Add Cargo package registry (#21888)

This PR implements a [Cargo registry](https://doc.rust-lang.org/cargo/)
to manage Rust packages. This package type was a little bit more
complicated because Cargo needs an additional Git repository to store
its package index.

Screenshots:

![grafik](https://user-images.githubusercontent.com/1666336/203102004-08d812ac-c066-4969-9bda-2fed818554eb.png)

![grafik](https://user-images.githubusercontent.com/1666336/203102141-d9970f14-dca6-4174-b17a-50ba1bd79087.png)

![grafik](https://user-images.githubusercontent.com/1666336/203102244-dc05743b-78b6-4d97-998e-ef76341a978f.png)

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/packages/cargo/parser_test.go

@@ -0,0 +1,86 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cargo
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const (
+	description = "Package Description"
+	author      = "KN4CK3R"
+	homepage    = "https://gitea.io/"
+	license     = "MIT"
+)
+
+func TestParsePackage(t *testing.T) {
+	createPackage := func(name, version string) io.Reader {
+		metadata := `{
+   "name":"` + name + `",
+   "vers":"` + version + `",
+   "description":"` + description + `",
+   "authors": ["` + author + `"],
+   "deps":[
+      {
+         "name":"dep",
+         "version_req":"1.0"
+      }
+   ],
+   "homepage":"` + homepage + `",
+   "license":"` + license + `"
+}`
+
+		var buf bytes.Buffer
+		binary.Write(&buf, binary.LittleEndian, uint32(len(metadata)))
+		buf.WriteString(metadata)
+		binary.Write(&buf, binary.LittleEndian, uint32(4))
+		buf.WriteString("test")
+		return &buf
+	}
+
+	t.Run("InvalidName", func(t *testing.T) {
+		for _, name := range []string{"", "0test", "-test", "_test", strings.Repeat("a", 65)} {
+			data := createPackage(name, "1.0.0")
+
+			cp, err := ParsePackage(data)
+			assert.Nil(t, cp)
+			assert.ErrorIs(t, err, ErrInvalidName)
+		}
+	})
+
+	t.Run("InvalidVersion", func(t *testing.T) {
+		for _, version := range []string{"", "1.", "-1.0", "1.0.0/1"} {
+			data := createPackage("test", version)
+
+			cp, err := ParsePackage(data)
+			assert.Nil(t, cp)
+			assert.ErrorIs(t, err, ErrInvalidVersion)
+		}
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		data := createPackage("test", "1.0.0")
+
+		cp, err := ParsePackage(data)
+		assert.NotNil(t, cp)
+		assert.NoError(t, err)
+
+		assert.Equal(t, "test", cp.Name)
+		assert.Equal(t, "1.0.0", cp.Version)
+		assert.Equal(t, description, cp.Metadata.Description)
+		assert.Equal(t, []string{author}, cp.Metadata.Authors)
+		assert.Len(t, cp.Metadata.Dependencies, 1)
+		assert.Equal(t, "dep", cp.Metadata.Dependencies[0].Name)
+		assert.Equal(t, homepage, cp.Metadata.ProjectURL)
+		assert.Equal(t, license, cp.Metadata.License)
+		content, _ := io.ReadAll(cp.Content)
+		assert.Equal(t, "test", string(content))
+	})
+}