react-native/Libraries/Image/RCTImageCache.m

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#import "RCTImageCache.h"

#import <objc/runtime.h>

#import <ImageIO/ImageIO.h>

#import <React/RCTConvert.h>
#import <React/RCTNetworking.h>
#import <React/RCTUtils.h>
#import <React/RCTResizeMode.h>

#import "RCTImageUtils.h"

static const NSUInteger RCTMaxCachableDecodedImageSizeInBytes = 1048576; // 1MB

static NSString *RCTCacheKeyForImage(NSString *imageTag, CGSize size, CGFloat scale,
                                     RCTResizeMode resizeMode)
{
  return [NSString stringWithFormat:@"%@|%g|%g|%g|%lld",
          imageTag, size.width, size.height, scale, (long long)resizeMode];
}

@implementation RCTImageCache
{
  NSOperationQueue *_imageDecodeQueue;
  NSCache *_decodedImageCache;
  NSMutableDictionary *_cacheStaleTimes;

  NSDateFormatter *_headerDateFormatter;
}

- (instancetype)init
{
  _decodedImageCache = [NSCache new];
  _decodedImageCache.totalCostLimit = 5 * 1024 * 1024; // 5MB
  _cacheStaleTimes = [[NSMutableDictionary alloc] init];

  [[NSNotificationCenter defaultCenter] addObserver:self
                                           selector:@selector(clearCache)
                                               name:UIApplicationDidReceiveMemoryWarningNotification
                                             object:nil];
  [[NSNotificationCenter defaultCenter] addObserver:self
                                           selector:@selector(clearCache)
                                               name:UIApplicationWillResignActiveNotification
                                             object:nil];
  
  return self;
}

- (void)dealloc
{
  [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)clearCache
{
  [_decodedImageCache removeAllObjects];
  @synchronized(_cacheStaleTimes) {
    [_cacheStaleTimes removeAllObjects];
  }
}

- (void)addImageToCache:(UIImage *)image
                 forKey:(NSString *)cacheKey
{
  if (!image) {
    return;
  }
  CGFloat bytes = image.size.width * image.size.height * image.scale * image.scale * 4;
  if (bytes <= RCTMaxCachableDecodedImageSizeInBytes) {
    [self->_decodedImageCache setObject:image
                                 forKey:cacheKey
                                   cost:bytes];
  }
}

- (UIImage *)imageForUrl:(NSString *)url
                    size:(CGSize)size
                   scale:(CGFloat)scale
              resizeMode:(RCTResizeMode)resizeMode
{
  NSString *cacheKey = RCTCacheKeyForImage(url, size, scale, resizeMode);
  @synchronized(_cacheStaleTimes) {
    id staleTime = _cacheStaleTimes[cacheKey];
    if (staleTime) {
      if ([[NSDate new] compare:(NSDate *)staleTime] == NSOrderedDescending) {
        // cached image has expired, clear it out to make room for others
        [_cacheStaleTimes removeObjectForKey:cacheKey];
        [_decodedImageCache removeObjectForKey:cacheKey];
        return nil;
      }
    }
  }
  return [_decodedImageCache objectForKey:cacheKey];
}

- (void)addImageToCache:(UIImage *)image
                    URL:(NSString *)url
                   size:(CGSize)size
                  scale:(CGFloat)scale
             resizeMode:(RCTResizeMode)resizeMode
           responseDate:(NSString *)responseDate
           cacheControl:(NSString *)cacheControl
{
  NSString *cacheKey = RCTCacheKeyForImage(url, size, scale, resizeMode);
  BOOL shouldCache = YES;
  NSDate *staleTime;
  NSArray<NSString *> *components = [cacheControl componentsSeparatedByString:@","];
  for (NSString *component in components) {
    if ([component containsString:@"no-cache"] || [component containsString:@"no-store"] || [component hasSuffix:@"max-age=0"]) {
      shouldCache = NO;
      break;
    } else {
      NSRange range = [component rangeOfString:@"max-age="];
      if (range.location != NSNotFound) {
        NSInteger seconds = [[component substringFromIndex:range.location + range.length] integerValue];
        NSDate *originalDate = [self dateWithHeaderString:responseDate];
        staleTime = [originalDate dateByAddingTimeInterval:(NSTimeInterval)seconds];
      }
    }
  }
  if (shouldCache) {
    if (staleTime) {
      @synchronized(_cacheStaleTimes) {
        _cacheStaleTimes[cacheKey] = staleTime;
      }
    }
    return [self addImageToCache:image forKey:cacheKey];
  }
}

- (NSDate *)dateWithHeaderString:(NSString *)headerDateString {
  if (_headerDateFormatter == nil) {
    _headerDateFormatter = [[NSDateFormatter alloc] init];
    _headerDateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
    _headerDateFormatter.dateFormat = @"EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'";
    _headerDateFormatter.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
  }

  return [_headerDateFormatter dateFromString:headerDateString];
}

@end