openssl/crypto/comp/c_zlib.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/objects.h>
#include <openssl/comp.h>
#include <openssl/err.h>

COMP_METHOD *COMP_zlib(void );

static COMP_METHOD zlib_method_nozlib={
	NID_undef,
	"(undef)",
	NULL,
	NULL,
	NULL,
	NULL,
	NULL,
	NULL,
	};

#ifndef ZLIB
#undef ZLIB_SHARED
#else

#include <zlib.h>

static int zlib_stateful_init(COMP_CTX *ctx);
static void zlib_stateful_finish(COMP_CTX *ctx);
static int zlib_stateful_compress_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen);
static int zlib_stateful_expand_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen);


/* memory allocations functions for zlib intialization */
static void* zlib_zalloc(void* opaque, unsigned int no, unsigned int size)
{
	void *p;
	
	p=OPENSSL_malloc(no*size);
	if (p)
		memset(p, 0, no*size);
	return p;
}


static void zlib_zfree(void* opaque, void* address)
{
	OPENSSL_free(address);
}

#if 0
static int zlib_compress_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen);
static int zlib_expand_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen);

static int zz_uncompress(Bytef *dest, uLongf *destLen, const Bytef *source,
	uLong sourceLen);

static COMP_METHOD zlib_stateless_method={
	NID_zlib_compression,
	LN_zlib_compression,
	NULL,
	NULL,
	zlib_compress_block,
	zlib_expand_block,
	NULL,
	NULL,
	};
#endif

static COMP_METHOD zlib_stateful_method={
	NID_zlib_compression,
	LN_zlib_compression,
	zlib_stateful_init,
	zlib_stateful_finish,
	zlib_stateful_compress_block,
	zlib_stateful_expand_block,
	NULL,
	NULL,
	};

/* 
 * When OpenSSL is built on Windows, we do not want to require that
 * the ZLIB.DLL be available in order for the OpenSSL DLLs to
 * work.  Therefore, all ZLIB routines are loaded at run time
 * and we do not link to a .LIB file when ZLIB_SHARED is set.
 */
#if defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_WIN32)
# include <windows.h>
#endif /* !(OPENSSL_SYS_WINDOWS || OPENSSL_SYS_WIN32) */

#ifdef ZLIB_SHARED
#include <openssl/dso.h>

/* Function pointers */
typedef int (*compress_ft)(Bytef *dest,uLongf *destLen,
	const Bytef *source, uLong sourceLen);
typedef int (*inflateEnd_ft)(z_streamp strm);
typedef int (*inflate_ft)(z_streamp strm, int flush);
typedef int (*inflateInit__ft)(z_streamp strm,
	const char * version, int stream_size);
typedef int (*deflateEnd_ft)(z_streamp strm);
typedef int (*deflate_ft)(z_streamp strm, int flush);
typedef int (*deflateInit__ft)(z_streamp strm, int level,
	const char * version, int stream_size);
typedef const char * (*zError__ft)(int err);
static compress_ft	p_compress=NULL;
static inflateEnd_ft	p_inflateEnd=NULL;
static inflate_ft	p_inflate=NULL;
static inflateInit__ft	p_inflateInit_=NULL;
static deflateEnd_ft	p_deflateEnd=NULL;
static deflate_ft	p_deflate=NULL;
static deflateInit__ft	p_deflateInit_=NULL;
static zError__ft	p_zError=NULL;

static int zlib_loaded = 0;     /* only attempt to init func pts once */
static DSO *zlib_dso = NULL;

#define compress                p_compress
#define inflateEnd              p_inflateEnd
#define inflate                 p_inflate
#define inflateInit_            p_inflateInit_
#define deflateEnd              p_deflateEnd
#define deflate                 p_deflate
#define deflateInit_            p_deflateInit_
#define zError			p_zError
#endif /* ZLIB_SHARED */

struct zlib_state
	{
	z_stream istream;
	z_stream ostream;
	};

static int zlib_stateful_ex_idx = -1;

