gzguts.h

@@ -190,6 +190,7 @@ typedef struct {
         /* just for writing */
     int level;              /* compression level */
     int strategy;           /* compression strategy */
+    int reset;              /* true if a reset is pending after a Z_FINISH */
         /* seek request */
     z_off64_t skip;         /* amount to skip (already rewound if backwards) */
     int seek;               /* true if seek request pending */

gzlib.c

@@ -81,6 +81,8 @@ local void gz_reset(state)
         state->past = 0;            /* have not read past end yet */
         state->how = LOOK;          /* look for gzip header */
     }
+    else                            /* for writing ... */
+        state->reset = 0;           /* no deflateReset pending */
     state->seek = 0;                /* no seek request pending */
     gz_error(state, Z_OK, NULL);    /* clear error */
     state->x.pos = 0;               /* no uncompressed data yet */

gzwrite.c

@@ -97,6 +97,15 @@ local int gz_comp(state, flush)
         return 0;
     }
+    /* check for a pending reset */
+    if (state->reset) {
+        /* don't start a new gzip member unless there is data to write */
+        if (strm->avail_in == 0)
+            return 0;
+        deflateReset(strm);
+        state->reset = 0;
+    }
+
     /* run deflate() on provided input until it produces no more output */
     ret = Z_OK;
     do {
@@ -134,7 +143,7 @@ local int gz_comp(state, flush)
     /* if that completed a deflate stream, allow another to start */
     if (flush == Z_FINISH)
-        deflateReset(strm);
+        state->reset = 1;
     /* all done, no errors */
     return 0;

zlib.h

@@ -1690,8 +1690,9 @@ ZEXTERN void ZEXPORT gzclearerr OF((gzFile file));
 ZEXTERN uLong ZEXPORT adler32 OF((uLong adler, const Bytef *buf, uInt len));
 /*
      Update a running Adler-32 checksum with the bytes buf[0..len-1] and
-   return the updated checksum.  If buf is Z_NULL, this function returns the
-   required initial value for the checksum.
+   return the updated checksum. An Adler-32 value is in the range of a 32-bit
+   unsigned integer. If buf is Z_NULL, this function returns the required
+   initial value for the checksum.
      An Adler-32 checksum is almost as reliable as a CRC-32 but can be computed
    much faster.
@@ -1727,9 +1728,10 @@ ZEXTERN uLong ZEXPORT adler32_combine OF((uLong adler1, uLong adler2,
 ZEXTERN uLong ZEXPORT crc32 OF((uLong crc, const Bytef *buf, uInt len));
 /*
      Update a running CRC-32 with the bytes buf[0..len-1] and return the
-   updated CRC-32.  If buf is Z_NULL, this function returns the required
-   initial value for the crc.  Pre- and post-conditioning (one's complement) is
-   performed within this function so it shouldn't be done by the application.
+   updated CRC-32. A CRC-32 value is in the range of a 32-bit unsigned integer.
+   If buf is Z_NULL, this function returns the required initial value for the
+   crc. Pre- and post-conditioning (one's complement) is performed within this
+   function so it shouldn't be done by the application.
    Usage example: