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TCP_DEFER_ACCEPT test program for client
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| #include <stdio.h> //printf(), fprintf(), perror() | |
| #include <sys/socket.h> //socket(), connect(), recv() | |
| #include <arpa/inet.h> // struct sockaddr_in, struct sockaddr, inet_ntoa(), inet_aton() | |
| #include <stdlib.h> //atoi(), exit(), EXIT_FAILURE, EXIT_SUCCESS | |
| #include <string.h> //memset() | |
| #include <unistd.h> //close(), sleep() | |
| #include <linux/tcp.h> //TCP_DEFER_ACCEPT | |
| #define MSGSIZE 32 | |
| #define MAX_MSGSIZE 1024 | |
| #define BUFSIZE (MSGSIZE + 1) | |
| int main(int argc, char *argv[]){ | |
| int clientSock; | |
| struct sockaddr_in servSockAddr; | |
| char sendBuffer[BUFSIZE]; | |
| char recvBuffer[BUFSIZE]; | |
| int byteRcvd; | |
| int defer = 1; | |
| if((clientSock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0){ | |
| perror("socket() failed"); | |
| exit(EXIT_FAILURE); | |
| } | |
| memset(&servSockAddr, 0, sizeof(servSockAddr)); | |
| servSockAddr.sin_family = AF_INET; | |
| servSockAddr.sin_addr.s_addr = inet_addr("127.0.0.1"); | |
| /* | |
| * host = gethostbyname("DNS"); | |
| * if(host != NULL){ | |
| * servSockAddr.sin_addr.s_addr = *(unsigned int *)host->h_addr_list[0]; | |
| * } | |
| */ | |
| servSockAddr.sin_port = htons(8080); | |
| setsockopt(clientSock, IPPROTO_TCP, TCP_DEFER_ACCEPT, &defer, sizeof(defer) ); | |
| if(connect(clientSock, (struct sockaddr*) &servSockAddr, sizeof(servSockAddr)) < 0){ | |
| perror("connect() failed."); | |
| exit(EXIT_FAILURE); | |
| } | |
| printf("connect to %s\n", inet_ntoa(servSockAddr.sin_addr)); | |
| sleep(1); | |
| sprintf(sendBuffer, "%s", "GET / HTTP/1.1\r\nHost: localhost"); | |
| if(send(clientSock, sendBuffer, MSGSIZE, 0) <= 0){ | |
| printf("%s\n",sendBuffer); | |
| } | |
| if(recv(clientSock, recvBuffer, MSGSIZE, 0) < 0){ | |
| printf("recv() failed."); | |
| exit(EXIT_FAILURE); | |
| } | |
| printf("received: %s\n",recvBuffer); | |
| return 0; | |
| } |
If I remove sleep(1) right after connect(), we can find that the first data packet is sent with the final ACK. (piggybacking)
$ grep sleep client.c
#include <unistd.h> //close(), sleep()
//sleep(1);
$ gcc client.c -o client
$ ./client
connect to 127.0.0.1
received: HTTP/1.1 200 OK
$ sudo tcpdump -i lo tcp port 8080
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
17:07:14.709483 IP localhost.47208 > localhost.webcache: Flags [S], seq 2354986443, win 43690, options [mss 65495,sackOK,TS val 408030044 ecr 0,nop,wscale 7], length 0
17:07:14.709493 IP localhost.webcache > localhost.47208: Flags [S.], seq 3089570465, ack 2354986444, win 43690, options [mss 65495,sackOK,TS val 408030044 ecr 408030044,nop,wscale 7], length 0
17:07:14.709609 IP localhost.47208 > localhost.webcache: Flags [P.], seq 1:33, ack 1, win 342, options [nop,nop,TS val 408030044 ecr 408030044], length 32: HTTP: GET / HTTP/1.1
17:07:14.709622 IP localhost.webcache > localhost.47208: Flags [.], ack 33, win 342, options [nop,nop,TS val 408030044 ecr 408030044], length 0
17:07:14.712511 IP localhost.webcache > localhost.47208: Flags [P.], seq 1:16, ack 33, win 342, options [nop,nop,TS val 408030047 ecr 408030044], length 15: HTTP: HTTP/1.1 200 OK[!http]
17:07:14.712650 IP localhost.47208 > localhost.webcache: Flags [F.], seq 33, ack 16, win 342, options [nop,nop,TS val 408030047 ecr 408030047], length 0
17:07:14.712688 IP localhost.webcache > localhost.47208: Flags [F.], seq 16, ack 34, win 342, options [nop,nop,TS val 408030047 ecr 408030047], length 0
17:07:14.712699 IP localhost.47208 > localhost.webcache: Flags [.], ack 17, win 342, options [nop,nop,TS val 408030047 ecr 408030047], length 0
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TCP_DEFER_ACCEPT on connecting at client side delays final ACK until the first data packet is sent.
However, it only waits up to 200 ms.