Source/TNLPseudoURLProtocol.m

//
//  TNLPseudoURLProtocol.m
//  TwitterNetworkLayer
//
//  Created on 10/29/14.
//  Copyright © 2020 Twitter. All rights reserved.
//

#import "NSData+TNLAdditions.h"
#import "NSDictionary+TNLAdditions.h"
#import "TNL_Project.h"
#import "TNLPseudoURLProtocol.h"

NS_ASSUME_NONNULL_BEGIN

#define ABORT_IF_NECESSARY() \
do { \
    if (self.stopped) { \
        return; \
    } \
} while (0)

NSString * const TNLPseudoURLProtocolErrorDomain = @"TNLPseudoURLProtocolErrorDomain";

static NSMutableDictionary *sOriginToResponseDictionary;
static dispatch_queue_t sOriginQueue;

static NSString * __nullable _UnderlyingURLString(NSURL * __nullable url);
static NSHTTPURLResponse * _UpdateResponse(NSHTTPURLResponse *response,
                                           NSUInteger contentLength,
                                           NSInteger statusCode);
static NSRange _RangeForRequest(NSURLRequest *request,
                                NSUInteger dataLength,
                                NSString *stringForIfRange);

typedef void(^TNLPseudoURLClientBlock)(id<NSURLProtocolClient> client);

TNL_OBJC_DIRECT_MEMBERS
@interface TNLPseudoURLProtocol ()

@property (atomic) BOOL stopped;
@property (nonatomic, nullable) NSCachedURLResponse *responseToUse;
@property (nonatomic, nullable) dispatch_queue_t protocolQueue;
@property (nonatomic, nullable) CFRunLoopRef protocolRunLoop;

- (void)_executeClientBlock:(TNLPseudoURLClientBlock)block;
- (BOOL)_handleRedirectForRequest:(NSURLRequest *)request
                         response:(NSHTTPURLResponse *)httpResponse
                         behavior:(const TNLPseudoURLProtocolRedirectBehavior)behavior;
- (void)_chunkData:(NSData *)data
               bps:(NSUInteger)bps
         bytesSent:(NSUInteger)bytesSent
           latency:(NSTimeInterval)latency;
@end

@implementation TNLPseudoURLProtocol

+ (void)registerURLResponse:(NSHTTPURLResponse *)response
                       body:(nullable NSData *)body
               withEndpoint:(NSURL *)endpoint
{
    [self registerURLResponse:response
                         body:body
                       config:nil
                 withEndpoint:endpoint];
}

+ (void)registerURLResponse:(NSHTTPURLResponse *)response
                       body:(nullable NSData *)body
                     config:(nullable TNLPseudoURLResponseConfig *)config
               withEndpoint:(NSURL *)endpoint
{
    NSCachedURLResponse *cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:response
                                                                                   data:body
                                                                               userInfo:(config) ? @{ @"config" : [config copy] } : nil
                                                                          storagePolicy:NSURLCacheStorageAllowed];

    tnl_dispatch_barrier_async_autoreleasing(sOriginQueue, ^{
        sOriginToResponseDictionary[_UnderlyingURLString(endpoint)] = cachedResponse;
    });
}

+ (void)unregisterEndpoint:(NSURL *)endpoint
{
    tnl_dispatch_barrier_async_autoreleasing(sOriginQueue, ^{
        [sOriginToResponseDictionary removeObjectForKey:_UnderlyingURLString(endpoint)];
    });
}

+ (void)unregisterAllEndpoints
{
    tnl_dispatch_barrier_async_autoreleasing(sOriginQueue, ^{
        [sOriginToResponseDictionary removeAllObjects];
    });
}

+ (BOOL)isEndpointRegistered:(NSURL *)endpoint
{
    __block BOOL isRegistered = NO;
    dispatch_sync(sOriginQueue, ^{
        isRegistered = (sOriginToResponseDictionary[_UnderlyingURLString(endpoint)] != nil);
    });
    return isRegistered;
}

+ (void)initialize
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sOriginToResponseDictionary = [[NSMutableDictionary alloc] init];
        sOriginQueue = dispatch_queue_create("tnl.pseudo.url.protocol.origin.queue", DISPATCH_QUEUE_CONCURRENT);
    });
}

+ (BOOL)canInitWithRequest:(NSURLRequest *)request
{
    NSString *url = _UnderlyingURLString(request.URL);
    if (!url) {
        return NO;
    }

