feat: add a translate stack

internal/marian/download.go

@@ -0,0 +1,109 @@
+package marian
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+)
+
+// RemoteFile is a model file to download, checked against its size and
+// SHA-256 digest.
+type RemoteFile struct {
+	Name   string
+	URL    string
+	Size   int64
+	SHA256 string
+}
+
+// Installed reports whether dir holds every file of a model.
+func Installed(dir string) bool {
+	for _, f := range Files {
+		if st, err := os.Stat(filepath.Join(dir, f)); err != nil || st.Size() == 0 {
+			return false
+		}
+	}
+	return true
+}
+
+// Download fetches files into dir. Each file is written next to its
+// final name and renamed once its digest is checked, so an interrupted
+// download never leaves a half-written model behind. progress receives
+// the bytes downloaded so far and the total.
+func Download(ctx context.Context, client *http.Client, dir string, files []RemoteFile, progress func(done, total int64)) error {
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return err
+	}
+	var total, done int64
+	for _, f := range files {
+		total += f.Size
+	}
+	for _, f := range files {
+		n, err := download(ctx, client, dir, f, func(n int64) {
+			if progress != nil {
+				progress(done+n, total)
+			}
+		})
+		if err != nil {
+			return fmt.Errorf("downloading %s: %w", f.Name, err)
+		}
+		done += n
+	}
+	return nil
+}
+
+func download(ctx context.Context, client *http.Client, dir string, f RemoteFile, progress func(int64)) (int64, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, f.URL, nil)
+	if err != nil {
+		return 0, err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return 0, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return 0, fmt.Errorf("server answered %s", resp.Status)
+	}
+	tmp, err := os.CreateTemp(dir, "."+f.Name+".*")
+	if err != nil {
+		return 0, err
+	}
+	defer os.Remove(tmp.Name()) // no-op once renamed
+	hash := sha256.New()
+	w := &countingWriter{w: io.MultiWriter(tmp, hash), progress: progress}
+	_, err = io.Copy(w, io.LimitReader(resp.Body, f.Size+1))
+	if cerr := tmp.Close(); err == nil {
+		err = cerr
+	}
+	if err != nil {
+		return 0, err
+	}
+	if w.n != f.Size {
+		return 0, fmt.Errorf("got %d bytes, expected %d", w.n, f.Size)
+	}
+	if sum := hex.EncodeToString(hash.Sum(nil)); sum != f.SHA256 {
+		return 0, fmt.Errorf("checksum mismatch")
+	}
+	if err := os.Chmod(tmp.Name(), 0o644); err != nil {
+		return 0, err
+	}
+	return w.n, os.Rename(tmp.Name(), filepath.Join(dir, f.Name))
+}
+
+type countingWriter struct {
+	w        io.Writer
+	n        int64
+	progress func(int64)
+}
+
+func (c *countingWriter) Write(p []byte) (int, error) {
+	n, err := c.w.Write(p)
+	c.n += int64(n)
+	c.progress(c.n)
+	return n, err
+}