lighttpd/src/mod_compress.c

#include <sys/types.h>
#include <sys/stat.h>

#include <fcntl.h>
#include <unistd.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>

#include "base.h"
#include "log.h"
#include "buffer.h"
#include "response.h"
#include "stat_cache.h"

#include "plugin.h"

#include "crc32.h"
#include "etag.h"

#if defined HAVE_ZLIB_H && defined HAVE_LIBZ
# define USE_ZLIB
# include <zlib.h>
#endif

#if defined HAVE_BZLIB_H && defined HAVE_LIBBZ2
# define USE_BZ2LIB
/* we don't need stdio interface */
# define BZ_NO_STDIO
# include <bzlib.h>
#endif

#include "sys-mmap.h"

/* request: accept-encoding */
#define HTTP_ACCEPT_ENCODING_IDENTITY BV(0)
#define HTTP_ACCEPT_ENCODING_GZIP     BV(1)
#define HTTP_ACCEPT_ENCODING_DEFLATE  BV(2)
#define HTTP_ACCEPT_ENCODING_COMPRESS BV(3)
#define HTTP_ACCEPT_ENCODING_BZIP2    BV(4)

#ifdef __WIN32
#define mkdir(x,y) mkdir(x)
#endif

typedef struct {
	buffer *compress_cache_dir;
	array  *compress;
	off_t   compress_max_filesize; /** max filesize in kb */
} plugin_config;

typedef struct {
	PLUGIN_DATA;
	buffer *ofn;
	buffer *b;

	plugin_config **config_storage;
	plugin_config conf;
} plugin_data;

INIT_FUNC(mod_compress_init) {
	plugin_data *p;

	p = calloc(1, sizeof(*p));

	p->ofn = buffer_init();
	p->b = buffer_init();

	return p;
}

FREE_FUNC(mod_compress_free) {
	plugin_data *p = p_d;

	UNUSED(srv);

	if (!p) return HANDLER_GO_ON;

	buffer_free(p->ofn);
	buffer_free(p->b);

	if (p->config_storage) {
		size_t i;
		for (i = 0; i < srv->config_context->used; i++) {
			plugin_config *s = p->config_storage[i];

			if (!s) continue;

			array_free(s->compress);
			buffer_free(s->compress_cache_dir);

			free(s);
		}
		free(p->config_storage);
	}


	free(p);

	return HANDLER_GO_ON;
}

// 0 on success, -1 for error
int mkdir_recursive(char *dir) {
	char *p = dir;

	if (!dir || !dir[0])
		return 0;

	while ((p = strchr(p + 1, '/')) != NULL) {

		*p = '\0';
		if ((mkdir(dir, 0700) != 0) && (errno != EEXIST)) {
			*p = '/';
			return -1;
		}

		*p++ = '/';
		if (!*p) return 0; // Ignore trailing slash
	}

	return (mkdir(dir, 0700) != 0) && (errno != EEXIST) ? -1 : 0;
}

// 0 on success, -1 for error
int mkdir_for_file(char *filename) {
	char *p = filename;

	if (!filename || !filename[0])
		return -1;

	while ((p = strchr(p + 1, '/')) != NULL) {

		*p = '\0';
		if ((mkdir(filename, 0700) != 0) && (errno != EEXIST)) {
			*p = '/';
			return -1;
		}

		*p++ = '/';
		if (!*p) return -1; // Unexpected trailing slash in filename
	}

	return 0;
}

SETDEFAULTS_FUNC(mod_compress_setdefaults) {
	plugin_data *p = p_d;
	size_t i = 0;

	config_values_t cv[] = {
		{ "compress.cache-dir",             NULL, T_CONFIG_STRING, T_CONFIG_SCOPE_CONNECTION },
		{ "compress.filetype",              NULL, T_CONFIG_ARRAY, T_CONFIG_SCOPE_CONNECTION },
		{ "compress.max-filesize",          NULL, T_CONFIG_SHORT, T_CONFIG_SCOPE_CONNECTION },
		{ NULL,                             NULL, T_CONFIG_UNSET, T_CONFIG_SCOPE_UNSET }
	};

	p->config_storage = calloc(1, srv->config_context->used * sizeof(specific_config *));

	for (i = 0; i < srv->config_context->used; i++) {
		plugin_config *s;

