source: binary-improvements/7dtd-server-fixes/src/FileCache/MapTileCache.cs@ 345

using System;
using System.IO;
using UnityEngine;
using UnityEngine.Profiling;
using Object = UnityEngine.Object;

namespace AllocsFixes.FileCache {
        // Special "cache" for map tile folder as both map rendering and webserver access files in there.
        // Only map rendering tiles are cached. Writing is done by WriteThrough.
        public class MapTileCache : AbstractCache {
                private readonly byte[] transparentTile;
                private CurrentZoomFile[] cache;

                public MapTileCache (int _tileSize) {
                        Texture2D tex = new Texture2D (_tileSize, _tileSize);
                        Color nullColor = new Color (0, 0, 0, 0);
                        for (int x = 0; x < _tileSize; x++) {
                                for (int y = 0; y < _tileSize; y++) {
                                        tex.SetPixel (x, y, nullColor);
                                }
                        }

                        transparentTile = tex.EncodeToPNG ();
                        Object.Destroy (tex);
                }

                public void SetZoomCount (int count) {
                        cache = new CurrentZoomFile[count];
                        for (int i = 0; i < cache.Length; i++) {
                                cache [i] = new CurrentZoomFile ();
                        }
                }

                public byte[] LoadTile (int zoomlevel, string filename) {
                        try {
                                lock (cache) {
                                        CurrentZoomFile cacheEntry = cache [zoomlevel];
                                        
                                        if (cacheEntry.filename == null || !cacheEntry.filename.Equals (filename)) {
                                                cacheEntry.filename = filename;

                                                if (!File.Exists (filename)) {
                                                        cacheEntry.pngData = null;
                                                        return null;
                                                }

                                                Profiler.BeginSample ("ReadPng");
                                                cacheEntry.pngData = ReadAllBytes (filename);
                                                Profiler.EndSample ();
                                        }

                                        return cacheEntry.pngData;
                                }
                        } catch (Exception e) {
                                Log.Warning ("Error in MapTileCache.LoadTile: " + e);
                        }

                        return null;
                }

                public void SaveTile (int zoomlevel, byte[] contentPng) {
                        try {
                                lock (cache) {
                                        CurrentZoomFile cacheEntry = cache [zoomlevel];

                                        string file = cacheEntry.filename;
                                        if (string.IsNullOrEmpty (file)) {
                                                return;
                                        }
                                        
                                        cacheEntry.pngData = contentPng;

                                        Profiler.BeginSample ("WritePng");
                                        using (Stream stream = new FileStream (file, FileMode.Create, FileAccess.ReadWrite, FileShare.None,
                                                4096)) {
                                                stream.Write (contentPng, 0, contentPng.Length);
                                        }
                                        Profiler.EndSample ();
                                }
                        } catch (Exception e) {
                                Log.Warning ("Error in MapTileCache.SaveTile: " + e);
                        }
                }

                public override byte[] GetFileContent (string filename) {
                        try {
                                lock (cache) {
                                        foreach (CurrentZoomFile czf in cache) {
                                                if (czf.filename != null && czf.filename.Equals (filename)) {
                                                        return czf.pngData;
                                                }
                                        }

                                        if (!File.Exists (filename)) {
                                                return transparentTile;
                                        }

                                        return ReadAllBytes (filename);
                                }
                        } catch (Exception e) {
                                Log.Warning ("Error in MapTileCache.GetFileContent: " + e);
                        }

                        return null;
                }

                private static byte[] ReadAllBytes (string _path) {
                        using (FileStream fileStream = new FileStream(_path, FileMode.Open, FileAccess.Read, FileShare.Read, 4096)) {
                                int bytesRead = 0;
                                int bytesLeft = (int) fileStream.Length;
                                byte[] result = new byte[bytesLeft];
                                while (bytesLeft > 0) {
                                        int readThisTime = fileStream.Read (result, bytesRead, bytesLeft);
                                        if (readThisTime == 0) {
                                                throw new IOException ("Unexpected end of stream");
                                        }

                                        bytesRead += readThisTime;
                                        bytesLeft -= readThisTime;
                                }

                                return result;
                        }
                }


                private class CurrentZoomFile {
                        public string filename;
                        public byte[] pngData;
                }
        }
}