lib/string-buffer-reversed.h

/* A buffer that accumulates a string by piecewise concatenation, from the end
   to the start.
   Copyright (C) 2021-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation, either version 3 of the
   License, or (at your option) any later version.

   This file 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 Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>, 2025.  */

/* Before including this file, you may define:
     SBR_NO_PREPENDF         Provides for more efficient code, assuming that
                             sbr_prependvf and sbr_prependf will not be called
                             and that 'struct string_buffer_reversed' instances
                             are not used across different compilation units.
 */

#ifndef _STRING_BUFFER_REVERSED_H
#define _STRING_BUFFER_REVERSED_H

/* This file uses _GL_ATTRIBUTE_MALLOC, _GL_ATTRIBUTE_RETURNS_NONNULL,
   _GL_ATTRIBUTE_CAPABILITY_TYPE, _GL_ATTRIBUTE_ACQUIRE_CAPABILITY,
   _GL_ATTRIBUTE_RELEASE_CAPABILITY.  */
#if !_GL_CONFIG_H_INCLUDED
 #error "Please include config.h first."
#endif

#include <stdarg.h>
#include <stdlib.h>

#include "attribute.h"
#include "string-desc.h"

typedef char * _GL_ATTRIBUTE_CAPABILITY_TYPE ("memory resource")
        sbr_heap_allocated_pointer_t;

/* A string buffer type.  */
struct string_buffer_reversed
{
  /* data[allocated-length .. allocated-1] are used.  */
  sbr_heap_allocated_pointer_t data;
  size_t length;     /* used bytes, <= allocated */
  size_t allocated;  /* allocated bytes */
  bool oom;          /* true if there was an out-of-memory error */
  bool error;        /* true if there was an error other than out-of-memory */
  char space[1024];  /* stack allocated space */
};

#ifdef __cplusplus
extern "C" {
#endif

/* ================== Functions in module 'string-buffer' ================== */

/* Initializes BUFFER to the empty string.  */
extern void sbr_init (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_ACQUIRE_CAPABILITY (buffer->data);

/* Prepends the character C to BUFFER.
   Returns 0, or -1 in case of out-of-memory error.  */
extern int sbr_prepend1 (struct string_buffer_reversed *buffer, char c);

/* Prepends the contents of the memory area S to BUFFER.
   Returns 0, or -1 in case of out-of-memory error.  */
extern int sbr_prepend_desc (struct string_buffer_reversed *buffer,
                            string_desc_t s);

/* Prepends the contents of the C string STR to BUFFER.
   Returns 0, or -1 in case of out-of-memory error.  */
extern int sbr_prepend_c (struct string_buffer_reversed *buffer,
                         const char *str);

#ifndef SBR_NO_PREPENDF

/* Prepends the result of the printf-compatible FORMATSTRING with the argument
   list LIST to BUFFER.
   Returns 0, or -1 with errno set in case of error.
   Error code EOVERFLOW can only occur when a width > INT_MAX is used.
   Therefore, if the format string is valid and does not use %ls/%lc
   directives nor widths, the only possible error code is ENOMEM.  */
extern int sbr_prependvf (struct string_buffer_reversed *buffer,
                          const char *formatstring, va_list list)
  #if (__GNUC__ + (__GNUC_MINOR__ >= 4) > 4) && !defined __clang__
  ATTRIBUTE_FORMAT ((__gnu_printf__, 2, 0))
  #else
  ATTRIBUTE_FORMAT ((__printf__, 2, 0))
  #endif
  ;

/* Prepends the result of the printf-compatible FORMATSTRING with the following
   arguments to BUFFER.
   Returns 0, or -1 with errno set in case of error.
   Error code EOVERFLOW can only occur when a width > INT_MAX is used.
   Therefore, if the format string is valid and does not use %ls/%lc
   directives nor widths, the only possible error code is ENOMEM.  */
extern int sbr_prependf (struct string_buffer_reversed *buffer,
                         const char *formatstring, ...)
  #if (__GNUC__ + (__GNUC_MINOR__ >= 4) > 4) && !defined __clang__
  ATTRIBUTE_FORMAT ((__gnu_printf__, 2, 3))
  #else
  ATTRIBUTE_FORMAT ((__printf__, 2, 3))
  #endif
  ;

#endif

/* Frees the memory held by BUFFER.  */
extern void sbr_free (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_RELEASE_CAPABILITY (buffer->data);

