Add some higher-level file-read APIs and use them.

Add wtap_read_bytes(), which takes a FILE_T, a pointer, a byte count, an
error number pointer, and an error string pointer as arguments, and that
treats a short read of any sort, including a read that returns 0 bytes,
as a WTAP_ERR_SHORT_READ error, and that returns the error number and
string through its last two arguments.

Add wtap_read_bytes_or_eof(), which is similar, but that treats a read
that returns 0 bytes as an EOF, supplying an error number of 0 as an EOF
indication.

Use those in file readers; that simplifies the code and makes it less
likely that somebody will fail to supply the error number and error
string on a file read error.

Change-Id: Ia5dba2a6f81151e87b614461349d611cffc16210
Reviewed-on: https://code.wireshark.org/review/4512
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 7 insertions, 7 deletions

diff --git a/wiretap/iseries.c b/wiretap/iseries.c
index 09c4f6c30e..b3074ca493 100644
--- a/wiretap/iseries.c
+++ b/wiretap/iseries.c
@@ -197,7 +197,6 @@ static gboolean iseries_parse_hex_string (const char * ascii, guint8 * buf,
 int
 iseries_open (wtap * wth, int *err, gchar ** err_info)
 {
-  int  bytes_read;
   gint offset;
   char magic[ISERIES_LINE_LENGTH];
   char unicodemagic[] =
@@ -211,13 +210,14 @@ iseries_open (wtap * wth, int *err, gchar ** err_info)
    * by scanning for it in the first line
    */
   errno = WTAP_ERR_CANT_READ;
-  bytes_read = file_read (&magic, sizeof magic, wth->fh);
-  if (bytes_read != sizeof magic)
+  if (!wtap_read_bytes (wth->fh, &magic, sizeof magic, err, err_info))
     {
-      *err = file_error (wth->fh, err_info);
-      if (*err != 0 && *err != WTAP_ERR_SHORT_READ)
-        return -1;
-      return 0;
+      if (*err == WTAP_ERR_SHORT_READ)
+        {
+          /* Not enough bytes for a magic string, so not an iSeries trace */
+          return 0;
+        }
+      return -1;
     }
 
   /*