Note the use of gzungetc() to run a deferred seek while reading.

Upstream: https://github.com/madler/zlib/commit/a9bb8c48

diff --git a/zlib-ng.h.in b/zlib-ng.h.in
index fe6b6d88df2d68241674a27efd634aa47d3bb24d..4e44c4f4c610847f1e03f8ca4fa195f14b94d1e8 100644 (file)
--- a/zlib-ng.h.in
+++ b/zlib-ng.h.in
@@ -1552,6 +1552,11 @@ int32_t zng_gzungetc(int32_t c, gzFile file);
    output buffer size of pushed characters is allowed.  (See gzbuffer above.)
    The pushed character will be discarded if the stream is repositioned with
    gzseek() or gzrewind().
+
+     gzungetc(-1, file) will force any pending seek to execute. Then gztell()
+   will report the position, even if the requested seek reached end of file.
+   This can be used to determine the number of uncompressed bytes in a gzip
+   file without having to read it into a buffer.
 */
 
 Z_EXTERN Z_EXPORT

diff --git a/zlib.h.in b/zlib.h.in
index 25a80c4ef44dd52a7a0c88bbedbba3a100a2e2d5..188d25a2c64f438ea1a1b43e28b875de316669e2 100644 (file)
--- a/zlib.h.in
+++ b/zlib.h.in
@@ -1532,6 +1532,11 @@ Z_EXTERN int Z_EXPORT gzungetc(int c, gzFile file);
    output buffer size of pushed characters is allowed.  (See gzbuffer above.)
    The pushed character will be discarded if the stream is repositioned with
    gzseek() or gzrewind().
+
+     gzungetc(-1, file) will force any pending seek to execute. Then gztell()
+   will report the position, even if the requested seek reached end of file.
+   This can be used to determine the number of uncompressed bytes in a gzip
+   file without having to read it into a buffer.
 */
 
 Z_EXTERN int Z_EXPORT gzflush(gzFile file, int flush);