		s = calloc(1, sizeof(plugin_config));
		s->compress_cache_dir = buffer_init();
		s->compress = array_init();
		s->compress_max_filesize = 0;

		cv[0].destination = s->compress_cache_dir;
		cv[1].destination = s->compress;
		cv[2].destination = &(s->compress_max_filesize);

		p->config_storage[i] = s;

		if (0 != config_insert_values_global(srv, ((data_config *)srv->config_context->data[i])->value, cv)) {
			return HANDLER_ERROR;
		}

		if (!buffer_is_empty(s->compress_cache_dir)) {
			mkdir_recursive(s->compress_cache_dir->ptr);

			struct stat st;
			if (0 != stat(s->compress_cache_dir->ptr, &st)) {
				log_error_write(srv, __FILE__, __LINE__, "sbs", "can't stat compress.cache-dir",
						s->compress_cache_dir, strerror(errno));

				return HANDLER_ERROR;
			}
		}
	}

	return HANDLER_GO_ON;

}

#ifdef USE_ZLIB
static int deflate_file_to_buffer_gzip(server *srv, connection *con, plugin_data *p, char *start, off_t st_size, time_t mtime) {
	unsigned char *c;
	unsigned long crc;
	z_stream z;

	UNUSED(srv);
	UNUSED(con);

	z.zalloc = Z_NULL;
	z.zfree = Z_NULL;
	z.opaque = Z_NULL;

	if (Z_OK != deflateInit2(&z,
				 Z_DEFAULT_COMPRESSION,
				 Z_DEFLATED,
				 -MAX_WBITS,  /* supress zlib-header */
				 8,
				 Z_DEFAULT_STRATEGY)) {
		return -1;
	}

	z.next_in = (unsigned char *)start;
	z.avail_in = st_size;
	z.total_in = 0;


	buffer_prepare_copy(p->b, (z.avail_in * 1.1) + 12 + 18);

	/* write gzip header */

	c = (unsigned char *)p->b->ptr;
	c[0] = 0x1f;
	c[1] = 0x8b;
	c[2] = Z_DEFLATED;
	c[3] = 0; /* options */
	c[4] = (mtime >>  0) & 0xff;
	c[5] = (mtime >>  8) & 0xff;
	c[6] = (mtime >> 16) & 0xff;
	c[7] = (mtime >> 24) & 0xff;
	c[8] = 0x00; /* extra flags */
	c[9] = 0x03; /* UNIX */

	p->b->used = 10;
	z.next_out = (unsigned char *)p->b->ptr + p->b->used;
	z.avail_out = p->b->size - p->b->used - 8;
	z.total_out = 0;

	if (Z_STREAM_END != deflate(&z, Z_FINISH)) {
		deflateEnd(&z);
		return -1;
	}

	/* trailer */
	p->b->used += z.total_out;

	crc = generate_crc32c(start, st_size);

	c = (unsigned char *)p->b->ptr + p->b->used;

	c[0] = (crc >>  0) & 0xff;
	c[1] = (crc >>  8) & 0xff;
	c[2] = (crc >> 16) & 0xff;
	c[3] = (crc >> 24) & 0xff;
	c[4] = (z.total_in >>  0) & 0xff;
	c[5] = (z.total_in >>  8) & 0xff;
	c[6] = (z.total_in >> 16) & 0xff;
	c[7] = (z.total_in >> 24) & 0xff;
	p->b->used += 8;

	if (Z_OK != deflateEnd(&z)) {
		return -1;
	}

	return 0;
}

static int deflate_file_to_buffer_deflate(server *srv, connection *con, plugin_data *p, unsigned char *start, off_t st_size) {
	z_stream z;

	UNUSED(srv);
	UNUSED(con);

	z.zalloc = Z_NULL;
	z.zfree = Z_NULL;
	z.opaque = Z_NULL;

	if (Z_OK != deflateInit2(&z,
				 Z_DEFAULT_COMPRESSION,
				 Z_DEFLATED,
				 -MAX_WBITS,  /* supress zlib-header */
				 8,
				 Z_DEFAULT_STRATEGY)) {
		return -1;
	}

	z.next_in = start;
	z.avail_in = st_size;
	z.total_in = 0;

	buffer_prepare_copy(p->b, (z.avail_in * 1.1) + 12);

	z.next_out = (unsigned char *)p->b->ptr;
	z.avail_out = p->b->size;
	z.total_out = 0;

	if (Z_STREAM_END != deflate(&z, Z_FINISH)) {
		deflateEnd(&z);
		return -1;
	}

	/* trailer */
	p->b->used += z.total_out;

	if (Z_OK != deflateEnd(&z)) {
		return -1;
	}

	return 0;
}

#endif

#ifdef USE_BZ2LIB
static int deflate_file_to_buffer_bzip2(server *srv, connection *con, plugin_data *p, unsigned char *start, off_t st_size) {
	bz_stream bz;

