libevent evbuffer缓冲源码分析

参考文章：http://blog.sina.com.cn/s/blog_4ab24dd501013d0h.html

struct evbuffer* evbuffer_new(void)

动态分配一个struct evbuffer结构，需要调用evbuffer_free释放内存。

 

void evbuffer_free(struct evbuffer *buffer)

释放buffer所占用的内存。

 

int evbuffer_add(struct evbuffer *buf, const void *data, size_t datlen)

将data追加到evbuffer中

先判断缓冲区的大小是否可以容纳的下datlen大小， 如果不能，则使用evbuffer_expand扩充容量。然后将data追加到evbuffer->buffer + evbuffer->off后。 并且更新有效缓冲区长度off。

如果datlen > 0， 并且设置了回调函数，则调用回调函数
返回值：成功返回0，失败返回-1。

 

int evbuffer_add_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)

移动数据从一个evbuffer到另一个evbuffer。

实际上还是调用了evbuffer_add添加数据到outbuf中。但会清除inbuf中的数据。

返回值：成功返回0，失败返回-1。

 

int evbuffer_add_printf( struct evbuffer *, const char* fmt, ...)

添加一个格式化的字符串到evbuffer尾部。

 

int evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap)

添加一个va_list格式的字符串到evbuffer尾部。

void evbuffer_drain(struct evbuffer *buf, size_t len)

从evbuffer起始位置删除指定长度len字节数据

如果len的长度大于等于缓冲区的off的长度，则表明缓冲区的数据都被清空。 

如果缓冲区发生变化，并且设置了回调函数，则调用回调函数。

 

int evbuffer_expand(struct evbuffer *buf, size_t datlen)

该函数用于扩充evbuffer的容量。每次向evbuffer写数据时，都是将数据写到buffer+off后，buffer到buffer+off之间已被使用，保存的是有效数据，而orig_buffer和buffer之间则是因为读取数据移动指针而形成的无效区域。

 

evbuffer_expand的扩充策略在于：

1，计算出加上datlen后需要的缓冲区大小need

2, 判断当前缓冲区的长度是否可以容纳的下need大小，如果可以则不需要改变缓冲区的大小，直接返回。

3，如果当前缓冲哦你去的长度容纳不下need大小，则判断orig_buffer和buffer之间的空闲区域是否可以容纳添加的数据，如果

可以，则移动buffer和buffer+off之间的数据到orig_buffer和orig_buffer+off之间，然后把新的数据拷贝到orig_buffer+off之后；

4，如果misalign不可以容纳，那么重新分配更大的空间(realloc)，同样会移动数据。

 

扩充内存的策略为：确保新的内存区域最小尺寸为256，且以乘以2的方式逐步扩大(256、512、1024、...)。

返回值：成功返回0，失败返回-1。

 

u_char *evbuffer_find(struct evbuffer *buffer, const u_char *what, size_tlen)

查找缓冲区中是否存在指定的字符串what。

注意这里使用的是u_char类型，说明有可能查找的数据不是以’\0’结尾

如果存在返回指向字符串what的指针，没有则返回NULL。

 

int evbuffer_read(struct evbuffer *buf, int fd, int howmuch)

调用read/recv函数，从文件描述符fd上读取数据到evbuffer中。如果缓冲区不够，调用evbuffer_expand扩充缓冲区。

int evbuffer_write(struct evbuffer *buffer, int fd)

把缓冲区中的数据，调用send/write函数写入文件描述符fd上， 如果send/write函数写入的字节数大于0，则调用evbuffer_drain删除已写的数据。

char *evbuffer_readline(struct evbuffer *buffer)

读取数据以"\r\n","\n\r", "\r" 或者 "\n"结尾。

返回动态分配内存，需要调用者自己使用free来释放内存。返回一个以“\0”结尾的字符串。

int evbuffer_remove(struct evbuffer *buf, void *data, size_t datlen)

将evbuffer缓冲区中的数据读到data中， 最多读datlen字节。如果缓冲区里的数据小于datlen，则拷贝缓冲区中全部数据。

然后调用evbuffer_drain删除已读数据。

 

void evbuffer_setcb(struct evbuffer *buffer,     void (*cb)(struct evbuffer *, size_t, size_t, void *),     void *cbarg)

设置回调函数。当缓冲区中发生变化时， 调用设置的回调函数。

 

