Add a transparent write mode to gzopen() when 'T' is in the mode.

gzguts.h

@@ -136,11 +136,11 @@ typedef struct {
     unsigned want;          /* requested buffer size, default is GZBUFSIZE */
     unsigned char *in;      /* input buffer */
     unsigned char *out;     /* output buffer (double-sized when reading) */
+    int direct;             /* 0 if processing gzip, 1 if transparent */
         /* just for reading */
     int eof;                /* true if end of input file reached */
     z_off64_t start;        /* where the gzip data started, for rewinding */
     int how;                /* 0: get header, 1: copy, 2: decompress */
-    int direct;             /* true if last read direct, false if gzip */
         /* just for writing */
     int level;              /* compression level */
     int strategy;           /* compression strategy */

gzlib.c

@@ -79,7 +79,6 @@ local void gz_reset(state)
     if (state->mode == GZ_READ) {   /* for reading ... */
         state->eof = 0;             /* not at end of file */
         state->how = LOOK;          /* look for gzip header */
-        state->direct = 1;          /* default for empty file */
     }
     state->seek = 0;                /* no seek request pending */
     gz_error(state, Z_OK, NULL);    /* clear error */
@@ -111,6 +110,7 @@ local gzFile gz_open(path, fd, mode)
     state->mode = GZ_NONE;
     state->level = Z_DEFAULT_COMPRESSION;
     state->strategy = Z_DEFAULT_STRATEGY;
+    state->direct = 0;
     while (*mode) {
         if (*mode >= '0' && *mode <= '9')
             state->level = *mode - '0';
@@ -143,6 +143,8 @@ local gzFile gz_open(path, fd, mode)
                 break;
             case 'F':
                 state->strategy = Z_FIXED;
+            case 'T':
+                state->direct = 1;
             default:        /* could consider as an error, but just ignore */
                 ;
             }
@@ -155,6 +157,15 @@ local gzFile gz_open(path, fd, mode)
         return NULL;
     }
 
+    /* can't force transparent read */
+    if (state->mode == GZ_READ) {
+        if (state->direct) {
+            free(state);
+            return NULL;
+        }
+        state->direct = 1;      /* for empty file */
+    }
+
     /* save the path name for error messages */
     state->path = malloc(strlen(path) + 1);
     if (state->path == NULL) {

gzread.c

@@ -535,16 +535,12 @@ int ZEXPORT gzdirect(file)
         return 0;
     state = (gz_statep)file;
 
-    /* check that we're reading */
-    if (state->mode != GZ_READ)
-        return 0;
-
     /* if the state is not known, but we can find out, then do so (this is
        mainly for right after a gzopen() or gzdopen()) */
-    if (state->how == LOOK && state->x.have == 0)
+    if (state->mode == GZ_READ && state->how == LOOK && state->x.have == 0)
         (void)gz_look(state);
 
-    /* return 1 if reading direct, 0 if decompressing a gzip stream */
+    /* return 1 if transparent, 0 if processing a gzip stream */
     return state->direct;
 }
 

gzwrite.c

@@ -18,13 +18,18 @@ local int gz_init(state)
     int ret;
     z_streamp strm = &(state->strm);
 
-    /* allocate input and output buffers */
+    /* allocate input buffer */
     state->in = malloc(state->want);
+    if (state->in == NULL) {
+        gz_error(state, Z_MEM_ERROR, "out of memory");
+        return -1;
+    }
+
+    /* only need output buffer and deflate state if compressing */
+    if (!state->direct) {
+        /* allocate output buffer */
         state->out = malloc(state->want);
-    if (state->in == NULL || state->out == NULL) {
+        if (state->out == NULL) {
-        if (state->out != NULL)
-            free(state->out);
-        if (state->in != NULL)
             free(state->in);
             gz_error(state, Z_MEM_ERROR, "out of memory");
             return -1;
@@ -37,25 +42,31 @@ local int gz_init(state)
         ret = deflateInit2(strm, state->level, Z_DEFLATED,
                            15 + 16, 8, state->strategy);
         if (ret != Z_OK) {
+            free(state->out);
             free(state->in);
             gz_error(state, Z_MEM_ERROR, "out of memory");
             return -1;
         }
+    }
 
