/*

     File: CacheStoragePolicy.m

 Abstract: A function to determine the cache storage policy for a request.

  Version: 1.1

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 */

#import "CacheStoragePolicy.h"

extern NSURLCacheStoragePolicy CacheStoragePolicyForRequestAndResponse(NSURLRequest * request, NSHTTPURLResponse * response)

    // See comment in header.

{

    BOOL                        cacheable;

    NSURLCacheStoragePolicy     result;

    assert(request != NULL);

    assert(response != NULL);

    // First determine if the request is cacheable based on its status code.

    switch ([response statusCode]) {

        case 200:

        case 203:

        case 206:

        case 301:

        case 304:

        case 404:

        case 410: {

            cacheable = YES;

        } break;

        default: {

            cacheable = NO;

        } break;

    }

    // If the response might be cacheable, look at the "Cache-Control" header in 

    // the response.

    // IMPORTANT: We can't rely on -rangeOfString: returning valid results if the target 

    // string is nil, so we have to explicitly test for nil in the following two cases.

    if (cacheable) {

        NSString *  responseHeader;

        responseHeader = [[response allHeaderFields][@"Cache-Control"] lowercaseString];

        if ( (responseHeader != nil) && [responseHeader rangeOfString:@"no-store"].location != NSNotFound) {

            cacheable = NO;

        }

    }

    // If we still think it might be cacheable, look at the "Cache-Control" header in 

    // the request.

    if (cacheable) {

        NSString *  requestHeader;

        requestHeader = [[request allHTTPHeaderFields][@"Cache-Control"] lowercaseString];

        if ( (requestHeader != nil) 

          && ([requestHeader rangeOfString:@"no-store"].location != NSNotFound)

          && ([requestHeader rangeOfString:@"no-cache"].location != NSNotFound) ) {

            cacheable = NO;

        }

    }

    // Use the cacheable flag to determine the result.

    if (cacheable) {

        // This code only caches HTTPS data in memory.  This is inline with earlier versions of 

        // iOS.  Modern versions of iOS use file protection to protect the cache, and thus are 

        // happy to cache HTTPS on disk.  I've not made the correspondencing change because 

        // it's nice to see all three cache policies in action.

        if ([[[[request URL] scheme] lowercaseString] isEqual:@"https"]) {

            result = NSURLCacheStorageAllowedInMemoryOnly;

        } else {

            result = NSURLCacheStorageAllowed;

        }

    } else {

        result = NSURLCacheStorageNotAllowed;

    }

    return result;

}