C 库函数 void *calloc(size_t nitems, size_t size) 分配所需的内存空间，并返回一个指向它的指针。malloc 和 calloc 之间的不同点是，malloc 不会设置内存为零，而 calloc 会设置分配的内存为零

struct evbuffer{
   u_char *buffer; // 当前有效数据的内存起始地址
   u_char *orig_buffer;//整个缓冲区的内存起始地址
   size_t misalign; // origin_buffer和buffer之间的字节数
   size_t totallen; // 整个分配用来缓冲的内存字节数
   size_t off; // 当前有效数据的总长度(字节数)

   //回到函数，当缓冲区有变化的时候会被调用
  void (*cb)(struct evbuffer *, size_t, size_t, void *);
   void *cbarg; //回调函数的参数

};

 

 

 

下面是 realloc() 函数的声明。

void *realloc(void *ptr, size_t size)

参数

• ptr -- 指针指向一个要重新分配内存的内存块，该内存块之前是通过调用 malloc、calloc 或 realloc 进行分配内存的。如果为空指针，则会分配一个新的内存块，且函数返回一个指向它的指针。
• size -- 内存块的新的大小，以字节为单位。如果大小为 0，且 ptr 指向一个已存在的内存块，则 ptr 所指向的内存块会被释放，并返回一个空指针。

返回值

该函数返回一个指针 ，指向重新分配大小的内存。如果请求失败，则返回 NULL。

 

/*
 * Copyright (c) 2002, 2003 Niels Provos <[email protected]>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef WIN32
#include <winsock2.h>
#include <windows.h>
#endif

#ifdef HAVE_VASPRINTF
/* If we have vasprintf, we need to define this before we include stdio.h. */
#define _GNU_SOURCE
#endif

#include <sys/types.h>

#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef HAVE_STDARG_H
#include <stdarg.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "event.h"
#include "config.h"
#include "evutil.h"
#include "./log.h"

struct evbuffer *
evbuffer_new(void)
{
	struct evbuffer *buffer;
	
	buffer = calloc(1, sizeof(struct evbuffer));

	return (buffer);
}

void
evbuffer_free(struct evbuffer *buffer)
{
	if (buffer->orig_buffer != NULL)
		free(buffer->orig_buffer);
	free(buffer);
}

/* 
 * This is a destructive add.  The data from one buffer moves into
 * the other buffer.
 */

#define SWAP(x,y) do { \
	(x)->buffer = (y)->buffer; \
	(x)->orig_buffer = (y)->orig_buffer; \
	(x)->misalign = (y)->misalign; \
	(x)->totallen = (y)->totallen; \
	(x)->off = (y)->off; \
} while (0)

int
evbuffer_add_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
	int res;

	/* Short cut for better performance */
	if (outbuf->off == 0) {
		struct evbuffer tmp;
		size_t oldoff = inbuf->off;

		/* Swap them directly */
		SWAP(&tmp, outbuf);
		SWAP(outbuf, inbuf);
		SWAP(inbuf, &tmp);

		/* 
		 * Optimization comes with a price; we need to notify the
		 * buffer if necessary of the changes. oldoff is the amount
		 * of data that we transfered from inbuf to outbuf
		 */
		if (inbuf->off != oldoff && inbuf->cb != NULL)
			(*inbuf->cb)(inbuf, oldoff, inbuf->off, inbuf->cbarg);
		if (oldoff && outbuf->cb != NULL)
			(*outbuf->cb)(outbuf, 0, oldoff, outbuf->cbarg);
		
		return (0);
	}

	res = evbuffer_add(outbuf, inbuf->buffer, inbuf->off);
	if (res == 0) {
		/* We drain the input buffer on success */
		evbuffer_drain(inbuf, inbuf->off);
	}

	return (res);
}

int
evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap)
{
	char *buffer;
	size_t space;
	size_t oldoff = buf->off;
	int sz;
	va_list aq;

	/* make sure that at least some space is available */
	evbuffer_expand(buf, 64);
	for (;;) {
		size_t used = buf->misalign + buf->off;
		buffer = (char *)buf->buffer + buf->off;
		assert(buf->totallen >= used);
		space = buf->totallen - used;

#ifndef va_copy
#define	va_copy(dst, src)	memcpy(&(dst), &(src), sizeof(va_list))
#endif
		va_copy(aq, ap);

		sz = evutil_vsnprintf(buffer, space, fmt, aq);

		va_end(aq);

		if (sz < 0)
			return (-1);
		if ((size_t)sz < space) {
			buf->off += sz;
			if (buf->cb != NULL)
				(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);
			return (sz);
		}
		if (evbuffer_expand(buf, sz + 1) == -1)
			return (-1);

