wiretap: add a routine to add a "fake" IDB.

It generates a fake IDB for files that don't have interface information
and that have a per-file encapsulation type, snapshot length, and time
stamp precision, and adds it to the file's list of IDBs.

Use it for libpcap.

We will use it later for other file formats, so that code such as the
mergecap code to merge into a pcapng file can handle input files that
don't have interface information.

(We should have a way to indicate whether the IDBs are real or fake, so
that capinfos and Statistics > Capture File Properties don't report
meaningless IDB information and make it look as if it's known that the
capture was done on one interface with the properties in question.)

Change-Id: Iec124bf3c7cbd4c69ec2ac7d0dd776e5287f8576
Reviewed-on: https://code.wireshark.org/review/37982
Petri-Dish: Guy Harris <gharris@sonic.net>
Tested-by: Petri Dish Buildbot
Reviewed-by: Guy Harris <gharris@sonic.net>

1 files changed, 91 insertions, 0 deletions

diff --git a/wiretap/wtap.c b/wiretap/wtap.c
index 7d7ca232e0..84d26064b6 100644
--- a/wiretap/wtap.c
+++ b/wiretap/wtap.c
@@ -162,6 +162,97 @@ wtap_add_idb(wtap *wth, wtap_block_t idb)
 }
 
 void
+wtap_add_generated_idb(wtap *wth)
+{
+	wtap_block_t idb;
+	wtapng_if_descr_mandatory_t *if_descr_mand;
+	int snaplen;
+
+	g_assert(wth->file_encap != WTAP_ENCAP_UNKNOWN &&
+	    wth->file_encap != WTAP_ENCAP_PER_PACKET);
+	g_assert(wth->file_tsprec != WTAP_TSPREC_UNKNOWN &&
+	    wth->file_tsprec != WTAP_TSPREC_PER_PACKET);
+
+	idb = wtap_block_create(WTAP_BLOCK_IF_DESCR);
+
+	if_descr_mand = (wtapng_if_descr_mandatory_t*)wtap_block_get_mandatory_data(idb);
+	if_descr_mand->wtap_encap = wth->file_encap;
+	if_descr_mand->tsprecision = wth->file_tsprec;
+	switch (wth->file_tsprec) {
+
+	case WTAP_TSPREC_SEC:
+		if_descr_mand->time_units_per_second = 1;
+		wtap_block_add_uint8_option(idb, OPT_IDB_TSRESOL, 0);
+		break;
+
+	case WTAP_TSPREC_DSEC:
+		if_descr_mand->time_units_per_second = 10;
+		wtap_block_add_uint8_option(idb, OPT_IDB_TSRESOL, 1);
+		break;
+
+	case WTAP_TSPREC_CSEC:
+		if_descr_mand->time_units_per_second = 100;
+		wtap_block_add_uint8_option(idb, OPT_IDB_TSRESOL, 2);
+		break;
+
+	case WTAP_TSPREC_MSEC:
+		if_descr_mand->time_units_per_second = 1000;
+		wtap_block_add_uint8_option(idb, OPT_IDB_TSRESOL, 3);
+		break;
+
+	case WTAP_TSPREC_USEC:
+		if_descr_mand->time_units_per_second = 1000000;
+		/* This is the default, so no need to add an option */
+		break;
+
+	case WTAP_TSPREC_NSEC:
+		if_descr_mand->time_units_per_second = 1000000000;
+		wtap_block_add_uint8_option(idb, OPT_IDB_TSRESOL, 9);
+		break;
+
+	case WTAP_TSPREC_PER_PACKET:
+	case WTAP_TSPREC_UNKNOWN:
+	default:
+		/*
+		 * Don't do this.
+		 */
+		g_assert_not_reached();
+		break;
+	}
+	snaplen = wth->snapshot_length;
+	if (snaplen == 0) {
+		/*
+		 * No snapshot length was specified.  Pick an
+		 * appropriate snapshot length for this
+		 * link-layer type.
+		 *
+		 * We use WTAP_MAX_PACKET_SIZE_STANDARD for everything except
+		 * D-Bus, which has a maximum packet size of 128MB,
+		 * and EBHSCR, which has a maximum packet size of 8MB,
+		 * which is more than we want to put into files
+		 * with other link-layer header types, as that
+		 * might cause some software reading those files
+		 * to allocate an unnecessarily huge chunk of
+		 * memory for a packet buffer.
+		 */
+		if (wth->file_encap == WTAP_ENCAP_DBUS)
+			snaplen = 128*1024*1024;
+		else if (wth->file_encap == WTAP_ENCAP_EBHSCR)
+			snaplen = 8*1024*1024;
+		else
+			snaplen = WTAP_MAX_PACKET_SIZE_STANDARD;
+	}
+	if_descr_mand->snap_len = snaplen;
+	if_descr_mand->num_stat_entries = 0;          /* Number of ISBs */
+	if_descr_mand->interface_statistics = NULL;
+
+	/*
+	 * Add this IDB.
+	 */
+	wtap_add_idb(wth, idb);
+}
+
+void
 wtap_free_idb_info(wtapng_iface_descriptions_t *idb_info)
 {
 	if (idb_info == NULL)