	UNUSED(srv);
	UNUSED(con);

	bz.bzalloc = NULL;
	bz.bzfree = NULL;
	bz.opaque = NULL;

	if (BZ_OK != BZ2_bzCompressInit(&bz,
					9, /* blocksize = 900k */
					0, /* no output */
					0)) { /* workFactor: default */
		return -1;
	}

	bz.next_in = (char *)start;
	bz.avail_in = st_size;
	bz.total_in_lo32 = 0;
	bz.total_in_hi32 = 0;

	buffer_prepare_copy(p->b, (bz.avail_in * 1.1) + 12);

	bz.next_out = p->b->ptr;
	bz.avail_out = p->b->size;
	bz.total_out_lo32 = 0;
	bz.total_out_hi32 = 0;

	if (BZ_STREAM_END != BZ2_bzCompress(&bz, BZ_FINISH)) {
		BZ2_bzCompressEnd(&bz);
		return -1;
	}

	/* file is too large for now */
	if (bz.total_out_hi32) return -1;

	/* trailer */
	p->b->used = bz.total_out_lo32;

	if (BZ_OK != BZ2_bzCompressEnd(&bz)) {
		return -1;
	}

	return 0;
}
#endif

static int deflate_file_to_file(server *srv, connection *con, plugin_data *p, buffer *fn, stat_cache_entry *sce, int type) {
	int ifd, ofd;
	int ret = -1;
	void *start;
	const char *filename = fn->ptr;
	ssize_t r;

	/* overflow */
	if ((off_t)(sce->st.st_size * 1.1) < sce->st.st_size) return -1;

	/* don't mmap files > 128Mb
	 *
	 * we could use a sliding window, but currently there is no need for it
	 */

	if (sce->st.st_size > 128 * 1024 * 1024) return -1;

	buffer_reset(p->ofn);
	buffer_copy_string_buffer(p->ofn, p->conf.compress_cache_dir);
	BUFFER_APPEND_SLASH(p->ofn);

	if (0 == strncmp(con->physical.path->ptr, con->physical.doc_root->ptr, con->physical.doc_root->used-1)) {
		buffer_append_string(p->ofn, con->physical.path->ptr + con->physical.doc_root->used - 1);
		buffer_copy_string_buffer(p->b, p->ofn);
	} else {
		buffer_append_string_buffer(p->ofn, con->uri.path);
	}

	switch(type) {
	case HTTP_ACCEPT_ENCODING_GZIP:
		buffer_append_string(p->ofn, "-gzip-");
		break;
	case HTTP_ACCEPT_ENCODING_DEFLATE:
		buffer_append_string(p->ofn, "-deflate-");
		break;
	case HTTP_ACCEPT_ENCODING_BZIP2:
		buffer_append_string(p->ofn, "-bzip2-");
		break;
	default:
		log_error_write(srv, __FILE__, __LINE__, "sd", "unknown compression type", type);
		return -1;
	}

	buffer_append_string_buffer(p->ofn, sce->etag);

	if (-1 == mkdir_for_file(p->ofn->ptr)) {
		log_error_write(srv, __FILE__, __LINE__, "sb", "couldn't create directory for file", p->ofn);
		return -1;
	}

	if (-1 == (ofd = open(p->ofn->ptr, O_WRONLY | O_CREAT | O_EXCL | O_BINARY, 0600))) {
		if (errno == EEXIST) {
			/* cache-entry exists */
#if 0
			log_error_write(srv, __FILE__, __LINE__, "bs", p->ofn, "compress-cache hit");
#endif
			buffer_copy_string_buffer(con->physical.path, p->ofn);

			return 0;
		}

		log_error_write(srv, __FILE__, __LINE__, "sbss", "creating cachefile", p->ofn, "failed", strerror(errno));

		return -1;
	}
#if 0
	log_error_write(srv, __FILE__, __LINE__, "bs", p->ofn, "compress-cache miss");
#endif
	if (-1 == (ifd = open(filename, O_RDONLY | O_BINARY))) {
		log_error_write(srv, __FILE__, __LINE__, "sbss", "opening plain-file", fn, "failed", strerror(errno));

		close(ofd);

