Permissive stream open mode strings.

There is more to this patch than just more permissive
mode strings. Now if a socket can be opened with mode
"l2" for instance, and these options are effectively applied
to the socket-specific "r+b" default, not to "r".

* stream.c (parse_mode): New argument specifying a default
mode. The syntax is relaxed, allowing previously required
elements to be omitted.
(normalize_mode): New argument specifying a default mode.
Format mode is always called now, because an input string
is no longer necessarily a valid fopen string even in cases
when it doesn't specify any extensions.
(open_file, open_fileno, open_tail, open_command,
open_process): Use new normalize_mode argument for defaulting;
normalize_mode no longer defaults to "r".

* stream.h (stdio_mode_init_trivial): Macro removed.
(stdio_mode_init_blank, stdio_mode_init_r,
stdio_mode_init_rpb): New initializer macros.
(parse_mode, normalize_mode): Declarations updated.

* socket.c (sock_accept): In datagram socket case, use new
parse_mode argument for defaulting using stdio_mode_init_rpb,
rather than overriding a missing string with "r+b".
(open_sockfd): Likewise, and use new normalize_mode
argument similarly for defaulting the mode on a stream socket.

* txr.1: Documented mode string permissiveness.

1 files changed, 31 insertions, 3 deletions

diff --git a/txr.1 b/txr.1
index ff3d6481..8129b2f4 100644
--- a/txr.1
+++ b/txr.1
@@ -34416,7 +34416,7 @@ The
 argument is a string which uses the same
 conventions as the mode argument of the C language
 .code fopen
-function, with some extensions.
+function, with greater permissiveness, and some extensions.
 The mode string determines whether the stream is an input stream
 or output stream. Note that the
 .str b
@@ -34426,9 +34426,13 @@ are invoked on it.
 
 If the
 .meta mode-string
-argument is omitted, mode
+argument is omitted, the behavior is as if mode
 .str r
-is used.
+were specified. This default is not true of all functions which accepts a
+.meta mode-string
+argument: socket-related functions have a
+.str r+b
+default mode.
 
 Additional option letters are supported in
 .meta mode-string
@@ -34482,6 +34486,30 @@ stream uses a default buffer size. It is erroneous for the
 size order digit to be present together with the option
 .strn u .
 
+\*(TX mode strings are more permissive than the C
+.code fopen
+mode strings in two regards.
+Firstly, the data direction or disposition letter
+.strn r ,
+.str w
+or
+.str a
+may be omitted. If it is missing, and if the optional
+.str +
+is also missing, then the function-specific default mode applies
+(which is
+.str r
+in the case of
+.codn open-file )
+and any remaining options in apply on top of that default.
+This implies that a completely empty mode string is valid,
+and denotes the default mode.
+Secondly, if the
+.str +
+is present, but not preceded by anything, then defaulting is not
+applied; it is taken as equivalent to
+.strn r+ .
+
 .coNP Function @ open-tail
 .synb
 .mets (open-tail < path >> [ mode-string <> [ seek-to-end-p ]])