1 package main
2 
3 import (
4 	"archive/tar"
5 	"errors"
6 	"fmt"
7 	"io"
8 	"io/fs"
9 	"log"
10 	"net/http"
11 	"os"
12 	"path"
13 	"time"
14 )
15 
16 func cacheDir() (string, error) {
17 	d, err := os.UserCacheDir()
18 	return path.Join(d, "tarweb"), err
19 }
20 
21 func Extract(r *tar.Reader, dir string) error {
22 	for {
23 		hdr, err := r.Next()
24 		if err == io.EOF {
25 			break // End of archive
26 		}
27 		if err != nil {
28 			return err
29 		}
30 		fmt.Println(hdr.Name)
31 		if hdr.FileInfo().IsDir() {
32 			err := os.MkdirAll(path.Join(dir, hdr.Name), 0755)
33 			if err != nil && !errors.Is(err, fs.ErrExist) {
34 				return fmt.Errorf("extract %s: %w", hdr.Name, err)
35 			}
36 			continue
37 		}
38 		dst := path.Join(dir, hdr.Name)
39 		f, err := os.Create(dst)
40 		if err != nil {
41 			return fmt.Errorf("extract %s: %v", hdr.Name, err)
42 		}
43 		if _, err := io.Copy(f, r); err != nil {
44 			return fmt.Errorf("extract %s: %v", hdr.Name, err)
45 		}
46 		f.Close()
47 	}
48 	return nil
49 }
50 
51 var urls []string = []string{"http://127.0.0.1:8000/test.tar"}
52 
53 var archives = make(map[string]time.Time)
54 
55 func getIfModified(url string, since time.Time) (*http.Response, error) {
56 	req, err := http.NewRequest(http.MethodGet, url, nil)
57 	if err != nil {
58 		return nil, err
59 	}
60 	req.Header.Add("If-Modified-Since", since.UTC().Format(time.RFC1123Z))
61 	return http.DefaultClient.Do(req)
62 }
63 
64 func fetchloop(root string, sleep time.Duration) {
65 	for {
66 		for url, since := range archives {
67 			resp, err := getIfModified(url, since)
68 			if err != nil {
69 				log.Println("get archive:", err)
70 				continue
71 			}
72 			if resp.StatusCode == http.StatusNotModified {
73 				log.Printf("%s unmodified", url)
74 				continue
75 			}
76 			if resp.Header.Get("Last-Modified") != "" {
77 				modified, err := time.Parse(time.RFC1123, resp.Header.Get("Last-Modified"))
78 				if err != nil {
79 					log.Printf("parse last modified time for %s: %v", url, err)
80 					continue
81 				}
82 				archives[url] = modified
83 			}
84 			rd := tar.NewReader(resp.Body)
85 			if err := Extract(rd, root); err != nil {
86 				log.Printf("extract %s: %v", url, err)
87 			}
88 			resp.Body.Close()
89 		}
90 		time.Sleep(sleep)
91 	}
92 }
93 
94 func main() {
95 	archives["http://127.0.0.1:8000/test.tar"] = time.Time{}
96 	archives["http://127.0.0.1:8000/meerkat.tar"] = time.Time{}
97 	cache, err := cacheDir()
98 	if err != nil {
99 		log.Fatal(err)
100 	}
101 	if err := os.MkdirAll(cache, 0755); err != nil {
102 		log.Fatal(err)
103 	}
104 	log.Println("serving archives from", cache)
105 	go fetchloop(cache, 20*time.Second)
106 	log.Fatal(http.ListenAndServe(":6969", http.FileServer(http.FS(os.DirFS(cache)))))
107 }