	}
	/* NOTREACHED */
}

int
evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...)
{
	int res = -1;
	va_list ap;

	va_start(ap, fmt);
	res = evbuffer_add_vprintf(buf, fmt, ap);
	va_end(ap);

	return (res);
}

/* Reads data from an event buffer and drains the bytes read */

int
evbuffer_remove(struct evbuffer *buf, void *data, size_t datlen)
{
	size_t nread = datlen;
	if (nread >= buf->off)
		nread = buf->off;

	memcpy(data, buf->buffer, nread);
	evbuffer_drain(buf, nread);
	
	return (nread);
}

/*
 * Reads a line terminated by either '\r\n', '\n\r' or '\r' or '\n'.
 * The returned buffer needs to be freed by the called.
 */

char *
evbuffer_readline(struct evbuffer *buffer)
{
	u_char *data = EVBUFFER_DATA(buffer);
	size_t len = EVBUFFER_LENGTH(buffer);
	char *line;
	unsigned int i;

	for (i = 0; i < len; i++) {
		if (data[i] == '\r' || data[i] == '\n')
			break;
	}

	if (i == len)
		return (NULL);

	if ((line = malloc(i + 1)) == NULL) {
		fprintf(stderr, "%s: out of memory\n", __func__);
		return (NULL);
	}

	memcpy(line, data, i);
	line[i] = '\0';

	/*
	 * Some protocols terminate a line with '\r\n', so check for
	 * that, too.
	 */
	if ( i < len - 1 ) {
		char fch = data[i], sch = data[i+1];

		/* Drain one more character if needed */
		if ( (sch == '\r' || sch == '\n') && sch != fch )
			i += 1;
	}

	evbuffer_drain(buffer, i + 1);

	return (line);
}


char *
evbuffer_readln(struct evbuffer *buffer, size_t *n_read_out,
		enum evbuffer_eol_style eol_style)
{
	u_char *data = EVBUFFER_DATA(buffer);
	u_char *start_of_eol, *end_of_eol;
	size_t len = EVBUFFER_LENGTH(buffer);
	char *line;
	unsigned int i, n_to_copy, n_to_drain;

	if (n_read_out)
		*n_read_out = 0;

	/* depending on eol_style, set start_of_eol to the first character
	 * in the newline, and end_of_eol to one after the last character. */
	switch (eol_style) {
	case EVBUFFER_EOL_ANY:
		for (i = 0; i < len; i++) {
			if (data[i] == '\r' || data[i] == '\n')
				break;
		}
		if (i == len)
			return (NULL);
		start_of_eol = data+i;
		++i;
		for ( ; i < len; i++) {
			if (data[i] != '\r' && data[i] != '\n')
				break;
		}
		end_of_eol = data+i;
		break;
	case EVBUFFER_EOL_CRLF:
		end_of_eol = memchr(data, '\n', len);
		if (!end_of_eol)
			return (NULL);
		if (end_of_eol > data && *(end_of_eol-1) == '\r')
			start_of_eol = end_of_eol - 1;
		else
			start_of_eol = end_of_eol;
		end_of_eol++; /*point to one after the LF. */
		break;
	case EVBUFFER_EOL_CRLF_STRICT: {
		u_char *cp = data;
		while ((cp = memchr(cp, '\r', len-(cp-data)))) {
			if (cp < data+len-1 && *(cp+1) == '\n')
				break;
			if (++cp >= data+len) {
				cp = NULL;
				break;
			}
		}
		if (!cp)
			return (NULL);
		start_of_eol = cp;
		end_of_eol = cp+2;
		break;
	}
	case EVBUFFER_EOL_LF:
		start_of_eol = memchr(data, '\n', len);
		if (!start_of_eol)
			return (NULL);
		end_of_eol = start_of_eol + 1;
		break;
	default:
		return (NULL);
	}

	n_to_copy = start_of_eol - data;
	n_to_drain = end_of_eol - data;

	if ((line = malloc(n_to_copy+1)) == NULL) {
		event_warn("%s: out of memory\n", __func__);
		return (NULL);
	}

	memcpy(line, data, n_to_copy);
	line[n_to_copy] = '\0';

	evbuffer_drain(buffer, n_to_drain);
	if (n_read_out)
		*n_read_out = (size_t)n_to_copy;

	return (line);
}

/* Adds data to an event buffer */

static void
evbuffer_align(struct evbuffer *buf)
{
	memmove(buf->orig_buffer, buf->buffer, buf->off);
	buf->buffer = buf->orig_buffer;
	buf->misalign = 0;
}

/* Expands the available space in the event buffer to at least datlen */

int
evbuffer_expand(struct evbuffer *buf, size_t datlen)
{
	size_t need = buf->misalign + buf->off + datlen;