		/* Remove the incomplete cache file, so that later hits aren't served from it */
		if (-1 == unlink(p->ofn->ptr)) {
			log_error_write(srv, __FILE__, __LINE__, "sbss", "unlinking incomplete cachefile", p->ofn, "failed:", strerror(errno));
		}

		return -1;
	}


	if (MAP_FAILED == (start = mmap(NULL, sce->st.st_size, PROT_READ, MAP_SHARED, ifd, 0))) {
		log_error_write(srv, __FILE__, __LINE__, "sbss", "mmaping", fn, "failed", strerror(errno));

		close(ofd);
		close(ifd);

		/* Remove the incomplete cache file, so that later hits aren't served from it */
		if (-1 == unlink(p->ofn->ptr)) {
			log_error_write(srv, __FILE__, __LINE__, "sbss", "unlinking incomplete cachefile", p->ofn, "failed:", strerror(errno));
		}

		return -1;
	}

	switch(type) {
#ifdef USE_ZLIB
	case HTTP_ACCEPT_ENCODING_GZIP:
		ret = deflate_file_to_buffer_gzip(srv, con, p, start, sce->st.st_size, sce->st.st_mtime);
		break;
	case HTTP_ACCEPT_ENCODING_DEFLATE:
		ret = deflate_file_to_buffer_deflate(srv, con, p, start, sce->st.st_size);
		break;
#endif
#ifdef USE_BZ2LIB
	case HTTP_ACCEPT_ENCODING_BZIP2:
		ret = deflate_file_to_buffer_bzip2(srv, con, p, start, sce->st.st_size);
		break;
#endif
	default:
		ret = -1;
		break;
	}

	if (ret == 0) {
		r = write(ofd, p->b->ptr, p->b->used);
		if (-1 == r) {
			log_error_write(srv, __FILE__, __LINE__, "sbss", "writing cachefile", p->ofn, "failed:", strerror(errno));
			ret = -1;
		} else if ((size_t)r != p->b->used) {
			log_error_write(srv, __FILE__, __LINE__, "sbs", "writing cachefile", p->ofn, "failed: not enough bytes written");
			ret = -1;
		}
	}

	munmap(start, sce->st.st_size);
	close(ofd);
	close(ifd);

	if (ret != 0) {
		/* Remove the incomplete cache file, so that later hits aren't served from it */
		if (-1 == unlink(p->ofn->ptr)) {
			log_error_write(srv, __FILE__, __LINE__, "sbss", "unlinking incomplete cachefile", p->ofn, "failed:", strerror(errno));
		}

		return -1;
	}

	buffer_copy_string_buffer(con->physical.path, p->ofn);

	return 0;
}

static int deflate_file_to_buffer(server *srv, connection *con, plugin_data *p, buffer *fn, stat_cache_entry *sce, int type) {
	int ifd;
	int ret = -1;
	void *start;
	buffer *b;

	/* overflow */
	if ((off_t)(sce->st.st_size * 1.1) < sce->st.st_size) return -1;

	/* don't mmap files > 128M
	 *
	 * we could use a sliding window, but currently there is no need for it
	 */

	if (sce->st.st_size > 128 * 1024 * 1024) return -1;


	if (-1 == (ifd = open(fn->ptr, O_RDONLY | O_BINARY))) {
		log_error_write(srv, __FILE__, __LINE__, "sbss", "opening plain-file", fn, "failed", strerror(errno));

		return -1;
	}


	if (MAP_FAILED == (start = mmap(NULL, sce->st.st_size, PROT_READ, MAP_SHARED, ifd, 0))) {
		log_error_write(srv, __FILE__, __LINE__, "sbss", "mmaping", fn, "failed", strerror(errno));

