session-ios/SignalUtilitiesKit/Messaging/OWSAttachmentDownloads.m

//
//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
//

#import "OWSAttachmentDownloads.h"
#import "AppContext.h"
#import "MIMETypeUtil.h"
#import "NSNotificationCenter+OWS.h"
#import "OWSBackgroundTask.h"
#import "OWSDispatch.h"
#import "OWSError.h"
#import "OWSFileSystem.h"
#import "OWSPrimaryStorage.h"

#import "SSKEnvironment.h"
#import "TSAttachmentPointer.h"
#import "TSAttachmentStream.h"
#import "TSGroupModel.h"
#import "TSGroupThread.h"
#import "TSInfoMessage.h"
#import "TSMessage.h"

#import "TSThread.h"
#import <PromiseKit/AnyPromise.h>
#import <SignalCoreKit/Cryptography.h>
#import <SignalUtilitiesKit/SignalUtilitiesKit-Swift.h>
#import <YapDatabase/YapDatabaseConnection.h>

NS_ASSUME_NONNULL_BEGIN

NSString *const kAttachmentDownloadProgressNotification = @"kAttachmentDownloadProgressNotification";
NSString *const kAttachmentDownloadProgressKey = @"kAttachmentDownloadProgressKey";
NSString *const kAttachmentDownloadAttachmentIDKey = @"kAttachmentDownloadAttachmentIDKey";

// Use a slightly non-zero value to ensure that the progress
// indicator shows up as quickly as possible.
static const CGFloat kAttachmentDownloadProgressTheta = 0.001f;

typedef void (^AttachmentDownloadSuccess)(TSAttachmentStream *attachmentStream);
typedef void (^AttachmentDownloadFailure)(NSError *error);

@interface OWSAttachmentDownloadJob : NSObject

@property (nonatomic, readonly) TSAttachmentPointer *attachmentPointer;
@property (nonatomic, readonly, nullable) TSMessage *message;
@property (nonatomic, readonly) AttachmentDownloadSuccess success;
@property (nonatomic, readonly) AttachmentDownloadFailure failure;
@property (atomic) CGFloat progress;

@end

#pragma mark -

@implementation OWSAttachmentDownloadJob

- (instancetype)initWithAttachmentPointer:(TSAttachmentPointer *)attachmentPointer
                                  message:(nullable TSMessage *)message
                                  success:(AttachmentDownloadSuccess)success
                                  failure:(AttachmentDownloadFailure)failure
{
    self = [super init];
    if (!self) {
        return self;
    }

    _attachmentPointer = attachmentPointer;
    _message = message;
    _success = success;
    _failure = failure;

    return self;
}

@end

#pragma mark -

@interface OWSAttachmentDownloads ()

// This property should only be accessed while synchronized on this class.
@property (nonatomic, readonly) NSMutableDictionary<NSString *, OWSAttachmentDownloadJob *> *downloadingJobMap;
// This property should only be accessed while synchronized on this class.
@property (nonatomic, readonly) NSMutableArray<OWSAttachmentDownloadJob *> *attachmentDownloadJobQueue;

@end

#pragma mark -

@implementation OWSAttachmentDownloads

#pragma mark - Dependencies

- (OWSPrimaryStorage *)primaryStorage
{
    return SSKEnvironment.shared.primaryStorage;
}

#pragma mark -

- (instancetype)init
{
    self = [super init];
    if (!self) {
        return self;
    }

    _downloadingJobMap = [NSMutableDictionary new];
    _attachmentDownloadJobQueue = [NSMutableArray new];

    return self;
}

#pragma mark -

- (nullable NSNumber *)downloadProgressForAttachmentId:(NSString *)attachmentId
{

    @synchronized(self) {
        OWSAttachmentDownloadJob *_Nullable job = self.downloadingJobMap[attachmentId];
        if (!job) {
            return nil;
        }
        return @(job.progress);
    }
}

