refactor(server): Extract build logic into separate module

This module is going to get more complex as the implementation of #32
progresses.

1 files changed, 131 insertions, 0 deletions

diff --git a/tools/nixery/server/config/config.go b/tools/nixery/server/config/config.go
new file mode 100644
index 0000000000..4e3b70dcdc
--- /dev/null
+++ b/tools/nixery/server/config/config.go
@@ -0,0 +1,131 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+// Package config implements structures to store Nixery's configuration at
+// runtime as well as the logic for instantiating this configuration from the
+// environment.
+package config
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+
+	"cloud.google.com/go/storage"
+)
+
+// pkgSource represents the source from which the Nix package set used
+// by Nixery is imported. Users configure the source by setting one of
+// the supported environment variables.
+type PkgSource struct {
+	srcType string
+	args    string
+}
+
+// Convert the package source into the representation required by Nix.
+func (p *PkgSource) Render(tag string) string {
+	// The 'git' source requires a tag to be present.
+	if p.srcType == "git" {
+		if tag == "latest" || tag == "" {
+			tag = "master"
+		}
+
+		return fmt.Sprintf("git!%s!%s", p.args, tag)
+	}
+
+	return fmt.Sprintf("%s!%s", p.srcType, p.args)
+}
+
+// Retrieve a package source from the environment. If no source is
+// specified, the Nix code will default to a recent NixOS channel.
+func pkgSourceFromEnv() *PkgSource {
+	if channel := os.Getenv("NIXERY_CHANNEL"); channel != "" {
+		log.Printf("Using Nix package set from Nix channel %q\n", channel)
+		return &PkgSource{
+			srcType: "nixpkgs",
+			args:    channel,
+		}
+	}
+
+	if git := os.Getenv("NIXERY_PKGS_REPO"); git != "" {
+		log.Printf("Using Nix package set from git repository at %q\n", git)
+		return &PkgSource{
+			srcType: "git",
+			args:    git,
+		}
+	}
+
+	if path := os.Getenv("NIXERY_PKGS_PATH"); path != "" {
+		log.Printf("Using Nix package set from path %q\n", path)
+		return &PkgSource{
+			srcType: "path",
+			args:    path,
+		}
+	}
+
+	return nil
+}
+
+// Load (optional) GCS bucket signing data from the GCS_SIGNING_KEY and
+// GCS_SIGNING_ACCOUNT envvars.
+func signingOptsFromEnv() *storage.SignedURLOptions {
+	path := os.Getenv("GCS_SIGNING_KEY")
+	id := os.Getenv("GCS_SIGNING_ACCOUNT")
+
+	if path == "" || id == "" {
+		log.Println("GCS URL signing disabled")
+		return nil
+	}
+
+	log.Printf("GCS URL signing enabled with account %q\n", id)
+	k, err := ioutil.ReadFile(path)
+	if err != nil {
+		log.Fatalf("Failed to read GCS signing key: %s\n", err)
+	}
+
+	return &storage.SignedURLOptions{
+		GoogleAccessID: id,
+		PrivateKey:     k,
+		Method:         "GET",
+	}
+}
+
+func getConfig(key, desc string) string {
+	value := os.Getenv(key)
+	if value == "" {
+		log.Fatalln(desc + " must be specified")
+	}
+
+	return value
+}
+
+// config holds the Nixery configuration options.
+type Config struct {
+	Bucket  string                    // GCS bucket to cache & serve layers
+	Signing *storage.SignedURLOptions // Signing options to use for GCS URLs
+	Port    string                    // Port on which to launch HTTP server
+	Pkgs    *PkgSource                // Source for Nix package set
+	WebDir  string
+}
+
+func FromEnv() *Config {
+	return &Config{
+		Bucket:  getConfig("BUCKET", "GCS bucket for layer storage"),
+		Port:    getConfig("PORT", "HTTP port"),
+		Pkgs:    pkgSourceFromEnv(),
+		Signing: signingOptsFromEnv(),
+		WebDir:  getConfig("WEB_DIR", "Static web file dir"),
+	}
+}