     /* mark state as initialized */
     state->size = state->want;
 
-    /* initialize write buffer */
+    /* initialize write buffer if compressing */
+    if (!state->direct) {
         strm->avail_out = state->size;
         strm->next_out = state->out;
         state->x.next = strm->next_out;
+    }
     return 0;
 }
 
 /* Compress whatever is at avail_in and next_in and write to the output file.
    Return -1 if there is an error writing to the output file, otherwise 0.
    flush is assumed to be a valid deflate() flush value.  If flush is Z_FINISH,
-   then the deflate() state is reset to start a new gzip stream. */
+   then the deflate() state is reset to start a new gzip stream.  If gz->direct
+   is true, then simply write to the output file without compressing, and
+   ignore flush. */
 local int gz_comp(state, flush)
     gz_statep state;
     int flush;
@@ -68,6 +79,17 @@ local int gz_comp(state, flush)
     if (state->size == 0 && gz_init(state) == -1)
         return -1;
 
+    /* write directly if requested */
+    if (state->direct) {
+        got = write(state->fd, strm->next_in, strm->avail_in);
+        if (got < 0 || (unsigned)got != strm->avail_in) {
+            gz_error(state, Z_ERRNO, zstrerror());
+            return -1;
+        }
+        strm->avail_in = 0;
+        return 0;
+    }
+
     /* run deflate() on provided input until it produces no more output */
     ret = Z_OK;
     do {
@@ -526,8 +548,10 @@ int ZEXPORT gzclose_w(file)
     /* flush, free memory, and close file */
     if (gz_comp(state, Z_FINISH) == -1)
         ret = state->err;
+    if (!state->direct) {
         (void)deflateEnd(&(state->strm));
         free(state->out);
+    }
     free(state->in);
     gz_error(state, Z_OK, NULL);
     free(state->path);

zlib.h

@@ -1196,10 +1196,13 @@ ZEXTERN gzFile ZEXPORT gzopen OF((const char *path, const char *mode));
    a strategy: 'f' for filtered data as in "wb6f", 'h' for Huffman-only
    compression as in "wb1h", 'R' for run-length encoding as in "wb1R", or 'F'
    for fixed code compression as in "wb9F".  (See the description of
-   deflateInit2 for more information about the strategy parameter.) Also "a"
+   deflateInit2 for more information about the strategy parameter.)  'T' will
-   can be used instead of "w" to request that the gzip stream that will be
+   request transparent writing or appending with no compression and not using
-   written be appended to the file.  "+" will result in an error, since reading
+   the gzip format.
-   and writing to the same gzip file is not supported.
+
+     "a" can be used instead of "w" to request that the gzip stream that will
+   be written be appended to the file.  "+" will result in an error, since
+   reading and writing to the same gzip file is not supported.
 
      These functions, as well as gzip, will read and decode a sequence of gzip
    streams in a file.  The append function of gzopen() can be used to create
@@ -1209,7 +1212,9 @@ ZEXTERN gzFile ZEXPORT gzopen OF((const char *path, const char *mode));
    will simply append a gzip stream to the existing file.
 
      gzopen can be used to read a file which is not in gzip format; in this
-   case gzread will directly read from the file without decompression.
+   case gzread will directly read from the file without decompression.  When
+   reading, this will be detected automatically by looking for the magic two-
+   byte gzip header.
 
      gzopen returns NULL if the file could not be opened, if there was
    insufficient memory to allocate the gzFile state, or if an invalid mode was
@@ -1440,6 +1445,13 @@ ZEXTERN int ZEXPORT gzdirect OF((gzFile file));
    cause buffers to be allocated to allow reading the file to determine if it
    is a gzip file.  Therefore if gzbuffer() is used, it should be called before
    gzdirect().
+
+     When writing, gzdirect() returns true (1) if transparent writing was
+   requested ("wT" for the gzopen() mode), or false (0) otherwise.  (Note:
+   gzdirect() is not needed when writing.  Transparent writing must be
+   explicitly requested, so the application already knows the answer.  When
+   linking statically, using gzdirect() will include all of the zlib code for
+   gzip file reading and decompression, which may not be desired.)
 */
 
 ZEXTERN int ZEXPORT    gzclose OF((gzFile file));