From b91aa1db386dd5eaf447ab41c5e13921af419dd2 Mon Sep 17 00:00:00 2001
From: Mukhtar Akere <akeremukhtar10@gmail.com>
Date: Sat, 15 Mar 2025 23:12:37 +0100
Subject: [PATCH] Add a precacher to significantly improve importing to
 arrs/plex

---
 doc/config.full.json      |  1 +
 internal/config/config.go |  1 +
 pkg/qbit/downloader.go    | 53 +++++++++++++++++++++++++++++++++++++++
 pkg/qbit/qbit.go          |  2 ++
 4 files changed, 57 insertions(+)

diff --git a/doc/config.full.json b/doc/config.full.json
index b3107e5..dda1890 100644
--- a/doc/config.full.json
+++ b/doc/config.full.json
@@ -51,6 +51,7 @@
     "download_folder": "/mnt/symlinks/",
     "categories": ["sonarr", "radarr"],
     "refresh_interval": 5,
+    "skip_pre_cache": false
   },
   "arrs": [
     {
diff --git a/internal/config/config.go b/internal/config/config.go
index 70f4372..bd9b816 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -41,6 +41,7 @@ type QBitTorrent struct {
 	DownloadFolder  string   `json:"download_folder"`
 	Categories      []string `json:"categories"`
 	RefreshInterval int      `json:"refresh_interval"`
+	SkipPreCache    bool     `json:"skip_pre_cache"`
 }
 
 type Arr struct {
diff --git a/pkg/qbit/downloader.go b/pkg/qbit/downloader.go
index c9ae894..d2ecb52 100644
--- a/pkg/qbit/downloader.go
+++ b/pkg/qbit/downloader.go
@@ -6,6 +6,7 @@ import (
 	"github.com/cavaliergopher/grab/v3"
 	"github.com/sirrobot01/debrid-blackhole/internal/utils"
 	debrid "github.com/sirrobot01/debrid-blackhole/pkg/debrid/torrent"
+	"io"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -202,4 +203,56 @@ func (q *QBit) createSymLink(path string, torrentMountPath string, file debrid.F
 		// It's okay if the symlink already exists
 		q.logger.Debug().Msgf("Failed to create symlink: %s: %v", fullPath, err)
 	}
+	if q.SkipPreCache {
+		return
+	}
+	go func() {
+		err := q.preCacheFile(torrentFilePath)
+		if err != nil {
+			q.logger.Debug().Msgf("Failed to pre-cache file: %s: %v", torrentFilePath, err)
+		}
+	}()
+}
+
+func (q *QBit) preCacheFile(filePath string) error {
+	q.logger.Trace().Msgf("Pre-caching file: %s", filePath)
+	file, err := os.Open(filePath)
+	if err != nil {
+		return fmt.Errorf("error opening file: %v", err)
+	}
+	defer file.Close()
+
+	// Pre-cache the file header (first 256KB) using 16KB chunks.
+	q.readSmallChunks(file, 0, 256*1024, 16*1024)
+	q.readSmallChunks(file, 1024*1024, 64*1024, 16*1024)
+
+	return nil
+}
+
+func (q *QBit) readSmallChunks(file *os.File, startPos int64, totalToRead int, chunkSize int) {
+	_, err := file.Seek(startPos, 0)
+	if err != nil {
+		return
+	}
+
+	buf := make([]byte, chunkSize)
+	bytesRemaining := totalToRead
+
+	for bytesRemaining > 0 {
+		toRead := chunkSize
+		if bytesRemaining < chunkSize {
+			toRead = bytesRemaining
+		}
+
+		n, err := file.Read(buf[:toRead])
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return
+		}
+
+		bytesRemaining -= n
+	}
+	return
 }
diff --git a/pkg/qbit/qbit.go b/pkg/qbit/qbit.go
index c7102dd..84726ea 100644
--- a/pkg/qbit/qbit.go
+++ b/pkg/qbit/qbit.go
@@ -19,6 +19,7 @@ type QBit struct {
 	logger          zerolog.Logger
 	Tags            []string
 	RefreshInterval int
+	SkipPreCache    bool
 }
 
 func New() *QBit {
@@ -35,5 +36,6 @@ func New() *QBit {
 		Storage:         NewTorrentStorage(filepath.Join(_cfg.Path, "torrents.json")),
 		logger:          logger.NewLogger("qbit", _cfg.LogLevel, os.Stdout),
 		RefreshInterval: refreshInterval,
+		SkipPreCache:    cfg.SkipPreCache,
 	}
 }