/* Copyright 2006 by Nils Maier
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * mod_xsendfile.c: Process X-SENDFILE header cgi/scripts may set
 *     Written by Nils Maier, MaierMan@web.de, March 2006
 *
 * Whenever an X-SENDFILE header occures in the response headers drop
 * the body and send the replacement file idenfitied by this header instead.
 *
 * Method inspired by lighttpd <http://lighttpd.net/>
 * Code inspired by mod_headers, mod_rewrite and such
 *
 * Configuration:
 *   You may turn on processing in any context, where perdir config overrides server config:
 *   XSendfile On|Off - Enable/disable(default) processing
 *
 * Installation:
 *     apxs2 -cia mod_xsendfile.c
 */

/*
    v0.9
    (peer-review still required)
*/

#include "apr.h"
#include "apr_lib.h"
#include "apr_strings.h"
#include "apr_buckets.h"
#include "apr_file_io.h"

#include "apr_hash.h"
#define APR_WANT_IOVEC
#define APR_WANT_STRFUNC
#include "apr_want.h"

#include "httpd.h"
#include "http_log.h"
#include "http_config.h"
#include "http_log.h"
#define CORE_PRIVATE
#include "http_request.h"
#include "http_core.h" /* needed for per-directory core-config */
#include "util_filter.h"
#include "http_protocol.h" /* ap_hook_insert_error_filter */

#define AP_XSENDFILE_HEADER "X-SENDFILE"

#if defined(__GNUC__) && (__GNUC__ > 2)
#   define AP_XSENDFILE_EXPECT_TRUE(x) __builtin_expect((x), 1);
#   define AP_XSENDFILE_EXPECT_FALSE(x) __builtin_expect((x), 0);
#else
#   define AP_XSENDFILE_EXPECT_TRUE(x) (x)
#   define AP_XSENDFILE_EXPECT_FALSE(x) (x)
#endif

module AP_MODULE_DECLARE_DATA xsendfile_module;

typedef enum {
    XSENDFILE_UNSET, XSENDFILE_ENABLED, XSENDFILE_DISABLED
} xsendfile_conf_active_t;

typedef struct xsendfile_conf_t
{
    xsendfile_conf_active_t enabled;
	xsendfile_conf_active_t allowAbove;
} xsendfile_conf_t;

static void *xsendfile_config_server_create(apr_pool_t *p, server_rec *s)
{
    xsendfile_conf_t *conf;

    conf = (xsendfile_conf_t *) apr_pcalloc(p, sizeof(xsendfile_conf_t));
    conf->allowAbove = conf->enabled = XSENDFILE_UNSET;

    return (void*)conf;
}

#define XSENDFILE_CFLAG(x) conf->x = overrides->x != XSENDFILE_UNSET ? overrides->x : base->x

static void *xsendfile_config_server_merge(apr_pool_t *p, void *basev, void *overridesv)
{
    xsendfile_conf_t *base = (xsendfile_conf_t *) basev;
    xsendfile_conf_t *overrides = (xsendfile_conf_t *) overridesv;
    xsendfile_conf_t *conf;

    conf = (xsendfile_conf_t *) apr_pcalloc(p, sizeof(xsendfile_conf_t));

    XSENDFILE_CFLAG(enabled);
    XSENDFILE_CFLAG(allowAbove);

    return (void*)conf;
}

static void *xsendfile_config_perdir_create(apr_pool_t *p, char *path)
{
    xsendfile_conf_t *conf;

    conf = (xsendfile_conf_t *)apr_pcalloc(p, sizeof(xsendfile_conf_t));
    conf->allowAbove = conf->enabled = XSENDFILE_UNSET;

    return (void*)conf;
}

static void *xsendfile_config_perdir_merge(apr_pool_t *p, void *basev, void *overridesv)
{
    xsendfile_conf_t *base = (xsendfile_conf_t *) basev;
    xsendfile_conf_t *overrides = (xsendfile_conf_t*)overridesv;
    xsendfile_conf_t *conf;

    conf = (xsendfile_conf_t*)apr_pcalloc(p, sizeof(xsendfile_conf_t));


