include/event2/buffer.h File Reference

Functions for buffering data for network sending or receiving. More...

#include <event-config.h>
#include <stdarg.h>
#include <sys/types.h>
#include <event2/util.h>

Go to the source code of this file.

Data Structures
struct	evbuffer_cb_info
	Structure passed to an evbuffer callback. More...
struct	evbuffer_ptr
	Points to a position within an evbuffer. More...
Defines
#define	EVBUFFER_CB_DISABLED   0
#define	EVBUFFER_CB_ENABLED   1
Typedefs
typedef void(*	evbuffer_cb_func )(struct evbuffer *buffer, const struct evbuffer_cb_info *info, void *arg)
	Type definition for a callback that is invoked whenever data is added or removed from an evbuffer.
Enumerations
enum	evbuffer_eol_style { EVBUFFER_EOL_ANY, EVBUFFER_EOL_CRLF, EVBUFFER_EOL_CRLF_STRICT, EVBUFFER_EOL_LF }
	Used to tell evbuffer_readln what kind of line-ending to look for. More...
enum	evbuffer_ptr_how { EVBUFFER_PTR_SET, EVBUFFER_PTR_ADD }
Functions
int	evbuffer_add (struct evbuffer *buf, const void *data, size_t datlen)
	Append data to the end of an evbuffer.
int	evbuffer_add_buffer (struct evbuffer *outbuf, struct evbuffer *inbuf)
	Move data from one evbuffer into another evbuffer.
struct evbuffer_cb_entry *	evbuffer_add_cb (struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
	Add a new callback to an evbuffer.
int	evbuffer_add_file (struct evbuffer *output, int fd, off_t offset, size_t length)
	Move data from a file into the evbuffer for writing to a socket.
int	evbuffer_add_printf (struct evbuffer *buf, const char *fmt,...)
	Append a formatted string to the end of an evbuffer.
int	evbuffer_add_reference (struct evbuffer *outbuf, const void *data, size_t datlen, void(*cleanupfn)(void *extra), void *extra)
	Reference memory into an evbuffer without copying.
int	evbuffer_add_vprintf (struct evbuffer *buf, const char *fmt, va_list ap)
	Append a va_list formatted string to the end of an evbuffer.
int	evbuffer_cb_set_flags (struct evbuffer *buffer, struct evbuffer_cb_entry *cb, ev_uint32_t flags)
	Change whether a given callback is enabled on a buffer or not.
int	evbuffer_commit_space (struct evbuffer *buf, size_t size)
	Commits previously reserved space.
int	evbuffer_defer_callbacks (struct evbuffer *buffer, struct event_base *base)
	Force all the callbacks on an evbuffer to be run, not immediately after the evbuffer is altered, but instead from inside the event loop.
int	evbuffer_drain (struct evbuffer *buf, size_t len)
	Remove a specified number of bytes data from the beginning of an evbuffer.
int	evbuffer_enable_locking (struct evbuffer *buf, void *lock)
	Enable locking on an evbuffer so that it can safely be used by multiple threads at the same time.
int	evbuffer_expand (struct evbuffer *buf, size_t datlen)
	Expands the available space in an event buffer.
void	evbuffer_free (struct evbuffer *buf)
	Deallocate storage for an evbuffer.
int	evbuffer_freeze (struct evbuffer *buf, int at_front)
	Prevent calls that modify an evbuffer from succeeding.
size_t	evbuffer_get_contiguous_space (const struct evbuffer *buf)
	Returns the number of contiguous available bytes in the first buffer chain.
size_t	evbuffer_get_length (const struct evbuffer *buf)
	Returns the total number of bytes stored in the event buffer.
void	evbuffer_lock (struct evbuffer *buf)
	Acquire the lock on an evbuffer.
struct evbuffer *	evbuffer_new (void)
	Allocate storage for a new evbuffer.
int	evbuffer_prepend (struct evbuffer *buf, const void *data, size_t size)
	Prepends data to the beginning of the evbuffer.
int	evbuffer_prepend_buffer (struct evbuffer *dst, struct evbuffer *src)
	Prepends all data from the src evbuffer to the beginning of the dst evbuffer.
int	evbuffer_ptr_set (struct evbuffer *buffer, struct evbuffer_ptr *pos, size_t position, enum evbuffer_ptr_how how)
	Sets the search pointer in the buffer to positiion.
unsigned char *	evbuffer_pullup (struct evbuffer *buf, ssize_t size)
	Makes the data at the begging of an evbuffer contiguous.
int	evbuffer_read (struct evbuffer *buffer, evutil_socket_t fd, int howmuch)
	Read from a file descriptor and store the result in an evbuffer.
char *	evbuffer_readln (struct evbuffer *buffer, size_t *n_read_out, enum evbuffer_eol_style eol_style)
	Read a single line from an event buffer.
int	evbuffer_remove (struct evbuffer *buf, void *data, size_t datlen)
	Read data from an event buffer and drain the bytes read.
int	evbuffer_remove_buffer (struct evbuffer *src, struct evbuffer *dst, size_t datlen)
	Read data from an event buffer into another event buffer draining the bytes from the src buffer read.
int	evbuffer_remove_cb (struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
	Remove a callback from an evbuffer, given the function and argument used to add it.
int	evbuffer_remove_cb_entry (struct evbuffer *buffer, struct evbuffer_cb_entry *ent)
	Remove a callback from an evbuffer, given a handle returned from evbuffer_add_cb.
unsigned char *	evbuffer_reserve_space (struct evbuffer *buf, size_t size)
	Reserves space in the last chain of an event buffer.
struct evbuffer_ptr	evbuffer_search (struct evbuffer *buffer, const char *what, size_t len, const struct evbuffer_ptr *start)
	Search for a string within an evbuffer.
int	evbuffer_unfreeze (struct evbuffer *buf, int at_front)
	Re-enable calls that modify an evbuffer.
void	evbuffer_unlock (struct evbuffer *buf)
	Release the lock on an evbuffer.
int	evbuffer_write (struct evbuffer *buffer, evutil_socket_t fd)
	Write the contents of an evbuffer to a file descriptor.
int	evbuffer_write_atmost (struct evbuffer *buffer, evutil_socket_t fd, ssize_t howmuch)
	Write some of the contents of an evbuffer to a file descriptor.

