/* gzio.c -- IO on .gz files
 * Copyright (C) 1995 Jean-loup Gailly.
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* $Id: gzio.c,v 1.4 1995/04/14 14:50:52 jloup Exp $ */

#include <stdio.h>

#include "zutil.h"

struct internal_state {int dummy;}; /* for buggy compilers */

#define Z_BUFSIZE 4096

#define ALLOC(size) zcalloc((voidp)0, 1, size)
#define TRYFREE(p) {if (p) zcfree((voidp)0, p);}

#define GZ_MAGIC_1 0x1f
#define GZ_MAGIC_2 0x8b

/* gzip flag byte */
#define ASCII_FLAG   0x01 /* bit 0 set: file probably ascii text */
#define HEAD_CRC     0x02 /* bit 1 set: header CRC present */
#define EXTRA_FIELD  0x04 /* bit 2 set: extra field present */
#define ORIG_NAME    0x08 /* bit 3 set: original file name present */
#define COMMENT      0x10 /* bit 4 set: file comment present */
#define RESERVED     0xE0 /* bits 5..7: reserved */

#ifndef SEEK_CUR
#  define SEEK_CUR 1
#endif

typedef struct gz_stream {
    z_stream stream;
    int      z_err;   /* error code for last stream operation */
    int      z_eof;   /* set if end of input file */
    FILE     *file;   /* .gz file */
    Byte     *inbuf;  /* input buffer */
    Byte     *outbuf; /* output buffer */
    uLong    crc;     /* crc32 of uncompressed data */
    char     *msg;    /* error message */
    char     *path;   /* path name for debugging only */
    int      transparent; /* 1 if input file is not a .gz file */
    char     mode;    /* 'w' or 'r' */
} gz_stream;


/* ===========================================================================
 * Cleanup then free the given gz_stream. Return a zlib error code.
 */
local int destroy (s)
    gz_stream *s;
{
    int err = Z_OK;

    if (!s) return Z_STREAM_ERROR;

    TRYFREE(s->inbuf);
    TRYFREE(s->outbuf);
    TRYFREE(s->path);
    TRYFREE(s->msg);

    if (s->stream.state != NULL) {
       if (s->mode == 'w') {
	   err = deflateEnd(&(s->stream));
       } else if (s->mode == 'r') {
	   err = inflateEnd(&(s->stream));
       }
    }
    if (s->file != NULL && fclose(s->file)) {
	err = Z_ERRNO;
    }
    if (s->z_err < 0) err = s->z_err;
    zcfree((voidp)0, s);
    return err;
}

/* ===========================================================================
     Opens a gzip (.gz) file for reading or writing. The mode parameter
   is as in fopen ("rb" or "wb"). The file is given either by file descritor
   or path name (if fd == -1).
     gz_open return NULL if the file could not be opened or if there was
   insufficient memory to allocate the (de)compression state; errno
   can be checked to distinguish the two cases (if errno is zero, the
   zlib error is Z_MEM_ERROR).
*/
local gzFile gz_open (path, mode, fd)
    char *path;
    char *mode;
    int  fd;
{
    int err;
    char *p = mode;
    gz_stream *s = (gz_stream *)ALLOC(sizeof(gz_stream));

    if (!s) return Z_NULL;

    s->stream.zalloc = (alloc_func)0;
    s->stream.zfree = (free_func)0;
    s->stream.next_in = s->inbuf = Z_NULL;
    s->stream.next_out = s->outbuf = Z_NULL;
    s->stream.avail_in = s->stream.avail_out = 0;
    s->file = NULL;
    s->z_err = Z_OK;
    s->z_eof = 0;
    s->crc = crc32(0L, Z_NULL, 0);
    s->msg = NULL;
    s->transparent = 0;

    s->path = (char*)ALLOC(strlen(path)+1);
    if (s->path == NULL) {
	return destroy(s), (gzFile)Z_NULL;
    }
    strcpy(s->path, path); /* do this early for debugging */

    s->mode = '\0';
    do {
	if (*p == 'r') s->mode = 'r';
	if (*p == 'w') s->mode = 'w';
    } while (*p++);
    if (s->mode == '\0') return destroy(s), (gzFile)Z_NULL;
    
    if (s->mode == 'w') {
	err = deflateInit2(&(s->stream), Z_DEFAULT_COMPRESSION,
			   DEFLATED, -WBITS, MEM_LEVEL, 0);
	/* windowBits is passed < 0 to suppress zlib header */

	s->stream.next_out = s->outbuf = ALLOC(Z_BUFSIZE);

	if (err != Z_OK || s->outbuf == Z_NULL) {
	    return destroy(s), (gzFile)Z_NULL;
	}
    } else {
	err = inflateInit2(&(s->stream), -WBITS);
	s->stream.next_in  = s->inbuf = ALLOC(Z_BUFSIZE);

	if (err != Z_OK || s->inbuf == Z_NULL) {
	    return destroy(s), (gzFile)Z_NULL;
	}
    }
    s->stream.avail_out = Z_BUFSIZE;

