HTTPCache.h

// -*- mode: c++; c-basic-offset:4 -*-

// This file is part of libdap, A C++ implementation of the OPeNDAP Data
// Access Protocol.

// Copyright (c) 2002,2008 OPeNDAP, Inc.
// Author: James Gallagher <jgallagher@opendap.org>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
//
// You can contact OPeNDAP, Inc. at PO Box 112, Saunderstown, RI. 02874-0112.

#ifndef _http_cache_h
#define _http_cache_h

#include <pthread.h>

#ifdef WIN32
#include <io.h>   // stat for win32? 09/05/02 jhrg
#endif

#include <string>
#include <vector>
#include <map>

#include "HTTPCacheTable.h" // included for macros

#include "HTTPCacheDisconnectedMode.h"
//using namespace std;

namespace libdap
{

class HTTPCacheTabe;

// This function is exported so the test code can use it too.
bool is_hop_by_hop_header(const string &header);

class HTTPCache
{
private:
    string d_cache_root;
    FILE *d_locked_open_file; // Lock for single process use.

    bool d_cache_enabled;
    bool d_cache_protected;
    CacheDisconnectedMode d_cache_disconnected;
    bool d_expire_ignored;
    bool d_always_validate;

    unsigned long d_total_size; // How much can we store?
    unsigned long d_folder_size; // How much of that is meta data?
    unsigned long d_gc_buffer; // How much memory needed as buffer?
    unsigned long d_max_entry_size; // Max individual entry size.
    int d_default_expiration;

    vector<string> d_cache_control;
    // these are values read from a request-directive Cache-Control header.
    // Not to be confused with values read from the response or a cached
    // response (e.g., CacheEntry has a max_age field, too). These fields are
    // set when the set_cache_control method is called.
    time_t d_max_age;
    time_t d_max_stale;  // -1: not set, 0:any response, >0 max time.
    time_t d_min_fresh;

    // Lock non-const methods (also ones that use the STL).
    pthread_mutex_t d_cache_mutex;
    
    HTTPCacheTable *d_http_cache_table;

    // d_open_files is used by the interrupt handler to clean up
    vector<string> d_open_files;

    static HTTPCache *_instance;

    friend class HTTPCacheTest; // Unit tests
    friend class HTTPConnectTest;

    friend class HTTPCacheInterruptHandler;

    // Private methods
    HTTPCache(const HTTPCache &);
    HTTPCache();
    HTTPCache &operator=(const HTTPCache &);

    HTTPCache(string cache_root, bool force);

    static void delete_instance(); // Run by atexit (hence static)
    
    void set_cache_root(const string &root = "");
    void create_cache_root(const string &cache_root);
    
    // These will go away when the cache can be used by multiple processes.
    bool get_single_user_lock(bool force = false);
    void release_single_user_lock();
    
    bool is_url_in_cache(const string &url);

    // I made these four methods so they could be tested by HTTPCacheTest.
    // Otherwise they would be static functions. jhrg 10/01/02
    void write_metadata(const string &cachename, const vector<string> &headers);
    void read_metadata(const string &cachename, vector<string> &headers);
    int write_body(const string &cachename, const FILE *src);
    FILE *open_body(const string &cachename);

    bool stopGC() const;
    bool startGC() const;

    void perform_garbage_collection();
    void too_big_gc();
    void expired_gc();
    void hits_gc();

public:
    static HTTPCache *instance(const string &cache_root, bool force = false);
    virtual ~HTTPCache();

    string get_cache_root() const;

    void set_cache_enabled(bool mode);
    bool is_cache_enabled() const;

    void set_cache_disconnected(CacheDisconnectedMode mode);
    CacheDisconnectedMode get_cache_disconnected() const;

    void set_expire_ignored(bool mode);
    bool is_expire_ignored() const;

    void set_max_size(unsigned long size);
    unsigned long get_max_size() const;

    void set_max_entry_size(unsigned long size);
    unsigned long get_max_entry_size() const;

    void set_default_expiration(int exp_time);
    int get_default_expiration() const;

    void set_always_validate(bool validate);
    bool get_always_validate() const;

    void set_cache_control(const vector<string> &cc);
    vector<string> get_cache_control();

    void lock_cache_interface() {
        DBG(cerr << "Locking interface... ");
        LOCK(&d_cache_mutex);
        DBGN(cerr << "Done" << endl);
    }       
    void unlock_cache_interface() {
        DBG(cerr << "Unlocking interface... " );
        UNLOCK(&d_cache_mutex);
        DBGN(cerr << "Done" << endl);
    }
    
    // This must lock for writing
    bool cache_response(const string &url, time_t request_time,
                        const vector<string> &headers, const FILE *body);
    void update_response(const string &url, time_t request_time,
                         const vector<string> &headers);

    // This is separate from get_cached_response() because often an invalid
    // cache entry just needs a header update. That is best left to the HTTP
    // Connection code.
    bool is_url_valid(const string &url);
    
    // Lock these for reading
    vector<string> get_conditional_request_headers(const string &url);
    FILE *get_cached_response(const string &url, vector<string> &headers,
                              string &cacheName);
    FILE *get_cached_response(const string &url, vector<string> &headers);
    FILE *get_cached_response(const string &url);

    void release_cached_response(FILE *response);

    void purge_cache();
};

} // namespace libdap

#endif // _http_cache_h