From: Mark Adler <madler@alumni.caltech.edu>
Date: Mon, 21 Aug 2023 20:48:56 +0000 (-0700)
Subject: Fix bug when gzungetc() is used immediately after gzopen().
X-Git-Tag: 2.1.4~33
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=135cdad8ca64ec38407fcd3515515574f2015dcf;p=thirdparty%2Fzlib-ng.git

Fix bug when gzungetc() is used immediately after gzopen().
---

diff --git a/gzread.c.in b/gzread.c.in
index 67a21a3e4..1fc7b370f 100644
--- a/gzread.c.in
+++ b/gzread.c.in
@@ -445,6 +445,10 @@ int Z_EXPORT PREFIX(gzungetc)(int c, gzFile file) {
         return -1;
     state = (gz_state *)file;
 
+    /* in case this was just opened, set up the input buffer */
+    if (state->mode == GZ_READ && state->how == LOOK && state->x.have == 0)
+        (void)gz_look(state);
+
     /* check that we're reading and that there's no (serious) error */
     if (state->mode != GZ_READ || (state->err != Z_OK && state->err != Z_BUF_ERROR))
         return -1;