Port code to download themeball to Go

tools/themes/collection.go

@@ -0,0 +1,119 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package themes
+
+import (
+	"archive/zip"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"kitty/tools/utils"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+var _ = fmt.Print
+
+type JSONMetadata struct {
+	Etag      string `json:"etag"`
+	Timestamp string `json:"timestamp"`
+}
+
+var ErrNoCacheFound = errors.New("No cache found and max cache age is negative")
+
+func fetch_cached(name, url string, max_cache_age time.Duration) (string, error) {
+	cache_path := filepath.Join(utils.CacheDir(), name+".zip")
+	zf, err := zip.OpenReader(cache_path)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return "", err
+	}
+	var jm JSONMetadata
+	err = json.Unmarshal(utils.UnsafeStringToBytes(zf.Comment), &jm)
+	if err == nil {
+		if max_cache_age < 0 {
+			return cache_path, nil
+		}
+		cache_age, err := utils.ISO8601Parse(jm.Timestamp)
+		if err == nil {
+			if time.Now().Before(cache_age.Add(max_cache_age)) {
+				return cache_path, nil
+			}
+		}
+	}
+	if max_cache_age < 0 {
+		return "", ErrNoCacheFound
+	}
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		return "", err
+	}
+	if jm.Etag != "" {
+		req.Header.Add("If-None-Match", jm.Etag)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("Failed to download %s with error: %w", url, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("Failed to download %s with HTTP error: %s", url, resp.Status)
+	}
+	var tf, tf2 *os.File
+	tf, err = os.CreateTemp(filepath.Dir(cache_path), name+".temp-*")
+	if err == nil {
+		tf2, err = os.CreateTemp(filepath.Dir(cache_path), name+".temp-*")
+	}
+	defer func() {
+		if tf != nil {
+			tf.Close()
+			os.Remove(tf.Name())
+			tf = nil
+		}
+		if tf2 != nil {
+			tf2.Close()
+			os.Remove(tf2.Name())
+			tf2 = nil
+		}
+	}()
+	if err != nil {
+		return "", fmt.Errorf("Failed to create temp file in %s with error: %w", filepath.Dir(cache_path), err)
+	}
+	_, err = io.Copy(tf, resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("Failed to download %s with error: %w", url, err)
+	}
+	r, err := zip.OpenReader(tf.Name())
+	if err != nil {
+		return "", fmt.Errorf("Failed to open downloaded zip file with error: %w", err)
+	}
+	w := zip.NewWriter(tf2)
+	jm.Etag = resp.Header.Get("ETag")
+	jm.Timestamp = utils.ISO8601Format(time.Now())
+	comment, _ := json.Marshal(jm)
+	w.SetComment(utils.UnsafeBytesToString(comment))
+	for _, file := range r.File {
+		err = w.Copy(file)
+		if err != nil {
+			return "", fmt.Errorf("Failed to copy zip file from source to destination archive")
+		}
+	}
+	err = w.Close()
+	if err != nil {
+		return "", err
+	}
+	tf2.Close()
+	err = os.Rename(tf2.Name(), cache_path)
+	if err != nil {
+		return "", fmt.Errorf("Failed to atomic rename temp file to %s with error: %w", cache_path, err)
+	}
+	tf2 = nil
+	return cache_path, nil
+}
+
+func FetchCached(max_cache_age time.Duration) (string, error) {
+	return fetch_cached("kitty-themes", "https://codeload.github.com/kovidgoyal/kitty-themes/zip/master", max_cache_age)
+}