Librdkafka要和kakfa集群通讯, 网络操作肯定是少不了的,这就需要封装transport数据传输层;
Librdkafka毕竟是SDK, 作为访问kafka集群的客户端,不需要支持大并发, 在网络IO模型 上选用了 poll;
IO模型确定后, 发送和接收数据必不可少的缓冲区buffer, 我们前面已经介绍过, 请参考Librdkafka的基础数据结构 3 -- Buffer相关 ;
以上介绍的librdkafka中的poll模型和buffer, 完全可以独立出来, 用在其他项目上, 作者封装得很好;
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Librdkafka与kafka broker间是tcp连接, 在接收数据后就涉及到一个拆包组包的问题, 这个就和kafka的协议有关了, kafka的二进制协议:
- 前4个字节是payload长度;
- 后面紧接着是payload具体内容,这部分又分为header和body两部分;
收包时就可以先收4字节,拿到payload长度, 再根据这个长度收够payload内容, 这样一个完整的response就接收到了;
下面我们来结合代码分析一下, 其中有一部分是windows下的实现代码,我们将忽略掉
rd_kafka_transport_s
- 所在文件: src/rdkafka_transport_int.h srd/rdkafka_transport.c(.h)
- 定义:
struct rd_kafka_transport_s {
int rktrans_s; // 与broker通讯的socket
rd_kafka_broker_t *rktrans_rkb; // 与之通讯的broker, 一个broker一个tcp连接,也就对应着一个transport对象
#if WITH_SSL
SSL *rktrans_ssl; //ssl连接句柄
#endif
// sasl权限验证相关
struct {
void *state; /* SASL implementation
* state handle */
int complete; /* Auth was completed early
* from the client's perspective
* (but we might still have to
* wait for server reply). */
/* SASL framing buffers */
struct msghdr msg;
struct iovec iov[2];
char *recv_buf;
int recv_of; /* Received byte count */
int recv_len; /* Expected receive length for
* current frame. */
} rktrans_sasl;
// response接收buffer
rd_kafka_buf_t *rktrans_recv_buf; /* Used with framed_recvmsg */
// poll模型使用
/* Two pollable fds:
* - TCP socket
* - wake-up fd
*/
struct pollfd rktrans_pfd[2];
int rktrans_pfd_cnt;
size_t rktrans_rcvbuf_size; /**< Socket receive buffer size */
size_t rktrans_sndbuf_size; /**< Socket send buffer size */
};
typedef struct rd_kafka_transport_s rd_kafka_transport_t
- 异步连接到broker
rd_kafka_transport_connect:
rd_kafka_transport_t *rd_kafka_transport_connect (rd_kafka_broker_t *rkb,
const rd_sockaddr_inx_t *sinx,
char *errstr,
size_t errstr_size) {
rd_kafka_transport_t *rktrans;
int s = -1;
int on = 1;
int r;
rkb->rkb_addr_last = sinx;
// 建socket, 可以调用socket_cb, 用用户自定义的方式来得到socket, 默认用socket函数
s = rkb->rkb_rk->rk_conf.socket_cb(sinx->in.sin_family,
SOCK_STREAM, IPPROTO_TCP,
rkb->rkb_rk->rk_conf.opaque);
if (s == -1) {
rd_snprintf(errstr, errstr_size, "Failed to create socket: %s",
socket_strerror(socket_errno));
return NULL;
}
#ifdef SO_NOSIGPIPE
/* Disable SIGPIPE signalling for this socket on OSX */
if (setsockopt(s, SOL_SOCKET, SO_NOSIGPIPE, &on, sizeof(on)) == -1)
rd_rkb_dbg(rkb, BROKER, "SOCKET",
"Failed to set SO_NOSIGPIPE: %s",
socket_strerror(socket_errno));
#endif
/* Enable TCP keep-alives, if configured. */
if (rkb->rkb_rk->rk_conf.socket_keepalive) {
#ifdef SO_KEEPALIVE
