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TCP作為常用的網絡傳輸協議，數據流解析是網絡應用開發人員永遠繞不開的一個問題。 TCP數據傳輸是以無邊界的數據流傳輸形式，所謂無邊界是指數據發送端發送的字節數，在數據接收端接受時並不一定等於發送的字節數，可能會出現粘包情況。

一、TCP粘包情況：

1. 發送端發送了數量比較的數據，接收端讀取數據時候數據分批到達，造成一次發送多次讀取；通常網絡路由的緩存大小有關系，一個數據段大小超過緩存大小，那麽就要拆包發送。 2. 發送端發送了幾次數據，接收端一次性讀取了所有數據，造成多次發送一次讀取；通常是網絡流量優化，把多個小的數據段集滿達到一定的數據量，從而減少網絡鏈路中的傳輸次數。
TCP粘包的解決方案有很多種方法，最簡單的一種就是發送的數據協議定義發送的數據包的結構： 1. 數據頭：數據包的大小，固定長度。 2. 數據內容：數據內容，長度為數據頭定義的長度大小。 實際操作如下： a）發送端：先發送數據包的大小，再發送數據內容。 b）接收端：先解析本次數據包的大小N，在讀取N個字節，這N個字節就是一個完整的數據內容。 具體流程如下：
實現源碼 [cpp] view plain copy

1. /**
2. * read size of len from sock into buf.
3. */
4. bool readPack(int sock, char* buf, size_t len) {
5. if (NULL == buf || len < 1) {
6. return false;
7. }
8. memset(buf, 0, len); // only reset buffer len.
9. ssize_t read_len = 0, readsum = 0;
10. do {
11. read_len = read(sock, buf + readsum, len - readsum);
12. if (-1 == read_len) { // ignore error case
13. return false;
14. }
15. printf("receive data: %s\n", buf + readsum);
16. readsum += read_len;
17. } while (readsum < len && 0 != read_len);
18. return true;
19. }

二、測試用例介紹

本篇提供的demo主要流程如下： 1. 客戶端負責模擬發送數據，服務端負責接受數據，處理粘包問題 a）emulate_subpackage 模擬情況1，一個長數據經過多次才到達目的地， 在客戶端字符串“This is a test case for client send subpackage data. data is not send complete at once.”每次只發送6個字節長度。服務端要把字符串集滿才能處理數據（打印字符串） b）emulate_adheringpackage 模擬情況2，多個數據在一次性到達目的地 在客戶端將字符串“Hello I‘m lucky. Nice too me you”切成三個數據段（都包含數據頭和數據內容），然後一次性發送，服務端讀取數據時對三個數據段逐個處理。

