feat: find interface index from ip address

libtransmission/net.cc

@@ -16,8 +16,12 @@
 #include <utility> // std::pair
 
 #ifdef _WIN32
+#include <winsock2.h> // must come before iphlpapi.h
+#include <iphlpapi.h>
 #include <ws2tcpip.h>
 #else
+#include <ifaddrs.h>
+#include <net/if.h>
 #include <netinet/tcp.h> /* TCP_CONGESTION */
 #endif
 
@@ -556,6 +560,92 @@ std::pair<tr_address, std::byte const*> tr_address::from_compact_ipv6(std::byte
     return { address, compact };
 }
 
+std::optional<unsigned> tr_address::to_interface_index() const noexcept
+{
+    if (!is_valid())
+    {
+        tr_logAddDebug("Invalid target address to find interface index");
+        return {};
+    }
+
+    tr_logAddDebug(fmt::format("Find interface index for {}", display_name()));
+
+#ifdef _WIN32
+    auto p_addresses = std::unique_ptr<void, void (*)(void*)>{ nullptr, operator delete };
+    for (auto p_addesses_size = ULONG{ 15000 } /* 15KB */;;)
+    {
+        p_addresses.reset(operator new(p_addesses_size, std::nothrow));
+        if (!p_addresses)
+        {
+            tr_logAddDebug("Could not allocate memory for interface list");
+            return {};
+        }
+
+        if (auto ret = GetAdaptersAddresses(
+                AF_UNSPEC,
+                GAA_FLAG_SKIP_FRIENDLY_NAME,
+                nullptr,
+                reinterpret_cast<PIP_ADAPTER_ADDRESSES>(p_addresses.get()),
+                &p_addesses_size);
+            ret != ERROR_BUFFER_OVERFLOW)
+        {
+            if (ret != ERROR_SUCCESS)
+            {
+                tr_logAddDebug(fmt::format("Failed to retrieve interface list: {} ({})", ret, tr_win32_format_message(ret)));
+                return {};
+            }
+            break;
+        }
+    }
+
+    for (auto const* cur = reinterpret_cast<PIP_ADAPTER_ADDRESSES>(p_addresses.get()); cur != nullptr; cur = cur->Next)
+    {
+        if (cur->OperStatus != IfOperStatusUp)
+        {
+            continue;
+        }
+
+        for (auto const* sa_p = cur->FirstUnicastAddress; sa_p != nullptr; sa_p = sa_p->Next)
+        {
+            if (auto if_addr = tr_socket_address::from_sockaddr(sa_p->Address.lpSockaddr);
+                if_addr && if_addr->address() == *this)
+            {
+                auto const ret = type == TR_AF_INET ? cur->IfIndex : cur->Ipv6IfIndex;
+                tr_logAddDebug(fmt::format("Found interface index for {}: {}", display_name(), ret));
+                return ret;
+            }
+        }
+    }
+#else
+    struct ifaddrs* ifa = nullptr;
+    if (getifaddrs(&ifa) != 0)
+    {
+        auto err = errno;
+        tr_logAddDebug(fmt::format("Failed to retrieve interface list: {} ({})", err, tr_strerror(err)));
+        return {};
+    }
+    auto const ifa_uniq = std::unique_ptr<ifaddrs, void (*)(struct ifaddrs*)>{ ifa, freeifaddrs };
+
+    for (; ifa != nullptr; ifa = ifa->ifa_next)
+    {
+        if (ifa->ifa_addr == nullptr || (ifa->ifa_flags & IFF_UP) == 0U)
+        {
+            continue;
+        }
+
+        if (auto if_addr = tr_socket_address::from_sockaddr(ifa->ifa_addr); if_addr && if_addr->address() == *this)
+        {
+            auto const ret = if_nametoindex(ifa->ifa_name);
+            tr_logAddDebug(fmt::format("Found interface index for {}: {}", display_name(), ret));
+            return if_nametoindex(ifa->ifa_name);
+        }
+    }
+#endif
+
+    tr_logAddDebug(fmt::format("Could not find interface index for {}", display_name()));
+    return {};
+}
+
 int tr_address::compare(tr_address const& that) const noexcept // <=>
 {
     // IPv6 addresses are always "greater than" IPv4

libtransmission/net.h

@@ -161,11 +161,11 @@ struct tr_address
     [[nodiscard]] static std::pair<tr_address, std::byte const*> from_compact_ipv4(std::byte const* compact) noexcept;
     [[nodiscard]] static std::pair<tr_address, std::byte const*> from_compact_ipv6(std::byte const* compact) noexcept;
 
-    // write the text form of the address, e.g. inet_ntop()
+    // --- write the text form of the address, e.g. inet_ntop()
     std::string_view display_name(char* out, size_t outlen) const;
     [[nodiscard]] std::string display_name() const;
 
-    ///
+    // ---
 
     [[nodiscard]] constexpr auto is_ipv4() const noexcept
     {
@@ -177,7 +177,7 @@ struct tr_address
         return type == TR_AF_INET6;
     }
 
-    /// bt protocol compact form
+    // --- bt protocol compact form
 
     // compact addr only -- used e.g. as `yourip` value in extension protocol handshake
 
@@ -208,7 +208,11 @@ struct tr_address
         }
     }
 
-    // comparisons
+    // ---
+
+    [[nodiscard]] std::optional<unsigned> to_interface_index() const noexcept;
+
+    // --- comparisons
 
     [[nodiscard]] int compare(tr_address const& that) const noexcept;
 
@@ -232,7 +236,7 @@ struct tr_address
         return this->compare(that) > 0;
     }
 
-    //
+    // ---
 
     [[nodiscard]] bool is_global_unicast_address() const noexcept;
 

libtransmission/tr-lpd.cc

@@ -20,8 +20,8 @@
 #ifdef _WIN32
 #include <ws2tcpip.h>
 #else
-#include <sys/socket.h> /* socket(), bind() */
 #include <netinet/in.h> /* sockaddr_in */
+#include <sys/socket.h> /* socket(), bind() */
 #endif
 
 #include <event2/event.h>
@@ -410,7 +410,7 @@ private:
                 /* we want to join that LPD multicast group */
                 struct ipv6_mreq mcast_req = {};
                 mcast_req.ipv6mr_multiaddr = mcast6_addr_.sin6_addr;
-                mcast_req.ipv6mr_interface = 0; //FIXME
+                mcast_req.ipv6mr_interface = mediator_.bind_address(ip_protocol).to_interface_index().value_or(0);
 
                 if (setsockopt(
                         sock,