    XSENDFILE_CFLAG(enabled);
    XSENDFILE_CFLAG(allowAbove);
    
    return (void*)conf;
}
#undef XSENDFILE_CFLAG

static const char *xsendfile_cmd_flag(cmd_parms *cmd, void *perdir_confv, int flag)
{
    xsendfile_conf_t *conf = (xsendfile_conf_t *)perdir_confv;
    if (cmd->path == NULL)
    {
        conf = (xsendfile_conf_t*)ap_get_module_config(
            cmd->server->module_config,
            &xsendfile_module
            );
    }
    if (conf)
    {
        if (strcasecmp(cmd->cmd->name, "xsendfile") == 0)
        {
            conf->enabled = flag ? XSENDFILE_ENABLED : XSENDFILE_DISABLED;
        }
        else
        {
            conf->allowAbove = flag ? XSENDFILE_ENABLED : XSENDFILE_DISABLED;
        }
    }
    return NULL;
}

/*
    little helper function to get the original request path

    code borrowed from request.c and util_script.c
*/
static const char *ap_xsendfile_get_orginal_path(request_rec *rec)
{
    const char
        *rv = rec->the_request,
        *last;
    
    int dir = 0;
    size_t uri_len;

    /* skip method && spaces */
    while (*rv && !apr_isspace(*rv))
    {
        ++rv;
    }
    while (apr_isspace(*rv))
    {
        ++rv;
    }
    /* first space is the request end */
    last = rv;
    while (*last && !apr_isspace(*last))
    {
        ++last;
    }
    uri_len = last - rv;
    if (!uri_len)
    {
        return NULL;
    }

    /* alright, lets see if the request_uri changed! */
    if (strncmp(rv, rec->uri, uri_len) == 0)
    {
        rv = apr_pstrdup(rec->pool, rec->filename);
        dir = rec->finfo.filetype == APR_DIR;
    }
    else
    {
        /* need to lookup the url again as it changed */
        request_rec *sr = ap_sub_req_lookup_uri(
            apr_pstrmemdup(rec->pool, rv, uri_len),
            rec,
            NULL
            );
        if (!sr)
        {
            return NULL;
        }
        rv = apr_pstrdup(rec->pool, sr->filename);
        dir = rec->finfo.filetype == APR_DIR;
        ap_destroy_sub_req(sr);
    }

    /* now we need to truncate so we only have the directory */
    if (!dir && (last = ap_strrchr(rv, '/')) != NULL)
    {
        *((char*)last + 1) = '\0';
    }

    return rv;    
}

static apr_status_t ap_xsendfile_output_filter(
    ap_filter_t *f,
    apr_bucket_brigade *in
)
{
    request_rec *r = f->r, *sr = NULL;

    xsendfile_conf_active_t allowAbove = ((xsendfile_conf_t *)ap_get_module_config(r->per_dir_config, &xsendfile_module))->allowAbove;
    core_dir_config *coreconf = (core_dir_config *)ap_get_module_config(r->per_dir_config, &core_module);

    apr_status_t rv;
    apr_bucket *e;

    apr_file_t *fd = NULL;
    apr_finfo_t finfo;

    const char *file = NULL, *root = NULL;
    char *newpath = NULL;

    int errcode;

    if (XSENDFILE_UNSET == allowAbove)
    {
        allowAbove = ((xsendfile_conf_t*)ap_get_module_config(r->server->module_config, &xsendfile_module))->allowAbove;
    }

#ifdef _DEBUG
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: output_filter for %s", r->the_request);
#endif

    /*
        should we proceed with this request?

