haproxy/include/common/buffer.h

/*
 * include/common/buffer.h
 * Buffer management definitions, macros and inline functions.
 *
 * Copyright (C) 2000-2012 Willy Tarreau - w@1wt.eu
 *
 * This library 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, version 2.1
 * exclusively.
 *
 * This library 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 library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef _COMMON_BUFFER_H
#define _COMMON_BUFFER_H

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <common/config.h>


struct buffer {
	char *p;                        /* buffer's start pointer, separates in and out data */
	unsigned int size;              /* buffer size in bytes */
	unsigned int i;                 /* number of input bytes pending for analysis in the buffer */
	unsigned int o;                 /* number of out bytes the sender can consume from this buffer */
	char data[0];                   /* <size> bytes */
};


void buffer_dump(FILE *o, struct buffer *b, int from, int to);
void buffer_slow_realign(struct buffer *buf);
void buffer_bounce_realign(struct buffer *buf);

/*****************************************************************/
/* These functions are used to compute various buffer area sizes */
/*****************************************************************/

/* Returns an absolute pointer for a position relative to the current buffer's
 * pointer. It is written so that it is optimal when <ofs> is a const. It is
 * written as a macro instead of an inline function so that the compiler knows
 * when it can optimize out the sign test on <ofs> when passed an unsigned int.
 */
#define b_ptr(b, ofs) \
	({            \
		char *__ret = (b)->p + (ofs);                   \
		if ((ofs) > 0 && __ret >= (b)->data + (b)->size)    \
			__ret -= (b)->size;                     \
		else if ((ofs) < 0 && __ret < (b)->data)        \
			__ret += (b)->size;                     \
		__ret;                                          \
	})

/* Advances the buffer by <adv> bytes, which means that the buffer
 * pointer advances, and that as many bytes from in are transferred
 * to out. The caller is responsible for ensuring that adv is always
 * smaller than or equal to b->i.
 */
static inline void b_adv(struct buffer *b, unsigned int adv)
{
	b->i -= adv;
	b->o += adv;
	b->p = b_ptr(b, adv);
}

/* Rewinds the buffer by <adv> bytes, which means that the buffer pointer goes
 * backwards, and that as many bytes from out are moved to in. The caller is
 * responsible for ensuring that adv is always smaller than or equal to b->o.
 */
static inline void b_rew(struct buffer *b, unsigned int adv)
{
	b->i += adv;
	b->o -= adv;
	b->p = b_ptr(b, (int)-adv);
}

/* Returns the start of the input data in a buffer */
static inline char *bi_ptr(const struct buffer *b)
{
	return b->p;
}

/* Returns the end of the input data in a buffer (pointer to next
 * insertion point).
 */
static inline char *bi_end(const struct buffer *b)
{
	char *ret = b->p + b->i;

	if (ret >= b->data + b->size)
		ret -= b->size;
	return ret;
}

/* Returns the amount of input data that can contiguously be read at once */
static inline int bi_contig_data(const struct buffer *b)
{
	int data = b->data + b->size - b->p;

	if (data > b->i)
		data = b->i;
	return data;
}

/* Returns the start of the output data in a buffer */
static inline char *bo_ptr(const struct buffer *b)
{
	char *ret = b->p - b->o;

	if (ret < b->data)
		ret += b->size;
	return ret;
}

/* Returns the end of the output data in a buffer */
static inline char *bo_end(const struct buffer *b)
{
	return b->p;
}

/* Returns the amount of output data that can contiguously be read at once */
static inline int bo_contig_data(const struct buffer *b)
{
	char *beg = b->p - b->o;

	if (beg < b->data)
		return b->data - beg;
	return b->o;
}

/* Return the buffer's length in bytes by summing the input and the output */
static inline int buffer_len(const struct buffer *buf)
{
	return buf->i + buf->o;
}

/* Return non-zero only if the buffer is not empty */
static inline int buffer_not_empty(const struct buffer *buf)
{
	return buf->i | buf->o;
}

/* Return non-zero only if the buffer is empty */
static inline int buffer_empty(const struct buffer *buf)
{
	return !buffer_not_empty(buf);
}

/* Normalizes a pointer after a subtract */
static inline char *buffer_wrap_sub(const struct buffer *buf, char *ptr)
{
	if (ptr < buf->data)
		ptr += buf->size;
	return ptr;
}

/* Normalizes a pointer after an addition */
static inline char *buffer_wrap_add(const struct buffer *buf, char *ptr)
{
	if (ptr - buf->size >= buf->data)
		ptr -= buf->size;
	return ptr;
}

/* Return the maximum amount of bytes that can be written into the buffer,
 * including reserved space which may be overwritten.
 */
static inline int buffer_total_space(const struct buffer *buf)
{
	return buf->size - buffer_len(buf);
}