- (void)downloadAttachmentsForMessage:(TSMessage *)message
                          transaction:(YapDatabaseReadTransaction *)transaction
                              success:(void (^)(NSArray<TSAttachmentStream *> *attachmentStreams))success
                              failure:(void (^)(NSError *error))failure
{
    OWSAssertDebug(transaction);
    OWSAssertDebug(message);

    NSMutableArray<TSAttachmentStream *> *attachmentStreams = [NSMutableArray array];
    NSMutableArray<TSAttachmentPointer *> *attachmentPointers = [NSMutableArray new];

    for (TSAttachment *attachment in [message attachmentsWithTransaction:transaction]) {
        if ([attachment isKindOfClass:[TSAttachmentStream class]]) {
            TSAttachmentStream *attachmentStream = (TSAttachmentStream *)attachment;
            [attachmentStreams addObject:attachmentStream];
        } else if ([attachment isKindOfClass:[TSAttachmentPointer class]]) {
            TSAttachmentPointer *attachmentPointer = (TSAttachmentPointer *)attachment;
            if (attachmentPointer.pointerType != TSAttachmentPointerTypeIncoming) {
                OWSLogInfo(@"Ignoring restoring attachment.");
                continue;
            }
            [attachmentPointers addObject:attachmentPointer];
        } else {
            OWSFailDebug(@"Unexpected attachment type: %@", attachment.class);
        }
    }

    [self enqueueJobsForAttachmentStreams:attachmentStreams
                       attachmentPointers:attachmentPointers
                                  message:message
                                  success:success
                                  failure:failure];
}

- (void)downloadAttachmentPointer:(TSAttachmentPointer *)attachmentPointer
                          success:(void (^)(NSArray<TSAttachmentStream *> *attachmentStreams))success
                          failure:(void (^)(NSError *error))failure
{
    OWSAssertDebug(attachmentPointer);

    [self enqueueJobsForAttachmentStreams:@[]
                       attachmentPointers:@[ attachmentPointer ]
                                  message:nil
                                  success:success
                                  failure:failure];
}

- (void)enqueueJobsForAttachmentStreams:(NSArray<TSAttachmentStream *> *)attachmentStreamsParam
                     attachmentPointers:(NSArray<TSAttachmentPointer *> *)attachmentPointers
                                message:(nullable TSMessage *)message
                                success:(void (^)(NSArray<TSAttachmentStream *> *attachmentStreams))successHandler
                                failure:(void (^)(NSError *error))failureHandler
{
    OWSAssertDebug(attachmentStreamsParam);

    // To avoid deadlocks, synchronize on self outside of the transaction.
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        if (attachmentPointers.count < 1) {
            OWSAssertDebug(attachmentStreamsParam.count > 0);
            successHandler(attachmentStreamsParam);
            return;
        }

        NSMutableArray<TSAttachmentStream *> *attachmentStreams = [attachmentStreamsParam mutableCopy];
        NSMutableArray<AnyPromise *> *promises = [NSMutableArray array];
        for (TSAttachmentPointer *attachmentPointer in attachmentPointers) {
            AnyPromise *promise = [AnyPromise promiseWithResolverBlock:^(PMKResolver resolve) {
                [self enqueueJobForAttachmentPointer:attachmentPointer
                    message:message
                    success:^(TSAttachmentStream *attachmentStream) {
                        @synchronized(attachmentStreams) {
                            [attachmentStreams addObject:attachmentStream];
                        }

                        resolve(@(1));
                    }
                    failure:^(NSError *error) {
                        resolve(error);
                    }];
            }];
            [promises addObject:promise];
        }

        // We use PMKJoin(), not PMKWhen(), because we don't want the
        // completion promise to execute until _all_ promises
        // have either succeeded or failed. PMKWhen() executes as
        // soon as any of its input promises fail.
        AnyPromise *completionPromise
            = PMKJoin(promises)
                  .then(^(id value) {
                      NSArray<TSAttachmentStream *> *attachmentStreamsCopy;
                      @synchronized(attachmentStreams) {
                          attachmentStreamsCopy = [attachmentStreams copy];
                      }
                      OWSLogInfo(@"Attachment downloads succeeded: %lu.", (unsigned long)attachmentStreamsCopy.count);