        * sub-requests suck
        * furthermore default-handled requests suck, as they actually shouldn't be able to set headers
    */
    if (
        r->status != HTTP_OK
        || r->main
        || (r->handler && strcmp(r->handler, "default-handler") == 0) /* those table-keys are lower-case, right? */
    )
    {
#ifdef _DEBUG
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: not met [%d]", r->status);
#endif
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    /*
        alright, look for x-sendfile
    */
    file = apr_table_get(r->headers_out, AP_XSENDFILE_HEADER);
    apr_table_unset(r->headers_out, AP_XSENDFILE_HEADER);

    /* cgi/fastcgi will put the stuff into err_headers_out */
    if (!file || !*file)
    {
        file = apr_table_get(r->err_headers_out, AP_XSENDFILE_HEADER);
        apr_table_unset(r->err_headers_out, AP_XSENDFILE_HEADER);
    }

    /* nothing there :p */
    if (!file || !*file)
    {
#ifdef _DEBUG
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: nothing found");
#endif
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    /*
        drop *everything*
        might be pretty expensive to generate content first that goes straight to the bitbucket,
        but actually the scripts that might set this flag won't output too much anyway
    */
    while (!APR_BRIGADE_EMPTY(in))
    {
        e = APR_BRIGADE_FIRST(in);
        apr_bucket_delete(e);
    }
    r->eos_sent = 0;

    /*
        grab the current path
        somewhat nasty...
        any better ways?

        freaking fix for cgi-alike handlers that overwrite our precious values :p
    */
    root = ap_xsendfile_get_orginal_path(r);

#ifdef _DEBUG
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: path is %s", root);
#endif

    /*
        alright, we now build our new path
    */
    if ((rv = apr_filepath_merge(
        &newpath,
        root,
        file,
        APR_FILEPATH_TRUENAME | (allowAbove != XSENDFILE_ENABLED ? APR_FILEPATH_SECUREROOT : 0),
        r->pool
    )) != OK)
    {
        ap_log_rerror(
            APLOG_MARK,
            APLOG_ERR,
            rv,
            r,
            "xsendfile: unable to find file: %s, aa=%d",
            file, allowAbove
        );
        ap_remove_output_filter(f);
        ap_die(HTTP_NOT_FOUND, r);
        return HTTP_NOT_FOUND;
    }

#ifdef _DEBUG
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: found %s", newpath);
#endif

    /*
        try open the file
    */
    if ((rv = apr_file_open(
        &fd,
        newpath,
        APR_READ | APR_BINARY
#if APR_HAS_SENDFILE
        | (coreconf->enable_sendfile == ENABLE_SENDFILE_ON ?  APR_SENDFILE_ENABLED : 0)
#endif
        ,
        0,
        r->pool
    )) != APR_SUCCESS)
    {
        ap_log_rerror(
            APLOG_MARK,
            APLOG_ERR,
            rv,
            r,
            "xsendfile: cannot open file: %s",
            newpath
        );
        ap_remove_output_filter(f);
        ap_die(HTTP_NOT_FOUND, r);
        return HTTP_NOT_FOUND;
    }
#if APR_HAS_SENDFILE && defined(_DEBUG)
    if (coreconf->enable_sendfile != ENABLE_SENDFILE_ON)
    {

        ap_log_error(
            APLOG_MARK,
            APLOG_WARNING,
            0,
            r->server,
            "xsendfile: sendfile configured, but not active %d",
            coreconf->enable_sendfile
            );
    }
#endif
    /*
        stat (for etag/cache/content-length stuff)
    */
    if ((rv = apr_file_info_get(&finfo, APR_FINFO_NORM, fd)) != APR_SUCCESS)
    {
        ap_log_rerror(
            APLOG_MARK,
            APLOG_ERR,
            rv,
            r,
            "xsendfile: unable to stat file: %s",
            newpath
        );
        apr_file_close(fd);
        ap_remove_output_filter(f);
        ap_die(HTTP_FORBIDDEN, r);
        return HTTP_FORBIDDEN;
    }
    /*
        no inclusion of directories!
        we're serving files!
    */
    if (finfo.filetype != APR_REG)
    {
        ap_log_rerror(
            APLOG_MARK,
            APLOG_ERR,
            APR_EBADPATH,
            r,
            "xsendfile: not a file %s",
            newpath
        );
        apr_file_close(fd);
        ap_remove_output_filter(f);
        ap_die(HTTP_NOT_FOUND, r);
        return HTTP_NOT_FOUND;
    }