static void zlib_stateful_free_ex_data(void *obj, void *item,
	CRYPTO_EX_DATA *ad, int ind,long argl, void *argp)
	{
	struct zlib_state *state = (struct zlib_state *)item;
	inflateEnd(&state->istream);
	deflateEnd(&state->ostream);
	OPENSSL_free(state);
	}

static int zlib_stateful_init(COMP_CTX *ctx)
	{
	int err;
	struct zlib_state *state =
		(struct zlib_state *)OPENSSL_malloc(sizeof(struct zlib_state));

	if (state == NULL)
		goto err;

	state->istream.zalloc = zlib_zalloc;
	state->istream.zfree = zlib_zfree;
	state->istream.opaque = Z_NULL;
	state->istream.next_in = Z_NULL;
	state->istream.next_out = Z_NULL;
	state->istream.avail_in = 0;
	state->istream.avail_out = 0;
	err = inflateInit_(&state->istream,
		ZLIB_VERSION, sizeof(z_stream));
	if (err != Z_OK)
		goto err;

	state->ostream.zalloc = zlib_zalloc;
	state->ostream.zfree = zlib_zfree;
	state->ostream.opaque = Z_NULL;
	state->ostream.next_in = Z_NULL;
	state->ostream.next_out = Z_NULL;
	state->ostream.avail_in = 0;
	state->ostream.avail_out = 0;
	err = deflateInit_(&state->ostream,Z_DEFAULT_COMPRESSION,
		ZLIB_VERSION, sizeof(z_stream));
	if (err != Z_OK)
		goto err;

	CRYPTO_new_ex_data(CRYPTO_EX_INDEX_COMP,ctx,&ctx->ex_data);
	CRYPTO_set_ex_data(&ctx->ex_data,zlib_stateful_ex_idx,state);
	return 1;
 err:
	if (state) OPENSSL_free(state);
	return 0;
	}

static void zlib_stateful_finish(COMP_CTX *ctx)
	{
	CRYPTO_free_ex_data(CRYPTO_EX_INDEX_COMP,ctx,&ctx->ex_data);
	}

static int zlib_stateful_compress_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen)
	{
	int err = Z_OK;
	struct zlib_state *state =
		(struct zlib_state *)CRYPTO_get_ex_data(&ctx->ex_data,
			zlib_stateful_ex_idx);

	if (state == NULL)
		return -1;

	state->ostream.next_in = in;
	state->ostream.avail_in = ilen;
	state->ostream.next_out = out;
	state->ostream.avail_out = olen;
	if (ilen > 0)
		err = deflate(&state->ostream, Z_SYNC_FLUSH);
	if (err != Z_OK)
		return -1;
#ifdef DEBUG_ZLIB
	fprintf(stderr,"compress(%4d)->%4d %s\n",
		ilen,olen - state->ostream.avail_out,
		(ilen != olen - state->ostream.avail_out)?"zlib":"clear");
#endif
	return olen - state->ostream.avail_out;
	}

static int zlib_stateful_expand_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen)
	{
	int err = Z_OK;

	struct zlib_state *state =
		(struct zlib_state *)CRYPTO_get_ex_data(&ctx->ex_data,
			zlib_stateful_ex_idx);

	if (state == NULL)
		return 0;

	state->istream.next_in = in;
	state->istream.avail_in = ilen;
	state->istream.next_out = out;
	state->istream.avail_out = olen;
	if (ilen > 0)
		err = inflate(&state->istream, Z_SYNC_FLUSH);
	if (err != Z_OK)
		return -1;
#ifdef DEBUG_ZLIB
	fprintf(stderr,"expand(%4d)->%4d %s\n",
		ilen,olen - state->istream.avail_out,
		(ilen != olen - state->istream.avail_out)?"zlib":"clear");
#endif
	return olen - state->istream.avail_out;
	}

