1 files changed, 149 insertions, 0 deletions
diff --git a/src/libstdbuf.c b/src/libstdbuf.c
new file mode 100644
index 0000000..3d171e9
--- /dev/null
+++ b/src/libstdbuf.c
@@ -0,0 +1,149 @@
+/* libstdbuf -- a shared lib to preload to setup stdio buffering for a command
+   Copyright (C) 2009-2020 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Pádraig Brady.  LD_PRELOAD idea from Brian Dessent.  */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdint.h>
+#include "system.h"
+#include "minmax.h"
+
+/* Deactivate config.h's "rpl_"-prefixed definition of malloc,
+   since we don't link gnulib here, and the replacement isn't
+   needed in this case as we don't malloc(0).  */
+#undef malloc
+
+/* Note currently for glibc (2.3.5) the following call does not change
+   the buffer size, and more problematically does not give any indication
+   that the new size request was ignored:
+
+       setvbuf (stdout, (char*)NULL, _IOFBF, 8192);
+
+   The ISO C99 standard section 7.19.5.6 on the setvbuf function says:
+
+   ... If buf is not a null pointer, the array it points to _may_ be used
+   instead of a buffer allocated by the setvbuf function and the argument
+   size specifies the size of the array; otherwise, size _may_ determine
+   the size of a buffer allocated by the setvbuf function. ...
+
+   Obviously some interpret the above to mean setvbuf(....,size)
+   is only a hint from the application which I don't agree with.
+
+   FreeBSD's libc seems more sensible in this regard. From the man page:
+
+   The size argument may be given as zero to obtain deferred optimal-size
+   buffer allocation as usual.  If it is not zero, then except for
+   unbuffered files, the buf argument should point to a buffer at least size
+   bytes long; this buffer will be used instead of the current buffer.  (If
+   the size argument is not zero but buf is NULL, a buffer of the given size
+   will be allocated immediately, and released on close.  This is an extension
+   to ANSI C; portable code should use a size of 0 with any NULL buffer.)
+   --------------------
+   Another issue is that on glibc-2.7 the following doesn't buffer
+   the first write if it's greater than 1 byte.
+
+       setvbuf(stdout,buf,_IOFBF,127);
+
+   Now the POSIX standard says that "allocating a buffer of size bytes does
+   not necessarily imply that all of size bytes are used for the buffer area".
+   However I think it's just a buggy implementation due to the various
+   inconsistencies with write sizes and subsequent writes.  */
+
+static const char *
+fileno_to_name (const int fd)
+{
+  const char *ret = NULL;
+
+  switch (fd)
+    {
+    case 0:
+      ret = "stdin";
+      break;
+    case 1:
+      ret = "stdout";
+      break;
+    case 2:
+      ret = "stderr";
+      break;
+    default:
+      ret = "unknown";
+      break;
+    }
+
+  return ret;
+}
+
+static void
+apply_mode (FILE *stream, const char *mode)
+{
+  char *buf = NULL;
+  int setvbuf_mode;
+  uintmax_t size = 0;
+
+  if (*mode == '0')
+    setvbuf_mode = _IONBF;
+  else if (*mode == 'L')
+    setvbuf_mode = _IOLBF;      /* FIXME: should we allow 1ML  */
+  else
+    {
+      setvbuf_mode = _IOFBF;
+      char *mode_end;
+      size = strtoumax (mode, &mode_end, 10);
+      if (size == 0 || *mode_end)
+        {
+          fprintf (stderr, _("invalid buffering mode %s for %s\n"),
+                   mode, fileno_to_name (fileno (stream)));
+          return;
+        }
+
+      buf = size <= SIZE_MAX ? malloc (size) : NULL;
+      if (!buf)
+        {
+          /* We could defer the allocation to libc, however since
+             glibc currently ignores the combination of NULL buffer
+             with non zero size, we'll fail here.  */
+          fprintf (stderr,
+                   _("failed to allocate a %" PRIuMAX
+                     " byte stdio buffer\n"),
+                   size);
+          return;
+        }
+      /* buf will be freed by fclose.  */
+    }
+
+  if (setvbuf (stream, buf, setvbuf_mode, size) != 0)
+    {
+      fprintf (stderr, _("could not set buffering of %s to mode %s\n"),
+               fileno_to_name (fileno (stream)), mode);
+      free (buf);
+    }
+}
+
+/* Use __attribute to avoid elision of __attribute__ on SUNPRO_C etc.  */
+static void __attribute ((constructor))
+stdbuf (void)
+{
+  char *e_mode = getenv ("_STDBUF_E");
+  char *i_mode = getenv ("_STDBUF_I");
+  char *o_mode = getenv ("_STDBUF_O");
+  if (e_mode) /* Do first so can write errors to stderr  */
+    apply_mode (stderr, e_mode);
+  if (i_mode)
+    apply_mode (stdin, i_mode);
+  if (o_mode)
+    apply_mode (stdout, o_mode);
+}