		close(ifd);
		return -1;
	}

	switch(type) {
#ifdef USE_ZLIB
	case HTTP_ACCEPT_ENCODING_GZIP:
		ret = deflate_file_to_buffer_gzip(srv, con, p, start, sce->st.st_size, sce->st.st_mtime);
		break;
	case HTTP_ACCEPT_ENCODING_DEFLATE:
		ret = deflate_file_to_buffer_deflate(srv, con, p, start, sce->st.st_size);
		break;
#endif
#ifdef USE_BZ2LIB
	case HTTP_ACCEPT_ENCODING_BZIP2:
		ret = deflate_file_to_buffer_bzip2(srv, con, p, start, sce->st.st_size);
		break;
#endif
	default:
		ret = -1;
		break;
	}

	munmap(start, sce->st.st_size);
	close(ifd);

	if (ret != 0) return -1;

	chunkqueue_reset(con->write_queue);
	b = chunkqueue_get_append_buffer(con->write_queue);
	buffer_copy_memory(b, p->b->ptr, p->b->used + 1);

	buffer_reset(con->physical.path);

	con->file_finished = 1;
	con->file_started  = 1;

	return 0;
}


#define PATCH(x) \
	p->conf.x = s->x;
static int mod_compress_patch_connection(server *srv, connection *con, plugin_data *p) {
	size_t i, j;
	plugin_config *s = p->config_storage[0];

	PATCH(compress_cache_dir);
	PATCH(compress);
	PATCH(compress_max_filesize);

	/* skip the first, the global context */
	for (i = 1; i < srv->config_context->used; i++) {
		data_config *dc = (data_config *)srv->config_context->data[i];
		s = p->config_storage[i];

		/* condition didn't match */
		if (!config_check_cond(srv, con, dc)) continue;

		/* merge config */
		for (j = 0; j < dc->value->used; j++) {
			data_unset *du = dc->value->data[j];

			if (buffer_is_equal_string(du->key, CONST_STR_LEN("compress.cache-dir"))) {
				PATCH(compress_cache_dir);
			} else if (buffer_is_equal_string(du->key, CONST_STR_LEN("compress.filetype"))) {
				PATCH(compress);
			} else if (buffer_is_equal_string(du->key, CONST_STR_LEN("compress.max-filesize"))) {
				PATCH(compress_max_filesize);
			}
		}
	}

	return 0;
}
#undef PATCH

PHYSICALPATH_FUNC(mod_compress_physical) {
	plugin_data *p = p_d;
	size_t m;
	off_t max_fsize;
	stat_cache_entry *sce = NULL;

	if (con->mode != DIRECT || con->http_status) return HANDLER_GO_ON;

	/* only GET and POST can get compressed */
	if (con->request.http_method != HTTP_METHOD_GET &&
	    con->request.http_method != HTTP_METHOD_POST) {
		return HANDLER_GO_ON;
	}

	if (buffer_is_empty(con->physical.path)) {
		return HANDLER_GO_ON;
	}

	mod_compress_patch_connection(srv, con, p);

	max_fsize = p->conf.compress_max_filesize;

	stat_cache_get_entry(srv, con, con->physical.path, &sce);

	/* don't compress files that are too large as we need to much time to handle them */
	if (max_fsize && (sce->st.st_size >> 10) > max_fsize) return HANDLER_GO_ON;

	/* don't try to compress files less than 128 bytes
	 *
	 * - extra overhead for compression
	 * - mmap() fails for st_size = 0 :)
	 */
	if (sce->st.st_size < 128) return HANDLER_GO_ON;

	/* check if mimetype is in compress-config */
	for (m = 0; m < p->conf.compress->used; m++) {
		data_string *compress_ds = (data_string *)p->conf.compress->data[m];

		if (!compress_ds) {
			log_error_write(srv, __FILE__, __LINE__, "sbb", "evil", con->physical.path, con->uri.path);

			return HANDLER_GO_ON;
		}

		if (buffer_is_equal(compress_ds->value, sce->content_type)) {
			/* mimetype found */
			data_string *ds;

			/* the response might change according to Accept-Encoding */
			response_header_insert(srv, con, CONST_STR_LEN("Vary"), CONST_STR_LEN("Accept-Encoding"));

			if (NULL != (ds = (data_string *)array_get_element(con->request.headers, "Accept-Encoding"))) {
				int accept_encoding = 0;
				char *value = ds->value->ptr;
				int srv_encodings = 0;
				int matched_encodings = 0;