三、源碼實現

server.cpp [cpp] view plain copy

1. #include <cstdio>
2. #include <cstdlib>
3. #include <cstring>
4. #include <errno.h>
5. #include <sys/socket.h>
6. #include <sys/types.h>
7. #include <arpa/inet.h>
8. #include <unistd.h>
10. void newclient(int sock);
11. bool readPack(int sock, char* buf, size_t len);
12. void safe_close(int &sock);
14. int main(int argc, char *argv[]) {
15. int sockfd = -1, newsockfd = -1;
16. socklen_t c = 0;
17. struct sockaddr_in serv_addr, cli_addr;
19. // Create socket
20. sockfd = socket(AF_INET, SOCK_STREAM, 0);
21. if (-1 == sockfd) {
22. printf("new socket failed. errno: %d, error: %s\n", errno, strerror(errno));
23. exit(-1);
24. }
26. // Prepare the sockaddr_in structure
27. serv_addr.sin_family = AF_INET;
28. serv_addr.sin_addr.s_addr = INADDR_ANY;
29. serv_addr.sin_port = htons(7890);
31. // bind
32. if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
33. printf("bind failed. errno: %d, error: %s\n", errno, strerror(errno));
34. exit(-1);
35. }
37. // listen
38. listen(sockfd, 5);
40. printf("listening...\n");
41. // accept new connection.
42. c = sizeof(struct sockaddr_in);
43. int i = 0;
44. while (i++ < 3) {
45. printf("waiting for new socket accept.\n");
46. newsockfd = accept(sockfd, (struct sockaddr*)&cli_addr, (socklen_t*)&c);
47. if (newsockfd < 0) {
48. printf("accept connect failed. errno: %d, error: %s\n", errno, strerror(errno));
49. safe_close(sockfd);
50. exit(-1);
51. }
52. pid_t pid = fork();
53. if (0 == pid) {
54. newclient(newsockfd);
55. safe_close(sockfd);
56. break;
57. } else if (pid > 0) {
58. safe_close(newsockfd);
59. }
60. }
61. safe_close(sockfd);
62. return 0;
63. }
65. void newclient(int sock) {
66. printf("newclient sock fd: %d\n", sock);
67. int datasize = 0;
68. const int HEAD_SIZE = 9;
69. char buf[512] = {0};
70. while (true) {
71. memset(buf, 0, sizeof(buf));
72. if (! readPack(sock, buf, HEAD_SIZE)) {
73. printf("read head buffer failed.\n");
74. safe_close(sock);
75. return;
76. }
78. datasize = atoi(buf);
79. printf("data size: %s, value:%d\n", buf, datasize);
80. memset(buf, 0, sizeof(buf));
81. if (! readPack(sock, buf, datasize)) {
82. printf("read data buffer failed\n");
83. safe_close(sock);
84. return;
85. }
86. printf("data size: %d, text: %s\n", datasize, buf);
87. if (0 == strcmp(buf, "exit")) {
88. break;
89. }
90. }
91. memset(buf, 0, sizeof(buf));
92. snprintf(buf, sizeof(buf), "from server read complete.");
93. write(sock, buf, strlen(buf) + 1);
94. printf("newclient sockfd: %d, finish.\n", sock);
95. safe_close(sock);
96. }
98. void safe_close(int &sock) {
99. if (sock > 0) {
100. close(sock);
101. sock = -1;
102. }
103. }
105. /**
106. * read size of len from sock into buf.
107. */
108. bool readPack(int sock, char* buf, size_t len) {
109. if (NULL == buf || len < 1) {
110. return false;
111. }
112. memset(buf, 0, len); // only reset buffer len.
113. ssize_t read_len = 0, readsum = 0;
114. do {
115. read_len = read(sock, buf + readsum, len - readsum);
116. if (-1 == read_len) { // ignore error case
117. return false;
118. }
119. printf("receive data: %s\n", buf + readsum);
120. readsum += read_len;
121. } while (readsum < len && 0 != read_len);
122. return true;
123. }