---

Detailed Description

Functions for buffering data for network sending or receiving.

An evbuffer can be used for preparing data before sending it to the network or conversely for reading data from the network. Evbuffers try to avoid memory copies as much as possible. As a result evbuffers can be used to pass data around witout actually incurring the overhead of copying the data.

A new evbuffer can be allocated with evbuffer_new(), and can be freed with evbuffer_free().

There are several guide lines for using evbuffers.

• if you already know how much data you are going to add as a result of calling evbuffer_add() multiple times, it makes sense to use evbuffer_expand() first to make sure that enough memory is allocated before hand.

• evbuffer_add_buffer() adds the contents of one buffer to the other without incurring any unnecessary memory copies.

• evbuffer_add() and evbuffer_add_buffer() do not mix very well: if you use them, you will wind up with fragmented memory in your buffer.

As the contents of an evbuffer can be stored into multiple different memory blocks, it cannot be accessed directly. Instead, evbuffer_pullup() can be used to force a specified number of bytes to be continuous. This will cause memory reallocation and memory copies if the data is split across multiple blocks.

---

Typedef Documentation

typedef void(* evbuffer_cb_func)(struct evbuffer *buffer, const struct evbuffer_cb_info *info, void *arg)

Type definition for a callback that is invoked whenever data is added or removed from an evbuffer.

An evbuffer may have one or more callbacks set at a time. The order in which they are exectuded is undefined.

A callback function may add more callbacks, or remove itself from the list of callbacks, or add or remove data from the buffer. It may not remove another callback from the list.

If a callback adds or removes data from the buffer or from another buffer, this can cause a recursive invocation of your callback or other callbacks. If you ask for an infinite loop, you might just get one: watch out!

Parameters:

	buffer	the buffer whose size has changed
	info	a structure describing how the buffer changed.
	arg	a pointer to user data

---

Enumeration Type Documentation

enum evbuffer_eol_style

Used to tell evbuffer_readln what kind of line-ending to look for.

Enumerator:

EVBUFFER_EOL_ANY	Any sequence of CR and LF characters is acceptable as an EOL.
EVBUFFER_EOL_CRLF	An EOL is an LF, optionally preceded by a CR. This style is most useful for implementing text-based internet protocols.
EVBUFFER_EOL_CRLF_STRICT	An EOL is a CR followed by an LF.
EVBUFFER_EOL_LF	An EOL is a LF.

enum evbuffer_ptr_how

Enumerator:

EVBUFFER_PTR_SET	Sets the pointer to the position; can be called on with an uninitalized evbuffer_ptr.
EVBUFFER_PTR_ADD	Advances the pointer by adding to the current position.

---

Function Documentation

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

Append data to the end of an evbuffer.