    errno = 0;
    s->file = fd < 0 ? FOPEN(path, mode) : fdopen(fd, mode);

    if (s->file == NULL) {
	return destroy(s), (gzFile)Z_NULL;
    }
    if (s->mode == 'w') {
	/* Write a very simple .gz header:
	 */
	fprintf(s->file, "%c%c%c%c%c%c%c%c%c%c", GZ_MAGIC_1, GZ_MAGIC_2,
	       DEFLATED, 0 /*flags*/, 0,0,0,0 /*time*/, 0 /*xflags*/, OS_CODE);
    } else {
	/* Check and skip the header:
         */
	Byte c1 = 0, c2 = 0;
	Byte method = 0;
	Byte flags = 0;
	Byte xflags = 0;
	Byte time[4];
	Byte osCode;
	int c;

	s->stream.avail_in = fread(s->inbuf, 1, 2, s->file);
	if (s->stream.avail_in != 2 || s->inbuf[0] != GZ_MAGIC_1
	    || s->inbuf[1] != GZ_MAGIC_2) {
	    s->transparent = 1;
	    return (gzFile)s;
	}
	s->stream.avail_in = 0;
	fscanf(s->file,"%c%c%4c%c%c", &method, &flags, time, &xflags, &osCode);

	if (method != DEFLATED || feof(s->file) || (flags & RESERVED) != 0) {
	    s->z_err = Z_DATA_ERROR;
	    return (gzFile)s;
	}
	if ((flags & EXTRA_FIELD) != 0) { /* skip the extra field */
	    long len;
	    fscanf(s->file, "%c%c", &c1, &c2);
	    len = c1 + ((long)c2<<8);
	    fseek(s->file, len, SEEK_CUR);
	}
	if ((flags & ORIG_NAME) != 0) { /* skip the original file name */
	    while ((c = getc(s->file)) != 0 && c != EOF) ;
	}
	if ((flags & COMMENT) != 0) {   /* skip the .gz file comment */
	    while ((c = getc(s->file)) != 0 && c != EOF) ;
	}
	if ((flags & HEAD_CRC) != 0) {  /* skip the header crc */
	    fscanf(s->file, "%c%c", &c1, &c2);
	}
	if (feof(s->file)) {
	    s->z_err = Z_DATA_ERROR;
	}
    }
    return (gzFile)s;
}

/* ===========================================================================
     Opens a gzip (.gz) file for reading or writing.
*/
gzFile gzopen (path, mode)
    char *path;
    char *mode;
{
    return gz_open (path, mode, -1);
}

/* ===========================================================================
     Associate a gzFile with the file descriptor fd.
*/
gzFile gzdopen (fd, mode)
    int fd;
    char *mode;
{
    char name[20];
    sprintf(name, "_fd:%d_", fd); /* for debugging */

    return gz_open (name, mode, fd);
}

/* ===========================================================================
     Reads the given number of uncompressed bytes from the compressed file.
   gzread returns the number of bytes actually read (0 for end of file).
*/
int gzread (file, buf, len)
    gzFile file;
    voidp buf;
    unsigned len;
{
    gz_stream *s = (gz_stream*)file;

    if (s == NULL || s->mode != 'r') return Z_STREAM_ERROR;

    if (s->transparent) {
	unsigned n = 0;
	Byte *b = (Byte*)buf;
	/* Copy the first two (non-magic) bytes if not done already */
	while (s->stream.avail_in > 0 && len > 0) {
	    *b++ = *s->stream.next_in++;
	    s->stream.avail_in--;
	    len--; n++;
	}
	if (len == 0) return n;
	return n + fread(buf, 1, len, s->file);
    }
    if (s->z_err == Z_DATA_ERROR) return -1; /* bad .gz file */
    if (s->z_err == Z_STREAM_END) return 0;  /* don't read crc as data */

    s->stream.next_out = buf;
    s->stream.avail_out = len;

    while (s->stream.avail_out != 0) {

	if (s->stream.avail_in == 0 && !s->z_eof) {

	    errno = 0;
	    s->stream.avail_in =
		fread(s->inbuf, 1, Z_BUFSIZE, s->file);
	    if (s->stream.avail_in == 0) {
		s->z_eof = 1;
	    } else if (s->stream.avail_in == (uInt)EOF) {
		s->stream.avail_in = 0;
		s->z_eof = 1;
		s->z_err = Z_ERRNO;
		break;
	    }
	    s->stream.next_in = s->inbuf;
	}
	s->z_err = inflate(&(s->stream), Z_NO_FLUSH);

	if (s->z_err == Z_STREAM_END ||
            s->z_err != Z_OK  || s->z_eof) break;
    }
    len -= s->stream.avail_out;
    s->crc = crc32(s->crc, buf, len);
    return len;
}

