stdio-common/Xprintf_buffer_flush.c

   1 /* Flush wrapper for struct __*printf_buffer.  Generic version.
   2    Copyright (C) 2022-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <printf_buffer.h>
  20
  21 #include <assert.h>
  22 #include <stdint.h>
  23
  24 /* Xprintf (buffer_do_flush) (BUF) performs the flush operation.  The
  25    actual implementation is specific to the multibyte and wide
  26    variants.
  27
  28    If the flush fails, Xprintf_buffer_mark_failed (BUF) must be
  29    called, and BUF->write_ptr and BUF->write_end can be left
  30    unchanged.
  31
  32    The function must not do anything if failure has already occurred,
  33    that is, if BUF->mode == Xprintf (buffer_mode_failed).
  34
  35    The framework implicitly invokes flush with BUF->write_ptr ==
  36    BUF->write_end only.  (This is particularly relevant to the
  37    __sprintf_chk flush, which just calls __chk_fail.)  But in some
  38    cases, Xprintf_buffer_flush may be called explicitly (when
  39    BUF->mode/the backing function is known).  In that case, it is
  40    possible that BUF->write_ptr < BUF->write_end is true.
  41
  42    If the flush succeeds, the pointers are changed so that
  43    BUF->write_ptr < BUF->write_end.  It is possible to switch to a
  44    completely different buffer here.  If the buffer is moved, it may
  45    be necessary to updated BUF->write_base and BUF->written from the
  46    flush function as well.
  47
  48    Note that when chaining buffers, in the flush function for the
  49    outer buffer (to which data is written first), it is necessary to
  50    check for BUF->next->failed (for the inner buffer) and set
  51    BUF->base.failed to true (for the outer buffer).  This should come
  52    towards the end of the outer flush function.  Usually, there is
  53    also some unwrapping step afterwards; it has to check the outer
  54    buffer (BUF->base.failed) and propagate any error to the inner
  55    buffer (BUF->next->failed), so essentially in the other
  56    direction.  */
  57 static void Xprintf (buffer_do_flush) (struct Xprintf_buffer *buf);
  58
  59 bool
  60 Xprintf_buffer_flush (struct Xprintf_buffer *buf)
  61 {
  62   if (__glibc_unlikely (Xprintf_buffer_has_failed (buf)))
  63     return false;
  64
  65   Xprintf (buffer_do_flush) (buf);
  66   if (Xprintf_buffer_has_failed (buf))
  67     return false;
  68
  69   /* Ensure that the flush has made available some bytes.  */
  70   assert (buf->write_ptr != buf->write_end);
  71   return true;
  72 }