refactor: Reshuffle file structure for better code layout

This gets rid of the package called "server" and instead moves
everything into the project root, such that Go actually builds us a
binary called `nixery`.

This is the first step towards factoring out CLI-based functionality
for Nixery.

tools/nixery/server/storage/filesystem.go

@@ -1,96 +0,0 @@
-// 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.
-
-// Filesystem storage backend for Nixery.
-package storage
-
-import (
-	"context"
-	"fmt"
-	"io"
-	"net/http"
-	"os"
-	"path"
-
-	log "github.com/sirupsen/logrus"
-)
-
-type FSBackend struct {
-	path string
-}
-
-func NewFSBackend() (*FSBackend, error) {
-	p := os.Getenv("STORAGE_PATH")
-	if p == "" {
-		return nil, fmt.Errorf("STORAGE_PATH must be set for filesystem storage")
-	}
-
-	p = path.Clean(p)
-	err := os.MkdirAll(p, 0755)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create storage dir: %s", err)
-	}
-
-	return &FSBackend{p}, nil
-}
-
-func (b *FSBackend) Name() string {
-	return fmt.Sprintf("Filesystem (%s)", b.path)
-}
-
-func (b *FSBackend) Persist(ctx context.Context, key string, f Persister) (string, int64, error) {
-	full := path.Join(b.path, key)
-	dir := path.Dir(full)
-	err := os.MkdirAll(dir, 0755)
-	if err != nil {
-		log.WithError(err).WithField("path", dir).Error("failed to create storage directory")
-		return "", 0, err
-	}
-
-	file, err := os.OpenFile(full, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
-	if err != nil {
-		log.WithError(err).WithField("file", full).Error("failed to write file")
-		return "", 0, err
-	}
-	defer file.Close()
-
-	return f(file)
-}
-
-func (b *FSBackend) Fetch(ctx context.Context, key string) (io.ReadCloser, error) {
-	full := path.Join(b.path, key)
-	return os.Open(full)
-}
-
-func (b *FSBackend) Move(ctx context.Context, old, new string) error {
-	newpath := path.Join(b.path, new)
-	err := os.MkdirAll(path.Dir(newpath), 0755)
-	if err != nil {
-		return err
-	}
-
-	return os.Rename(path.Join(b.path, old), newpath)
-}
-
-func (b *FSBackend) ServeLayer(digest string, r *http.Request, w http.ResponseWriter) error {
-	p := path.Join(b.path, "layers", digest)
-
-	log.WithFields(log.Fields{
-		"layer": digest,
-		"path":  p,
-	}).Info("serving layer from filesystem")
-
-	http.ServeFile(w, r, p)
-	return nil
-}