365 Days of Code - Day 029

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170

#define _POSIX_C_SOURCE 200112L

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

#define PORT_HTTP "80"
#define RECV_BUF 4096

static int connect_http(const char *host) {
        struct addrinfo hints;
        struct addrinfo *res = NULL, *p = NULL;

        memset (&hints, 0, sizeof(hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_STREAM;

        int rc = getaddrinfo(host, PORT_HTTP, &hints, &res);
        if (rc != 0) {
                fprintf(stderr, "getaddrinfo(%s): %s\n", host, gai_strerror(rc));
                return -1;
        }

        int sockfd = -1;

        for (p = res; p != NULL; p = p->ai_next) {
                sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
                if (sockfd < 0) {
                        continue;
                }
                if (connect(sockfd, p->ai_addr, p->ai_addrlen) == 0) {
                        break;
                }
                close(sockfd);
                sockfd = -1;
        }

        freeaddrinfo(res);

        if (sockfd < 0) {
                fprintf(stderr, "Failed to connect to %s:%s (%s)\n", host, PORT_HTTP, strerror(errno));
                return -1;
        }

        return sockfd;
}

static int send_http_get(int sockfd, const char *host) {
        char req[1024];
        int n = snprintf(req, sizeof(req),
                        "GET / HTTP/1.1\r\n"
                        "Host: %s\r\n"
                        "User-Agent: c-probe/0.1\r\n"
                        "Accept: */*\r\n"
                        "Connection: close\r\n"
                        "\r\n",
                        host);

        if (n<0 || (size_t)n >= sizeof(req)) {
                fprintf(stderr, "Request too large\n");
                return -1;
        }

        size_t total = 0;
        while (total < (size_t)n) {
                ssize_t sent = send(sockfd, req + total, (size_t)n - total, 0);
                if (sent < 0) {
                        fprintf(stderr, "send(): %s\n", strerror(errno));
                        return -1;
                }
                total += (size_t)sent;
        }
        return 0;
}

static int read_status_line(int sockfd, char *out_line, size_t out_sz) {
        char buf[RECV_BUF];
        size_t used = 0;

        for (;;) {
                ssize_t r = recv(sockfd, buf, sizeof(buf), 0);
                if (r < 0) {
                        fprintf(stderr, "recv(): %s\n", strerror(errno));
                        return -1;
                }
                if (r == 0) {
                        fprintf(stderr, "Connection closed before receiving a status line\n");
                        return -1;
                }

                size_t to_copy = (size_t)r;
                if (to_copy > out_sz - 1 - used) {
                        to_copy = out_sz - 1 - used;
                }
                memcpy(out_line + used, buf, to_copy);
                used += to_copy;
                out_line[used] = '\0';

                char *eol = strstr(out_line, "\r\n");
                if (eol) {
                        *eol = '\0';
                        return 0;
                }

                if (used >= out_sz - 1) {
                        fprintf(stderr, "Status line too long (buffer limit)\n");
                        return -1;
                }
        }
}

static int print_code_reason(const char *status_line) {
        char proto[32] = {0};
        int code = 0;
        char reason[256] = {0};

        int matched = sscanf(status_line, "%31s %d %255[^\n]", proto, &code, reason);
        if (matched < 2) {
                fprintf(stderr, "Unexpected status line: %s\n", status_line);
                return -1;
        }
        }

        if (matched == 2) {
                printf("%d\n", code);
        }
        else {
                printf("%d %s\n", code, reason);
        }
        return 0;
}

int main(int argc, char **argv) {
        if (argc != 2) {
                fprintf(stderr, "Usage: %s <host>\nExample: %s www.example.com\n", argv[0], argv[0]);
                return 2;
        }

        const char *host = argv[1];

        int sockfd = connect_http(host);
        if (sockfd < 0) return 1;

        if (send_http_get(sockfd, host) != 0) {
                close(sockfd);
                return 1;
        }

        char status_line[1024];
        if (read_status_line(sockfd, status_line, sizeof(status_line)) != 0) {
                close(sockfd);
                return 1;
        }

        printf("Status line: %s\n", status_line);

        if (print_code_reason(status_line) != 0) {
                close(sockfd);
                return 1;
        }

        close(sockfd);
        return 0;
}

1

❯ gcc -std=c11 -Wall -Wextra -O2 -o http-status-probe http-status-probe.c

1
2
3

❯ ./http-status-probe www.jimdiroffii.com
Status line: HTTP/1.1 308 Permanent Redirect
308 Permanent Redirect