    __block BOOL originsMatch;
    dispatch_sync(sOriginQueue, ^{
        originsMatch = sOriginToResponseDictionary[url] != nil;
    });
    return originsMatch;
}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
    NSMutableURLRequest *mRequest = [request mutableCopy];
    mRequest.URL = [NSURL URLWithString:request.URL.absoluteString.lowercaseString];
    NSDictionary *allFields = request.allHTTPHeaderFields;
    NSMutableDictionary *mDictionary = [[NSMutableDictionary alloc] init];
    for (NSString *key in allFields.allKeys) {
        [mDictionary tnl_setObject:allFields[key]
             forCaseInsensitiveKey:key.lowercaseString];
    }
    mRequest.allHTTPHeaderFields = mDictionary;
    return mRequest;
}

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b
{
    return [a isEqual:b];
}

- (void)startLoading
{
    self.protocolRunLoop = CFRunLoopGetCurrent();
    tnl_dispatch_async_autoreleasing(_protocolQueue, ^{
        ABORT_IF_NECESSARY();

        NSURLRequest *request = self.request;
        NSString *url = _UnderlyingURLString(request.URL);
        TNLAssert(url);
        __block NSCachedURLResponse *response;
        dispatch_sync(sOriginQueue, ^{
            response = sOriginToResponseDictionary[url];
        });

        if (response) {
            if (self.cachedResponse) {
                tnl_dispatch_async_autoreleasing(self->_protocolQueue, ^{
                    ABORT_IF_NECESSARY();
                    [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                        [client URLProtocol:self cachedResponseIsValid:self.cachedResponse];
                    }];
                    tnl_dispatch_async_autoreleasing(self->_protocolQueue, ^{
                        ABORT_IF_NECESSARY();
                        self.stopped = YES;
                        [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                            [client URLProtocolDidFinishLoading:self];
                        }];
                    });
                });
            } else {

                TNLPseudoURLResponseConfig *config = response.userInfo[@"config"];

                if (config.extraRequestHeaders.count > 0) {
                    NSMutableDictionary *fullHeaders = [NSMutableDictionary dictionaryWithDictionary:config.extraRequestHeaders];
                    [fullHeaders addEntriesFromDictionary:request.allHTTPHeaderFields];
                    NSMutableURLRequest *mRequest = [request mutableCopy];
                    mRequest.allHTTPHeaderFields = fullHeaders;
                    request = mRequest;
                }

                NSTimeInterval delay, latency;
                delay = ((double)config.delay) / 1000.0;
                latency = ((double)config.latency) / 1000.0;

                dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)((delay + latency) * NSEC_PER_SEC)), self->_protocolQueue, ^{
                    @autoreleasepool {
                        ABORT_IF_NECESSARY();

                        if (config.failureError) {
                            self.stopped = YES;
                            [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                                [client URLProtocol:self didFailWithError:config.failureError];
                            }];
                            return;
                        }

                        NSHTTPURLResponse *httpResponse = (id)response.response;
                        NSData *data = response.data;
                        NSInteger statusCode = (config.statusCode > 0) ? config.statusCode : httpResponse.statusCode;

                        // See if we need to change to a 206
                        if (200 == statusCode && config.canProvideRange) {

                            const NSRange range = _RangeForRequest(request, data.length, config.stringForIfRange);
                            if (range.location != NSNotFound) {
                                // subrange requested, provide it
                                statusCode = 206;
                                data = [data subdataWithRange:range];
                            }

                        }

                        // On 3xx (when `Location` is provided), execute redirection based on config behavior.
                        if (statusCode >= 300 && statusCode < 400) {
                            const TNLPseudoURLProtocolRedirectBehavior behavior = (config) ? config.redirectBehavior : TNLPseudoURLProtocolRedirectBehaviorFollowLocation;
                            if ([self _handleRedirectForRequest:request response:httpResponse behavior:behavior]) {
                                // was handled, return
                                return;
                            }
                        }

                        httpResponse = _UpdateResponse(httpResponse, data.length, statusCode);

                        tnl_dispatch_async_autoreleasing(self->_protocolQueue, ^{
                            ABORT_IF_NECESSARY();
                            [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                                [client URLProtocol:self
                                 didReceiveResponse:httpResponse
                                 cacheStoragePolicy:response.storagePolicy];
                            }];