Parameters:

	buf	the event buffer to be appended to
	data	pointer to the beginning of the data buffer
	datlen	the number of bytes to be copied from the data buffer

Returns:

0 on success, -1 on failure.

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

Move data from one evbuffer into another evbuffer.

This is a destructive add. The data from one buffer moves into the other buffer. However, no unnecessary memory copies occur.

Parameters:

	outbuf	the output buffer
	inbuf	the input buffer

Returns:

0 if successful, or -1 if an error occurred

struct evbuffer_cb_entry* evbuffer_add_cb	(	struct evbuffer *	buffer,
		evbuffer_cb_func	cb,
		void *	cbarg
	)			[read]

Add a new callback to an evbuffer.

Subsequent calls to evbuffer_add_cb() add new callbacks. To remove this callback, call evbuffer_remove_cb or evbuffer_remove_cb_entry.

Parameters:

	buffer	the evbuffer to be monitored
	cb	the callback function to invoke when the evbuffer is modified, or NULL to remove all callbacks.
	cbarg	an argument to be provided to the callback function

Returns:

a handle to the callback on success, or NULL on failure.

int evbuffer_add_file	(	struct evbuffer *	output,
		int	fd,
		off_t	offset,
		size_t	length
	)

Move data from a file into the evbuffer for writing to a socket.

This function avoids unnecessary data copies between userland and kernel. Where available, it uses sendfile or splice.

The function owns the resulting file descriptor and will close it when finished transferring data.

The results of using evbuffer_remove() or evbuffer_pullup() are undefined.

Parameters:

	outbuf	the output buffer
	fd	the file descriptor
	off	the offset from which to read data
	length	how much data to read

Returns:

0 if successful, or -1 if an error occurred

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

Append a formatted string to the end of an evbuffer.

Parameters:

	buf	the evbuffer that will be appended to
	fmt	a format string
	...	arguments that will be passed to printf(3)

Returns:

The number of bytes added if successful, or -1 if an error occurred.

int evbuffer_add_reference	(	struct evbuffer *	outbuf,
		const void *	data,
		size_t	datlen,
		void(*)(void *extra)	cleanupfn,
		void *	extra
	)

Reference memory into an evbuffer without copying.

The memory needs to remain valid until all the added data has been read. This function keeps just a reference to the memory without actually incurring the overhead of a copy.

Parameters:

	outbuf	the output buffer
	data	the memory to reference
	datlen	how memory to reference
	cleanupfn	callback to be invokved when the memory is no longer referenced
	extra	optional argument to the cleanup callback

Returns:

0 if successful, or -1 if an error occurred

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

Append a va_list formatted string to the end of an evbuffer.

Parameters:

	buf	the evbuffer that will be appended to
	fmt	a format string
	ap	a varargs va_list argument array that will be passed to vprintf(3)

Returns:

The number of bytes added if successful, or -1 if an error occurred.

int evbuffer_cb_set_flags	(	struct evbuffer *	buffer,
		struct evbuffer_cb_entry *	cb,
		ev_uint32_t	flags
	)

Change whether a given callback is enabled on a buffer or not.

A disabled callback is not invoked even when the buffer size changes.

Parameters:

	buffer	the evbuffer that the callback is watching.
	cb	the callback whose status we want to change.
	flags	EVBUFFER_CB_ENABLED to enable the callback, or EVBUFFER_CB_DISABLED to disable it.

Returns:

0 on success, -1 on failure.

int evbuffer_commit_space	(	struct evbuffer *	buf,
		size_t	size
	)

Commits previously reserved space.

Commits some of the space previously reserved with evbuffer_reserve_space(). It then becomes available for reading.

Parameters:

	buf	the event buffer in which to reserve space.
	size	how much space to commit.

Returns:

0 on success, -1 on error

See also:

evbuffer_reserve_space

int evbuffer_defer_callbacks	(	struct evbuffer *	buffer,
		struct event_base *	base
	)

Force all the callbacks on an evbuffer to be run, not immediately after the evbuffer is altered, but instead from inside the event loop.

This can be used to serialize all the callbacks to a single thread of execution.

int evbuffer_drain	(	struct evbuffer *	buf,
		size_t	len
	)

Remove a specified number of bytes data from the beginning of an evbuffer.

Parameters:

	buf	the evbuffer to be drained
	len	the number of bytes to drain from the beginning of the buffer

Returns:

0 on success, -1 on failure.

int evbuffer_enable_locking	(	struct evbuffer *	buf,
		void *	lock
	)

Enable locking on an evbuffer so that it can safely be used by multiple threads at the same time.

