Add support for reading from TAR archives to flatdata-cpp (heremaps#182)

Signed-off-by: Christian Ocker <christian.ocker@here.com>

flatdata-cpp/include/flatdata/MemoryMappedTarFileStorage.h

@@ -0,0 +1,75 @@
+/**
+ * Copyright (c) 2021 HERE Europe B.V.
+ * See the LICENSE file in the root of this project for license details.
+ */
+
+#pragma once
+
+#include "MemoryDescriptor.h"
+#include "internal/TarReader.h"
+
+#include <boost/interprocess/file_mapping.hpp>
+#include <boost/interprocess/mapped_region.hpp>
+
+#include <cstdio>
+#include <map>
+#include <memory>
+
+namespace flatdata
+{
+class MemoryMappedTarFileStorage
+{
+public:
+    explicit MemoryMappedTarFileStorage( const char* tar_path );
+
+    MemoryDescriptor read( const char* path ) const;
+
+private:
+    boost::interprocess::mapped_region m_region;
+    std::map< std::string, MemoryDescriptor > m_files;
+};
+
+inline MemoryMappedTarFileStorage::MemoryMappedTarFileStorage( const char* tar_path )
+{
+    try
+    {
+        boost::interprocess::file_mapping file( tar_path, boost::interprocess::read_only );
+        boost::interprocess::mapped_region region( file, boost::interprocess::read_only );
+        if ( region.get_size( ) == 0 )
+        {
+            return;
+        }
+
+        m_region = std::move( region );
+    }
+    catch ( boost::interprocess::interprocess_exception& )
+    {
+        return;
+    }
+
+    auto files = internal::read_tar_files( tar_path );
+
+    for ( const auto& file : files )
+    {
+        std::string path = file.name.substr( 0, 2 ) == "./" ? file.name.substr( 2 ) : file.name;
+        m_files.emplace(
+            std::move( path ),
+            MemoryDescriptor(
+                static_cast< const unsigned char* >( m_region.get_address( ) ) + file.offset,
+                std::min( file.size, m_region.get_size( ) - file.offset ) ) );
+    }
+}
+
+inline MemoryDescriptor
+MemoryMappedTarFileStorage::read( const char* path ) const
+{
+    auto found = m_files.find( path );
+    if ( found != m_files.end( ) )
+    {
+        return found->second;
+    }
+
+    return MemoryDescriptor( );
+}
+
+}  // namespace flatdata

flatdata-cpp/include/flatdata/TarFileResourceStorage.h

@@ -0,0 +1,119 @@
+/**
+ * Copyright (c) 2021 HERE Europe B.V.
+ * See the LICENSE file in the root of this project for license details.
+ */
+
+#pragma once
+
+#include "MemoryMappedTarFileStorage.h"
+#include "ResourceStorage.h"
+
+#include <boost/filesystem.hpp>
+
+#include <fstream>
+
+namespace flatdata
+{
+/**
+ * @brief Read-only resource storage for reading flatdata archives inside a TAR file.
+ */
+class TarFileResourceStorage : public ResourceStorage
+{
+public:
+    /**
+     * @brief Create resource storage for a TAR file
+     * @param tar_path The path to the TAR file
+     * @param tar_path The path inside the TAR file
+     * @throws std::runtime_error if the reading of the TAR file fails
+     * @return TarFileResourceStorage or nullptr on error
+     */
+    static std::unique_ptr< TarFileResourceStorage > create( const char* tar_path,
+                                                             const char* sub_path = "" );
+
+    std::unique_ptr< ResourceStorage > create_directory( const char* key ) override;
+    std::unique_ptr< ResourceStorage > directory( const char* key ) override;
+    bool exists( const char* key ) override;
+
+protected:
+    std::shared_ptr< std::ostream > create_output_stream( const char* key ) override;
+    MemoryDescriptor read_resource( const char* key ) override;
+
+private:
+    TarFileResourceStorage( std::shared_ptr< const MemoryMappedTarFileStorage > storage,
+                            const std::string& tar_path,
+                            const std::string& sub_path );
+    std::string get_path( const char* key ) const;
+
+private:
+    std::shared_ptr< const MemoryMappedTarFileStorage > m_storage;
+    std::string m_tar_path;
+    std::string m_sub_path;
+};
+
+// -------------------------------------------------------------------------------------------------
+
+inline std::unique_ptr< TarFileResourceStorage >
+TarFileResourceStorage::create( const char* tar_path, const char* sub_path )
+{
+    std::shared_ptr< const MemoryMappedTarFileStorage > storage(
+        new MemoryMappedTarFileStorage( tar_path ) );
+
+    return std::unique_ptr< TarFileResourceStorage >(
+        new TarFileResourceStorage( storage, tar_path, sub_path ) );
+}
+
+inline std::shared_ptr< std::ostream >
+TarFileResourceStorage::create_output_stream( const char* )
+{
+    // Writing to TAR files is not supported
+    return nullptr;
+}
+
+inline TarFileResourceStorage::TarFileResourceStorage(
+    std::shared_ptr< const MemoryMappedTarFileStorage > storage,
+    const std::string& tar_path,
+    const std::string& sub_path )
+    : m_storage( std::move( storage ) )
+    , m_tar_path( tar_path )
+    , m_sub_path( sub_path )
+{
+}
+
+inline std::string
+TarFileResourceStorage::get_path( const char* key ) const
+{
+    const char TAR_PATH_SEPARATOR = '/';
+
+    return m_sub_path.empty( ) ? std::string( key ) : m_sub_path + TAR_PATH_SEPARATOR + key;
+}
+
+inline MemoryDescriptor
+TarFileResourceStorage::read_resource( const char* key )
+{
+    if ( !exists( key ) )
+    {
+        return MemoryDescriptor( );
+    }
+    return m_storage->read( get_path( key ).c_str( ) );
+}
+
+inline std::unique_ptr< ResourceStorage >
+TarFileResourceStorage::create_directory( const char* key )
+{
+    return directory( key );
+}
+
+inline std::unique_ptr< ResourceStorage >
+TarFileResourceStorage::directory( const char* key )
+{
+    return std::unique_ptr< TarFileResourceStorage >(
+        new TarFileResourceStorage( m_storage, m_tar_path, get_path( key ) ) );
+}
+
+inline bool
+TarFileResourceStorage::exists( const char* key )
+{
+    return m_storage->read( get_path( key ).c_str( ) ).data( ) != nullptr;
+}
+
+}  // namespace flatdata

flatdata-cpp/include/flatdata/flatdata.h

@@ -23,4 +23,5 @@
 #include "MultiVector.h"
 #include "ResourceStorage.h"
 #include "Struct.h"
-#include "Vector.h"
+#include "TarFileResourceStorage.h"
+#include "Vector.h"

flatdata-cpp/include/flatdata/internal/Reader.h

@@ -13,6 +13,7 @@
 #include <boost/optional/optional_io.hpp>
 
 #include <cstring>
+#include <utility>
 
 namespace flatdata
 {

flatdata-cpp/include/flatdata/internal/TarReader.h

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2021 HERE Europe B.V.
+ * See the LICENSE file in the root of this project for license details.
+ */
+
+#pragma once
+
+#include <stddef.h>
+#include <string>
+#include <vector>
+
+namespace flatdata
+{
+namespace internal
+{
+struct TarFileEntry
+{
+    std::string name;
+    size_t offset = 0;
+    size_t size = 0;
+};
+
+std::vector< TarFileEntry > read_tar_files( const char* tar_path );
+}  // namespace internal
+}  // namespace flatdata