#if 0
static int zlib_compress_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen)
	{
	unsigned long l;
	int i;
	int clear=1;

	if (ilen > 128)
		{
		out[0]=1;
		l=olen-1;
		i=compress(&(out[1]),&l,in,(unsigned long)ilen);
		if (i != Z_OK)
			return(-1);
		if (ilen > l)
			{
			clear=0;
			l++;
			}
		}
	if (clear)
		{
		out[0]=0;
		memcpy(&(out[1]),in,ilen);
		l=ilen+1;
		}
#ifdef DEBUG_ZLIB
	fprintf(stderr,"compress(%4d)->%4d %s\n",
		ilen,(int)l,(clear)?"clear":"zlib");
#endif
	return((int)l);
	}

static int zlib_expand_block(COMP_CTX *ctx, unsigned char *out,
	unsigned int olen, unsigned char *in, unsigned int ilen)
	{
	unsigned long l;
	int i;

	if (in[0])
		{
		l=olen;
		i=zz_uncompress(out,&l,&(in[1]),(unsigned long)ilen-1);
		if (i != Z_OK)
			return(-1);
		}
	else
		{
		memcpy(out,&(in[1]),ilen-1);
		l=ilen-1;
		}
#ifdef DEBUG_ZLIB
        fprintf(stderr,"expand  (%4d)->%4d %s\n",
		ilen,(int)l,in[0]?"zlib":"clear");
#endif
	return((int)l);
	}

static int zz_uncompress (Bytef *dest, uLongf *destLen, const Bytef *source,
	     uLong sourceLen)
{
    z_stream stream;
    int err;

    stream.next_in = (Bytef*)source;
    stream.avail_in = (uInt)sourceLen;
    /* Check for source > 64K on 16-bit machine: */
    if ((uLong)stream.avail_in != sourceLen) return Z_BUF_ERROR;

    stream.next_out = dest;
    stream.avail_out = (uInt)*destLen;
    if ((uLong)stream.avail_out != *destLen) return Z_BUF_ERROR;

    stream.zalloc = (alloc_func)0;
    stream.zfree = (free_func)0;

    err = inflateInit_(&stream,
	    ZLIB_VERSION, sizeof(z_stream));
    if (err != Z_OK) return err;

    err = inflate(&stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        inflateEnd(&stream);
        return err;
    }
    *destLen = stream.total_out;

    err = inflateEnd(&stream);
    return err;
}
#endif

#endif

COMP_METHOD *COMP_zlib(void)
	{
	COMP_METHOD *meth = &zlib_method_nozlib;

#ifdef ZLIB_SHARED
	if (!zlib_loaded)
		{
#if defined(OPENSSL_SYS_WINDOWS) || defined(OPENSSL_SYS_WIN32)
		zlib_dso = DSO_load(NULL, "ZLIB1", NULL, 0);
#else
		zlib_dso = DSO_load(NULL, "z", NULL, 0);
#endif
		if (zlib_dso != NULL)
			{
			p_compress
				= (compress_ft) DSO_bind_func(zlib_dso,
					"compress");
			p_inflateEnd
				= (inflateEnd_ft) DSO_bind_func(zlib_dso,
					"inflateEnd");
			p_inflate
				= (inflate_ft) DSO_bind_func(zlib_dso,
					"inflate");
			p_inflateInit_
				= (inflateInit__ft) DSO_bind_func(zlib_dso,
					"inflateInit_");
			p_deflateEnd
				= (deflateEnd_ft) DSO_bind_func(zlib_dso,
					"deflateEnd");
			p_deflate
				= (deflate_ft) DSO_bind_func(zlib_dso,
					"deflate");
			p_deflateInit_
				= (deflateInit__ft) DSO_bind_func(zlib_dso,
					"deflateInit_");
			p_zError
				= (zError__ft) DSO_bind_func(zlib_dso,
					"zError");

			if (p_compress && p_inflateEnd && p_inflate
				&& p_inflateInit_ && p_deflateEnd
				&& p_deflate && p_deflateInit_ && p_zError)
				zlib_loaded++;
			}
		}

