Packaging up a Go app as a snap

After building my first Python snap I was asked to try to build a Go snap.

There is a video about building Go snaps with snapcraft here so after watching it I gave Kurly a try. 

"Kurly is an alternative to the widely popular curl program and is designed to operate in a similar manner to curl, with select features. Notably, kurly is not aiming for feature parity, but common flags and mechanisms particularly within the HTTP(S) realm are to be expected.".

First of all I got familiar with the code and got it on my PC:

$ git clone https://github.com/davidjpeacock/kurly.git

I entered the kurly directory:

$ cd kurly

 I created a snap directory and entered it:

$ mkdir snap
$ cd snap

I created a snapcraft.yaml file with the go plugin (plugin: go):

name: kurly
version: master
summary: kurly is an alternative to the widely popular curl program.
description: |
                     kurly is designed to operate in a similar manner to curl, with select features. Notably, kurly is not aiming for feature parity, but common flags and mechanisms particularly within the HTTP(S) realm are to be expected.

confinement: devmode

apps:
  kurly:
     command: kurly

parts:
  kurly:
     source: .                                              
     plugin: go
     go-importpath: github.com/davidjpeacock/kurly

The go-importpath keyword is important and tells the checked out source to live within a certain path with 'GOPATH'. This is required to work with absolute imports and path checking.


I went back to the root of the project and launched the snapcraft command to build the snap:

$ cd ..
$ snapcraft

Once snapcraft has finished building you will find a kurly_master_amd64.snap file in the root directory of the project.

I installed the kurly snap in devmode to test it and see if worked well in non confined mode so that then I could run it in confined mode and add the plugs needed by the snap to work properly:

$ sudo snap install --dangerous --devmode kurly_master_amd64.snap

If you run:

$ snap list

you will see the kurly snap installed in devmode:

Name    Version  Rev   Developer  Notes
core    16-2     2312  canonical  -
kurly   master   x1               devmode

Now i tried kurly out a bit to see if it worked well, for instance:

$ kurly -v https://httpbin.org/ip

$  kurly -R -O -L http://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-8.7.1-amd64-netinst.iso

Ok fine, it worked so now I tried to install it in confined mode changing the snapcraft.yaml file accordingly (confinement: strict).

I ran snapcraft again and installed the snap:

$ snapcraft
$ sudo snap install --dangerous kurly_master_amd64.snap

You can see from  the snap list command that the app is installed not in devmode anymore:

$ snap list

Name    Version  Rev   Developer  Notes
core    16-2     2312  canonical  -
kurly   master   x2               -

I tried out kurly again and got some errors:

$ kurly -v https://httpbin.org/ip

> GET /ip HTTP/1.1
> User-Agent [Kurly/1.0]
> Accept [*/*]
> Host [httpbin.org]
*Error: Unable to get URL; Get https://httpbin.org/ip: dial tcp: lookup httpbin.org: Temporary failure in name resolution

From the error I could understand that kurly needs the network plug (plugs: [network]) so I changed the snapcraft.yaml file so:

name: kurly
version: master
summary: kurly is an alternative to the widely popular curl program.
description: |
                     kurly is designed to operate in a similar manner to curl, with select features. Notably, kurly is not aiming for feature parity, but common flags and mechanisms particularly within the HTTP(S) realm are to be expected.

confinement: strict

apps:
  kurly:
     command: kurly
     plugs: [network]

parts:
  kurly:
     source: .
     plugin: go
     go-importpath: github.com/davidjpeacock/kurly

 I ran snapcraft and installed the kurly snap again:

$ snapcraft
$ sudo snap install --dangerous kurly_master_amd64.snap

But when I ran a kurly command for downloading a file I got another error:

$kurly -R -O -L http://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-8.7.1-amd64-netinst.iso
*Error: Unable to create file 'debian-8.7.1-amd64-netinst.iso' for output

Kurly could not write the file to my home direcotry, so I added the home plug to the snapcraft.yaml file, ran snapcraft and installed the snap again.
This time kurly worked fine.

So here's the final snapcraft.yaml file ready for a PR in Git Hub:
 

name: kurly
version: master
summary: kurly is an alternative to the widely popular curl program.
description: |
                     kurly is designed to operate in a similar manner to curl, with select features. Notably, kurly is not aiming for feature parity, but common flags and mechanisms particularly within the HTTP(S) realm are to be expected.

confinement: strict

apps:
  kurly:
     command: kurly
     plugs: [network, home]

parts:
  kurly:
     source: .
     plugin: go
     go-importpath: github.com/davidjpeacock/kurly

That's it.
The Go snap is done!