Add Alpine package registry (#23714)

This PR adds an Alpine package registry. You can follow [this
tutorial](https://wiki.alpinelinux.org/wiki/Creating_an_Alpine_package)
to build a *.apk package for testing.

This functionality is similar to the Debian registry (#22854) and
therefore shares some methods. I marked this PR as blocked because it
should be merged after #22854.


![grafik](https://user-images.githubusercontent.com/1666336/227779595-b76163aa-eea1-4a79-9583-775c24ad74e8.png)

---------

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

modules/packages/alpine/metadata_test.go

@@ -0,0 +1,143 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package alpine
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const (
+	packageName        = "gitea"
+	packageVersion     = "1.0.1"
+	packageDescription = "Package Description"
+	packageProjectURL  = "https://gitea.io"
+	packageMaintainer  = "KN4CK3R <dummy@gitea.io>"
+)
+
+func createPKGINFOContent(name, version string) []byte {
+	return []byte(`pkgname = ` + name + `
+pkgver = ` + version + `
+pkgdesc = ` + packageDescription + `
+url = ` + packageProjectURL + `
+# comment
+builddate = 1678834800
+packager = Gitea <pack@ag.er>
+size = 123456
+arch = aarch64
+origin = origin
+commit = 1111e709613fbc979651b09ac2bc27c6591a9999
+maintainer = ` + packageMaintainer + `
+license = MIT
+depend = common
+install_if = value
+depend = gitea
+provides = common
+provides = gitea`)
+}
+
+func TestParsePackage(t *testing.T) {
+	createPackage := func(name string, content []byte) io.Reader {
+		names := []string{"first.stream", name}
+		contents := [][]byte{{0}, content}
+
+		var buf bytes.Buffer
+		zw := gzip.NewWriter(&buf)
+
+		for i := range names {
+			if i != 0 {
+				zw.Close()
+				zw.Reset(&buf)
+			}
+
+			tw := tar.NewWriter(zw)
+			hdr := &tar.Header{
+				Name: names[i],
+				Mode: 0o600,
+				Size: int64(len(contents[i])),
+			}
+			tw.WriteHeader(hdr)
+			tw.Write(contents[i])
+			tw.Close()
+		}
+
+		zw.Close()
+
+		return &buf
+	}
+
+	t.Run("MissingPKGINFOFile", func(t *testing.T) {
+		data := createPackage("dummy.txt", []byte{})
+
+		pp, err := ParsePackage(data)
+		assert.Nil(t, pp)
+		assert.ErrorIs(t, err, ErrMissingPKGINFOFile)
+	})
+
+	t.Run("InvalidPKGINFOFile", func(t *testing.T) {
+		data := createPackage(".PKGINFO", []byte{})
+
+		pp, err := ParsePackage(data)
+		assert.Nil(t, pp)
+		assert.ErrorIs(t, err, ErrInvalidName)
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		data := createPackage(".PKGINFO", createPKGINFOContent(packageName, packageVersion))
+
+		p, err := ParsePackage(data)
+		assert.NoError(t, err)
+		assert.NotNil(t, p)
+
+		assert.Equal(t, "Q1SRYURM5+uQDqfHSwTnNIOIuuDVQ=", p.FileMetadata.Checksum)
+	})
+}
+
+func TestParsePackageInfo(t *testing.T) {
+	t.Run("InvalidName", func(t *testing.T) {
+		data := createPKGINFOContent("", packageVersion)
+
+		p, err := ParsePackageInfo(bytes.NewReader(data))
+		assert.Nil(t, p)
+		assert.ErrorIs(t, err, ErrInvalidName)
+	})
+
+	t.Run("InvalidVersion", func(t *testing.T) {
+		data := createPKGINFOContent(packageName, "")
+
+		p, err := ParsePackageInfo(bytes.NewReader(data))
+		assert.Nil(t, p)
+		assert.ErrorIs(t, err, ErrInvalidVersion)
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		data := createPKGINFOContent(packageName, packageVersion)
+
+		p, err := ParsePackageInfo(bytes.NewReader(data))
+		assert.NoError(t, err)
+		assert.NotNil(t, p)
+
+		assert.Equal(t, packageName, p.Name)
+		assert.Equal(t, packageVersion, p.Version)
+		assert.Equal(t, packageDescription, p.VersionMetadata.Description)
+		assert.Equal(t, packageMaintainer, p.VersionMetadata.Maintainer)
+		assert.Equal(t, packageProjectURL, p.VersionMetadata.ProjectURL)
+		assert.Equal(t, "MIT", p.VersionMetadata.License)
+		assert.Empty(t, p.FileMetadata.Checksum)
+		assert.Equal(t, "Gitea <pack@ag.er>", p.FileMetadata.Packager)
+		assert.EqualValues(t, 1678834800, p.FileMetadata.BuildDate)
+		assert.EqualValues(t, 123456, p.FileMetadata.Size)
+		assert.Equal(t, "aarch64", p.FileMetadata.Architecture)
+		assert.Equal(t, "origin", p.FileMetadata.Origin)
+		assert.Equal(t, "1111e709613fbc979651b09ac2bc27c6591a9999", p.FileMetadata.CommitHash)
+		assert.Equal(t, "value", p.FileMetadata.InstallIf)
+		assert.ElementsMatch(t, []string{"common", "gitea"}, p.FileMetadata.Provides)
+		assert.ElementsMatch(t, []string{"common", "gitea"}, p.FileMetadata.Dependencies)
+	})
+}