/* Returns a read-only view of the current contents of BUFFER.
   The result is only valid until the next operation on BUFFER.  */
extern string_desc_t sbr_contents (struct string_buffer_reversed *buffer);

/* Ensures the contents of BUFFER is followed by a NUL byte (without
   incrementing the length of the contents).
   Then returns a read-only view of the current contents of BUFFER,
   that is, the current contents of BUFFER as a C string.
   The result is only valid until the next operation on BUFFER.  */
extern const char * sbr_contents_c (struct string_buffer_reversed *buffer);

/* Returns the contents of BUFFER and frees all other memory held by BUFFER.
   Returns (0, NULL) upon failure or if there was an error earlier.
   It is the responsibility of the caller to sd_free() the result.  */
extern rw_string_desc_t sbr_dupfree (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_RELEASE_CAPABILITY (buffer->data);

/* Returns the contents of BUFFER (with an added trailing NUL, that is,
   as a C string), and frees all other memory held by BUFFER.
   Returns NULL upon failure or if there was an error earlier.
   It is the responsibility of the caller to free() the result.  */
extern char * sbr_dupfree_c (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_RELEASE_CAPABILITY (buffer->data);

/* ================== Functions in module 'xstring-buffer' ================== */

#if GNULIB_XSTRING_BUFFER_REVERSED

/* The following functions invoke xalloc_die () in case of out-of-memory
   error.  */

/* Prepends the character C to BUFFER.  */
extern void sbr_xprepend1 (struct string_buffer_reversed *buffer, char c);

/* Prepends the contents of the memory area S to BUFFER.  */
extern void sbr_xprepend_desc (struct string_buffer_reversed *buffer,
                               string_desc_t s);

/* Prepends the contents of the C string STR to BUFFER.  */
extern void sbr_xprepend_c (struct string_buffer_reversed *buffer,
                            const char *str);

# ifndef SBR_NO_PREPENDF

/* Prepends the result of the printf-compatible FORMATSTRING with the argument
   list LIST to BUFFER.
   Returns 0, or -1 in case of error other than out-of-memory error.
   Error code EOVERFLOW can only occur when a width > INT_MAX is used.
   Therefore, if the format string is valid and does not use %ls/%lc
   directives nor widths, no error is possible.  */
extern int sbr_xprependvf (struct string_buffer_reversed *buffer,
                           const char *formatstring, va_list list)
  #if (__GNUC__ + (__GNUC_MINOR__ >= 4) > 4) && !defined __clang__
  ATTRIBUTE_FORMAT ((__gnu_printf__, 2, 0))
  #else
  ATTRIBUTE_FORMAT ((__printf__, 2, 0))
  #endif
  ;

/* Prepends the result of the printf-compatible FORMATSTRING with the following
   arguments to BUFFER.
   Returns 0, or -1 in case of error other than out-of-memory error.
   Error code EOVERFLOW can only occur when a width > INT_MAX is used.
   Therefore, if the format string is valid and does not use %ls/%lc
   directives nor widths, no error is possible.  */
extern int sbr_xprependf (struct string_buffer_reversed *buffer,
                          const char *formatstring, ...)
  #if (__GNUC__ + (__GNUC_MINOR__ >= 4) > 4) && !defined __clang__
  ATTRIBUTE_FORMAT ((__gnu_printf__, 2, 3))
  #else
  ATTRIBUTE_FORMAT ((__printf__, 2, 3))
  #endif
  ;

# endif

/* Returns the contents of BUFFER and frees all other memory held by BUFFER.
   Returns (0, NULL) if there was an error earlier.
   It is the responsibility of the caller to sd_free() the result.  */
extern rw_string_desc_t sbr_xdupfree (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_RELEASE_CAPABILITY (buffer->data);

/* Returns the contents of BUFFER (with an added trailing NUL, that is,
   as a C string), and frees all other memory held by BUFFER.
   Returns NULL if there was an error earlier.
   It is the responsibility of the caller to free() the result.  */
extern char * sbr_xdupfree_c (struct string_buffer_reversed *buffer)
  _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC_FREE
# ifdef SBR_NO_PREPENDF
  _GL_ATTRIBUTE_RETURNS_NONNULL /* because buffer->error is always false */
# endif
  _GL_ATTRIBUTE_RELEASE_CAPABILITY (buffer->data);

#endif /* GNULIB_XSTRING_BUFFER_REVERSED */

/* ========================================================================== */

#ifdef __cplusplus
}
#endif

#endif /* _STRING_BUFFER_REVERSED_H */