if (setsockopt(s, SOL_SOCKET, SO_KEEPALIVE,
(void *)&on, sizeof(on)) == SOCKET_ERROR)
rd_rkb_dbg(rkb, BROKER, "SOCKET",
"Failed to set SO_KEEPALIVE: %s",
socket_strerror(socket_errno));
#else
rd_rkb_dbg(rkb, BROKER, "SOCKET",
"System does not support "
"socket.keepalive.enable (SO_KEEPALIVE)");
#endif
}
/* Set the socket to non-blocking */
if ((r = rd_fd_set_nonblocking(s))) {
rd_snprintf(errstr, errstr_size,
"Failed to set socket non-blocking: %s",
socket_strerror(r));
goto err;
}
/* Connect to broker */
// 可以用用户自定义的连接方式connect, 回调没set的话调用connect
if (rkb->rkb_rk->rk_conf.connect_cb) {
r = rkb->rkb_rk->rk_conf.connect_cb(
s, (struct sockaddr *)sinx, RD_SOCKADDR_INX_LEN(sinx),
rkb->rkb_name, rkb->rkb_rk->rk_conf.opaque);
} else {
if (connect(s, (struct sockaddr *)sinx,
RD_SOCKADDR_INX_LEN(sinx)) == SOCKET_ERROR &&
(socket_errno != EINPROGRESS
))
r = socket_errno;
else
r = 0;
}
if (r != 0) {
rd_snprintf(errstr, errstr_size,
"Failed to connect to broker at %s: %s",
rd_sockaddr2str(sinx, RD_SOCKADDR2STR_F_NICE),
socket_strerror(r));
goto err;
}
/* Create transport handle */
// 创建并初始化rd_kafka_transport_s
rktrans = rd_calloc(1, sizeof(*rktrans));
rktrans->rktrans_rkb = rkb;
rktrans->rktrans_s = s;
rktrans->rktrans_pfd[rktrans->rktrans_pfd_cnt++].fd = s;
// 添加poll事件
if (rkb->rkb_wakeup_fd[0] != -1) {
rktrans->rktrans_pfd[rktrans->rktrans_pfd_cnt].events = POLLIN;
rktrans->rktrans_pfd[rktrans->rktrans_pfd_cnt++].fd = rkb->rkb_wakeup_fd[0];
}
/* Poll writability to trigger on connection success/failure. */
rd_kafka_transport_poll_set(rktrans, POLLOUT);
return rktrans;
err:
if (s != -1)
rd_kafka_transport_close0(rkb->rkb_rk, s);
return NULL;
}
- 对 poll方法的封装
rd_kafka_transport_poll:
int rd_kafka_transport_poll(rd_kafka_transport_t *rktrans, int tmout) {
int r;
// 调用poll, 失败直接return
r = poll(rktrans->rktrans_pfd, rktrans->rktrans_pfd_cnt, tmout);
if (r <= 0)
return r;
rd_atomic64_add(&rktrans->rktrans_rkb->rkb_c.wakeups, 1);
// 没什么实际用处
if (rktrans->rktrans_pfd[1].revents & POLLIN) {
/* Read wake-up fd data and throw away, just used for wake-ups*/
char buf[512];
if (rd_read((int)rktrans->rktrans_pfd[1].fd,
buf, sizeof(buf)) == -1) {
/* Ignore warning */
}
}
// 返回poll到的有效事件
return rktrans->rktrans_pfd[0].revents;
}
- transport io 事件循环
rd_kafka_transport_io_serve:
void rd_kafka_transport_io_serve (rd_kafka_transport_t *rktrans,
int timeout_ms) {
rd_kafka_broker_t *rkb = rktrans->rktrans_rkb;
int events;
// 如果没收到response的请求个数没超过最大限制, 并且有需要发送的buf, 就把POLLOUT事件加入
if (rd_kafka_bufq_cnt(&rkb->rkb_waitresps) < rkb->rkb_max_inflight &&
