Add support for Pub packages (#20560)

* Added support for Pub packages.

* Update docs/content/doc/packages/overview.en-us.md

Co-authored-by: Gergely Nagy <algernon@users.noreply.github.com>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Gergely Nagy <algernon@users.noreply.github.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

modules/packages/pub/metadata.go

@@ -0,0 +1,154 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pub
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"errors"
+	"io"
+	"regexp"
+	"strings"
+
+	"code.gitea.io/gitea/modules/validation"
+
+	"github.com/hashicorp/go-version"
+	"gopkg.in/yaml.v2"
+)
+
+var (
+	ErrMissingPubspecFile  = errors.New("Pubspec file is missing")
+	ErrPubspecFileTooLarge = errors.New("Pubspec file is too large")
+	ErrInvalidName         = errors.New("Package name is invalid")
+	ErrInvalidVersion      = errors.New("Package version is invalid")
+)
+
+var namePattern = regexp.MustCompile(`\A[a-zA-Z_][a-zA-Z0-9_]*\z`)
+
+// https://github.com/dart-lang/pub-dev/blob/4d582302a8d10152a5cd6129f65bf4f4dbca239d/pkg/pub_package_reader/lib/pub_package_reader.dart#L143
+const maxPubspecFileSize = 128 * 1024
+
+// Package represents a Pub package
+type Package struct {
+	Name     string
+	Version  string
+	Metadata *Metadata
+}
+
+// Metadata represents the metadata of a Pub package
+type Metadata struct {
+	Description      string      `json:"description,omitempty"`
+	ProjectURL       string      `json:"project_url,omitempty"`
+	RepositoryURL    string      `json:"repository_url,omitempty"`
+	DocumentationURL string      `json:"documentation_url,omitempty"`
+	Readme           string      `json:"readme,omitempty"`
+	Pubspec          interface{} `json:"pubspec"`
+}
+
+type pubspecPackage struct {
+	Name          string `yaml:"name"`
+	Version       string `yaml:"version"`
+	Description   string `yaml:"description"`
+	Homepage      string `yaml:"homepage"`
+	Repository    string `yaml:"repository"`
+	Documentation string `yaml:"documentation"`
+}
+
+// ParsePackage parses the Pub package file
+func ParsePackage(r io.Reader) (*Package, error) {
+	gzr, err := gzip.NewReader(r)
+	if err != nil {
+		return nil, err
+	}
+	defer gzr.Close()
+
+	var p *Package
+	var readme string
+
+	tr := tar.NewReader(gzr)
+	for {
+		hd, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+
+		if hd.Typeflag != tar.TypeReg {
+			continue
+		}
+
+		if hd.Name == "pubspec.yaml" {
+			if hd.Size > maxPubspecFileSize {
+				return nil, ErrPubspecFileTooLarge
+			}
+			p, err = ParsePubspecMetadata(tr)
+			if err != nil {
+				return nil, err
+			}
+		} else if strings.ToLower(hd.Name) == "readme.md" {
+			data, err := io.ReadAll(tr)
+			if err != nil {
+				return nil, err
+			}
+			readme = string(data)
+		}
+	}
+
+	if p == nil {
+		return nil, ErrMissingPubspecFile
+	}
+
+	p.Metadata.Readme = readme
+
+	return p, nil
+}
+
+// ParsePubspecMetadata parses a Pubspec file to retrieve the metadata of a Pub package
+func ParsePubspecMetadata(r io.Reader) (*Package, error) {
+	buf, err := io.ReadAll(io.LimitReader(r, maxPubspecFileSize))
+	if err != nil {
+		return nil, err
+	}
+
+	var p pubspecPackage
+	if err := yaml.Unmarshal(buf, &p); err != nil {
+		return nil, err
+	}
+
+	if !namePattern.MatchString(p.Name) {
+		return nil, ErrInvalidName
+	}
+
+	v, err := version.NewSemver(p.Version)
+	if err != nil {
+		return nil, ErrInvalidVersion
+	}
+
+	if !validation.IsValidURL(p.Homepage) {
+		p.Homepage = ""
+	}
+	if !validation.IsValidURL(p.Repository) {
+		p.Repository = ""
+	}
+
+	var pubspec interface{}
+	if err := yaml.Unmarshal(buf, &pubspec); err != nil {
+		return nil, err
+	}
+
+	return &Package{
+		Name:    p.Name,
+		Version: v.String(),
+		Metadata: &Metadata{
+			Description:      p.Description,
+			ProjectURL:       p.Homepage,
+			RepositoryURL:    p.Repository,
+			DocumentationURL: p.Documentation,
+			Pubspec:          pubspec,
+		},
+	}, nil
+}