                      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                          successHandler(attachmentStreamsCopy);
                      });
                  })
                  .catch(^(NSError *error) {
                      OWSLogError(@"Attachment downloads failed.");

                      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                          failureHandler(error);
                      });
                  });
        [completionPromise retainUntilComplete];
    });
}

- (void)enqueueJobForAttachmentPointer:(TSAttachmentPointer *)attachmentPointer
                               message:(nullable TSMessage *)message
                               success:(void (^)(TSAttachmentStream *attachmentStream))success
                               failure:(void (^)(NSError *error))failure
{
    OWSAssertDebug(attachmentPointer);

    OWSAttachmentDownloadJob *job = [[OWSAttachmentDownloadJob alloc] initWithAttachmentPointer:attachmentPointer
                                                                                        message:message
                                                                                        success:success
                                                                                        failure:failure];

    @synchronized(self) {
        [self.attachmentDownloadJobQueue addObject:job];
    }

    [self startDownloadIfPossible];
}

- (void)startDownloadIfPossible
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        OWSAttachmentDownloadJob *_Nullable job;

        @synchronized(self) {
            const NSUInteger kMaxSimultaneousDownloads = 4;
            if (self.downloadingJobMap.count >= kMaxSimultaneousDownloads) {
                return;
            }
            job = self.attachmentDownloadJobQueue.firstObject;
            if (!job) {
                return;
            }
            if (self.downloadingJobMap[job.attachmentPointer.uniqueId] != nil) {
                // Ensure we only have one download in flight at a time for a given attachment.
                OWSLogWarn(@"Ignoring duplicate download.");
                return;
            }
            [self.attachmentDownloadJobQueue removeObjectAtIndex:0];
            self.downloadingJobMap[job.attachmentPointer.uniqueId] = job;
        }

        [LKStorage writeSyncWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
            job.attachmentPointer.state = TSAttachmentPointerStateDownloading;
            [job.attachmentPointer saveWithTransaction:transaction];

            if (job.message) {
                [job.message saveWithTransaction:transaction];
                [job.message touchWithTransaction:transaction];
            }
        }];

        [self retrieveAttachmentForJob:job
            success:^(TSAttachmentStream *attachmentStream) {
                OWSLogVerbose(@"Attachment download succeeded.");

                [LKStorage writeSyncWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
                    [attachmentStream saveWithTransaction:transaction];

                    if (job.message) {
                        [job.message touchWithTransaction:transaction];
                    }
                }];

                job.success(attachmentStream);

                @synchronized(self) {
                    [self.downloadingJobMap removeObjectForKey:job.attachmentPointer.uniqueId];
                }

                [self startDownloadIfPossible];
            }
            failure:^(NSError *error) {
                OWSLogError(@"Attachment download failed with error: %@", error);

                [LKStorage writeSyncWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
                    job.attachmentPointer.mostRecentFailureLocalizedText = error.localizedDescription;
                    job.attachmentPointer.state = TSAttachmentPointerStateFailed;
                    [job.attachmentPointer saveWithTransaction:transaction];

                    if (job.message) {
                        [job.message touchWithTransaction:transaction];
                    }
                }];

                @synchronized(self) {
                    [self.downloadingJobMap removeObjectForKey:job.attachmentPointer.uniqueId];
                }

                job.failure(error);

                [self startDownloadIfPossible];
            }];
    });
}

#pragma mark -

- (void)continueDownloadIfPossible
{
    if (self.attachmentDownloadJobQueue.count > 0) {
        NSLog(@"[Loki] Continuing unfinished attachment download tasks.");
        [self startDownloadIfPossible];
    }
}