/* Returns the number of contiguous bytes between <start> and <start>+<count>,
 * and enforces a limit on buf->data + buf->size. <start> must be within the
 * buffer.
 */
static inline int buffer_contig_area(const struct buffer *buf, const char *start, int count)
{
	if (count > buf->data - start + buf->size)
		count = buf->data - start + buf->size;
	return count;
}

/* Return the amount of bytes that can be written into the buffer at once,
 * including reserved space which may be overwritten.
 */
static inline int buffer_contig_space(const struct buffer *buf)
{
	const char *left, *right;

	if (buf->data + buf->o <= buf->p)
		right = buf->data + buf->size;
	else
		right = buf->p + buf->size - buf->o;

	left = buffer_wrap_add(buf, buf->p + buf->i);
	return right - left;
}

/* Return the amount of bytes that can be written into the buffer at once,
 * excluding the amount of reserved space passed in <res>, which is
 * preserved.
 */
static inline int buffer_contig_space_with_res(const struct buffer *buf, int res)
{
	/* Proceed differently if the buffer is full, partially used or empty.
	 * The hard situation is when it's partially used and either data or
	 * reserved space wraps at the end.
	 */
	int spare = buf->size - res;

	if (buffer_len(buf) >= spare)
		spare = 0;
	else if (buffer_len(buf)) {
		spare = buffer_contig_space(buf) - res;
		if (spare < 0)
			spare = 0;
	}
	return spare;
}


/* Normalizes a pointer which is supposed to be relative to the beginning of a
 * buffer, so that wrapping is correctly handled. The intent is to use this
 * when increasing a pointer. Note that the wrapping test is only performed
 * once, so the original pointer must be between ->data-size and ->data+2*size-1,
 * otherwise an invalid pointer might be returned.
 */
static inline const char *buffer_pointer(const struct buffer *buf, const char *ptr)
{
	if (ptr < buf->data)
		ptr += buf->size;
	else if (ptr - buf->size >= buf->data)
		ptr -= buf->size;
	return ptr;
}

/* Returns the distance between two pointers, taking into account the ability
 * to wrap around the buffer's end.
 */
static inline int buffer_count(const struct buffer *buf, const char *from, const char *to)
{
	int count = to - from;
	if (count < 0)
		count += buf->size;
	return count;
}

/* returns the amount of pending bytes in the buffer. It is the amount of bytes
 * that is not scheduled to be sent.
 */
static inline int buffer_pending(const struct buffer *buf)
{
	return buf->i;
}

/* Returns the size of the working area which the caller knows ends at <end>.
 * If <end> equals buf->r (modulo size), then it means that the free area which
 * follows is part of the working area. Otherwise, the working area stops at
 * <end>. It always starts at buf->p. The work area includes the
 * reserved area.
 */
static inline int buffer_work_area(const struct buffer *buf, const char *end)
{
	end = buffer_pointer(buf, end);
	if (end == buffer_wrap_add(buf, buf->p + buf->i))
		/* pointer exactly at end, lets push forwards */
		end = buffer_wrap_sub(buf, buf->p - buf->o);
	return buffer_count(buf, buf->p, end);
}

/* Return 1 if the buffer has less than 1/4 of its capacity free, otherwise 0 */
static inline int buffer_almost_full(const struct buffer *buf)
{
	if (buffer_total_space(buf) < buf->size / 4)
		return 1;
	return 0;
}

/* Cut the first <n> pending bytes in a contiguous buffer. It is illegal to
 * call this function with remaining data waiting to be sent (o > 0). The
 * caller must ensure that <n> is smaller than the actual buffer's length.
 * This is mainly used to remove empty lines at the beginning of a request
 * or a response.
 */
static inline void bi_fast_delete(struct buffer *buf, int n)
{
	buf->i -= n;
	buf->p += n;
}

/*
 * Tries to realign the given buffer, and returns how many bytes can be written
 * there at once without overwriting anything.
 */
static inline int buffer_realign(struct buffer *buf)
{
	if (!(buf->i | buf->o)) {
		/* let's realign the buffer to optimize I/O */
		buf->p = buf->data;
	}
	return buffer_contig_space(buf);
}

/* Schedule all remaining buffer data to be sent. ->o is not touched if it
 * already covers those data. That permits doing a flush even after a forward,
 * although not recommended.
 */
static inline void buffer_flush(struct buffer *buf)
{
	buf->p = buffer_wrap_add(buf, buf->p + buf->i);
	buf->o += buf->i;
	buf->i = 0;
}

#endif /* _COMMON_BUFFER_H */

/*
 * Local variables:
 *  c-indent-level: 8
 *  c-basic-offset: 8
 * End:
 */