first commit

server.c

@@ -0,0 +1,67 @@
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+
+#define PORT 6008
+#define BACKLOG 16
+#define RECV_BUF 1024
+
+int main() {
+    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
+    int opt = 1;
+    setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
+
+    struct sockaddr_in addr = {0};
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = INADDR_ANY;
+    addr.sin_port = htons(PORT);
+
+    bind(server_fd, (struct sockaddr *)&addr, sizeof(addr));
+    listen(server_fd, BACKLOG);
+
+    printf("listening port %d\nbacklog %d\nrecv buffer %d\n", PORT, BACKLOG, RECV_BUF);
+
+    char buf[RECV_BUF];
+    const char *hdr = "X-Forwarded-For:";
+    const size_t hdrlen = strlen(hdr);
+
+    while(1) {
+        int client = accept(server_fd, NULL, NULL);
+        if (client < 0) continue;
+        ssize_t r = recv(client, buf, sizeof(buf) -1, 0);
+        if (r <= 0) { close(client); continue; }
+        buf[r] = 0;
+
+        //find header
+        char *ip = NULL;
+        for (ssize_t i = 0; i < r - (ssize_t)hdrlen; ++i) {
+            if (strncasecmp(buf + i, hdr, hdrlen) == 0) {
+                ip = buf + i + hdrlen;
+                while (*ip == ' ' || *ip == '\t') ip++;
+                break;
+            }
+        }
+        //find end
+        char *end = ip;
+        if (ip) {
+            while (*end && *end != '\r' && *end != '\n') end++;
+            *end = 0;
+        }
+        
+        //response
+        const char *head = "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: ";
+        char lenbuf[32];
+        int iplen = ip ? strlen(ip) : 0;
+        int len = snprintf(lenbuf, sizeof(lenbuf), "%d\r\n\r\n", iplen);
+
+        send(client, head, strlen(head), 0);
+        send(client, lenbuf, len, 0);
+        if (iplen > 0) send(client, ip, iplen, 0);
+
+        close(client);
+
+    }
+}