NOTE: when locking is enabled, the lock will be held when callbacks are invoked. This could result in deadlock if you aren't careful. Plan accordingly!

Parameters:

	buf	An evbuffer to make lockable.
	lock	A lock object, or NULL if we should allocate our own.

Returns:

0 on success, -1 on failure.

int evbuffer_expand	(	struct evbuffer *	buf,
		size_t	datlen
	)

Expands the available space in an event buffer.

Expands the available space in the event buffer to at least datlen, so that appending datlen additional bytes will not require any new allocations.

Parameters:

	buf	the event buffer to be expanded
	datlen	the new minimum length requirement

Returns:

0 if successful, or -1 if an error occurred

void evbuffer_free

(

struct evbuffer *

buf

)

Deallocate storage for an evbuffer.

Parameters:

buf

pointer to the evbuffer to be freed

int evbuffer_freeze	(	struct evbuffer *	buf,
		int	at_front
	)

Prevent calls that modify an evbuffer from succeeding.

A buffer may frozen at the front, at the back, or at both the front and the back.

If the front of a buffer is frozen, operations that drain data from the front of the buffer, or that prepend data to the buffer, will fail until it is unfrozen. If the back a buffer is frozen, operations that append data from the buffer will fail until it is unfrozen.

Parameters:

	buf	The buffer to freeze
	at_front	If true, we freeze the front of the buffer. If false, we freeze the back.

Returns:

0 on success, -1 on failure.

size_t evbuffer_get_contiguous_space

(

const struct evbuffer *

buf

)

Returns the number of contiguous available bytes in the first buffer chain.

This is useful when procesing data that might be split into multiple chains, or that might all be in the first chain. Calls to evbuffer_pullup() that cause reallocation and copying of data can thus be avoided.

Parameters:

buf

pointer to the evbuffer

Returns:

0 if no data is available, otherwise the number of available bytes in the first buffer chain.

size_t evbuffer_get_length

(

const struct evbuffer *

buf

)

Returns the total number of bytes stored in the event buffer.

Parameters:

buf

pointer to the evbuffer

Returns:

the number of bytes stored in the event buffer

void evbuffer_lock

(

struct evbuffer *

buf

)

Acquire the lock on an evbuffer.

Has no effect if locking was not enabled with evbuffer_enable_locking.

struct evbuffer* evbuffer_new

(

void

)

[read]

Allocate storage for a new evbuffer.

Returns:

a pointer to a newly allocated evbuffer struct, or NULL if an error occurred

int evbuffer_prepend	(	struct evbuffer *	buf,
		const void *	data,
		size_t	size
	)

Prepends data to the beginning of the evbuffer.

Parameters:

	buf	the evbuffer to which to prepend data
	data	a pointer to the memory to prepend
	size	the number of bytes to prepend

Returns:

0 if successful, or -1 otherwise

int evbuffer_prepend_buffer	(	struct evbuffer *	dst,
		struct evbuffer *	src
	)

Prepends all data from the src evbuffer to the beginning of the dst evbuffer.

Parameters:

	dst	the evbuffer to which to prepend data
	src	the evbuffer to prepend; it will be emptied as a result

Returns:

0 if successful, or -1 otherwise

int evbuffer_ptr_set	(	struct evbuffer *	buffer,
		struct evbuffer_ptr *	pos,
		size_t	position,
		enum evbuffer_ptr_how	how
	)

Sets the search pointer in the buffer to positiion.

If evbuffer_ptr is not initalized. This function can only be called with EVBUFFER_PTR_SET.

Parameters:

	buffer	the evbuffer to be search
	ptr	a pointer to a struct evbuffer_ptr
	position	the position at which to start the next search
	how	determines how the pointer should be manipulated.

Returns:

0 on success or -1 otherwise

unsigned char* evbuffer_pullup	(	struct evbuffer *	buf,
		ssize_t	size
	)

Makes the data at the begging of an evbuffer contiguous.

Parameters:

	buf	the evbuffer to make contiguous
	size	the number of bytes to make contiguous, or -1 to make the entire buffer contiguous.

Returns:

a pointer to the contigous memory areay

int evbuffer_read	(	struct evbuffer *	buffer,
		evutil_socket_t	fd,
		int	howmuch
	)

Read from a file descriptor and store the result in an evbuffer.

Parameters:

	buf	the evbuffer to store the result
	fd	the file descriptor to read from
	howmuch	the number of bytes to be read

Returns:

the number of bytes read, or -1 if an error occurred

See also:

evbuffer_write()

char* evbuffer_readln	(	struct evbuffer *	buffer,
		size_t *	n_read_out,
		enum evbuffer_eol_style	eol_style
	)

Read a single line from an event buffer.

