urbit/nix/lib/fetch-github-lfs.nix

108 lines
3.3 KiB
Nix

{ lib, stdenvNoCC, runCommandLocal, cacert, curl, jq }:
{ src
# `name` shouldn't use `baseNameOf` otherwise we'll
# get `is not allowed to refer to a store path` errors.
, name ? baseNameOf src, owner ? "urbit", repo ? "urbit"
, preferLocalBuild ? true }:
assert builtins.isPath src;
let
# Parse the first 7 characters of the supplied `src` path for the required
# `version` key as defined by the lfs specification:
# https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
#
# If `version` exists we assume we're dealing with a lfs pointer and parse
# the `oid` and `size` from the pointer and write these into a JSON object.
#
# If the first 7 characters are unrecognised we assume the path is a binary
# file and set both `oid` and `size` to `null`.
#
# The `oid` and `size` are then JSON decoded into an expression to use
# as the fixed-output derivation's `sha256 = oid`, and to form a download
# operation payload to request the actual lfs blob's real url.
pointer = builtins.fromJSON (builtins.readFile
(runCommandLocal "lfs-pointer-${name}" { } ''
oid="null"
size="null"
if [[ "$(head -c 7 "${src}")" != "version" ]]; then
header "lfs ${src} is a binary blob, skipping"
else
header "reading lfs pointer from ${src}"
contents=($(awk '{print $2}' "${src}"))
oid="''${contents[1]#sha256:}"
size="''${contents[2]}"
fi
cat <<EOF > "$out"
{"oid": "$oid", "size": $size}
EOF
''));
downloadUrl =
"https://github.com/${owner}/${repo}.git/info/lfs/objects/batch";
# Encode `oid` and `size` into a download operation per:
# https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md
#
# This is done using toJSON to avoid bash quotation issues.
downloadPayload = builtins.toJSON {
operation = "download";
objects = [ pointer ];
};
# Define a fixed-output derivation using the lfs pointer's `oid` as the
# expected sha256 output hash, if `oid` is not null.
#
# 1. Request the actual url of the binary file from the lfs batch api.
# 2. Download the binary file contents to `$out`.
download = stdenvNoCC.mkDerivation {
name = "lfs-blob-${name}";
nativeBuildInputs = [ curl jq ];
phases = [ "installPhase" ];
installPhase = ''
curl=(
curl
--location
--max-redirs 20
--retry 3
--disable-epsv
--cookie-jar cookies
$NIX_CURL_FLAGS
)
header "reading lfs metadata from ${downloadUrl}"
href=$("''${curl[@]}" \
-d '${downloadPayload}' \
-H 'Accept: application/vnd.git-lfs+json' \
'${downloadUrl}' \
| jq -r '.objects[0].actions.download.href')
header "download lfs data from remote"
# Pozor/Achtung: the href contains credential and signature information,
# so we avoid echoing it to stdout/err.
"''${curl[@]}" -s --output "$out" "$href"
'';
impureEnvVars = stdenvNoCC.lib.fetchers.proxyImpureEnvVars;
SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
outputHashAlgo = "sha256";
outputHashMode = "flat";
outputHash = pointer.oid;
inherit preferLocalBuild;
};
# If `pointer.oid` is null then supplied the `src` must be a binary
# blob and can be returned directly.
in if pointer.oid == null || pointer.size == null then src else download