BackgroundHttpFileHashHelper.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Containers/Map.h"
#include "Containers/UnrealString.h"
#include "CoreTypes.h"
#include "Templates/SharedPointer.h"
 
//Simple data wrapper used to hold a mapping of a URL to the temp file holding the finished download of that URL in the BackgroundHTTP Temp folder
struct FURLTempFileMapping
{
public:
    FString URL;
    FString TempFilename;
    
    FURLTempFileMapping()
        : URL()
        , TempFilename()
    {
    }
    
    FURLTempFileMapping(const FString& URLIn, const FString& TempFilenameIn)
        : URL(URLIn)
        , TempFilename(TempFilenameIn)
    {
    }
    
    //Creates an FString representation of this FURLTempFileMapping
    FString ToString() const;
    
    //Sets the values of this FURLTempFileMapping from the string representation
    //Returns if the parse was successful or not
    bool InitFromString(const FString& StringIn);
};
 
class FBackgroundHttpFileHashHelper
{
public:
    FBackgroundHttpFileHashHelper()
        : bHasLoadedURLData(false)
        , bIsDirty(false)
        , URLFileMappings()
        , URLFileMappingsLock()
    {
    }
 
    // Handles loading URL Mapping data from disk. No operation if data has previously been loaded.
    BACKGROUNDHTTPFILEHASH_API void LoadData();
 
    // Handles saving URL Mapping data to disk. No operation if data isn't dirty
    BACKGROUNDHTTPFILEHASH_API void SaveData();
 
    // Creates an FString representation of this FBackgroundHttpFileHashHelper's URL mappings. Used for serializing to/from disk
    BACKGROUNDHTTPFILEHASH_API FString ToString() const;
 
    // Sets the values of this FBackgroundHttpFileHashHelper from the string representation
    // Returns if the parse was successful or not
    BACKGROUNDHTTPFILEHASH_API bool InitFromString(const FString& StringIn);
 
    // Looks for a temp filename mapping for the given URL. If one isn't found returns nullptr and does NOT generate one.
    BACKGROUNDHTTPFILEHASH_API bool FindTempFilenameMappingForURL(const FString& URL, FString& OutTempFilename) const;
 
    UE_DEPRECATED(5.7, "Please use FindTempFilenameMappingForURL with reference out argument instead")
    BACKGROUNDHTTPFILEHASH_API const FString* FindTempFilenameMappingForURL(const FString& URL) const;
 
    // Looks for a temp filename mapping for the given URL. If one isn't found a new one is generated and returned.
    BACKGROUNDHTTPFILEHASH_API const FString& FindOrAddTempFilenameMappingForURL(const FString& URL);
 
    // Removes URL mapping
    BACKGROUNDHTTPFILEHASH_API void RemoveURLMapping(const FString& URL);
 
    // Looks for a URL mapped to the supplied TempFilename. Nullptr returned if one isn't found
    BACKGROUNDHTTPFILEHASH_API bool FindMappedURLForTempFilename(const FString& TempFilename, FString& OutMappedURL) const;
 
    UE_DEPRECATED(5.7, "Please use FindMappedURLForTempFilename with reference out argument instead")
    BACKGROUNDHTTPFILEHASH_API const FString* FindMappedURLForTempFilename(const FString& TempFilename) const;
 
    // Deletes any URLMapping that doesn't have a corresponding Temp file actually on disk.
    BACKGROUNDHTTPFILEHASH_API void DeleteURLMappingsWithoutTempFiles();
 
    // Get our base directory used to store Temp files
    static BACKGROUNDHTTPFILEHASH_API const FString& GetTemporaryRootPath();
 
    // Helper function that returns the file extension used by our BackgroundHTTP temp files
    static BACKGROUNDHTTPFILEHASH_API const FString& GetTempFileExtension();
 
    // Helper function that returns a full path representation of hte given TempFilename
    static BACKGROUNDHTTPFILEHASH_API FString GetFullPathOfTempFilename(const FString& TempFilename);
 
private:
    // Same as ToString but doesn't take a lock 
    BACKGROUNDHTTPFILEHASH_API FString ToStringNoLock() const;
 
    // Same as InitFromString but doesn't take a lock 
    BACKGROUNDHTTPFILEHASH_API bool InitFromStringNoLock(const FString& StringIn);
 
    // Helper function that just returns the filepath we use to save/load our URL mapping data
    static BACKGROUNDHTTPFILEHASH_API const FString& GetURLMappingFilePathNoLock();
 
    // Looks for a temp filename mapping for the given URL. If one isn't found returns nullptr an does NOT generate one.
    BACKGROUNDHTTPFILEHASH_API const FURLTempFileMapping* FindMappingForURLNoLock(const FString& URL) const;
 
    // Finds the hash that should be used to refer to this URL. Either finds the hash used in the map to reference the
    // URLFileMappings entry for this URL or returns the hash we should use (the next valid hash entry) without inserting it into the map.
    BACKGROUNDHTTPFILEHASH_API FString FindValidFilenameHashForURLNoLock(const FString& URL) const;
 
    // Creates a hashed Filename with a modifier for the given collision count.
    static BACKGROUNDHTTPFILEHASH_API FString GenerateHashedFilenameForURLNoLock(const FString& URL, uint32 CollisionCount);
 
    // Used to make sure that we have called LoadData before any operations that depend on it
    std::atomic<bool> bHasLoadedURLData;
 
    // Tracks if we have changed data since our last call to SaveData()
    std::atomic<bool> bIsDirty;
 
    // Stores our FURLTempFileMapping mapped to a Hashed filename
    TMap<FString, FURLTempFileMapping> URLFileMappings;
 
    // Access lock for URLFileMappings
    mutable FRWLock URLFileMappingsLock;
};
 
typedef TSharedRef<FBackgroundHttpFileHashHelper, ESPMode::ThreadSafe> BackgroundHttpFileHashHelperRef;
typedef TSharedPtr<FBackgroundHttpFileHashHelper, ESPMode::ThreadSafe> BackgroundHttpFileHashHelperPtr;