rd_kafka_bufq_cnt(&rkb->rkb_outbufs) > 0)
rd_kafka_transport_poll_set(rkb->rkb_transport, POLLOUT);
// poll啊poll
if ((events = rd_kafka_transport_poll(rktrans, timeout_ms)) <= 0)
return;
// 暂时去掉POLLOUT
rd_kafka_transport_poll_clear(rktrans, POLLOUT);
// 处理poll到的io events
rd_kafka_transport_io_event(rktrans, events);
}
- IO事件处理
rd_kafka_transport_io_event:
broker有一个简单的状态机转换,有如下几个状态:
enum {
RD_KAFKA_BROKER_STATE_INIT,
RD_KAFKA_BROKER_STATE_DOWN,
RD_KAFKA_BROKER_STATE_CONNECT,
RD_KAFKA_BROKER_STATE_AUTH,
/* Any state >= STATE_UP means the Kafka protocol layer
* is operational (to some degree). */
RD_KAFKA_BROKER_STATE_UP,
RD_KAFKA_BROKER_STATE_UPDATE,
RD_KAFKA_BROKER_STATE_APIVERSION_QUERY,
RD_KAFKA_BROKER_STATE_AUTH_HANDSHAKE
} rkb_state;
根据这个broker当前的状态,有不同的操作和状态转换
static void rd_kafka_transport_io_event (rd_kafka_transport_t *rktrans,
int events) {
char errstr[512];
int r;
rd_kafka_broker_t *rkb = rktrans->rktrans_rkb;
switch (rkb->rkb_state)
{
case RD_KAFKA_BROKER_STATE_CONNECT:
#if WITH_SSL
if (rktrans->rktrans_ssl) {
/* Currently setting up SSL connection:
* perform handshake. */
rd_kafka_transport_ssl_handshake(rktrans);
return;
}
#endif
/* Asynchronous connect finished, read status. */
if (!(events & (POLLOUT|POLLERR|POLLHUP)))
return;
if (rd_kafka_transport_get_socket_error(rktrans, &r) == -1) {
rd_kafka_broker_fail(
rkb, LOG_ERR, RD_KAFKA_RESP_ERR__TRANSPORT,
"Connect to %s failed: "
"unable to get status from "
"socket %d: %s",
rd_sockaddr2str(rkb->rkb_addr_last,
RD_SOCKADDR2STR_F_PORT |
RD_SOCKADDR2STR_F_FAMILY),
rktrans->rktrans_s,
rd_strerror(socket_errno));
} else if (r != 0) {
/* Connect failed */
errno = r;
rd_snprintf(errstr, sizeof(errstr),
"Connect to %s failed: %s",
rd_sockaddr2str(rkb->rkb_addr_last,
RD_SOCKADDR2STR_F_PORT |
RD_SOCKADDR2STR_F_FAMILY),
rd_strerror(r));
rd_kafka_transport_connect_done(rktrans, errstr);
} else {
/* Connect succeeded */
rd_kafka_transport_connected(rktrans);
}
break;
case RD_KAFKA_BROKER_STATE_AUTH:
/* SASL handshake */
if (rd_kafka_sasl_io_event(rktrans, events,
errstr, sizeof(errstr)) == -1) {
errno = EINVAL;
rd_kafka_broker_fail(rkb, LOG_ERR,
RD_KAFKA_RESP_ERR__AUTHENTICATION,
"SASL authentication failure: %s",
errstr);
return;
}
break;
case RD_KAFKA_BROKER_STATE_APIVERSION_QUERY:
case RD_KAFKA_BROKER_STATE_AUTH_HANDSHAKE:
case RD_KAFKA_BROKER_STATE_UP:
case RD_KAFKA_BROKER_STATE_UPDATE:
if (events & POLLIN) {
while (rkb->rkb_state >= RD_KAFKA_BROKER_STATE_UP &&
rd_kafka_recv(rkb) > 0)
;
}
if (events & POLLHUP) {
rd_kafka_broker_fail(rkb,
rkb->rkb_rk->rk_conf.
log_connection_close ?
