From 945910d319f19bd99c74d121f48842225af0cadc Mon Sep 17 00:00:00 2001
From: Frostie314159 <iam.an.programmer@gmail.com>
Date: Mon, 25 Mar 2024 00:45:13 +0100
Subject: [PATCH] Added if_indextoname function. (#2340)

* Added if_indextoname function.

* Added changelog.

* Fixed pointer cast.

* Applied suggestions.
---
 changelog/2340.added.md |  1 +
 src/net/if_.rs          | 21 +++++++++++++++++----
 test/test_net.rs        | 11 +++++++++++
 3 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 changelog/2340.added.md

diff --git a/changelog/2340.added.md b/changelog/2340.added.md
new file mode 100644
index 0000000000..9d120d4879
--- /dev/null
+++ b/changelog/2340.added.md
@@ -0,0 +1 @@
+Add if_indextoname function.
diff --git a/src/net/if_.rs b/src/net/if_.rs
index c66b5dc0b3..5b6c2e77a5 100644
--- a/src/net/if_.rs
+++ b/src/net/if_.rs
@@ -3,9 +3,9 @@
 //! Uses Linux and/or POSIX functions to resolve interface names like "eth0"
 //! or "socan1" into device numbers.
 
-use std::fmt;
-use crate::{Error, NixPath, Result};
-use libc::c_uint;
+use std::{ffi::{CStr, CString}, fmt};
+use crate::{errno::Errno, Error, NixPath, Result};
+use libc::{c_uint, IF_NAMESIZE};
 
 #[cfg(not(solarish))]
 /// type alias for InterfaceFlags
@@ -14,7 +14,7 @@ pub type IflagsType = libc::c_int;
 /// type alias for InterfaceFlags
 pub type IflagsType = libc::c_longlong;
 
-/// Resolve an interface into a interface number.
+/// Resolve an interface into an interface number.
 pub fn if_nametoindex<P: ?Sized + NixPath>(name: &P) -> Result<c_uint> {
     let if_index = name
         .with_nix_path(|name| unsafe { libc::if_nametoindex(name.as_ptr()) })?;
@@ -26,6 +26,19 @@ pub fn if_nametoindex<P: ?Sized + NixPath>(name: &P) -> Result<c_uint> {
     }
 }
 
+/// Resolve an interface number into an interface.
+pub fn if_indextoname(index: c_uint) -> Result<CString> {
+    // We need to allocate this anyway, so doing it directly is faster.
+    let mut buf = vec![0u8; IF_NAMESIZE];
+
+    let return_buf = unsafe {
+        libc::if_indextoname(index, buf.as_mut_ptr().cast())
+    };
+
+    Errno::result(return_buf.cast())?;
+    Ok(CStr::from_bytes_until_nul(buf.as_slice()).unwrap().to_owned())
+}
+
 libc_bitflags!(
     /// Standard interface flags, used by `getifaddrs`
     pub struct InterfaceFlags: IflagsType {
diff --git a/test/test_net.rs b/test/test_net.rs
index faba8503fe..46a3efd501 100644
--- a/test/test_net.rs
+++ b/test/test_net.rs
@@ -13,3 +13,14 @@ const LOOPBACK: &[u8] = b"loop";
 fn test_if_nametoindex() {
     if_nametoindex(LOOPBACK).expect("assertion failed");
 }
+
+#[test]
+fn test_if_indextoname() {
+    let loopback_index = if_nametoindex(LOOPBACK).expect("assertion failed");
+    assert_eq!(
+        if_indextoname(loopback_index)
+            .expect("assertion failed")
+            .as_bytes(),
+        LOOPBACK
+    );
+}