From 1ef8071c738db67214e7d20502496146d2a40821 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 18 Mar 2016 06:29:25 -0700
Subject: New l and u letters in stream open mode strings.

* stream.c (parse_mode): Recognize "l" and "u", and
set new flags.
(set_mode_props): More complicated behavior to
integrate the new options with the line mode defaulting
behavior of "i".

* stream.h (struct stdio_mode): New members unbuf
and linebuf. All members become bit fields of width 1.
(stdio_mode_init_trivial): Initializers for new members.

* txr.1: Documented.
---
 stream.c | 28 ++++++++++++++++++++++++----
 stream.h | 18 ++++++++++--------
 txr.1    | 33 ++++++++++++++++++++++++++++++---
 3 files changed, 64 insertions(+), 15 deletions(-)

diff --git a/stream.c b/stream.c
index e9ba359b..5798efcb 100644
--- a/stream.c
+++ b/stream.c
@@ -1186,6 +1186,20 @@ static struct stdio_mode parse_mode(val mode_str)
     case 'i':
       m.interactive = 1;
       break;
+    case 'l':
+      if (m.unbuf) {
+        m.malformed = 1;
+        return m;
+      }
+      m.linebuf = 1;
+      break;
+    case 'u':
+      if (m.linebuf) {
+        m.malformed = 1;
+        return m;
+      }
+      m.unbuf = 1;
+      break;
     default:
       m.malformed = 1;
       return m;
@@ -1245,12 +1259,18 @@ val normalize_mode(struct stdio_mode *m, val mode_str)
 
 val set_mode_props(const struct stdio_mode m, val stream)
 {
-  if (m.interactive) {
+  if (m.interactive || m.linebuf || m.unbuf) {
     struct stdio_handle *h = coerce(struct stdio_handle *,
                                     cobj_handle(stream, stdio_stream_s));
-    if (h->f && m.write)
-      setvbuf(h->f, (char *) NULL, _IOLBF, 0);
-    stream_set_prop(stream, real_time_k, t);
+    if (h->f) {
+      if (m.write && (m.linebuf || (m.interactive && !m.unbuf)))
+        setvbuf(h->f, 0, _IOLBF, 0);
+      else if (m.unbuf)
+        setbuf(h->f, 0);
+    }
+
+    if (m.interactive)
+      stream_set_prop(stream, real_time_k, t);
   }
   return stream;
 }
diff --git a/stream.h b/stream.h
index b96a0ae6..2474ce13 100644
--- a/stream.h
+++ b/stream.h
@@ -83,16 +83,18 @@ struct strm_ops {
 }
 
 struct stdio_mode {
-  int malformed;
-  int read;
-  int write;
-  int create;
-  int append;
-  int binary;
-  int interactive;
+  unsigned malformed : 1;
+  unsigned read : 1;
+  unsigned write : 1;
+  unsigned create : 1;
+  unsigned append : 1;
+  unsigned binary : 1;
+  unsigned interactive : 1;
+  unsigned unbuf : 1;
+  unsigned linebuf : 1;
 };
 
-#define stdio_mode_init_trivial(read) { 0, read, 0, 0, 0, 0, 0 }
+#define stdio_mode_init_trivial(read) { 0, read, 0, 0, 0, 0, 0, 0, 0 }
 
 #define std_input (deref(lookup_var_l(nil, stdin_s)))
 #define std_output (deref(lookup_var_l(nil, stdout_s)))
diff --git a/txr.1 b/txr.1
index a86c4ca1..8dcc2c6b 100644
--- a/txr.1
+++ b/txr.1
@@ -34430,17 +34430,44 @@ argument is omitted, mode
 .str r
 is used.
 
+Additional option letters are supported in
+.meta mode-string
+which are not feature of the standard C
+.code fopen
+function. These letters cannot occur anywhere in the string. They can occur in the
+same position as the
+.str b
+option, in any order with respect to that
+.str b
+or each other. Their relative order doesn't matter.
+
+The letter
+.str l
+indicates that the stream will be line buffered.  This means that an implicit
+flush operation takes place whenever the newline character is output.
+
+The letter
+.str u
+indicates that the stream will be unbuffered.
+
+It is erroneous for both
+.str l
+and
+.str u
+to be specified.
+
 The option letter
 .str i
-is supported. If present, it will create a stream which has the real-time
+indicates that the stream will have the real-time
 property set. For a description of the semantics, see the
 .code real-time-stream-p
 function. Briefly, this property affects the semantics of lazy lists which draw
 input from the stream.
 In addition, for a stream opened for writing or reading and writing, the
 .str i
-mode letter specifies that the stream will be line-buffered. This means that an
-implicit flush operation takes place whenever the newline character is output.
+mode letter specifies that the stream will be line buffered, unless
+specified as unbuffered with
+.strn u .
 
 .coNP Function @ open-tail
 .synb
-- 
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