When reading packets from a capture file, don't seek around record

header fields we don't look at - some implementations of the standard
I/O library routines (e.g., the ones in Solaris 2.5.1, at least) appear
not to be clever enough to handle seeks that occur within the buffer by
moving the current buffer position; instead, they do a seek on the
underlying file descriptor *and* appear to throw out the buffer, forcing
them to do another read.

Instead, read the entire record header into a structure, and pick the
relevant bits out of it.

Also, skip over the FCS in LAPB captures by reading it rather than
seeking around it (should we put it in the pseudo-header?).

svn path=/trunk/; revision=625

1 files changed, 49 insertions, 50 deletions

diff --git a/wiretap/radcom.c b/wiretap/radcom.c
index 9443128622..3e39af37ed 100644
--- a/wiretap/radcom.c
+++ b/wiretap/radcom.c
@@ -37,10 +37,33 @@ struct frame_date {
 	guint32	usec;
 };
 
+struct unaligned_frame_date {
+	char	year[2];
+	char	month;
+	char	day;
+	char	sec[4];		/* seconds since midnight */
+	char	usec[4];
+};
+
 static char radcom_magic[8] = {
 	0x42, 0xD2, 0x00, 0x34, 0x12, 0x66, 0x22, 0x88
 };
 
+/* RADCOM record header - followed by frame data (perhaps including FCS).
+   The first two bytes of "xxz" appear to equal "length", as do the
+   second two bytes; if a RADCOM box can be told not to save all of
+   the captured packet, might one or the other of those be the
+   captured length of the packet? */
+struct radcomrec_hdr {
+	char	xxx[4];		/* unknown */
+	char	length[2];	/* packet length */
+	char	xxy[5];		/* unknown */
+	struct unaligned_frame_date date; /* date/time stamp of packet */
+	char	xxz[6];		/* unknown */
+	char	dce;		/* DCE/DTE flag (and other flags?) */
+	char	xxw[9];		/* unknown */
+};
+
 static int radcom_read(wtap *wth, int *err);
 
 int radcom_open(wtap *wth, int *err)
@@ -202,22 +225,17 @@ read_error:
 static int radcom_read(wtap *wth, int *err)
 {
 	int	bytes_read;
+	struct radcomrec_hdr hdr;
 	guint16 length;
-	struct frame_date date;
 	guint32 sec;
-	int	data_offset;
 	struct tm tm;
-	char dce;
-
-	fseek(wth->fh, 4, SEEK_CUR);
-	wth->data_offset += 4;
+	int	data_offset;
+	char	fcs[2];
 
-	/*
-	 * Read the frame size
-	 */
+	/* Read record header. */
 	errno = WTAP_ERR_CANT_READ;
-	bytes_read = fread(&length, 1, 2, wth->fh);
-	if (bytes_read != 2) {
+	bytes_read = fread(&hdr, 1, sizeof hdr, wth->fh);
+	if (bytes_read != sizeof hdr) {
 		if (ferror(wth->fh)) {
 			*err = errno;
 			return -1;
@@ -228,8 +246,8 @@ static int radcom_read(wtap *wth, int *err)
 		}
 		return 0;
 	}
-	wth->data_offset += 2;
-	length = pletohs(&length);
+	wth->data_offset += sizeof hdr;
+	length = pletohs(&hdr.length);
 	if (length == 0) return 0;
 
 	if (wth->file_encap == WTAP_ENCAP_LAPB)
@@ -238,46 +256,17 @@ static int radcom_read(wtap *wth, int *err)
 	wth->phdr.len = length;
 	wth->phdr.caplen = length;
 
-	fseek(wth->fh, 5, SEEK_CUR);
-	wth->data_offset += 5;
-	errno = WTAP_ERR_CANT_READ;
-	bytes_read = fread(&date, 1, sizeof(struct frame_date), wth->fh);
-	if (bytes_read != sizeof(struct frame_date)) {
-		if (ferror(wth->fh))
-			*err = errno;
-		else
-			*err = WTAP_ERR_SHORT_READ;
-		return -1;
-	}
-	wth->data_offset += sizeof(struct frame_date);
-
-	tm.tm_year = pletohs(&date.year)-1900;
-	tm.tm_mon = date.month-1;
-	tm.tm_mday = date.day;
-	sec = pletohl(&date.sec);
+	tm.tm_year = pletohs(&hdr.date.year)-1900;
+	tm.tm_mon = hdr.date.month-1;
+	tm.tm_mday = hdr.date.day;
+	sec = pletohl(&hdr.date.sec);
 	tm.tm_hour = sec/3600;
 	tm.tm_min = (sec%3600)/60;
 	tm.tm_sec = sec%60;
 	tm.tm_isdst = -1;
 	wth->phdr.ts.tv_sec = mktime(&tm);
-	wth->phdr.ts.tv_usec = pletohl(&date.usec);
-
-	fseek(wth->fh, 6, SEEK_CUR);
-	wth->data_offset += 6;
-	errno = WTAP_ERR_CANT_READ;
-	bytes_read = fread(&dce, 1, 1, wth->fh);
-	if (bytes_read != 1) {
-		if (ferror(wth->fh))
-			*err = errno;
-		else
-			*err = WTAP_ERR_SHORT_READ;
-		return -1;
-	}
-	wth->data_offset += 1;
-	wth->phdr.pseudo_header.x25.flags = (dce & 0x1) ? 0x00 : 0x80;
-
-	fseek(wth->fh, 9, SEEK_CUR);
-	wth->data_offset += 9;
+	wth->phdr.ts.tv_usec = pletohl(&hdr.date.usec);
+	wth->phdr.pseudo_header.x25.flags = (hdr.dce & 0x1) ? 0x00 : 0x80;
 
 	/*
 	 * Read the packet data.
@@ -300,8 +289,18 @@ static int radcom_read(wtap *wth, int *err)
 	wth->phdr.pkt_encap = wth->file_encap;
 
 	if (wth->file_encap == WTAP_ENCAP_LAPB) {
-		fseek(wth->fh, 2, SEEK_CUR); /* FCS */
-		wth->data_offset += 2;
+		/* Read the FCS.
+		   XXX - should we put it in the pseudo-header? */
+		errno = WTAP_ERR_CANT_READ;
+		bytes_read = fread(&fcs, 1, sizeof fcs, wth->fh);
+		if (bytes_read != sizeof fcs) {
+			if (ferror(wth->fh))
+				*err = errno;
+			else
+				*err = WTAP_ERR_SHORT_READ;
+			return -1;
+		}
+		wth->data_offset += sizeof fcs;
 	}
 
 	return data_offset;