add: starts_with in MultiAddr

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 0.18.3
+
+- Add `starts_with` on `Multiaddr`. See [PR ].
+
+[PR ]:
+
 # 0.18.2
 
 - Implement missing protocols. See [PR 110].
@@ -42,7 +48,7 @@
 - Rename string representation of `WebRTC` protocol from `/webrtc` to `/webrt-direct`.
   For backwards compatibility `/webrtc` will still be decoded to `Protocol::WebRTC`, but `Protocol::WebRTC` will from now on always be encoded as `/webrtc-direct`.
   See [multiformats/multiaddr discussion] and [PR 84] for context.
-  ``` rust
+  ```rust
   assert_eq!(
       Multiaddr::empty().with(Protocol::WebRTC),
       "/webrtc".parse().unwrap(),
@@ -114,15 +120,15 @@
 
 # 0.12.0 [2021-05-26]
 
-- Merge  [multiaddr] and [parity-multiaddr] (see [PR 40]).
+- Merge [multiaddr] and [parity-multiaddr] (see [PR 40]).
 
-    - Functionality to go from a `u64` to a `multiadddr::Protocol` and back is
-      removed. Please open an issue on [multiaddr] in case this is still needed.
+  - Functionality to go from a `u64` to a `multiadddr::Protocol` and back is
+    removed. Please open an issue on [multiaddr] in case this is still needed.
 
-    - Given that `multiaddr::Protocol` now represents both the protocol
-      identifier as well as the protocol data (e.g. protocol identifier `55`
-      (`dns6`) and protocol data `some-domain.example`) `multiaddr::Protocol` is
-      no longer `Copy`.
+  - Given that `multiaddr::Protocol` now represents both the protocol
+    identifier as well as the protocol data (e.g. protocol identifier `55`
+    (`dns6`) and protocol data `some-domain.example`) `multiaddr::Protocol` is
+    no longer `Copy`.
 
 [multiaddr]: https://github.com/multiformats/rust-multiaddr
 [parity-multiaddr]: https://github.com/libp2p/rust-libp2p/blob/master/misc/multiaddr/

Cargo.toml

@@ -8,7 +8,7 @@ keywords = ["multiaddr", "ipfs"]
 license = "MIT"
 name = "multiaddr"
 readme = "README.md"
-version = "0.18.2"
+version = "0.18.3"
 
 [features]
 default = ["url"]

src/lib.rs

@@ -210,6 +210,16 @@ impl Multiaddr {
         self.bytes[(n - m)..] == other.bytes[..]
     }
 
+    /// Checks whether the given `Multiaddr` is a prefix of this `Multiaddr`.
+    pub fn starts_with(&self, other: &Multiaddr) -> bool {
+        let n = self.bytes.len();
+        let m = other.bytes.len();
+        if n < m {
+            return false;
+        }
+        self.bytes[..m] == other.bytes[..]
+    }
+
     /// Returns &str identifiers for the protocol names themselves.
     /// This omits specific info like addresses, ports, peer IDs, and the like.
     /// Example: `"/ip4/127.0.0.1/tcp/5001"` would return `["ip4", "tcp"]`

tests/lib.rs

@@ -68,6 +68,18 @@ fn ends_with() {
     QuickCheck::new().quickcheck(prop as fn(_))
 }
 
+#[test]
+fn starts_with() {
+    fn prop(Ma(m): Ma) {
+        let n = m.iter().count();
+        for i in 0..n {
+            let prefix = m.iter().take(i + 1).collect::<Multiaddr>();
+            assert!(m.starts_with(&prefix));
+        }
+    }
+    QuickCheck::new().quickcheck(prop as fn(_))
+}
+
 // Arbitrary impls
 
 #[derive(PartialEq, Eq, Clone, Hash, Debug)]