Reads a line terminated by an EOL as determined by the evbuffer_eol_style argument. Returns a newly allocated nul-terminated string; the caller must free the returned value. The EOL is not included in the returned string.

Parameters:

	buffer	the evbuffer to read from
	n_read_out	if non-NULL, points to a size_t that is set to the number of characters in the returned string. This is useful for strings that can contain NUL characters.
	eol_style	the style of line-ending to use.

Returns:

pointer to a single line, or NULL if an error occurred

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

Read data from an event buffer and drain the bytes read.

Parameters:

	buf	the event buffer to be read from
	data	the destination buffer to store the result
	datlen	the maximum size of the destination buffer

Returns:

the number of bytes read, or -1 if we can't drain the buffer.

int evbuffer_remove_buffer	(	struct evbuffer *	src,
		struct evbuffer *	dst,
		size_t	datlen
	)

Read data from an event buffer into another event buffer draining the bytes from the src buffer read.

This function avoids memcpy as possible.

Parameters:

	src	the event buffer to be read from
	dst	the destination event buffer to store the result into
	datlen	the maximum numbers of bytes to transfer

Returns:

the number of bytes read

int evbuffer_remove_cb	(	struct evbuffer *	buffer,
		evbuffer_cb_func	cb,
		void *	cbarg
	)

Remove a callback from an evbuffer, given the function and argument used to add it.

Returns:

0 if a callback was removed, or -1 if no matching callback was found.

int evbuffer_remove_cb_entry	(	struct evbuffer *	buffer,
		struct evbuffer_cb_entry *	ent
	)

Remove a callback from an evbuffer, given a handle returned from evbuffer_add_cb.

Calling this function invalidates the handle.

Returns:

0 if a callback was removed, or -1 if no matching callback was found.

unsigned char* evbuffer_reserve_space	(	struct evbuffer *	buf,
		size_t	size
	)

Reserves space in the last chain of an event buffer.

Makes space available in the last chain of an event buffer that can be arbitrarily written to by a user. The space does not become available for reading until it has been committed with evbuffer_commit_space().

Multiple subsequent calls to this function will make the same space available until evbuffer_commit_space() has been called.

Parameters:

	buf	the event buffer in which to reserve space.
	size	how much space to make available.

Returns:

the pointer to the available space or NULL on error.

See also:

evbuffer_commit_space

struct evbuffer_ptr evbuffer_search	(	struct evbuffer *	buffer,
		const char *	what,
		size_t	len,
		const struct evbuffer_ptr *	start
	)			[read]

Search for a string within an evbuffer.

Parameters:

	buffer	the evbuffer to be searched
	what	the string to be searched for
	len	the length of the search string
	start	NULL or a pointer to a valid struct evbuffer_ptr.

Returns:

a struct evbuffer_ptr whose 'pos' field has the offset of the first occurrence of the string in the buffer after 'start'. The 'pos' field of the result is -1 if the string was not found.

int evbuffer_unfreeze	(	struct evbuffer *	buf,
		int	at_front
	)

Re-enable calls that modify an evbuffer.

Parameters:

	buf	The buffer to un-freeze
	at_front	If true, we unfreeze the front of the buffer. If false, we unfreeze the back.

Returns:

0 on success, -1 on failure.

void evbuffer_unlock

(

struct evbuffer *

buf

)

Release the lock on an evbuffer.

Has no effect if locking was not enabled with evbuffer_enable_locking.

int evbuffer_write	(	struct evbuffer *	buffer,
		evutil_socket_t	fd
	)

Write the contents of an evbuffer to a file descriptor.

The evbuffer will be drained after the bytes have been successfully written.

Parameters:

	buffer	the evbuffer to be written and drained
	fd	the file descriptor to be written to

Returns:

the number of bytes written, or -1 if an error occurred

See also:

evbuffer_read()

int evbuffer_write_atmost	(	struct evbuffer *	buffer,
		evutil_socket_t	fd,
		ssize_t	howmuch
	)

Write some of the contents of an evbuffer to a file descriptor.

The evbuffer will be drained after the bytes have been successfully written.

Parameters:

	buffer	the evbuffer to be written and drained
	fd	the file descriptor to be written to
	howmuch	the largest allowable number of bytes to write, or -1 to write as many bytes as we can.

Returns:

the number of bytes written, or -1 if an error occurred

See also:

evbuffer_read()