                            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(latency * NSEC_PER_SEC)), self->_protocolQueue, ^{
                                @autoreleasepool {
                                    ABORT_IF_NECESSARY();

                                    NSUInteger bps = NSUIntegerMax;
                                    if (config.bps > 0) {
                                        bps = (NSUInteger)MIN(config.bps / 8ULL, (uint64_t)NSUIntegerMax);
                                    }

                                    [self _chunkData:data
                                                 bps:bps
                                           bytesSent:0
                                             latency:MAX(latency, 0.25)];
                                }
                            });
                        });
                    }
                });
            }
        } else {
            tnl_dispatch_async_autoreleasing(self->_protocolQueue, ^{
                ABORT_IF_NECESSARY();
                self.stopped = YES;
                [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                    [client URLProtocol:self
                       didFailWithError:[NSError errorWithDomain:TNLPseudoURLProtocolErrorDomain
                                                            code:ENOENT
                                                        userInfo:nil]];
                }];
            });
        }
    });
}

- (BOOL)_handleRedirectForRequest:(NSURLRequest *)request
                         response:(NSHTTPURLResponse *)httpResponse
                         behavior:(const TNLPseudoURLProtocolRedirectBehavior)behavior
{
    TNLAssert(httpResponse.statusCode >= 300);
    TNLAssert(httpResponse.statusCode < 400);

    if (TNLPseudoURLProtocolRedirectBehaviorDontFollowLocation == behavior) {
        return NO;
    }

    NSString *location = httpResponse.allHeaderFields[@"Location"];
    if (!location) {
        return NO;
    }

    NSURL *locationURL = nil;
    @try {
        locationURL = [NSURL URLWithString:location];
    } @catch (NSException *e) {
        locationURL = nil;
    }
    if (!locationURL) {
        return NO;
    }

    // create the redirect request
    NSMutableURLRequest *mRedirectRequest = [request mutableCopy];
    mRedirectRequest.URL = locationURL;
    if (303 == httpResponse.statusCode) {
        mRedirectRequest.HTTPMethod = @"GET";
    }

    // get the cached redirect response (if requested)
    __block NSCachedURLResponse *redirectCachedResponse;
    if (TNLPseudoURLProtocolRedirectBehaviorFollowLocationIfRedirectResponseIsRegistered == behavior) {
        dispatch_sync(sOriginQueue, ^{
            redirectCachedResponse = sOriginToResponseDictionary[_UnderlyingURLString(locationURL)];
        });
    }

    // if we have a cached response or we follow the redirect anyway, tell the client we redirected
    if (redirectCachedResponse || TNLPseudoURLProtocolRedirectBehaviorFollowLocation == behavior) {
        /*
         radar://45880389
         The NSURLProtocolClient has always supported taking a `nil` redirectResponse.
         In recent years, `NS_ASSUME_NONNULL_BEGIN` was added to the interface's header and it mistakenly updates
            the redirectResponse argument to be a nonnull parameter.
         We can safely work around this by forcibly casting our potentially `nil` redirectResponse as __nonnull.
         Radar has been filed against Apple.
         */
        NSHTTPURLResponse * __nonnull redirectResponse = (NSHTTPURLResponse * __nonnull)redirectCachedResponse.response;
        [self _executeClientBlock:^(id<NSURLProtocolClient> client) {
            [client URLProtocol:self
         wasRedirectedToRequest:[mRedirectRequest copy]
               redirectResponse:redirectResponse];
        }];
        return YES;
    }

    return NO;
}

- (void)_chunkData:(NSData *)data
               bps:(NSUInteger)bps
         bytesSent:(NSUInteger)bytesSent
           latency:(NSTimeInterval)latency
{
    const NSUInteger bytesPerLatencyGap = (NSUInteger)MAX(bps * latency, 1UL);
    NSUInteger bytesToSend = 0;
    if (bytesSent < data.length) {
        bytesToSend = MIN(bytesPerLatencyGap, data.length - bytesSent);
    }

    if (bytesToSend > 0) {
        NSData *chunk = [data tnl_safeSubdataNoCopyWithRange:NSMakeRange(bytesSent, bytesToSend)];
        [self _executeClientBlock:^(id<NSURLProtocolClient> client){
            [client URLProtocol:self didLoadData:chunk];
        }];
        bytesSent += bytesToSend;
    }

    if (bytesSent >= data.length) {
        tnl_dispatch_async_autoreleasing(_protocolQueue, ^{
            ABORT_IF_NECESSARY();
            self.stopped = YES;
            [self _executeClientBlock:^(id<NSURLProtocolClient> client){
                [client URLProtocolDidFinishLoading:self];
            }];
        });
    } else {
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(latency * NSEC_PER_SEC)), _protocolQueue, ^{
            @autoreleasepool {
                ABORT_IF_NECESSARY();
                [self _chunkData:data
                             bps:bps
                       bytesSent:bytesSent
                         latency:latency];
            }
        });
    }
}