#pragma mark -

- (void)retrieveAttachmentForJob:(OWSAttachmentDownloadJob *)job
                         success:(void (^)(TSAttachmentStream *attachmentStream))successHandler
                         failure:(void (^)(NSError *error))failureHandler
{
    OWSAssertDebug(job);
    TSAttachmentPointer *attachmentPointer = job.attachmentPointer;

    __block OWSBackgroundTask *_Nullable backgroundTask =
        [OWSBackgroundTask backgroundTaskWithLabelStr:__PRETTY_FUNCTION__];

    void (^markAndHandleFailure)(NSError *) = ^(NSError *error) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            failureHandler(error);

            OWSAssertDebug(backgroundTask);
            backgroundTask = nil;
        });
    };

    void (^markAndHandleSuccess)(TSAttachmentStream *attachmentStream) = ^(TSAttachmentStream *attachmentStream) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            successHandler(attachmentStream);

            OWSAssertDebug(backgroundTask);
            backgroundTask = nil;
        });
    };

    __block NSUInteger retryCount = 0;
    NSUInteger maxRetryCount = 4;
    __block void (^attempt)();
    attempt = ^() {
        dispatch_async([OWSDispatch attachmentsQueue], ^{
            [self downloadFromLocation:attachmentPointer.downloadURL
                job:job
                success:^(NSString *encryptedDataFilePath) {
                    [self decryptAttachmentPath:encryptedDataFilePath
                              attachmentPointer:attachmentPointer
                                        success:markAndHandleSuccess
                                        failure:markAndHandleFailure];
                }
                failure:^(NSURLSessionTask *task, NSError *error) {
                    if (retryCount == maxRetryCount) {
                        markAndHandleFailure(error);
                    } else {
                        retryCount += 1;
                        attempt();
                    }
                }];
        });
    };
    attempt();
}

- (void)decryptAttachmentPath:(NSString *)encryptedDataFilePath
            attachmentPointer:(TSAttachmentPointer *)attachmentPointer
                      success:(void (^)(TSAttachmentStream *attachmentStream))success
                      failure:(void (^)(NSError *error))failure
{
    OWSAssertDebug(encryptedDataFilePath.length > 0);
    OWSAssertDebug(attachmentPointer);

    // Use attachmentDecryptSerialQueue to ensure that we only load into memory
    // & decrypt a single attachment at a time.
    dispatch_async(self.attachmentDecryptSerialQueue, ^{
        @autoreleasepool {
            NSData *_Nullable encryptedData = [NSData dataWithContentsOfFile:encryptedDataFilePath];
            if (!encryptedData) {
                OWSLogError(@"Could not load encrypted data.");
                NSError *error = OWSErrorWithCodeDescription(
                    OWSErrorCodeInvalidMessage, NSLocalizedString(@"ERROR_MESSAGE_INVALID_MESSAGE", @""));
                return failure(error);
            }

            [self decryptAttachmentData:encryptedData
                      attachmentPointer:attachmentPointer
                                success:success
                                failure:failure];

            if (![OWSFileSystem deleteFile:encryptedDataFilePath]) {
                OWSLogError(@"Could not delete temporary file.");
            }
        }
    });
}

- (void)decryptAttachmentData:(NSData *)cipherText
            attachmentPointer:(TSAttachmentPointer *)attachmentPointer
                      success:(void (^)(TSAttachmentStream *attachmentStream))successHandler
                      failure:(void (^)(NSError *error))failureHandler
{
    OWSAssertDebug(attachmentPointer);

