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, 2 insertions, 6 deletions

diff --git a/wiretap/tnef.c b/wiretap/tnef.c
index 2e8b565485..3dcc5e40ca 100644
--- a/wiretap/tnef.c
+++ b/wiretap/tnef.c
@@ -98,14 +98,10 @@ static gboolean tnef_seek_read(wtap *wth, gint64 seek_off,
 
 int tnef_open(wtap *wth, int *err, gchar **err_info)
 {
-  int bytes_read;
   guint32 magic;
 
-  bytes_read = file_read(&magic, sizeof magic, wth->fh);
-  if (bytes_read != sizeof magic) {
-    *err = file_error(wth->fh, err_info);
-    return (*err != 0) ? -1 : 0;
-  }
+  if (!wtap_read_bytes(wth->fh, &magic, sizeof magic, err, err_info))
+    return (*err != WTAP_ERR_SHORT_READ) ? -1 : 0;
 
   if (GUINT32_TO_LE(magic) != TNEF_SIGNATURE)
      /* Not a tnef file */