#endif
#ifdef ZLIB_SHARED
	if (zlib_loaded)
#endif
#if defined(ZLIB) || defined(ZLIB_SHARED)
		{
		/* init zlib_stateful_ex_idx here so that in a multi-process
		 * application it's enough to intialize openssl before forking
		 * (idx will be inherited in all the children) */
		if (zlib_stateful_ex_idx == -1)
			{
			CRYPTO_w_lock(CRYPTO_LOCK_COMP);
			if (zlib_stateful_ex_idx == -1)
				zlib_stateful_ex_idx =
					CRYPTO_get_ex_new_index(CRYPTO_EX_INDEX_COMP,
						0,NULL,NULL,NULL,zlib_stateful_free_ex_data);
			CRYPTO_w_unlock(CRYPTO_LOCK_COMP);
			if (zlib_stateful_ex_idx == -1)
				goto err;
			}
		
		meth = &zlib_stateful_method;
		}
err:	
#endif

	return(meth);
	}

void COMP_zlib_cleanup(void)
	{
#ifdef ZLIB_SHARED
	if (zlib_dso)
		DSO_free(zlib_dso);
#endif
	}

#ifdef ZLIB

/* Zlib based compression/decompression filter BIO */

typedef struct
	{
	unsigned char *ibuf;	/* Input buffer */
	int ibufsize;		/* Buffer size */
	z_stream zin;		/* Input decompress context */
	unsigned char *obuf;	/* Output buffer */
	int obufsize;		/* Output buffer size */
	unsigned char *optr;	/* Position in output buffer */
	int ocount;		/* Amount of data in output buffer */
	int odone;		/* deflate EOF */
	int comp_level;		/* Compression level to use */
	z_stream zout;		/* Output compression context */
	} BIO_ZLIB_CTX;

#define ZLIB_DEFAULT_BUFSIZE 1024

static int bio_zlib_new(BIO *bi);
static int bio_zlib_free(BIO *bi);
static int bio_zlib_read(BIO *b, char *out, int outl);
static int bio_zlib_write(BIO *b, const char *in, int inl);
static long bio_zlib_ctrl(BIO *b, int cmd, long num, void *ptr);
static long bio_zlib_callback_ctrl(BIO *b, int cmd, bio_info_cb *fp);

static BIO_METHOD bio_meth_zlib = 
	{
	BIO_TYPE_COMP,
	"zlib",
	bio_zlib_write,
	bio_zlib_read,
	NULL,
	NULL,
	bio_zlib_ctrl,
	bio_zlib_new,
	bio_zlib_free,
	bio_zlib_callback_ctrl
	};

BIO_METHOD *BIO_f_zlib(void)
	{
	return &bio_meth_zlib;
	}


static int bio_zlib_new(BIO *bi)
	{
	BIO_ZLIB_CTX *ctx;
#ifdef ZLIB_SHARED
	(void)COMP_zlib();
	if (!zlib_loaded)
		{
		COMPerr(COMP_F_BIO_ZLIB_NEW, COMP_R_ZLIB_NOT_SUPPORTED);
		return 0;
		}
#endif
	ctx = OPENSSL_malloc(sizeof(BIO_ZLIB_CTX));
	if(!ctx)
		{
		COMPerr(COMP_F_BIO_ZLIB_NEW, ERR_R_MALLOC_FAILURE);
		return 0;
		}
	ctx->ibuf = NULL;
	ctx->obuf = NULL;
	ctx->ibufsize = ZLIB_DEFAULT_BUFSIZE;
	ctx->obufsize = ZLIB_DEFAULT_BUFSIZE;
	ctx->zin.zalloc = Z_NULL;
	ctx->zin.zfree = Z_NULL;
	ctx->zin.next_in = NULL;
	ctx->zin.avail_in = 0;
	ctx->zin.next_out = NULL;
	ctx->zin.avail_out = 0;
	ctx->zout.zalloc = Z_NULL;
	ctx->zout.zfree = Z_NULL;
	ctx->zout.next_in = NULL;
	ctx->zout.avail_in = 0;
	ctx->zout.next_out = NULL;
	ctx->zout.avail_out = 0;
	ctx->odone = 0;
	ctx->comp_level = Z_DEFAULT_COMPRESSION;
	bi->init = 1;
	bi->ptr = (char *)ctx;
	bi->flags = 0;
	return 1;
	}