- (void)stopLoading
{
    self.stopped = YES;
}

- (instancetype)initWithRequest:(NSURLRequest *)request
                 cachedResponse:(nullable NSCachedURLResponse *)cachedResponse
                         client:(nullable id<NSURLProtocolClient>)client
{
    self = [super initWithRequest:request
                   cachedResponse:cachedResponse
                           client:client];
    if (self) {
        _protocolQueue = dispatch_queue_create("TNLPseudoURLProtocol.queue", DISPATCH_QUEUE_SERIAL);
    }
    return self;
}

- (void)_executeClientBlock:(TNLPseudoURLClientBlock)block
{
    CFRunLoopPerformBlock(_protocolRunLoop, kCFRunLoopDefaultMode, ^{
        @autoreleasepool {
            block(self.client);
        }
    });
    CFRunLoopWakeUp(_protocolRunLoop);
}

@end

@implementation TNLPseudoURLResponseConfig

- (instancetype)init
{
    if (self = [super init]) {
        _canProvideRange = YES;
        _redirectBehavior = TNLPseudoURLProtocolRedirectBehaviorFollowLocation;
    }
    return self;
}

- (id)copyWithZone:(nullable NSZone *)zone
{
    TNLPseudoURLResponseConfig *config = [[[self class] allocWithZone:zone] init];

    config.bps = self.bps;
    config.latency = self.latency;
    config.delay = self.delay;
    config.failureError = self.failureError;
    config.statusCode = self.statusCode;
    config.canProvideRange = self.canProvideRange;
    config.stringForIfRange = self.stringForIfRange;
    config.redirectBehavior = self.redirectBehavior;
    config.extraRequestHeaders = self.extraRequestHeaders;

    return config;
}

@end

static NSString * __nullable _UnderlyingURLString(NSURL * __nullable url)
{
    return url.absoluteString.lowercaseString;
}

static NSHTTPURLResponse *_UpdateResponse(NSHTTPURLResponse *response, NSUInteger contentLength, NSInteger statusCode)
{
    NSMutableDictionary *responseHeaderFields = [response.allHeaderFields mutableCopy];
    [responseHeaderFields tnl_setObject:[@(contentLength) stringValue]
                  forCaseInsensitiveKey:@"Content-Length"];
    return [[NSHTTPURLResponse alloc] initWithURL:response.URL
                                       statusCode:statusCode
                                      HTTPVersion:@"HTTP/1.1"
                                     headerFields:responseHeaderFields];
}

static NSRange _RangeForRequest(NSURLRequest *request, NSUInteger dataLength, NSString *stringForIfRange)
{
    NSString *range = [request.allHTTPHeaderFields tnl_objectForCaseInsensitiveKey:@"Range"];
    NSString *ifRange = [request.allHTTPHeaderFields tnl_objectForCaseInsensitiveKey:@"If-Range"];
    if ((!ifRange || !stringForIfRange || [ifRange isEqualToString:stringForIfRange]) && [range hasPrefix:@"bytes="]) {
        range = [range substringFromIndex:[@"bytes=" length]];
        NSArray<NSString *> *ranges = [range componentsSeparatedByString:@","];
        if (ranges.count == 1) {
            range = ranges.firstObject;
            NSArray<NSString *> *indexes = [range componentsSeparatedByString:@"-"];
            if (indexes.count == 2) {
                const NSInteger startIndex = [indexes[0] integerValue];
                NSInteger endIndex = (NSInteger)dataLength - 1;
                if ([indexes[1] length] > 0) {
                    endIndex = [indexes[1] integerValue];
                }
                if (endIndex >= startIndex) {
                    return NSMakeRange((NSUInteger)startIndex, (NSUInteger)endIndex - (NSUInteger)startIndex);
                }
            }
        }
    }

    return NSMakeRange(NSNotFound, 0);
}

NS_ASSUME_NONNULL_END