Support cache (#25)

See [Caching dependencies to speed up workflows](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows).

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/25
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: Zettat123 <zettat123@noreply.gitea.io>
Co-authored-by: Jason Song <i@wolfogre.com>
Co-committed-by: Jason Song <i@wolfogre.com>

artifactcache/storage.go

@@ -0,0 +1,129 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package artifactcache
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+)
+
+type Storage struct {
+	rootDir string
+}
+
+func NewStorage(rootDir string) (*Storage, error) {
+	if err := os.MkdirAll(rootDir, 0o755); err != nil {
+		return nil, err
+	}
+	return &Storage{
+		rootDir: rootDir,
+	}, nil
+}
+
+func (s *Storage) Exist(id int64) (bool, error) {
+	name := s.filename(id)
+	if _, err := os.Stat(name); os.IsNotExist(err) {
+		return false, nil
+	} else if err != nil {
+		return false, err
+	}
+	return true, nil
+}
+
+func (s *Storage) Write(id int64, offset int64, reader io.Reader) error {
+	name := s.tempName(id, offset)
+	if err := os.MkdirAll(filepath.Dir(name), 0o755); err != nil {
+		return err
+	}
+	file, err := os.Create(name)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	_, err = io.Copy(file, reader)
+	return err
+}
+
+func (s *Storage) Commit(id int64, size int64) error {
+	defer func() {
+		_ = os.RemoveAll(s.tempDir(id))
+	}()
+
+	name := s.filename(id)
+	tempNames, err := s.tempNames(id)
+	if err != nil {
+		return err
+	}
+
+	if err := os.MkdirAll(filepath.Dir(name), 0o755); err != nil {
+		return err
+	}
+	file, err := os.Create(name)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	var written int64
+	for _, v := range tempNames {
+		f, err := os.Open(v)
+		if err != nil {
+			return err
+		}
+		n, err := io.Copy(file, f)
+		_ = f.Close()
+		if err != nil {
+			return err
+		}
+		written += n
+	}
+
+	if written != size {
+		_ = file.Close()
+		_ = os.Remove(name)
+		return fmt.Errorf("broken file: %v != %v", written, size)
+	}
+	return nil
+}
+
+func (s *Storage) Serve(w http.ResponseWriter, r *http.Request, id int64) {
+	name := s.filename(id)
+	http.ServeFile(w, r, name)
+}
+
+func (s *Storage) Remove(id int64) {
+	_ = os.Remove(s.filename(id))
+	_ = os.RemoveAll(s.tempDir(id))
+}
+
+func (s *Storage) filename(id int64) string {
+	return filepath.Join(s.rootDir, fmt.Sprintf("%02x", id%0xff), fmt.Sprint(id))
+}
+
+func (s *Storage) tempDir(id int64) string {
+	return filepath.Join(s.rootDir, "tmp", fmt.Sprint(id))
+}
+
+func (s *Storage) tempName(id, offset int64) string {
+	return filepath.Join(s.tempDir(id), fmt.Sprintf("%016x", offset))
+}
+
+func (s *Storage) tempNames(id int64) ([]string, error) {
+	dir := s.tempDir(id)
+	files, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, err
+	}
+	var names []string
+	for _, v := range files {
+		if !v.IsDir() {
+			names = append(names, filepath.Join(dir, v.Name()))
+		}
+	}
+	return names, nil
+}