feat: allow setting Kad K_VALUE using feat flag

.github/workflows/ci.yml

@@ -20,9 +20,9 @@ jobs:
     name: Test ${{ matrix.crate }}
     runs-on: ${{ fromJSON(
       github.repository == 'libp2p/rust-libp2p' && (
-        (contains(fromJSON('["libp2p-webrtc", "libp2p"]'), matrix.crate) && '["self-hosted", "linux", "x64", "2xlarge"]') ||
-        (contains(fromJSON('["libp2p-quic", "libp2p-perf"]'), matrix.crate) && '["self-hosted", "linux", "x64", "xlarge"]') ||
-        '["self-hosted", "linux", "x64", "large"]'
+      (contains(fromJSON('["libp2p-webrtc", "libp2p"]'), matrix.crate) && '["self-hosted", "linux", "x64", "2xlarge"]') ||
+      (contains(fromJSON('["libp2p-quic", "libp2p-perf"]'), matrix.crate) && '["self-hosted", "linux", "x64", "xlarge"]') ||
+      '["self-hosted", "linux", "x64", "large"]'
       ) || '"ubuntu-latest"') }}
     timeout-minutes: 10
     needs: gather_published_crates
@@ -47,7 +47,25 @@ jobs:
           save-if: false
 
       - name: Run all tests
-        run: cargo test --package "$CRATE" --all-features
+        run: |
+          if [ "$CRATE" = "libp2p-kad" ]; then
+            echo "Running tests for libp2p-kad with k-20 (default)"
+            cargo test --package libp2p-kad --all-features
+
+            echo "Running tests for libp2p-kad with k-4"
+            cargo test --package libp2p-kad --features serde,k-4
+
+            echo "Running tests for libp2p-kad with k-8"
+            cargo test --package libp2p-kad --features serde,k-8
+
+            echo "Running tests for libp2p-kad with k-12"
+            cargo test --package libp2p-kad --features serde,k-12
+
+            echo "Running tests for libp2p-kad with k-16"
+            cargo test --package libp2p-kad --features serde,k-16
+          else
+            cargo test --package "$CRATE" --all-features
+          fi
 
       - name: Check if we compile without any features activated
         run: cargo build --package "$CRATE" --no-default-features
@@ -338,7 +356,7 @@ jobs:
 
       - name: Ensure `full` feature contains all features
         run: |
-          ALL_FEATURES=$(cargo metadata --format-version=1 --no-deps | jq -r '.packages[] | select(.name == "libp2p") | .features | keys | map(select(. != "full")) | sort | join(" ")')
+          ALL_FEATURES=$(cargo metadata --format-version=1 --no-deps | jq -r '.packages[] | select(.name == "libp2p") | .features | keys | map(select(. != "full" and . != "k-4" and . != "k-8" and . != "k-12" and . != "k-16")) | sort | join(" ")')
           FULL_FEATURE=$(cargo metadata --format-version=1 --no-deps | jq -r '.packages[] | select(.name == "libp2p") | .features["full"] | sort | join(" ")')
 
           echo "$ALL_FEATURES";
@@ -382,10 +400,10 @@ jobs:
 
       - name: Ensure generated files are unmodified # https://stackoverflow.com/a/5737794
         run: |
-            git_status=$(git status --porcelain)
-
-            echo $git_status
-            test -z "$git_status"
+          git_status=$(git status --porcelain)
+          
+          echo $git_status
+          test -z "$git_status"
 
   ensure-lockfile-uptodate:
     name: Ensure that `Cargo.lock` is up-to-date
@@ -398,7 +416,7 @@ jobs:
   cargo-deny:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
-    - uses: EmbarkStudios/cargo-deny-action@v2
-      with:
-        command: check advisories bans licenses sources
+      - uses: actions/checkout@v4
+      - uses: EmbarkStudios/cargo-deny-action@v2
+        with:
+          command: check advisories bans licenses sources

libp2p/Cargo.toml

@@ -64,6 +64,10 @@ floodsub = ["dep:libp2p-floodsub"]
 gossipsub = ["dep:libp2p-gossipsub", "libp2p-metrics?/gossipsub"]
 identify = ["dep:libp2p-identify", "libp2p-metrics?/identify"]
 json = ["libp2p-request-response?/json"]
+k-4 = ["kad"]
+k-8 = ["kad"]
+k-12 = ["kad"]
+k-16 = ["kad"]
 kad = ["dep:libp2p-kad", "libp2p-metrics?/kad"]
 macros = ["libp2p-swarm/macros"]
 mdns = ["dep:libp2p-mdns"]

protocols/kad/Cargo.toml

@@ -45,6 +45,10 @@ tracing-subscriber = { workspace = true, features = ["env-filter"] }
 
 [features]
 serde = ["dep:serde", "bytes/serde"]
+k-4 = []
+k-8 = []
+k-12 = []
+k-16 = []
 
 # Passing arguments to the docsrs builder in order to properly document cfg's.
 # More information: https://docs.rs/about/builds#cross-compiling

protocols/kad/src/lib.rs

@@ -74,6 +74,33 @@ pub use protocol::{ConnectionType, KadPeer};
 pub use query::QueryId;
 pub use record::{store, Key as RecordKey, ProviderRecord, Record};
 
+#[cfg(all(
+    feature = "k-4",
+    not(any(feature = "k-8", feature = "k-12", feature = "k-16"))
+))]
+const K: usize = 4;
+#[cfg(all(
+    feature = "k-8",
+    not(any(feature = "k-4", feature = "k-12", feature = "k-16"))
+))]
+const K: usize = 8;
+#[cfg(all(
+    feature = "k-12",
+    not(any(feature = "k-4", feature = "k-8", feature = "k-16"))
+))]
+const K: usize = 12;
+#[cfg(all(
+    feature = "k-16",
+    not(any(feature = "k-4", feature = "k-8", feature = "k-12"))
+))]
+const K: usize = 16;
+// Enable if none of the k-n features are enabled or if all the k-n features are enabled.
+#[cfg(any(
+    not(any(feature = "k-4", feature = "k-8", feature = "k-12", feature = "k-16")),
+    all(feature = "k-4", feature = "k-8", feature = "k-12", feature = "k-16")
+))]
+const K: usize = 20;
+
 /// The `k` parameter of the Kademlia specification.
 ///
 /// This parameter determines:
@@ -86,9 +113,7 @@ pub use record::{store, Key as RecordKey, ProviderRecord, Record};
 /// The choice of (1) is fixed to this constant. The replication factor is configurable
 /// but should generally be no greater than `K_VALUE`. All nodes in a Kademlia
 /// DHT should agree on the choices made for (1) and (2).
-///
-/// The current value is `20`.
-pub const K_VALUE: NonZeroUsize = NonZeroUsize::new(20).unwrap();
+pub const K_VALUE: NonZeroUsize = NonZeroUsize::new(K).unwrap();
 
 /// The `α` parameter of the Kademlia specification.
 ///