blob: 22d2cc9a8cd2ee03bcb2b163bf4f94f11f77b295 [file] [log] [blame]
// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <stddef.h>
#include <algorithm>
#include <vector>
#include "base/basictypes.h"
#include "base/logging.h"
#include "net/base/iovec.h"
#include "net/base/net_export.h"
namespace net {
// Calculate the total number of bytes in an array of iovec structures.
inline size_t TotalIovecLength(const struct iovec* iov, size_t iovcnt) {
size_t length = 0;
if (iov != NULL) {
for (size_t i = 0; i < iovcnt; ++i) {
length += iov[i].iov_len;
return length;
// IOVector is a helper class that makes it easier to work with POSIX vector I/O
// struct. It is a thin wrapper by design and thus has no virtual functions and
// all inlined methods. This class makes no assumptions about the ordering of
// the pointer values of the blocks appended, it simply counts bytes when asked
// to consume bytes.
// IOVector is a bookkeeping object that collects a description of buffers to
// be read or written together and in order. It does not take ownership of the
// blocks appended.
// Because it is used for scatter-gather operations, the order in which the
// buffer blocks are added to the IOVector is important to the client. The
// intended usage pattern is:
// iovector.Append(p0, len0);
// ...
// iovector.Append(pn, lenn);
// int bytes_written = writev(fd, iovector.iovec(), iovector.Size());
// if (bytes_written > 0)
// iovector.Consume(bytes_written);
// The sequence is the same for readv, except that Consume() in this case is
// used to change the IOVector to only keep track of description of blocks of
// memory not yet written to.
// IOVector does not have any method to change the iovec entries that it
// accumulates. This is due to the block merging nature of Append(): we'd like
// to avoid accidentally change an entry that is assembled by two or more
// Append()'s by simply an index access.
// Provide a default constructor so it'll never be inhibited by adding other
// constructors.
// Provides a way to convert system call-like iovec representation to
// IOVector.
void AppendIovec(const struct iovec* iov, size_t iovcnt) {
for (size_t i = 0; i < iovcnt; ++i)
Append(static_cast<char*>(iov[i].iov_base), iov[i].iov_len);
// Appends at most max_bytes from iovec to the IOVector.
size_t AppendIovecAtMostBytes(const struct iovec* iov,
size_t iovcnt,
size_t max_bytes) {
size_t bytes_appended = 0;
for (size_t i = 0; i < iovcnt && max_bytes > 0; ++i) {
const size_t length = std::min(max_bytes, iov[i].iov_len);
Append(static_cast<char*>(iov[i].iov_base), length);
max_bytes -= length;
bytes_appended += length;
return bytes_appended;
// Append another block to the IOVector. Since IOVector can be used for read
// and write, it always takes char*. Clients that writes will need to cast
// away the constant of the pointer before appending a block.
void Append(char* buffer, size_t length) {
if (buffer != NULL && length > 0) {
if (iovec_.size() > 0) {
struct iovec& last = iovec_.back();
// If the new block is contiguous with the last block, just extend.
if (static_cast<char*>(last.iov_base) + last.iov_len == buffer) {
last.iov_len += length;
struct iovec tmp = {buffer, length};
// Same as Append, but doesn't do the tail merge optimization.
// Intended for testing.
void AppendNoCoalesce(char* buffer, size_t length) {
if (buffer != NULL && length > 0) {
struct iovec tmp = {buffer, length};
// Remove a number of bytes from the beginning of the IOVector. Since vector
// I/O operations always occur at the beginning of the block list, a method
// to remove bytes at the end is not provided.
// It returns the number of bytes actually consumed (it'll only be smaller
// than the requested number if the IOVector contains less data).
size_t Consume(size_t length) {
if (length == 0) return 0;
size_t bytes_to_consume = length;
std::vector<struct iovec>::iterator iter = iovec_.begin();
std::vector<struct iovec>::iterator end = iovec_.end();
for (; iter < end && bytes_to_consume >= iter->iov_len; ++iter) {
bytes_to_consume -= iter->iov_len;
iovec_.erase(iovec_.begin(), iter);
if (iovec_.size() > 0 && bytes_to_consume != 0) {
iovec_[0].iov_base =
static_cast<char*>(iovec_[0].iov_base) + bytes_to_consume;
iovec_[0].iov_len -= bytes_to_consume;
return length;
if (iovec_.size() == 0 && bytes_to_consume > 0) {
LOG(DFATAL) << "Attempting to consume " << bytes_to_consume
<< " non-existent bytes.";
// At this point bytes_to_consume is the number of wanted bytes left over
// after walking through all the iovec entries.
return length - bytes_to_consume;
// TODO(joechan): If capacity is large, swap out for a blank one.
// Clears the IOVector object to contain no blocks.
void Clear() { iovec_.clear(); }
// Swap the guts of two IOVector.
void Swap(IOVector* other) { iovec_.swap(other->iovec_); }
// Returns the number of valid blocks in the IOVector (not the number of
// bytes).
size_t Size() const { return iovec_.size(); }
// Returns the total storage used by the IOVector in number of blocks (not
// the number of bytes).
size_t Capacity() const { return iovec_.capacity(); }
// Returns true if there are no blocks in the IOVector.
bool Empty() const { return iovec_.empty(); }
// Returns the pointer to the beginning of the iovec to be used for vector
// I/O operations. If the IOVector has no blocks appened, this function
// returns NULL.
struct iovec* iovec() { return !Empty() ? &iovec_[0] : NULL; }
// Const version.
const struct iovec* iovec() const { return !Empty() ? &iovec_[0] : NULL; }
// Returns a pointer to one past the last byte of the last block. If the
// IOVector is empty, NULL is returned.
const char* LastBlockEnd() const {
return iovec_.size() > 0 ?
static_cast<char *>(iovec_.back().iov_base) + iovec_.back().iov_len :
// Returns the total number of bytes in the IOVector.
size_t TotalBufferSize() const { return TotalIovecLength(iovec(), Size()); }
void Resize(size_t count) {
std::vector<struct iovec> iovec_;
// IOVector has value-semantics; copy and assignment are allowed.
// This class does not explicitly define copy/move constructors or the
// assignment operator to preserve compiler-generated copy/move constructors
// and assignment operators. Note that since IOVector does not own the
// actual buffers that the struct iovecs point to, copies and assignments
// result in a shallow copy of the buffers; resulting IOVectors will point
// to the same copy of the underlying data.
} // namespace net