From 4d90ac2f4c09b32ae9a4878319d3b24d7afdb23d Mon Sep 17 00:00:00 2001
From: Patrick Ziegler <p.ziegler96@gmail.com>
Date: Fri, 15 Oct 2021 17:36:32 +0200
Subject: [PATCH] fix(net): Use canonical interface name (#2540)

One can define an 'altname' for an interface. That name is valid of
if_nametoindex but it doesn't appear in `/sys/class/net`:

```
sudo ip link property add dev enp0s31f6 altname eno
```

This creates an altname eno for the existing interface enp0s31f6

Before, using eno, would lead to an error in `realpath`.

Ref: https://www.reddit.com/r/Polybar/comments/q8f0ye/error_disabling_module_network_reason_realpath/hgqpq1m/?context=3
---
 CHANGELOG.md             |  2 ++
 include/adapters/net.hpp |  1 +
 src/adapters/net.cpp     | 25 +++++++++++++++++++++++++
 src/modules/network.cpp  |  8 ++++++++
 4 files changed, 36 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 64802916..b6fcd6b2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -187,6 +187,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     ([`#2491`](https://github.com/polybar/polybar/issues/2491))
   - Module would error if WM was not full started up.
     ([`#1915`](https://github.com/polybar/polybar/issues/1915))
+- `internal/network`: The module now properly supports 'altnames' for
+  interfaces.
 
 ## [3.5.7] - 2021-09-21
 ### Fixed
diff --git a/include/adapters/net.hpp b/include/adapters/net.hpp
index 27cf2c72..f9aa2920 100644
--- a/include/adapters/net.hpp
+++ b/include/adapters/net.hpp
@@ -38,6 +38,7 @@ namespace net {
   DEFINE_ERROR(network_error);
 
   bool is_interface_valid(const string& ifname);
+  std::pair<string, bool> get_canonical_interface(const string& ifname);
   bool is_wireless_interface(const string& ifname);
   std::string find_wireless_interface();
   std::string find_wired_interface();
diff --git a/src/adapters/net.cpp b/src/adapters/net.cpp
index 730372c8..e7853486 100644
--- a/src/adapters/net.cpp
+++ b/src/adapters/net.cpp
@@ -62,6 +62,31 @@ namespace net {
     return if_nametoindex(ifname.c_str()) != 0;
   }
 
+  /**
+   * Returns the canonical name of the given interface and whether that differs
+   * from the given name.
+   *
+   * The canonical name is the name that has an entry in `/sys/class/net`.
+   *
+   * This resolves any altnames that were defined (see man ip-link).
+   */
+  std::pair<string, bool> get_canonical_interface(const string& ifname) {
+    int idx = if_nametoindex(ifname.c_str());
+
+    if (idx == 0) {
+      throw system_error("if_nameindex(" + ifname + ")");
+    }
+
+    char canonical[IF_NAMESIZE];
+    if (!if_indextoname(idx, canonical)) {
+      throw system_error("if_indextoname(" + to_string(idx) + ")");
+    }
+
+    string str{canonical};
+
+    return {str, str != ifname};
+  }
+
   /**
    * Test if interface with given name is a wireless device
    */
diff --git a/src/modules/network.cpp b/src/modules/network.cpp
index 9e979bd8..0eac9f76 100644
--- a/src/modules/network.cpp
+++ b/src/modules/network.cpp
@@ -44,6 +44,14 @@ namespace modules {
       throw module_error("Invalid network interface \"" + m_interface + "\"");
     }
 
+    auto canonical = net::get_canonical_interface(m_interface);
+
+    if (canonical.second) {
+      m_log.info(
+          "%s: Replacing given interface '%s' with its canonical name '%s'", name(), m_interface, canonical.first);
+      m_interface = canonical.first;
+    }
+
     m_ping_nth_update = m_conf.get(name(), "ping-interval", m_ping_nth_update);
     m_udspeed_minwidth = m_conf.get(name(), "udspeed-minwidth", m_udspeed_minwidth);
     m_accumulate = m_conf.get(name(), "accumulate-stats", m_accumulate);