1const char *sip_invite =
2    "INVITE sip:alice@example.com SIP/2.0\r\n"
3    "Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bK776asdhds\r\n"
4    "Max-Forwards: 70\r\n"
5    "To: Alice <sip:alice@example.com>\r\n"
6    "From: Bob <sip:bob@example.org>;tag=456248\r\n"
7    "Call-ID: 843817637684230@998sdasdh09\r\n"
8    "CSeq: 1826 INVITE\r\n"
9    "Contact: <sip:bob@pc33.example.org>\r\n"
10    "Content-Length: 0\r\n\r\n";
11

1sip_project/
2    src/
3    include/
4    tests/
5    Makefile
6

1CC=gcc
2CFLAGS=-Iinclude -Wall -g
3SRCS=$(wildcard src/*.c)
4OBJS=$(SRCS:.c=.o)
5TARGET=sip_app
6
7all: $(TARGET)
8
9$(TARGET): $(OBJS)
10    $(CC) $(CFLAGS) -o $@ $^
11
12clean:
13    rm -f $(OBJS) $(TARGET)
14

1void parse_sip_headers(const char *msg) {
2    const char *line = msg;
3    while ((line = strstr(line, "\r\n")) != NULL) {
4        line += 2;
5        if (*line == '\0') break;
6        // Extract header name and value
7        char header_name[32], header_value[256];
8        if (sscanf(line, "%31[^:]: %255[^"]", header_name, header_value) == 2) {
9            printf("Header: %s => %s\n", header_name, header_value);
10        }
11    }
12}
13

1void build_sip_invite(char *buffer, size_t buflen) {
2    snprintf(buffer, buflen,
3        "INVITE sip:alice@example.com SIP/2.0\r\n"
4        "Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK3423\r\n"
5        "Max-Forwards: 70\r\n"
6        "To: <sip:alice@example.com>\r\n"
7        "From: <sip:bob@example.org>;tag=234234\r\n"
8        "Call-ID: 12345678@example.org\r\n"
9        "CSeq: 1 INVITE\r\n"
10        "Contact: <sip:bob@client.example.org>\r\n"
11        "Content-Length: 0\r\n\r\n");
12}
13

1void parse_sip_uri(const char *uri) {
2    char user[64], host[128];
3    if (sscanf(uri, "sip:%63[^@]@%127[^;\r\n]", user, host) == 2) {
4        printf("User: %s\nHost: %s\n", user, host);
5    }
6}
7

1void handle_invite(const char *msg) {
2    printf("Received INVITE: %s\n", msg);
3    // Parse headers and respond with 100 Trying
4}
5
6void handle_register(const char *msg) {
7    printf("Received REGISTER: %s\n", msg);
8    // Parse headers, authenticate, and respond
9}
10

1void process_sip_response(const char *msg) {
2    int code;
3    if (sscanf(msg, "SIP/2.0 %d", &code) == 1) {
4        printf("Received SIP Response: %d\n", code);
5        // Update transaction state
6    }
7}
8

1int create_udp_socket(int port) {
2    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
3    struct sockaddr_in addr;
4    memset(&addr, 0, sizeof(addr));
5    addr.sin_family = AF_INET;
6    addr.sin_addr.s_addr = htonl(INADDR_ANY);
7    addr.sin_port = htons(port);
8    bind(sockfd, (struct sockaddr *)&addr, sizeof(addr));
9    return sockfd;
10}
11

1ssize_t send_sip_message(int sockfd, const char *msg, const char *dest_ip, int dest_port) {
2    struct sockaddr_in dest_addr;
3    memset(&dest_addr, 0, sizeof(dest_addr));
4    dest_addr.sin_family = AF_INET;
5    dest_addr.sin_port = htons(dest_port);
6    inet_pton(AF_INET, dest_ip, &dest_addr.sin_addr);
7    return sendto(sockfd, msg, strlen(msg), 0,
8                  (struct sockaddr *)&dest_addr, sizeof(dest_addr));
9}
10
11ssize_t recv_sip_message(int sockfd, char *buffer, size_t buflen) {
12    return recvfrom(sockfd, buffer, buflen, 0, NULL, NULL);
13}
14

1int check_auth_header(const char *msg) {
2    return strstr(msg, "Authorization: Digest") != NULL;
3}
4

1void test_parse_sip_headers() {
2    const char *msg = "Via: SIP/2.0/UDP host;branch=xyz\r\n";
3    parse_sip_headers(msg);
4    // Assert header parsing result
5}
6