nix channels

channels.json

[
    {
        "name": "nixos",
        "repo": "NixOS/nixpkgs-channels",
        "branch": "nixos-18.03"
    },
    
    {
        "name": "nixos-unstable",
        "repo": "NixOS/nixpkgs-channels",
        "branch": "nixos-unstable"
    },
    
    {
        "name": "nixpkgs-master",
        "repo": "NixOS/nixpkgs"
    }
]

channels.pinned.json

[
    {
        "name": "nixos",
        "repo": "NixOS/nixpkgs-channels",
        "branch": "nixos-18.03",
        "rev": "2f6440eb09b7e6e3322720ac91ce7e2cdeb413f9"
    },
    {
        "name": "nixos-unstable",
        "repo": "NixOS/nixpkgs-channels",
        "branch": "nixos-unstable",
        "rev": "5da85431fb1df4fb3ac36730b2591ccc9bdf5c21"
    },
    {
        "name": "nixpkgs-master",
        "repo": "NixOS/nixpkgs",
        "rev": "97e376bf9cafa2d6c812221677f2e38163d0acb8"
    }
]

channels.py

#! /usr/bin/env nix-shell
#! nix-shell -I "nixpkgs=https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz" -i python3 -p python3
##! nix-shell -i python3 -p python3
import json
import urllib.request
import urllib.error
import tempfile
import os
import os.path
import tarfile
import shutil
import subprocess
import sys

channels_json = "channels.json"
channels_pinned_json = "channels.pinned.json"
channels_dir = "/nix/var/nix/profiles/per-user/root/channels"

# Github api
commit_url_template = 'https://api.github.com/repos/{repo}/commits/{ref}'
tarball_url_template = 'https://api.github.com/repos/{repo}/tarball/{ref}'

def read_url(url):
    try:
        with urllib.request.urlopen(url) as response:
            return response.read()
    except urllib.error.HTTPError:
        print(url)
        raise

def save_url(url):
    try:
        return urllib.request.urlretrieve(url)[0]
    except urllib.error.HTTPError:
        print(url)
        raise

def pin():
    with open(channels_json) as f:
        channels = json.load(f)

    print("Pinning channels")
    for channel in channels:
        print("channel: "+channel['name'])
        if not 'rev' in channel:
            ref = channel.get('branch', 'HEAD')
            url = commit_url_template.format(repo=channel['repo'], ref=ref)
            channel['rev'] = json.loads(read_url(url))['sha']

    with open(channels_pinned_json, 'w') as f:
        json.dump(channels, f, indent=4)

def update(usePython=False):
    with open(channels_pinned_json) as f:
        channels = json.load(f)

    print("Updating channels")
    for channel in channels:
        channel_dir = os.path.join(channels_dir, channel['name'])

        print("channel: "+channel['name'])
        with tempfile.NamedTemporaryFile() as temp_file:
            print("- downloading")
            temp_file = save_url(tarball_url_template.format(repo=channel['repo'], ref=channel['rev']))

            with tempfile.TemporaryDirectory() as temp_dir: 
                print("- extracting")
                subprocess.run(["tar", "xzf", temp_file, "-C", temp_dir], check=True)

                if os.path.isdir(channel_dir):
                    print("- cleaning")
                    subprocess.run(["rm", "-r", channel_dir], check=True)

                print("- moving")
                subprocess.run(["mv", os.path.join(temp_dir, os.listdir(temp_dir)[0]), channel_dir], check=True)

def clean():
    print("Cleaning all channels")
    subprocess.run(["rm", "-r", channels_dir], check=True)
    subprocess.run(["mkdir", channels_dir], check=True)
 

if __name__ ==  '__main__':
    if 'clean' in sys.argv[1:]:
        clean()
    if 'pin' in sys.argv[1:]:
        pin()
    if 'update' in sys.argv[1:]:
        update()