    NSError *decryptError;
    NSData *_Nullable plaintext;
    if (attachmentPointer.encryptionKey != nil) {
        plaintext = [Cryptography decryptAttachment:cipherText
                                            withKey:attachmentPointer.encryptionKey
                                             digest:attachmentPointer.digest
                                       unpaddedSize:attachmentPointer.byteCount
                                              error:&decryptError];
    } else {
        plaintext = cipherText; // Loki: Public chat attachments are unencrypted
    }

    if (decryptError) {
        OWSLogError(@"failed to decrypt with error: %@", decryptError);
        failureHandler(decryptError);
        return;
    }

    if (!plaintext) {
        NSError *error = OWSErrorWithCodeDescription(
            OWSErrorCodeFailedToDecryptMessage, NSLocalizedString(@"ERROR_MESSAGE_INVALID_MESSAGE", @""));
        failureHandler(error);
        return;
    }

    TSAttachmentStream *stream = [[TSAttachmentStream alloc] initWithPointer:attachmentPointer];

    NSError *writeError;
    [stream writeData:plaintext error:&writeError];
    if (writeError) {
        OWSLogError(@"Failed writing attachment stream with error: %@", writeError);
        failureHandler(writeError);
        return;
    }

    successHandler(stream);
}

- (dispatch_queue_t)attachmentDecryptSerialQueue
{
    static dispatch_queue_t _serialQueue;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _serialQueue = dispatch_queue_create("org.whispersystems.attachment.decrypt", DISPATCH_QUEUE_SERIAL);
    });

    return _serialQueue;
}

- (void)downloadFromLocation:(NSString *)location
                         job:(OWSAttachmentDownloadJob *)job
                     success:(void (^)(NSString *encryptedDataPath))successHandler
                     failure:(void (^)(NSURLSessionTask *_Nullable task, NSError *error))failureHandlerParam
{
    OWSAssertDebug(job);
    TSAttachmentPointer *attachmentPointer = job.attachmentPointer;

    // We want to avoid large downloads from a compromised or buggy service.
    const long kMaxDownloadSize = 10 * 1024 * 1024;
    __block BOOL hasCheckedContentLength = NO;

    NSString *tempFilePath =
        [OWSTemporaryDirectoryAccessibleAfterFirstAuth() stringByAppendingPathComponent:[NSUUID UUID].UUIDString];
    NSURL *tempFileURL = [NSURL fileURLWithPath:tempFilePath];
    __block NSURLSessionDownloadTask *task;
    void (^failureHandler)(NSError *) = ^(NSError *error) {
        OWSLogError(@"Failed to download attachment with error: %@", error.description);

        if (![OWSFileSystem deleteFileIfExists:tempFilePath]) {
            OWSLogError(@"Could not delete temporary file #1.");
        }

        failureHandlerParam(task, error);
    };
    
    [[SNFileServerAPI downloadAttachmentFrom:location].then(^(NSData *data) {
        BOOL success = [data writeToFile:tempFilePath atomically:YES];
        if (success) {
            successHandler(tempFilePath);
        }

        NSNumber *_Nullable fileSize = [OWSFileSystem fileSizeOfPath:tempFilePath];
        if (!fileSize) {
            OWSLogError(@"Could not determine attachment file size.");
            NSError *error = OWSErrorWithCodeDescription(
                OWSErrorCodeInvalidMessage, NSLocalizedString(@"ERROR_MESSAGE_INVALID_MESSAGE", @""));
            return failureHandler(error);
        }
        if (fileSize.unsignedIntegerValue > kMaxDownloadSize) {
            OWSLogError(@"Attachment download length exceeds max size.");
            NSError *error = OWSErrorWithCodeDescription(
                OWSErrorCodeInvalidMessage, NSLocalizedString(@"ERROR_MESSAGE_INVALID_MESSAGE", @""));
            return failureHandler(error);
        }
    }) retainUntilComplete];
}

- (void)fireProgressNotification:(CGFloat)progress attachmentId:(NSString *)attachmentId
{
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter postNotificationNameAsync:kAttachmentDownloadProgressNotification
                                           object:nil
                                         userInfo:@{
                                             kAttachmentDownloadProgressKey : @(progress),
                                             kAttachmentDownloadAttachmentIDKey : attachmentId
                                         }];
}

@end

NS_ASSUME_NONNULL_END