C: Linux Socket Programming, TCP, a simple HTTP client

C: Linux Socket Programming, TCP, a simple HTTP client - 安東尼隨手記 - Yahoo!奇摩部落格

 

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C: Linux Socket Programming, TCP, a simple HTTP client

分類： Linux程式設計 2009/04/16 10:46

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1. #include <stdio.h>
2. #include <sys/socket.h>
3. #include <arpa/inet.h>
4. #include <stdlib.h>
5. #include <netdb.h>
6. #include <string.h>
7. int create_tcp_socket ( );
8. char *get_ip ( char *host );
9. char *build_get_query ( char *host, char *page );
10. void usage ( );
12. #define HOST "coding.debuntu.org"
13. #define PAGE "/"
14. #define PORT 80
15. #define USERAGENT "HTMLGET 1.0"
17. int main ( int argc, char **argv )
18. {
19. struct sockaddr_in *remote;
20. int sock;
21. int tmpres;
22. char *ip;
23. char *get;
24. char buf [BUFSIZ +1 ];
25. char *host;
26. char *page;
28. if (argc == 1 ) {
29. usage ( );
30. exit ( 2 );
31. }  
32. host = argv [ 1 ];
33. if (argc > 2 ) {
34. page = argv [ 2 ];
35. } else {
36. page = PAGE;
37. }
38. sock = create_tcp_socket ( );
39. ip = get_ip (host );
40. fprintf (stderr, "IP is %s\n", ip );
41. remote = ( struct sockaddr_in * )malloc ( sizeof ( struct sockaddr_in * ) );
42. remote ->sin_family = AF_INET;
43. tmpres = inet_pton (AF_INET, ip, ( void * ) ( & (remote ->sin_addr. s_addr ) ) );
44. if ( tmpres < 0 )  
45. {
46. perror ( "Can't set remote->sin_addr.s_addr" );
47. exit ( 1 );
48. } else if (tmpres == 0 )
49. {
50. fprintf (stderr, "%s is not a valid IP address\n", ip );
51. exit ( 1 );
52. }
53. remote ->sin_port = htons (PORT );
55. if (connect (sock, ( struct sockaddr * )remote, sizeof ( struct sockaddr ) ) < 0 ) {
56. perror ( "Could not connect" );
57. exit ( 1 );
58. }
59. get = build_get_query (host, page );
60. fprintf (stderr, "Query is:\n<<START>>\n%s<<END>>\n", get );
62. //Send the query to the server
63. int sent = 0;
64. while (sent < strlen (get ) )
65. {
66. tmpres = send (sock, get +sent, strlen (get ) -sent, 0 );
67. if (tmpres == -1 ) {
68. perror ( "Can't send query" );
69. exit ( 1 );
70. }
71. sent += tmpres;
72. }
73. //now it is time to receive the page
74. memset (buf, 0, sizeof (buf ) );
75. int htmlstart = 0;
76. char * htmlcontent;
77. while ( (tmpres = recv (sock, buf, BUFSIZ, 0 ) ) > 0 ) {
78. if (htmlstart == 0 )
79. {
80. /* Under certain conditions this will not work.
81.       * If the \r\n\r\n part is splitted into two messages
82.       * it will fail to detect the beginning of HTML content
83.       */
84. htmlcontent = strstr (buf, "\r\n\r\n" );
85. if (htmlcontent != NULL ) {
86. htmlstart = 1;
87. htmlcontent += 4;
88. }
89. } else {
90. htmlcontent = buf;
91. }
92. if (htmlstart ) {
93. fprintf (stdout, htmlcontent );
94. }
96. memset (buf, 0, tmpres );
97. }
98. if (tmpres < 0 )
99. {
100. perror ( "Error receiving data" );
101. }
102. free (get );
103. free (remote );
104. free (ip );
105. close (sock );
106. return 0;
107. }
109. void usage ( )
110. {
111. fprintf (stderr, "USAGE: htmlget host [page]\n\
112. \thost: the website hostname. ex: coding.debuntu.org\n\
113. \tpage: the page to retrieve. ex: index.html, default: /\n" );
114. }
117. int create_tcp_socket ( )
118. {
119. int sock;
120. if ( (sock = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP ) ) < 0 ) {
121. perror ( "Can't create TCP socket" );
122. exit ( 1 );
123. }
124. return sock;
125. }
128. char *get_ip ( char *host )
129. {
130. struct hostent *hent;
131. int iplen = 15; //XXX.XXX.XXX.XXX
132. char *ip = ( char * )malloc (iplen +1 );
133. memset (ip, 0, iplen +1 );
134. if ( (hent = gethostbyname (host ) ) == NULL )
135. {
136. herror ( "Can't get IP" );
137. exit ( 1 );
138. }
139. if (inet_ntop (AF_INET, ( void * )hent ->h_addr_list [ 0 ], ip, iplen ) == NULL )
140. {
141. perror ( "Can't resolve host" );
142. exit ( 1 );
143. }
144. return ip;
145. }
147. char *build_get_query ( char *host, char *page )
148. {
149. char *query;
150. char *getpage = page;
151. char *tpl = "GET /%s HTTP/1.0\r\nHost: %s\r\nUser-Agent: %s\r\n\r\n";
152. if (getpage [ 0 ] == '/' ) {
153. getpage = getpage + 1;
154. fprintf (stderr, "Removing leading \"/\", converting %s to %s\n", page, getpage );
155. }
156. // -5 is to consider the %s %s %s in tpl and the ending \0
157. query = ( char * )malloc (strlen (host ) +strlen (getpage ) +strlen (USERAGENT ) +strlen (tpl ) -5 );
158. sprintf (query, tpl, getpage, host, USERAGENT );
159. return query;
160. }
161. 
     

To compile it, run:

$ gcc -o htmlget htmlget.c
$ ./htmlget 
USAGE: htmlget host [page]host: the website hostname. ex: coding.debuntu.orgpage: the page to retrieve. ex: index.html, default: /

Informative messages and errors are printed to stderr. The content of the page is printed to stdout. Thus, to save the HTML content of a page to a file, you will need to run:

$ ./htmlget coding.debuntu.org category > /tmp/page.html

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