static int bio_zlib_free(BIO *bi)
	{
	BIO_ZLIB_CTX *ctx;
	if(!bi) return 0;
	ctx = (BIO_ZLIB_CTX *)bi->ptr;
	if(ctx->ibuf)
		{
		/* Destroy decompress context */
		inflateEnd(&ctx->zin);
		OPENSSL_free(ctx->ibuf);
		}
	if(ctx->obuf)
		{
		/* Destroy compress context */
		deflateEnd(&ctx->zout);
		OPENSSL_free(ctx->obuf);
		}
	OPENSSL_free(ctx);
	bi->ptr = NULL;
	bi->init = 0;
	bi->flags = 0;
	return 1;
	}

static int bio_zlib_read(BIO *b, char *out, int outl)
	{
	BIO_ZLIB_CTX *ctx;
	int ret;
	z_stream *zin;
	if(!out || !outl) return 0;
	ctx = (BIO_ZLIB_CTX *)b->ptr;
	zin = &ctx->zin;
	BIO_clear_retry_flags(b);
	if(!ctx->ibuf)
		{
		ctx->ibuf = OPENSSL_malloc(ctx->ibufsize);
		if(!ctx->ibuf)
			{
			COMPerr(COMP_F_BIO_ZLIB_READ, ERR_R_MALLOC_FAILURE);
			return 0;
			}
		inflateInit(zin);
		zin->next_in = ctx->ibuf;
		zin->avail_in = 0;
		}

	/* Copy output data directly to supplied buffer */
	zin->next_out = (unsigned char *)out;
	zin->avail_out = (unsigned int)outl;
	for(;;)
		{
		/* Decompress while data available */
		while(zin->avail_in)
			{
			ret = inflate(zin, 0);
			if((ret != Z_OK) && (ret != Z_STREAM_END))
				{
				COMPerr(COMP_F_BIO_ZLIB_READ,
						COMP_R_ZLIB_INFLATE_ERROR);
				ERR_add_error_data(2, "zlib error:",
							zError(ret));
				return 0;
				}
			/* If EOF or we've read everything then return */
			if((ret == Z_STREAM_END) || !zin->avail_out)
				return outl - zin->avail_out;
			}

		/* No data in input buffer try to read some in,
		 * if an error then return the total data read.
		 */
		ret = BIO_read(b->next_bio, ctx->ibuf, ctx->ibufsize);
		if(ret <= 0)
			{
			/* Total data read */
			int tot = outl - zin->avail_out;
			BIO_copy_next_retry(b);
			if(ret < 0) return (tot > 0) ? tot : ret;
			return tot;
			}
		zin->avail_in = ret;
		zin->next_in = ctx->ibuf;
		}
	}

static int bio_zlib_write(BIO *b, const char *in, int inl)
	{
	BIO_ZLIB_CTX *ctx;
	int ret;
	z_stream *zout;
	if(!in || !inl) return 0;
	ctx = (BIO_ZLIB_CTX *)b->ptr;
	if(ctx->odone) return 0;
	zout = &ctx->zout;
	BIO_clear_retry_flags(b);
	if(!ctx->obuf)
		{
		ctx->obuf = OPENSSL_malloc(ctx->obufsize);
		/* Need error here */
		if(!ctx->obuf)
			{
			COMPerr(COMP_F_BIO_ZLIB_WRITE, ERR_R_MALLOC_FAILURE);
			return 0;
			}
		ctx->optr = ctx->obuf;
		ctx->ocount = 0;
		deflateInit(zout, ctx->comp_level);
		zout->next_out = ctx->obuf;
		zout->avail_out = ctx->obufsize;
		}
	/* Obtain input data directly from supplied buffer */
	zout->next_in = (void *)in;
	zout->avail_in = inl;
	for(;;)
		{
		/* If data in output buffer write it first */
		while(ctx->ocount) {
			ret = BIO_write(b->next_bio, ctx->optr, ctx->ocount);
			if(ret <= 0)
				{
				/* Total data written */
				int tot = inl - zout->avail_in;
				BIO_copy_next_retry(b);
				if(ret < 0) return (tot > 0) ? tot : ret;
				return tot;
				}
			ctx->optr += ret;
			ctx->ocount -= ret;
		}

		/* Have we consumed all supplied data? */
		if(!zout->avail_in)
			return inl;