	/* If we can fit all the data, then we don't have to do anything */
	if (buf->totallen >= need)
		return (0);

	/*
	 * If the misalignment fulfills our data needs, we just force an
	 * alignment to happen.  Afterwards, we have enough space.
	 */
	if (buf->misalign >= datlen) {
		evbuffer_align(buf);
	} else {
		void *newbuf;
		size_t length = buf->totallen;

		if (length < 256)
			length = 256;
		while (length < need)
			length <<= 1;

		if (buf->orig_buffer != buf->buffer)
			evbuffer_align(buf);
		if ((newbuf = realloc(buf->buffer, length)) == NULL)
			return (-1);

		buf->orig_buffer = buf->buffer = newbuf;
		buf->totallen = length;
	}

	return (0);
}

int
evbuffer_add(struct evbuffer *buf, const void *data, size_t datlen)
{
	size_t need = buf->misalign + buf->off + datlen;
	size_t oldoff = buf->off;

	if (buf->totallen < need) {
		if (evbuffer_expand(buf, datlen) == -1)
			return (-1);
	}

	memcpy(buf->buffer + buf->off, data, datlen);
	buf->off += datlen;

	if (datlen && buf->cb != NULL)
		(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);

	return (0);
}

void
evbuffer_drain(struct evbuffer *buf, size_t len)
{
	size_t oldoff = buf->off;

	if (len >= buf->off) {
		buf->off = 0;
		buf->buffer = buf->orig_buffer;
		buf->misalign = 0;
		goto done;
	}

	buf->buffer += len;
	buf->misalign += len;

	buf->off -= len;

 done:
	/* Tell someone about changes in this buffer */
	if (buf->off != oldoff && buf->cb != NULL)
		(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);

}

/*
 * Reads data from a file descriptor into a buffer.
 */

#define EVBUFFER_MAX_READ	4096

int
evbuffer_read(struct evbuffer *buf, int fd, int howmuch)
{
	u_char *p;
	size_t oldoff = buf->off;
	int n = EVBUFFER_MAX_READ;

#if defined(FIONREAD)
#ifdef WIN32
	long lng = n;
	if (ioctlsocket(fd, FIONREAD, &lng) == -1 || (n=lng) <= 0) {
#else
	if (ioctl(fd, FIONREAD, &n) == -1 || n <= 0) {
#endif
		n = EVBUFFER_MAX_READ;
	} else if (n > EVBUFFER_MAX_READ && n > howmuch) {
		/*
		 * It's possible that a lot of data is available for
		 * reading.  We do not want to exhaust resources
		 * before the reader has a chance to do something
		 * about it.  If the reader does not tell us how much
		 * data we should read, we artifically limit it.
		 */
		if ((size_t)n > buf->totallen << 2)
			n = buf->totallen << 2;
		if (n < EVBUFFER_MAX_READ)
			n = EVBUFFER_MAX_READ;
	}
#endif	
	if (howmuch < 0 || howmuch > n)
		howmuch = n;

	/* If we don't have FIONREAD, we might waste some space here */
	if (evbuffer_expand(buf, howmuch) == -1)
		return (-1);

	/* We can append new data at this point */
	p = buf->buffer + buf->off;

#ifndef WIN32
	n = read(fd, p, howmuch);
#else
	n = recv(fd, p, howmuch, 0);
#endif
	if (n == -1)
		return (-1);
	if (n == 0)
		return (0);

	buf->off += n;

	/* Tell someone about changes in this buffer */
	if (buf->off != oldoff && buf->cb != NULL)
		(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);

	return (n);
}

int
evbuffer_write(struct evbuffer *buffer, int fd)
{
	int n;

#ifndef WIN32
	n = write(fd, buffer->buffer, buffer->off);
#else
	n = send(fd, buffer->buffer, buffer->off, 0);
#endif
	if (n == -1)
		return (-1);
	if (n == 0)
		return (0);
	evbuffer_drain(buffer, n);

	return (n);
}

u_char *
evbuffer_find(struct evbuffer *buffer, const u_char *what, size_t len)
{
	u_char *search = buffer->buffer, *end = search + buffer->off;
	u_char *p;

	while (search < end &&
	    (p = memchr(search, *what, end - search)) != NULL) {
		if (p + len > end)
			break;
		if (memcmp(p, what, len) == 0)
			return (p);
		search = p + 1;
	}

	return (NULL);
}

void evbuffer_setcb(struct evbuffer *buffer,
    void (*cb)(struct evbuffer *, size_t, size_t, void *),
    void *cbarg)
{
	buffer->cb = cb;
	buffer->cbarg = cbarg;
}