feat: Allow passing in local and remote socket addresses (#16)

* feat: Allow passing in local and remote socket addresses @martinthomson, is this what you had in mind? Fixes #15 * Fix doctest * Fixes * Simplify * Update src/lib.rs Co-authored-by: Martin Thomson <mt@lowentropy.net> * Update src/lib.rs Co-authored-by: Martin Thomson <mt@lowentropy.net> * Drop `cfg-if`` * Stricter ordering * Compat * Docs * Suggestion from @martinthomson * Manual merge from `main` * Cleanups * str * Use Cloudflare's IPs, and find unused ports * No v6 on GitHub * loopback_0 * No copy * doctest * Fix Windows * Suggestions from @martinthomson * Rip out deprecated API support --------- Co-authored-by: Martin Thomson <mt@lowentropy.net>
mozilla · Sep 5, 2024 · 8af1e02 · 8af1e02
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diff --git a/Cargo.toml b/Cargo.toml
@@ -18,7 +18,9 @@ rust-version = "1.76.0"
 [dependencies]
 # Don't increase beyond what Firefox is currently using: https://searchfox.org/mozilla-central/source/Cargo.lock
 libc = { version = "0.2", default-features = false }
-log = { version = "0.4", default-features = false }
+
+[dev-dependencies]
+rand = { version = "0.8", default-features = false, features = ["std", "std_rng"] }
 
 [target."cfg(windows)".dependencies]
 # Don't increase beyond what Firefox is currently using: https://searchfox.org/mozilla-central/source/Cargo.lock

diff --git a/README.md b/README.md
@@ -1,17 +1,21 @@
 # MTU
 
-A crate to return the maximum transmission unit (MTU) of the local network interface towards a given destination `SocketAddr`.
+A crate to return the name and maximum transmission unit (MTU) of the local network interface towards a given destination `SocketAddr`, optionally from a given local `SocketAddr`.
 
 ## Usage
 
-This crate exports a single function
+This crate exports a single function `interface_and_mtu` that, given a pair of local and remote `SocketAddr`s, returns the name and [maximum transmission unit (MTU)](https://en.wikipedia.org/wiki/Maximum_transmission_unit) of the local network interface used by a socket bound to the local address and connected towards the remote destination.
+
+If the local address is `None`, the function will let the operating system choose the local address based on the given remote address. If the remote address is `None`, the function will return the name and MTU of the local network interface with the given local address.
+
+## Example
 
 ```rust
-pub fn interface_and_mtu(remote: &SocketAddr) -> Result<(String, usize), Error>
+let saddr = "127.0.0.1:443".parse().unwrap();
+let (name, mtu) = mtu::interface_and_mtu(&(None, saddr)).unwrap();
+println!("MTU for {saddr:?} is {mtu} on {name}");
 ```
 
-that returns the interface name and MTU of the local network interface used for transmission towards the `remote` destination, or an `Error` when the MTU could not be determined. It supports both IPv4 and IPv6.
-
 ## Supported Platforms
 
 * Linux