/* ===========================================================================
     Writes the given number of uncompressed bytes into the compressed file.
   gzwrite returns the number of bytes actually written (0 in case of error).
*/
int gzwrite (file, buf, len)
    gzFile file;
    voidp buf;
    unsigned len;
{
    gz_stream *s = (gz_stream*)file;

    if (s == NULL || s->mode != 'w') return Z_STREAM_ERROR;

    s->stream.next_in = buf;
    s->stream.avail_in = len;

    while (s->stream.avail_in != 0) {

	if (s->stream.avail_out == 0) {

	    s->stream.next_out = s->outbuf;
	    if (fwrite(s->outbuf, 1, Z_BUFSIZE, s->file) != Z_BUFSIZE) {
		s->z_err = Z_ERRNO;
		break;
	    }
	    s->stream.avail_out = Z_BUFSIZE;
	}
	s->z_err = deflate(&(s->stream), Z_NO_FLUSH);

	if (s->z_err != Z_OK) break;
    }
    s->crc = crc32(s->crc, buf, len);

    return len - s->stream.avail_in;
}

/* ===========================================================================
     Flushes all pending output into the compressed file. The parameter
   flush is as in the deflate() function.
     gzflush should be called only when strictly necessary because it can
   degrade compression.
*/
int gzflush (file, flush)
    gzFile file;
    int flush;
{
    uInt len;
    int done = 0;
    gz_stream *s = (gz_stream*)file;

    if (s == NULL || s->mode != 'w') return Z_STREAM_ERROR;

    s->stream.avail_in = 0; /* should be zero already anyway */

    for (;;) {
	len = Z_BUFSIZE - s->stream.avail_out;

	if (len != 0) {
	    if (fwrite(s->outbuf, 1, len, s->file) != len) {
		s->z_err = Z_ERRNO;
		break;
	    }
	    s->stream.next_out = s->outbuf;
	    s->stream.avail_out = Z_BUFSIZE;
	}
	if (done) break;
	s->z_err = deflate(&(s->stream), flush);

	if (s->z_err != Z_OK) break;

	/* deflate has finished flushing only when it hasn't used up
         * all the available space in the output buffer: 
         */
	done = (s->stream.avail_out != 0);
    }
    return s->z_err;
}

/* ===========================================================================
   Outputs a long in LSB order to the given file
*/
local void putLong (file, x)
    FILE *file;
    uLong x;
{
    int n;
    for (n = 0; n < 4; n++) {
	fputc((int)(x & 0xff), file);
	x >>= 8;
    }
}

/* ===========================================================================
   Reads a long in LSB order from the given buffer
*/
local uLong getLong (buf)
    Byte *buf;
{
    uLong x = 0;
    Byte *p = buf+4;

    do {
	x <<= 8;
	x |= *--p; 
    } while (p != buf);
    return x;
}

/* ===========================================================================
     Flushes all pending output if necessary, closes the compressed file
   and deallocates all the (de)compression state.
*/
int gzclose (file)
    gzFile file;
{
    uInt n;
    gz_stream *s = (gz_stream*)file;

    if (s == NULL) return Z_STREAM_ERROR;

    if (s->mode == 'w') {
	gzflush (file, Z_FINISH);
	putLong (s->file, s->crc);
	putLong (s->file, s->stream.total_in);

    } else if (s->mode == 'r' && s->z_err == Z_STREAM_END) {

	/* slide CRC and original size if they are at the end of inbuf */
	if ((n = s->stream.avail_in) < 8  && !s->z_eof) {
	    Byte *p = s->inbuf;
	    Byte *q = s->stream.next_in;
	    while (n--) { *p++ = *q++; };

	    n = s->stream.avail_in;
	    n += fread(p, 1, 8, s->file);
	    s->stream.next_in = s->inbuf;
	}
	/* check CRC and original size */
	if (n < 8 ||
	    getLong(s->stream.next_in) != s->crc ||
	    getLong(s->stream.next_in + 4) != s->stream.total_out) {

	    s->z_err = Z_DATA_ERROR;
	}
    }
    return destroy(file);
}

/* ===========================================================================
     Returns the error message for the last error which occured on the
   given compressed file. errnum is set to zlib error number. If an
   error occured in the file system and not in the compression library,
   errnum is set to Z_ERRNO and the application may consult errno
   to get the exact error code.
*/
char*  gzerror (file, errnum)
    gzFile file;
    int *errnum;
{
    char *m;
    gz_stream *s = (gz_stream*)file;

    if (s == NULL) {
	*errnum = Z_STREAM_ERROR;
	return z_errmsg[1-Z_STREAM_ERROR];
    }
    *errnum = s->z_err;
    if (*errnum == Z_OK) return "";

    m =  *errnum == Z_ERRNO ? zstrerror(errno) : s->stream.msg;

    if (m == NULL || *m == '\0') m = z_errmsg[1-s->z_err];

    TRYFREE(s->msg);
    s->msg = (char*)ALLOC(strlen(s->path) + strlen(m) + 3);
    strcpy(s->msg, s->path);
    strcat(s->msg, ": ");
    strcat(s->msg, m);
    return s->msg;
}