Fix no-ZLib builds.

Don't use ZLib routines or data types if we're built without ZLib.

Don't support --compress-type=gzip, or a gzip check box in the Output
pane of the Capture Options dialog, if we're built without ZLib.

Fixes #17899.

capture_opts.c

@@ -986,9 +986,18 @@ capture_opts_add_opt(capture_options *capture_opts, int opt, const char *optarg_
         if (strcmp(optarg_str_p, "none") == 0) {
             ;
         } else if (strcmp(optarg_str_p, "gzip") == 0) {
+#ifdef HAVE_ZLIB
             ;
+#else
+            cmdarg_err("'gzip' compression is not supported");
+            return 1;
+#endif
         } else {
+#ifdef HAVE_ZLIB
             cmdarg_err("parameter of --compress-type can be 'none' or 'gzip'");
+#else
+            cmdarg_err("parameter of --compress-type can only be 'none'");
+#endif
             return 1;
         }
         capture_opts->compress_type = g_strdup(optarg_str_p);

ringbuffer.c

@@ -124,6 +124,7 @@ static void CleanupOldCap(gchar* name)
   g_mutex_unlock(&rb_data.mutex);
 }
 
+#ifdef HAVE_ZLIB
 /*
  * compress capture file
  */
@@ -200,6 +201,7 @@ static int ringbuf_start_compress_file(rb_file* rfile)
   g_thread_new("exec_compress", &exec_compress_thread, name);
   return 0;
 }
+#endif
 
 /*
  * create the next filename and open a new binary file with that name
@@ -216,9 +218,11 @@ static int ringbuf_open_file(rb_file *rfile, int *err)
       /* remove old file (if any, so ignore error) */
       ws_unlink(rfile->name);
     }
+#ifdef HAVE_ZLIB
     else if (rb_data.compress_type != NULL && strcmp(rb_data.compress_type, "gzip") == 0) {
       ringbuf_start_compress_file(rfile);
     }
+#endif
     g_free(rfile->name);
   }
 

ui/qt/capture_options_dialog.cpp

@@ -549,7 +549,11 @@ void CaptureOptionsDialog::on_gbNewFileAuto_toggled(bool checked)
     ui->stopMBComboBox->setEnabled(checked?false:true);
     ui->gbCompression->setEnabled(checked);
     ui->rbCompressionNone->setEnabled(checked);
+#ifdef HAVE_ZLIB
     ui->rbCompressionGzip->setEnabled(checked);
+#else
+    ui->rbCompressionGzip->setEnabled(false);
+#endif
 }
 
 void CaptureOptionsDialog::on_cbUpdatePacketsRT_toggled(bool checked)