Feat: fetch public ip against from multiple services

src/ipcheck.c

@@ -0,0 +1,89 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <curl/curl.h>
+#include "ipcheck.h"
+#include "log.h"
+
+static const char *SERVICES[] = {
+    "https://ipv4.icanhazip.com",
+    "https://api4.ipify.org",
+    "https://ipv4.wtfismyip.com/text",
+    "https://v4.ident.me",
+    "https://ipv4.am.i.mullvad.net/ip",
+    "https://4.ident.me",
+    "https://4.tnedi.me",
+};
+
+#define SERVICE_COUNT (int)(sizeof(SERVICES) / sizeof(SERVICES[0]))
+
+typedef struct {
+    char buf[IPCHECK_MAX_IP_LEN];
+    size_t len;
+} IPBuf;
+
+static size_t write_cb(void *data, size_t size, size_t nmemb, void *userp) {
+    IPBuf *out = (IPBuf *)userp;
+    size_t total = size * nmemb;
+    if (out->len + total >= IPCHECK_MAX_IP_LEN) return 0;
+    memcpy(out->buf + out->len, data, total);
+    out->len += total;
+    return total;
+}
+
+int ipcheck_get_public_ip(char *out_ip) {
+    char results[SERVICE_COUNT][IPCHECK_MAX_IP_LEN];
+    int valid = 0;
+
+    CURL *curl = curl_easy_init();
+    if (!curl) return -1;
+
+    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
+    curl_easy_setopt(curl, CURLOPT_CAINFO, "/etc/ssl/certs/ca-certificates.crt");
+    curl_easy_setopt(curl, CURLOPT_CAPATH, "/etc/ssl/certs");
+    curl_easy_setopt(curl, CURLOPT_TIMEOUT, IPCHECK_TIMEOUT_SECS);
+    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
+
+    for (int i = 0; i < SERVICE_COUNT; i++) {
+        IPBuf buf = { .buf = {0}, .len = 0 };
+
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buf);
+        curl_easy_setopt(curl, CURLOPT_URL, SERVICES[i]);
+
+        CURLcode res = curl_easy_perform(curl);
+
+        if (res != CURLE_OK) continue;
+
+        long http_code = 0;
+        curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
+        if (http_code != 200) continue;
+
+        buf.buf[buf.len] = '\0';
+        if (sscanf(buf.buf, IPCHECK_IP_SCAN_FMT, results[valid]) != 1) continue;
+        valid++;
+    }
+
+    curl_easy_cleanup(curl);
+
+    if (valid < IPCHECK_MIN_RESPONDERS) {
+        log_warn("ipcheck: only %d/%d services responded, need at least %d",
+                valid, SERVICE_COUNT, IPCHECK_MIN_RESPONDERS);
+        return -1;
+    }
+
+    for (int i = 0; i < valid; i++) {
+        int count = 0;
+        for (int j = 0; j < valid; j++) {
+            if (strcmp(results[i], results[j]) == 0) count++;
+        }
+        if (count * 2 > valid) {
+            strncpy(out_ip, results[i], IPCHECK_MAX_IP_LEN - 1);
+            out_ip[IPCHECK_MAX_IP_LEN - 1] = '\0';
+            return 0;
+        }
+    }
+
+    log_warn("ipcheck: no strict majority among %d/%d responders",
+            valid, SERVICE_COUNT);
+    return -2;
+}

src/ipcheck.h

@@ -0,0 +1,20 @@
+#ifndef IPCHECK_H
+#define IPCHECK_H
+
+#define IPCHECK_MIN_RESPONDERS 3
+#define IPCHECK_TIMEOUT_SECS   10L
+#define IPCHECK_MAX_IP_LEN     46
+#define IPCHECK_IP_SCAN_FMT    "%45s"
+
+/*
+ * Tries to get the public IP by seeing if a strict majority
+ * of services agree. At least a minimum amount of services
+ * need to respond.
+ *
+ * Returns 0 on success.
+ * Returns -1 if fewer than IPCHECK_MIN_RESPONDERS answered.
+ * Returns -2 if no strict majority was reached (tie or split).
+ */
+int ipcheck_get_public_ip(char *out_ip);
+
+#endif /* IPCHECK_H */