Use wtap_read_bytes() to skip over bytes when reading a record.

Allow file_read() to take a null pointer as a buffer argument; a null
argument means "do everything except copy the bytes from the file to the
user buffer".  That means that wtap_read_bytes() and
wtap_read_bytes_or_eof() also support a null pointer as a buffer
argument.

Use wtap_read_bytes() with a null buffer argument rather than
file_skip() to skip forward over data.

This fixes some places where files were mis-identified as ERF files, as
the ERF open heuristics now get a short "read" error if they try to skip
over more bytes than exist in the file.

Change-Id: I4f73499d877c1f582e2bcf9b045034880cb09622
Reviewed-on: https://code.wireshark.org/review/17974
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 11 insertions, 13 deletions

diff --git a/wiretap/ngsniffer.c b/wiretap/ngsniffer.c
index 5c9d28a37a..829ba74526 100644
--- a/wiretap/ngsniffer.c
+++ b/wiretap/ngsniffer.c
@@ -536,7 +536,7 @@ static gboolean ng_read_bytes(wtap *wth, void *buffer, unsigned int nbytes,
     gboolean is_random, int *err, gchar **err_info);
 static gboolean read_blob(FILE_T infile, ngsniffer_comp_stream_t *comp_stream,
     int *err, gchar **err_info);
-static gboolean ng_file_skip_seq(wtap *wth, gint64 delta, int *err,
+static gboolean ng_skip_bytes_seq(wtap *wth, unsigned int count, int *err,
     gchar **err_info);
 static gboolean ng_file_seek_rand(wtap *wth, gint64 offset, int *err,
     gchar **err_info);
@@ -1056,7 +1056,7 @@ ngsniffer_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
 			 * Skip any extra data in the record.
 			 */
 			if (padding != 0) {
-				if (!ng_file_skip_seq(wth, padding, err,
+				if (!ng_skip_bytes_seq(wth, padding, err,
 				    err_info))
 					return FALSE;
 			}
@@ -1077,7 +1077,7 @@ ngsniffer_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
 			 * and keep looping.
 			 */
 			if (padding != 0) {
-				if (!ng_file_skip_seq(wth, padding, err,
+				if (!ng_skip_bytes_seq(wth, padding, err,
 				    err_info))
 					return FALSE;
 			}
@@ -2588,7 +2588,7 @@ read_blob(FILE_T infile, ngsniffer_comp_stream_t *comp_stream, int *err,
 
 /* Skip some number of bytes forward in the sequential stream. */
 static gboolean
-ng_file_skip_seq(wtap *wth, gint64 delta, int *err, gchar **err_info)
+ng_skip_bytes_seq(wtap *wth, unsigned int count, int *err, gchar **err_info)
 {
 	ngsniffer_t *ngsniffer;
 	char *buf;
@@ -2597,26 +2597,24 @@ ng_file_skip_seq(wtap *wth, gint64 delta, int *err, gchar **err_info)
 	ngsniffer = (ngsniffer_t *)wth->priv;
 
 	if (wth->file_type_subtype == WTAP_FILE_TYPE_SUBTYPE_NGSNIFFER_UNCOMPRESSED) {
-		ngsniffer->seq.uncomp_offset += delta;
-		return file_skip(wth->fh, delta, err);
+		ngsniffer->seq.uncomp_offset += count;
+		return wtap_read_bytes(wth->fh, NULL, count, err, err_info);
 	}
 
-	g_assert(delta >= 0);
-
-	/* Ok, now read and discard "delta" bytes. */
+	/* Ok, now read and discard "count" bytes. */
 	buf = (char *)g_malloc(INBUF_SIZE);
-	while (delta != 0) {
-		if (delta > INBUF_SIZE)
+	while (count != 0) {
+		if (count > INBUF_SIZE)
 			amount_to_read = INBUF_SIZE;
 		else
-			amount_to_read = (unsigned int) delta;
+			amount_to_read = count;
 
 		if (!ng_read_bytes(wth, buf, amount_to_read, FALSE, err, err_info)) {
 			g_free(buf);
 			return FALSE;	/* error */
 		}
 
-		delta -= amount_to_read;
+		count -= amount_to_read;
 	}
 
 	g_free(buf);