GetIp4 improvements for network interface IP addresses.

src/utils/io.cpp

@@ -14,7 +14,12 @@
 #include <queue>
 #include <stack>
 
+#include <arpa/inet.h>
 #include <dirent.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -183,4 +188,34 @@ void AppendPath(std::string &source, const std::string &target)
     source += target;
 }
 
+std::string GetIp4OfInterface(const std::string &ifName)
+{
+    std::string res;
+
+    struct ifreq ifr = {};
+
+    int fd = socket(AF_INET, SOCK_DGRAM, 0);
+    if (fd <= 0)
+        return "";
+
+    ifr.ifr_addr.sa_family = AF_INET;
+    strncpy(ifr.ifr_name, ifName.c_str(), IFNAMSIZ - 1);
+
+    if (ioctl(fd, SIOCGIFADDR, &ifr))
+    {
+        close(fd);
+        return "";
+    }
+
+    close(fd);
+
+    auto address = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr;
+
+    char str[INET_ADDRSTRLEN] = {0};
+    if (inet_ntop(AF_INET, &address, str, INET_ADDRSTRLEN) == nullptr)
+        return "";
+
+    return std::string{str};
+}
+
 } // namespace io

src/utils/io.hpp

@@ -40,4 +40,6 @@ std::string GetStem(const std::string &path);
 
 void AppendPath(std::string &source, const std::string &target);
 
+std::string GetIp4OfInterface(const std::string &ifName);
+
 } // namespace io

src/utils/yaml_utils.cpp

@@ -8,6 +8,7 @@
 
 #include "yaml_utils.hpp"
 #include "common.hpp"
+#include "io.hpp"
 
 #include <cctype>
 #include <stdexcept>
@@ -143,11 +144,19 @@ int64_t GetInt64(const YAML::Node &node, const std::string &name, std::optional<
 
 std::string GetIp4(const YAML::Node &node, const std::string &name)
 {
-    std::string ip = GetString(node, name);
-    int version = utils::GetIpVersion(ip);
-    if (version != 4)
-        FieldError(name, "must be a valid IPv4 address");
-    return ip;
+    std::string s = GetString(node, name);
+
+    int version = utils::GetIpVersion(s);
+    if (version == 6)
+        FieldError(name, "must be a valid IPv4 address or a valid network interface with a IPv4 address");
+    if (version == 4)
+        return s;
+
+    auto ipFromIf = io::GetIp4OfInterface(s);
+    if (ipFromIf.empty())
+        FieldError(name, "must be a valid IPv4 address or a valid network interface with a IPv4 address");
+
+    return ipFromIf;
 }
 
 void AssertHasBool(const YAML::Node &node, const std::string &name)