Allow avro C to be built on musl based systems.

[titouanc]

Currently, the avro C library can not be built for Linux systems based on the musl standard C library, which is often used on embedded systems. See the full commit message for more details.

This PR has been tested against the following C libraries, on x86 and arm architectures:

• uClibc
• musl
• glibc

---

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[kojiromike]

It should be possible to test this with an Alpine container. I took a crack at it, but I wasn't able to successfully build avro. It's probably more to do with my own ignorance of the build system.

[titouanc]

@kojiromike indeed, there are a few required packages to be able to compile within Alpine:

• bash (required by shebang lines in helper scripts)
• gcc (and g++ is also required somehow by cmake, not sure why)
• make, cmake
• jansson-dev and musl-dev (shared libs + headers needed)

I succeeded to build the C part with this Dockerfile (placed at the toplevel):

FROM alpine:latest

WORKDIR /root

RUN apk update
RUN apk add bash gcc g++ make cmake jansson-dev musl-dev

COPY . .

WORKDIR /root/lang/c
RUN mkdir build && cd build && cmake .. && make

Eventually running the same Dockerfile without the patch in this PR would not succeed

[RyanSkraba]

Hello! This is the one-liner I used for musl:

docker run --rm -it -v $PWD:$HOME/avro -w $HOME/avro alpine:3.7 sh -c "apk add g++ cmake bash jansson-dev make && cd lang/c && ./build.sh test"

I can confirm that it fails without the change in this PR, and succeeds with the change.

I know for glibc (like the build process uses), we can do the equivalent:

docker run --rm -it -v $PWD:$HOME/avro -w $HOME/avro gcc:9.2 bash -c "apt-get update -y && apt-get -y install cmake libjansson-dev && cd lang/c && ./build.sh test"

I'm not sure about uClibc.

[titouanc]

I tested a uClibc-ng build within Buildroot (which is by the way where this patch originated 🙂) and it succeeds. However, I did not find a Docker image based on uClibc after a quick Google search.

[titouanc]

Hello @kojiromike and @RyanSkraba , is there anything needed to make this move forward ? Please let me know if I can do anything to help

[kojiromike]

I was able to run this on alpine and confirm what Ryan said. However, I'm concerned that we don't have any automated test set up for TravisCI, so any future committer could accidentally break musl support again and not realize it.

[RyanSkraba]

Oh, I forgot to mention: I checked uClibc with an 4 year old version of alpine (not super satisfactory or confident about it):

docker run --rm -it -v $PWD:$HOME/avro -w $HOME/avro alpine:2.7 sh -c "apk update && apk add g++ cmake bash jansson-dev make && cd lang/c && ./build.sh test"

What do you think about merging this and creating a JIRA about improving the build with a "secondary" check on lang/c&musl? It would be consistent with the lang/csharp&windows check.

Edit: I created https://issues.apache.org/jira/browse/AVRO-2660.

[kojiromike]

@RyanSkraba Sounds good to me. Do you want to do the honors?

[RyanSkraba]

@RyanSkraba Sounds good to me. Do you want to do the honors?

I'd like to practice, if that's OK :D I'm on it!