Server v4 (#370)

* refactoring-1

introduced pipelines and abstracted download process.go in Downloader interface

* migrated to boltdb from sqlite + session files

* refactoring: config struct & pipelines

* added js runtime for yt-dlp

* updated dockerfile

* added external js runtime, metadata scraping refactor

* updated Dockerfile

* fixed env propagation in docker

* updated package name to v4

* updated readme and cd

server/internal/metadata/fetchers.go

@@ -0,0 +1,57 @@
+package metadata
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io"
+	"log/slog"
+	"os/exec"
+	"syscall"
+	"time"
+
+	"github.com/marcopiovanello/yt-dlp-web-ui/v4/server/common"
+	"github.com/marcopiovanello/yt-dlp-web-ui/v4/server/config"
+)
+
+func DefaultFetcher(url string) (*common.DownloadMetadata, error) {
+	cmd := exec.Command(config.Instance().Paths.DownloaderPath, url, "-J")
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	meta := common.DownloadMetadata{
+		URL:       url,
+		CreatedAt: time.Now(),
+	}
+
+	if err := cmd.Start(); err != nil {
+		return nil, err
+	}
+
+	var bufferedStderr bytes.Buffer
+
+	go func() {
+		io.Copy(&bufferedStderr, stderr)
+	}()
+
+	slog.Info("retrieving metadata", slog.String("url", url))
+
+	if err := json.NewDecoder(stdout).Decode(&meta); err != nil {
+		return nil, err
+	}
+
+	if err := cmd.Wait(); err != nil {
+		return nil, errors.New(bufferedStderr.String())
+	}
+
+	return &meta, nil
+}