[RFC] Implement Export PDU for tsharkbug/3444

This patch introduces the "-U tap_name[,filter]" tshark option and
is similar to the "Export PDUs as file" option in Wireshark.

Wireshark implements this feature by reopening a capture file, applying
a tap and finally opening the temporary file. Since tshark knows
in advance that a PDU export is needed, it can optimize by not creating
the temporary file and perform the export at the first opportunity.

This patch splits the opening/tapping functionality from error reporting
since tshark does not need a temp file and has no dialogs.

The capture file comment is now specified explicitly as there is no
"current file" anymore if the tap is running without active file.

TODO:
 - Do not '#ifdef 0' the GTK/Qt functionality, split the file
   to avoid a linking error with tshark.
 - Why is pkt_encap modifiable? Both Wireshark Qt and GTK set
   WTAP_ENCAP_WIRESHARK_UPPER_PDU, what is the idea behind this?
 - Review whether it is acceptable to overwrite save_file in tshark.
 - Add documentation (tshark manpage).

Bug: 3444
Change-Id: Ie159495d42c32c2ba7400f2991b7b8185b3fda09

1 files changed, 28 insertions, 0 deletions

diff --git a/ui/tap_export_pdu.h b/ui/tap_export_pdu.h
index df6b5bad45..5c2de947d2 100644
--- a/ui/tap_export_pdu.h
+++ b/ui/tap_export_pdu.h
@@ -32,8 +32,36 @@ typedef struct _exp_pdu_t {
     wtap_dumper* wdh;
 } exp_pdu_t;
 
+/**
+ * Filters the current opened capture file into a temporary file. On success,
+ * TRUE is returned and the filtered file is opened into the UI.
+ */
 gboolean do_export_pdu(const char *filter, gchar *tap_name, exp_pdu_t *data);
 
+/**
+ * Registers the tap listener which will add matching packets to the exported
+ * file. Must be called before exp_pdu_open.
+ *
+ * @param tap_name  One of the names registered with register_export_pdu_tap().
+ * @param filter    An tap filter, may be NULL to disable filtering which
+ * improves performance if you do not need a filter.
+ * @return NULL on success or an error string on failure which must be freed
+ * with g_free(). Failure could occur when the filter or tap_name are invalid.
+ */
+char *exp_pdu_pre_open(const char *tap_name, const char *filter,
+                       exp_pdu_t *exp_pdu_tap_data);
+
+/**
+ * Use the given file descriptor for writing an output file. Can only be called
+ * once and exp_pdu_pre_open() must be called before.
+ *
+ * @return 0 on success or a wtap error code.
+ */
+int exp_pdu_open(exp_pdu_t *data, int fd, char *comment);
+
+/* Stops the PDUs export. */
+int exp_pdu_close(exp_pdu_t *exp_pdu_tap_data);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */