Do not call wtap_file_read_unknown_bytes() or

wtap_file_read_expected_bytes() from an open routine - open routines are
supposed to return -1 on error, 0 if the file doesn't appear to be a
file of the specified type, or 1 if the file does appear to be a file of
the specified type, but those macros will cause the caller to return
FALSE on errors (so that, even if there's an I/O error, it reports "the
file isn't a file of the specified type" rather than "we got an error
trying to read the file").

When doing reads in an open routine before we've concluded that the file
is probably of the right type, return 0, rather than -1, if we get
WTAP_ERR_SHORT_READ - if we don't have enough data to check whether a
file is of a given type, we should keep trying other types, not give up.
For reads done *after* we've concluded the file is probably of the right
type, if a read doesn't return the number of bytes we asked for, but
returns an error of 0, return WTAP_ERR_SHORT_READ - the file is
apparently cut short.

For NetMon and NetXRay/Windows Sniffer files, use a #define for the
magic number size, and use that for both magic numbers.

svn path=/trunk/; revision=46803

1 files changed, 16 insertions, 13 deletions

diff --git a/wiretap/netmon.c b/wiretap/netmon.c
index 3c388e2fa7..f48c564ff9 100644
--- a/wiretap/netmon.c
+++ b/wiretap/netmon.c
@@ -43,14 +43,17 @@
 /* Capture file header, *including* magic number, is padded to 128 bytes. */
 #define	CAPTUREFILE_HEADER_SIZE	128
 
+/* Magic number size, for both 1.x and 2.x. */
+#define MAGIC_SIZE	4
+
 /* Magic number in Network Monitor 1.x files. */
-static const char netmon_1_x_magic[] = {
-	'R', 'T', 'S', 'S'
+static const char netmon_1_x_magic[MAGIC_SIZE] = {
+	"RTSS"
 };
 
 /* Magic number in Network Monitor 2.x files. */
-static const char netmon_2_x_magic[] = {
-	'G', 'M', 'B', 'U'
+static const char netmon_2_x_magic[MAGIC_SIZE] = {
+	"GMBU"
 };
 
 /* Network Monitor file header (minus magic number). */
@@ -193,7 +196,7 @@ static gboolean netmon_dump_close(wtap_dumper *wdh, int *err);
 int netmon_open(wtap *wth, int *err, gchar **err_info)
 {
 	int bytes_read;
-	char magic[sizeof netmon_1_x_magic];
+	char magic[MAGIC_SIZE];
 	struct netmon_hdr hdr;
 	int file_type;
 	struct tm tm;
@@ -209,16 +212,16 @@ int netmon_open(wtap *wth, int *err, gchar **err_info)
 	/* Read in the string that should be at the start of a Network
 	 * Monitor file */
 	errno = WTAP_ERR_CANT_READ;
-	bytes_read = file_read(magic, sizeof magic, wth->fh);
-	if (bytes_read != sizeof magic) {
+	bytes_read = file_read(magic, MAGIC_SIZE, wth->fh);
+	if (bytes_read != MAGIC_SIZE) {
 		*err = file_error(wth->fh, err_info);
-		if (*err != 0)
+		if (*err != 0 && *err != WTAP_ERR_SHORT_READ)
 			return -1;
 		return 0;
 	}
 
-	if (memcmp(magic, netmon_1_x_magic, sizeof netmon_1_x_magic) != 0
-	 && memcmp(magic, netmon_2_x_magic, sizeof netmon_1_x_magic) != 0) {
+	if (memcmp(magic, netmon_1_x_magic, MAGIC_SIZE) != 0 &&
+	    memcmp(magic, netmon_2_x_magic, MAGIC_SIZE) != 0) {
 		return 0;
 	}
 
@@ -227,9 +230,9 @@ int netmon_open(wtap *wth, int *err, gchar **err_info)
 	bytes_read = file_read(&hdr, sizeof hdr, wth->fh);
 	if (bytes_read != sizeof hdr) {
 		*err = file_error(wth->fh, err_info);
-		if (*err != 0)
-			return -1;
-		return 0;
+		if (*err == 0)
+			*err = WTAP_ERR_SHORT_READ;
+		return -1;
 	}
 
 	switch (hdr.ver_major) {