				/* get client side support encodings */
				if (NULL != strstr(value, "gzip")) accept_encoding |= HTTP_ACCEPT_ENCODING_GZIP;
				if (NULL != strstr(value, "deflate")) accept_encoding |= HTTP_ACCEPT_ENCODING_DEFLATE;
				if (NULL != strstr(value, "compress")) accept_encoding |= HTTP_ACCEPT_ENCODING_COMPRESS;
				if (NULL != strstr(value, "bzip2")) accept_encoding |= HTTP_ACCEPT_ENCODING_BZIP2;
				if (NULL != strstr(value, "identity")) accept_encoding |= HTTP_ACCEPT_ENCODING_IDENTITY;

				/* get server side supported ones */
#ifdef USE_BZ2LIB
				srv_encodings |= HTTP_ACCEPT_ENCODING_BZIP2;
#endif
#ifdef USE_ZLIB
				srv_encodings |= HTTP_ACCEPT_ENCODING_GZIP;
				srv_encodings |= HTTP_ACCEPT_ENCODING_DEFLATE;
#endif

				/* find matching entries */
				matched_encodings = accept_encoding & srv_encodings;

				if (matched_encodings) {
					const char *dflt_gzip = "gzip";
					const char *dflt_deflate = "deflate";
					const char *dflt_bzip2 = "bzip2";

					const char *compression_name = NULL;
					int compression_type = 0;

					/* select best matching encoding */
					if (matched_encodings & HTTP_ACCEPT_ENCODING_BZIP2) {
						compression_type = HTTP_ACCEPT_ENCODING_BZIP2;
						compression_name = dflt_bzip2;
					} else if (matched_encodings & HTTP_ACCEPT_ENCODING_GZIP) {
						compression_type = HTTP_ACCEPT_ENCODING_GZIP;
						compression_name = dflt_gzip;
					} else if (matched_encodings & HTTP_ACCEPT_ENCODING_DEFLATE) {
						compression_type = HTTP_ACCEPT_ENCODING_DEFLATE;
						compression_name = dflt_deflate;
					}

					/* deflate it */
					if (p->conf.compress_cache_dir->used) {
						if (0 == deflate_file_to_file(srv, con, p,
									      con->physical.path, sce, compression_type)) {
							buffer *mtime;

							response_header_overwrite(srv, con, CONST_STR_LEN("Content-Encoding"), compression_name, strlen(compression_name));

							mtime = strftime_cache_get(srv, sce->st.st_mtime);
							response_header_overwrite(srv, con, CONST_STR_LEN("Last-Modified"), CONST_BUF_LEN(mtime));

							etag_mutate(con->physical.etag, sce->etag);
							response_header_overwrite(srv, con, CONST_STR_LEN("ETag"), CONST_BUF_LEN(con->physical.etag));

							response_header_overwrite(srv, con, CONST_STR_LEN("Content-Type"), CONST_BUF_LEN(sce->content_type));

							return HANDLER_GO_ON;
						}
					} else if (0 == deflate_file_to_buffer(srv, con, p,
									       con->physical.path, sce, compression_type)) {
						buffer *mtime;

						response_header_overwrite(srv, con, CONST_STR_LEN("Content-Encoding"), compression_name, strlen(compression_name));

						mtime = strftime_cache_get(srv, sce->st.st_mtime);
						response_header_overwrite(srv, con, CONST_STR_LEN("Last-Modified"), CONST_BUF_LEN(mtime));

						etag_mutate(con->physical.etag, sce->etag);
						response_header_overwrite(srv, con, CONST_STR_LEN("ETag"), CONST_BUF_LEN(con->physical.etag));

						response_header_overwrite(srv, con, CONST_STR_LEN("Content-Type"), CONST_BUF_LEN(sce->content_type));

						return HANDLER_FINISHED;
					}
					break;
				}
			}
		}
	}

	return HANDLER_GO_ON;
}

int mod_compress_plugin_init(plugin *p) {
	p->version     = LIGHTTPD_VERSION_ID;
	p->name        = buffer_init_string("compress");

	p->init        = mod_compress_init;
	p->set_defaults = mod_compress_setdefaults;
	p->handle_subrequest_start  = mod_compress_physical;
	p->cleanup     = mod_compress_free;

	p->data        = NULL;

	return 0;
}