client.cpp [cpp] view plain copy

1. #include <cstdio>
2. #include <cstdlib>
3. #include <cstring>
4. #include <time.h>
5. #include <errno.h>
6. #include <sys/socket.h>
7. #include <arpa/inet.h>
8. #include <unistd.h>
10. void safe_close(int &sock);
11. void emulate_subpackage(int sock);
12. void emulate_adheringpackage(int sock);
14. int main(int argc, char *argv[]) {
15. char buf[128] = {0};
16. int sockfd = -1;
17. struct sockaddr_in serv_addr;
19. // Create sock
20. sockfd = socket(AF_INET, SOCK_STREAM, 0);
21. if (-1 == sockfd) {
22. printf("new socket failed. errno: %d, error: %s\n", errno, strerror(errno));
23. exit(-1);
24. }
26. serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
27. serv_addr.sin_family = AF_INET;
28. serv_addr.sin_port = htons(7890);
30. // Connect to remote server
31. if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
32. printf("connection failed. errno: %d, error: %s\n", errno, strerror(errno));
33. exit(-1);
34. }
35. emulate_subpackage(sockfd);
36. emulate_adheringpackage(sockfd);
38. const int HEAD_SIZE = 9;
39. const char temp[] = "exit";
40. memset(buf, 0, sizeof(buf));
41. snprintf(buf, sizeof(buf), "%0.*zu", HEAD_SIZE - 1, sizeof(temp));
42. write(sockfd, buf, HEAD_SIZE);
43. write(sockfd, temp, sizeof(temp));
45. printf("send complete.\n");
46. memset(buf, 0, sizeof(buf));
47. read(sockfd, buf, sizeof(buf));
48. printf("receive data: %s\n", buf);
49. printf("client finish.\n");
51. safe_close(sockfd);
52. return 0;
53. }
55. void safe_close(int &sock) {
56. if (sock > 0) {
57. close(sock);
58. sock = -1;
59. }
60. }
62. /**
63. * emulate socket data write multi part.
64. */
65. void emulate_subpackage(int sock) {
66. printf("emulate_subpackage...\n");
67. char text[] = "This is a test case for client send subpackage data. data is not send complete at once.";
68. const size_t TEXTSIZE = sizeof(text);
69. ssize_t len = 0;
70. size_t sendsize = 0, sendsum = 0;
72. const int HEAD_SIZE = 9;
73. char buf[64] = {0};
74. snprintf(buf, HEAD_SIZE, "%08zu", TEXTSIZE);
75. write(sock, buf, HEAD_SIZE);
76. printf("send data size: %s\n", buf);
78. do {
79. sendsize = 6;
80. if (sendsum + sendsize > TEXTSIZE) {
81. sendsize = TEXTSIZE - sendsum;
82. }
83. len = write(sock, text + sendsum, sendsize);
84. if (-1 == len) {
85. printf("send data failed. errno: %d, error: %s\n", errno, strerror(errno));
86. return;
87. }
88. memset(buf, 0, sizeof(buf));
89. snprintf(buf, len + 1, text + sendsum);
90. printf("send data: %s\n", buf);
91. sendsum += len;
92. sleep(1);
93. } while (sendsum < TEXTSIZE && 0 != len);
94. }
96. /**
97. * emualte socket data write adhering.
98. */
99. void emulate_adheringpackage(int sock) {
100. printf("emulate_adheringpackage...\n");
101. const int HEAD_SIZE = 9;
102. char buf[1024] = {0};
103. char text[128] = {0};
104. char *pstart = buf;
106. // append text
107. memset(text, 0, sizeof(text));
108. snprintf(text, sizeof(text), "Hello ");
109. snprintf(pstart, HEAD_SIZE, "%08zu", strlen(text) + 1);
110. pstart += HEAD_SIZE;
111. snprintf(pstart, strlen(text) + 1, "%s", text);
112. pstart += strlen(text) + 1;
114. // append text
115. memset(text, 0, sizeof(text));
116. snprintf(text, sizeof(text), "I‘m lucky.");
117. snprintf(pstart, HEAD_SIZE, "%08zu", strlen(text) + 1);
118. pstart += HEAD_SIZE;
119. snprintf(pstart, strlen(text) + 1, "%s", text);
120. pstart += strlen(text) + 1;
122. // append text
123. memset(text, 0, sizeof(text));
124. snprintf(text, sizeof(text), "Nice too me you");
125. snprintf(pstart, HEAD_SIZE, "%08zu", strlen(text) + 1);
126. pstart += HEAD_SIZE;
127. snprintf(pstart, strlen(text) + 1, "%s", text);
128. pstart += strlen(text) + 1;
129. write(sock, buf, pstart - buf);
130. }

Makefile [plain] view plain copy

1. CC=g++
2. CFLAGS=-I
4. all: server.o client.o
6. server.o: server.cpp
7. $(CC) -o server.o server.cpp
9. client.o: client.cpp
10. $(CC) -o client.o client.cpp
12. clean:
13. rm *.o

四、測試結果

編譯及運行 $ make g++ -o server.o server.cpp g++ -o client.o client.cpp 客戶端模擬發送數據 $ ./client.o emulate_subpackage... send data size: 00000088 send data: This i send data: s a te send data: st cas send data: e for send data: client send data: send send data: subpac send data: kage d send data: ata. d send data: ata is send data: not s send data: end co send data: mplete send data: at on send data: ce. emulate_adheringpackage... send complete. receive data: from server read complete. client finish.
服務端模擬接受數據 $ ./server.o listening... waiting for new socket accept. waiting for new socket accept. newclient sock fd: 4 receive data: 00000088 data size: 00000088, value:88 receive data: This i receive data: s a te receive data: st cas receive data: e for receive data: client receive data: send receive data: subpac receive data: kage d receive data: ata. d receive data: ata is receive data: not s receive data: end co receive data: mplete receive data: at on receive data: ce. data size: 88, text: This is a test case for client send subpackage data. data is not send complete at once. receive data: 00000007 data size: 00000007, value:7 receive data: Hello data size: 7, text: Hello receive data: 00000011 data size: 00000011, value:11 receive data: I‘m lucky. data size: 11, text: I‘m lucky. receive data: 00000016 data size: 00000016, value:16 receive data: Nice too me you data size: 16, text: Nice too me you receive data: 00000005 data size: 00000005, value:5 receive data: exit data size: 5, text: exit newclient sockfd: 4, finish. http://blog.csdn.net/sweettool/article/details/77018506

TCP網絡通訊如何解決分包粘包問題（有模擬代碼）