LOG_NOTICE : LOG_DEBUG,
RD_KAFKA_RESP_ERR__TRANSPORT,
"Connection closed");
return;
}
if (events & POLLOUT) {
while (rd_kafka_send(rkb) > 0)
;
}
break;
case RD_KAFKA_BROKER_STATE_INIT:
case RD_KAFKA_BROKER_STATE_DOWN:
rd_kafka_assert(rkb->rkb_rk, !*"bad state");
}
}
最主要的是以下两点:
- 有可读事件:
循环读, 读到不能读为止
if (events & POLLIN) {
while (rkb->rkb_state >= RD_KAFKA_BROKER_STATE_UP &&
rd_kafka_recv(rkb) > 0)
;
}
rd_kafka_recv按kafka的协议来收包, 先收4字节,拿到payload长度, 再根据这个长度收够payload内容, 这样一个完整的response就接收到了
- 有可写事件:
if (events & POLLOUT) {
while (rd_kafka_send(rkb) > 0)
;
}
循环写, 写到不能写为止
- 关闭transport
void rd_kafka_transport_close (rd_kafka_transport_t *rktrans) {
#if WITH_SSL
if (rktrans->rktrans_ssl) {
SSL_shutdown(rktrans->rktrans_ssl);
SSL_free(rktrans->rktrans_ssl);
}
#endif
rd_kafka_sasl_close(rktrans);
if (rktrans->rktrans_recv_buf)
rd_kafka_buf_destroy(rktrans->rktrans_recv_buf);
if (rktrans->rktrans_s != -1)
rd_kafka_transport_close0(rktrans->rktrans_rkb->rkb_rk,
rktrans->rktrans_s);
rd_free(rktrans);
}
- 封装sendmsg方法
ssize_t rd_kafka_transport_socket_sendmsg (rd_kafka_transport_t *rktrans,
rd_slice_t *slice,
char *errstr, size_t errstr_size) {
struct iovec iov[IOV_MAX];
struct msghdr msg = { .msg_iov = iov };
size_t iovlen;
ssize_t r;
// 从slice产生iovec数组, 然后再发送
rd_slice_get_iov(slice, msg.msg_iov, &iovlen, IOV_MAX,
/* FIXME: Measure the effects of this */
rktrans->rktrans_sndbuf_size);
msg.msg_iovlen = (typeof(msg.msg_iovlen))iovlen;
#ifdef sun
/* See recvmsg() comment. Setting it here to be safe. */
socket_errno = EAGAIN;
#endif
r = sendmsg(rktrans->rktrans_s, &msg, MSG_DONTWAIT
#ifdef MSG_NOSIGNAL
| MSG_NOSIGNAL
#endif
);
if (r == -1) {
if (socket_errno == EAGAIN)
return 0;
rd_snprintf(errstr, errstr_size, "%s", rd_strerror(errno));
}
/* Update buffer read position */
rd_slice_read(slice, NULL, (size_t)r);
return r;
}
- 封装 send方法:
rd_kafka_transport_socket_send0 (rd_kafka_transport_t *rktrans,
rd_slice_t *slice,
char *errstr, size_t errstr_size) {
ssize_t sum = 0;
const void *p;
size_t rlen;
// rd_slice_peeker相当于一个iterator接口,每次返回一个slice中有效的segment
while ((rlen = rd_slice_peeker(slice, &p))) {
ssize_t r;
//实际的发送
r = send(rktrans->rktrans_s, p, rlen, 0
);
// 如果非eagain错误的话,是真的有错误发生了,return -1
if (unlikely(r <= 0)) {
if (r == 0 || errno == EAGAIN)
return 0;
rd_snprintf(errstr, errstr_size, "%s",
socket_strerror(socket_errno));
return -1;
}
/* Update buffer read position */
//更新slice的读位置
rd_slice_read(slice, NULL, (size_t)r);
sum += r;
/* FIXME: remove this and try again immediately and let
* the next write() call fail instead? */
if ((size_t)r < rlen)
break;
}
return sum;
}
- 封装 recv方法:
rd_kafka_transport_socket_recv0 (rd_kafka_transport_t *rktrans,
rd_buf_t *rbuf,
char *errstr, size_t errstr_size) {
ssize_t sum = 0;
void *p;
size_t len;
// rbuf可写就一直写
while ((len = rd_buf_get_writable(rbuf, &p))) {
ssize_t r;
r = recv(rktrans->rktrans_s, p,
len,
0);
if (unlikely(r <= 0)) {
if (r == -1 && socket_errno == EAGAIN)
return 0;
else if (r == 0) {
/* Receive 0 after POLLIN event means
* connection closed. */
rd_snprintf(errstr, errstr_size,
"Disconnected");
return -1;
} else if (r == -1) {
rd_snprintf(errstr, errstr_size, "%s",
rd_strerror(errno));
return -1;
}
}
/* Update buffer write position */
// 更新buf的写位置
rd_buf_write(rbuf, NULL, (size_t)r);
sum += r;
/* FIXME: remove this and try again immediately and let
* the next recv() call fail instead? */
if ((size_t)r < len)
break;
}
return sum;
}