    /*
        need to cheat here a bit
        as etag generator will use those ;)
        and we want local_copy and cache
    */
    r->finfo.inode = finfo.inode;
    r->finfo.size = finfo.size;

    /*
        caching? why not :p
    */
    r->no_cache = r->no_local_copy = 0;

    ap_update_mtime(r, finfo.mtime);
    ap_set_last_modified(r);
    ap_set_content_length(r, finfo.size);
    ap_set_etag(r);

    /* as we dropped all the content this field is not valid anymore! */
    apr_table_unset(r->headers_out, "Content-Encoding");
    apr_table_unset(r->err_headers_out, "Content-Encoding");

    /* cache or something? */
    if ((errcode = ap_meets_conditions(r)) != OK)
    {
#ifdef _DEBUG
        ap_log_error(
            APLOG_MARK,
            APLOG_DEBUG,
            0,
            r->server,
            "xsendfile: met condition %d for %s",
            errcode,
            file
        );
#endif
        apr_file_close(fd);
        r->status = errcode;
    }
    else
    {
        e = apr_bucket_file_create(
            fd,
            0,
            (apr_size_t)finfo.size,
            r->pool,
            in->bucket_alloc
        );
#if APR_HAS_MMAP
        if (coreconf->enable_mmap == ENABLE_MMAP_ON)
        {
            apr_bucket_file_enable_mmap(e, 0);
        }
#if defined(_DEBUG)
        else
        {
            ap_log_error(
                APLOG_MARK,
                APLOG_WARNING,
                0,
                r->server,
                "xsendfile: mmap configured, but not active %d",
                coreconf->enable_mmap
                );
        }
#endif /* _DEBUG */
#endif /* APR_HAS_MMAP */
        APR_BRIGADE_INSERT_TAIL(in, e);
    }

    e = apr_bucket_eos_create(in->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(in, e);

    /* remove ourselves from the filter chain */
    ap_remove_output_filter(f);

#ifdef _DEBUG
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, "xsendfile: sending %d bytes", (int)finfo.size);
#endif

    /* send the data up the stack */
    return ap_pass_brigade(f->next, in);
}

static void ap_xsendfile_insert_output_filter(request_rec *r)
{
    xsendfile_conf_active_t enabled = ((xsendfile_conf_t *)ap_get_module_config(r->per_dir_config, &xsendfile_module))->enabled;
    if (XSENDFILE_UNSET == enabled)
    {
        enabled = ((xsendfile_conf_t*)ap_get_module_config(r->server->module_config, &xsendfile_module))->enabled;
    }

    if (XSENDFILE_ENABLED != enabled)
    {
        return;
    }

    ap_add_output_filter(
        "XSENDFILE",
        NULL,
        r,
        r->connection
    );
}
static const command_rec xsendfile_command_table[] = {
    AP_INIT_FLAG(
        "XSendFile",
        xsendfile_cmd_flag,
        NULL,
        OR_OPTIONS,
        "On|Off - Enable/disable(default) processing"
        ),
    AP_INIT_FLAG(
        "XSendFileAllowAbove",
        xsendfile_cmd_flag,
        NULL,
        OR_OPTIONS,
        "On|Off - Allow/disallow(default) sending files above Request path"
        ),
    { NULL }
};
static void xsendfile_register_hooks(apr_pool_t *p)
{
    ap_register_output_filter(
        "XSENDFILE",
        ap_xsendfile_output_filter,
        NULL,
        AP_FTYPE_CONTENT_SET
        );

    ap_hook_insert_filter(
        ap_xsendfile_insert_output_filter,
        NULL,
        NULL,
        APR_HOOK_LAST + 1
        );
}
module AP_MODULE_DECLARE_DATA xsendfile_module =
{
    STANDARD20_MODULE_STUFF,
    xsendfile_config_perdir_create,
    xsendfile_config_perdir_merge,
    xsendfile_config_server_create,
    xsendfile_config_server_merge,
    xsendfile_command_table,
    xsendfile_register_hooks
};