add json returns

server.c

@@ -1,18 +1,18 @@
 #include <arpa/inet.h>
 #include <netinet/in.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <strings.h>
 #include <sys/socket.h>
 #include <unistd.h>
-#include <string.h>
-#include <stdio.h>
-/* #include <stdatomic.h>
-#include <time.h>
-#include <pthread.h> */
 
 #define PORT 6008
 #define BACKLOG 16
 #define RECV_BUF 256
 
-int main() {
+int main()
+{
     int server_fd = socket(AF_INET, SOCK_STREAM, 0);
     int opt = 1;
     setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
@@ -31,38 +31,115 @@ int main() {
     const char *hdr = "X-Forwarded-For:";
     const size_t hdrlen = strlen(hdr);
 
-    while(1) {
+    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; }
+        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
+        // detect optional JSON response request on the first line
+        bool wants_json = false;
+        const char *line_end = strstr(buf, "\r\n");
+        size_t line_len = line_end ? (size_t)(line_end - buf) : (size_t)r;
+        const char *space1 = memchr(buf, ' ', line_len);
+        if (space1 && space1 < buf + line_len)
+        {
+            const char *path = space1 + 1;
+            const char *space2 = memchr(path, ' ', line_len - (size_t)(path - buf));
+            if (space2 && space2 > path)
+            {
+                const char *query = memchr(path, '?', (size_t)(space2 - path));
+                if (query && ++query < space2)
+                {
+                    size_t remaining = (size_t)(space2 - query);
+                    const char *token = query;
+                    while (remaining > 0)
+                    {
+                        size_t token_len = 0;
+                        while (token_len < remaining && token[token_len] != '&')
+                            token_len++;
+                        if (token_len == 11 && strncasecmp(token, "format=json", 11) == 0)
+                        {
+                            wants_json = true;
+                            break;
+                        }
+                        if (token_len >= 7 && strncasecmp(token, "format=", 7) == 0)
+                        {
+                            size_t value_len = token_len - 7;
+                            if (value_len == 4 && strncasecmp(token + 7, "json", 4) == 0)
+                            {
+                                wants_json = true;
+                                break;
+                            }
+                        }
+                        if (token_len == remaining)
+                            break;
+                        token += token_len + 1;
+                        remaining -= token_len + 1;
+                    }
+                }
+            }
+        }
+
+        // find header
         char *ip = NULL;
-        for (ssize_t i = 0; i < r - (ssize_t)hdrlen; ++i) {
-            if (strncasecmp(buf + i, hdr, hdrlen) == 0) {
+        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++;
+                while (*ip == ' ' || *ip == '\t')
+                    ip++;
                 break;
             }
         }
-        //find end
+        // find end
         char *end = ip;
-        if (ip) {
-            while (*end && *end != '\r' && *end != '\n') end++;
+        if (ip)
+        {
+            while (*end && *end != '\r' && *end != '\n' && *end != ',')
+                end++;
+            while (end > ip && (end[-1] == ' ' || end[-1] == '\t'))
+                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);
+        // response
+        char head[128];
+        char jsonbuf[RECV_BUF];
+        const char *body = ip ? ip : "";
+        const char *content_type = "text/plain";
+        int body_len = ip ? (int)strlen(ip) : 0;
+
+        if (wants_json)
+        {
+            content_type = "application/json";
+            if (ip && *ip)
+            {
+                body_len = snprintf(jsonbuf, sizeof(jsonbuf), "{\"ip\":\"%s\"}", ip);
+                if (body_len < 0 || body_len >= (int)sizeof(jsonbuf))
+                    body_len = snprintf(jsonbuf, sizeof(jsonbuf), "{\"ip\":\"%s\"}", "");
+            }
+            else
+            {
+                body_len = snprintf(jsonbuf, sizeof(jsonbuf), "{\"ip\":null}");
+            }
+            body = jsonbuf;
+        }
+
+        int head_len = snprintf(head, sizeof(head),
+                                "HTTP/1.1 200 OK\r\nContent-Type: %s\r\nContent-Length: %d\r\n\r\n",
+                                content_type, body_len);
+        if (head_len > 0)
+            send(client, head, (size_t)head_len, 0);
+        if (body_len > 0)
+            send(client, body, (size_t)body_len, 0);
         close(client);
-
     }
 }