repository on hub.docker.com. Also, there are assets in jq-* releases in this repo on github.

glibc build is known to work in debian:stretch, debian:buster, ubuntu:18.04, ubuntu:20.04 (and seems to work in alpine).

musl build is known to work in alpine:3.7+ (You can even compile your program using golang:1.11-alpine3.7!)

Inspired projects

There are other jq bindings in Go:

Also these projects was very helpful in understanding jq sources:

License

Apache License 2.0, see LICENSE.