		/* Compress some more */

		/* Reset buffer */
		ctx->optr = ctx->obuf;
		zout->next_out = ctx->obuf;
		zout->avail_out = ctx->obufsize;
		/* Compress some more */
		ret = deflate(zout, 0);
		if(ret != Z_OK)
			{
			COMPerr(COMP_F_BIO_ZLIB_WRITE,
						COMP_R_ZLIB_DEFLATE_ERROR);
			ERR_add_error_data(2, "zlib error:", zError(ret));
			return 0;
			}
		ctx->ocount = ctx->obufsize - zout->avail_out;
		}
	}

static int bio_zlib_flush(BIO *b)
	{
	BIO_ZLIB_CTX *ctx;
	int ret;
	z_stream *zout;
	ctx = (BIO_ZLIB_CTX *)b->ptr;
	/* If no data written or already flush show success */
	if(!ctx->obuf || (ctx->odone && !ctx->ocount)) return 1;
	zout = &ctx->zout;
	BIO_clear_retry_flags(b);
	/* No more input data */
	zout->next_in = NULL;
	zout->avail_in = 0;
	for(;;)
		{
		/* If data in output buffer write it first */
		while(ctx->ocount)
			{
			ret = BIO_write(b->next_bio, ctx->optr, ctx->ocount);
			if(ret <= 0)
				{
				BIO_copy_next_retry(b);
				return ret;
				}
			ctx->optr += ret;
			ctx->ocount -= ret;
			}
		if(ctx->odone) return 1;

		/* Compress some more */

		/* Reset buffer */
		ctx->optr = ctx->obuf;
		zout->next_out = ctx->obuf;
		zout->avail_out = ctx->obufsize;
		/* Compress some more */
		ret = deflate(zout, Z_FINISH);
		if(ret == Z_STREAM_END) ctx->odone = 1;
		else if(ret != Z_OK)
			{
			COMPerr(COMP_F_BIO_ZLIB_FLUSH,
						COMP_R_ZLIB_DEFLATE_ERROR);
			ERR_add_error_data(2, "zlib error:", zError(ret));
			return 0;
			}
		ctx->ocount = ctx->obufsize - zout->avail_out;
		}
	}

static long bio_zlib_ctrl(BIO *b, int cmd, long num, void *ptr)
	{
	BIO_ZLIB_CTX *ctx;
	int ret, *ip;
	int ibs, obs;
	if(!b->next_bio) return 0;
	ctx = (BIO_ZLIB_CTX *)b->ptr;
	switch (cmd)
		{

	case BIO_CTRL_RESET:
		ctx->ocount = 0;
		ctx->odone = 0;
		break;

	case BIO_CTRL_FLUSH:
		ret = bio_zlib_flush(b);
		if (ret > 0)
			ret = BIO_flush(b->next_bio);
		break;

	case BIO_C_SET_BUFF_SIZE:
		ibs = -1;
		obs = -1;
		if (ptr != NULL)
			{
			ip = ptr;
			if (*ip == 0)
				ibs = (int) num;
			else 
				obs = (int) num;
			}
		else
			{
			ibs = (int)num;
			obs = ibs;
			}

		if (ibs != -1)
			{
			if (ctx->ibuf)
				{
				OPENSSL_free(ctx->ibuf);
				ctx->ibuf = NULL;
				}
			ctx->ibufsize = ibs;
			}

		if (obs != -1)
			{
			if (ctx->obuf)
				{
				OPENSSL_free(ctx->obuf);
				ctx->obuf = NULL;
				}
			ctx->obufsize = obs;
			}

		break;

	case BIO_C_DO_STATE_MACHINE:
		BIO_clear_retry_flags(b);
		ret = BIO_ctrl(b->next_bio, cmd, num, ptr);
		BIO_copy_next_retry(b);
		break;

	default:
		ret = BIO_ctrl(b->next_bio, cmd, num, ptr);
		break;

		}

	return ret;
	}


static long bio_zlib_callback_ctrl(BIO *b, int cmd, bio_info_cb *fp)
	{
	if(!b->next_bio)
		return 0;
	return
		BIO_callback_ctrl(b->next_bio, cmd, fp);
	}

#endif