Check for errors or short files on every call to fread() and fwrite()
and return errors as appropriate.  Also, print a message if an error
is encountered.
--- a/formats/ctf/ctf.c
+++ b/formats/ctf/ctf.c
@@ -1022,6 +1022,8 @@
 
 	len = fread(&magic, sizeof(magic), 1, fp);
 	if (len != 1) {
+                fprintf(stderr, "[error] error reading packet metadata\n");
+                ret = -1;
 		goto end;
 	}
 	if (magic == TSDL_MAGIC) {
@@ -1075,8 +1077,13 @@
 	int ret = 0;
 
 	readlen = fread(&header, header_sizeof(header), 1, in);
-	if (readlen < 1)
+	if (readlen < 1) {
+		if (feof(in) ) {
+			return 0;
+		}
+                fprintf(stderr, "[error] error reading packet header\n");
 		return -EINVAL;
+        }
 
 	if (td->byte_order != BYTE_ORDER) {
 		header.magic = GUINT32_SWAP_LE_BE(header.magic);
@@ -1117,8 +1124,14 @@
 	toread = (header.content_size / CHAR_BIT) - header_sizeof(header);
 
 	for (;;) {
+		if (toread == 0) {
+			ret = 0;	/* continue reading next packet */
+			goto read_padding;
+		}
+
 		readlen = fread(buf, sizeof(char), min(sizeof(buf) - 1, toread), in);
-		if (ferror(in)) {
+		if (readlen == 0 || ferror(in) ) {
+                        fprintf(stderr, "[error] error reading packet\n");
 			ret = -EINVAL;
 			break;
 		}
@@ -1130,6 +1143,7 @@
 
 		writelen = fwrite(buf, sizeof(char), readlen, out);
 		if (writelen < readlen) {
+                        fprintf(stderr, "[error] error writing packet\n");
 			ret = -EIO;
 			break;
 		}
@@ -1138,10 +1152,6 @@
 			break;
 		}
 		toread -= readlen;
-		if (!toread) {
-			ret = 0;	/* continue reading next packet */
-			goto read_padding;
-		}
 	}
 	return ret;
 
@@ -1842,7 +1852,14 @@
 
 	len = fread(&index_hdr, sizeof(index_hdr), 1, pos->index_fp);
 	if (len != 1) {
-		perror("read index file header");
+                char *msg = "File is too short";
+
+                if (ferror(pos->index_fp) ) {
+                        msg = "I/O error";
+                }
+                fprintf(stderr, "[error] error reading a '*.idx' file under %s: %s\n",
+                        td->parent.path, msg);
+                ret = -1;
 		goto error;
 	}
 
@@ -1913,6 +1930,12 @@
 		/* add index to packet array */
 		g_array_append_val(file_stream->pos.packet_index, index);
 	}
+        if (ferror(pos->index_fp) ) {
+                fprintf(stderr, "[error] error reading a '*.idx' file under %s: I/O error\n",
+                        td->parent.path);
+                ret = -1;
+                goto error;
+        }
 
 	/* Index containing only the header. */
 	if (!file_stream->parent.stream_class) {