Add an allocator for packet IDs.

Cargo.lock

@@ -847,6 +847,15 @@ dependencies = [
  "rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "range-set"
+version = "0.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-traits 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "rayon"
 version = "1.3.0"
@@ -1040,6 +1049,14 @@ name = "slab"
 version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "smallvec"
+version = "0.6.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "maybe-uninit 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "smallvec"
 version = "1.2.0"
@@ -1187,6 +1204,7 @@ dependencies = [
  "fswatcher 0.1.0 (git+https://github.com/mgottschlag/fswatcher-rs.git)",
  "futures 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "range-set 0.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rmp-serde 0.14.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.45 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1473,6 +1491,7 @@ dependencies = [
 "checksum rand_chacha 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "03a2a90da8c7523f554344f921aa97283eadf6ac484a6d2a7d0212fa7f8d6853"
 "checksum rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "90bde5296fc891b0cef12a6d03ddccc162ce7b2aff54160af9338f8d40df6d19"
 "checksum rand_hc 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
+"checksum range-set 0.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "e51c363412e87a2d92e8730f95cbdae590a46959bbcb17d0b5c1ad2c7af98d11"
 "checksum rayon 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "db6ce3297f9c85e16621bb8cca38a06779ffc31bb8184e1be4bed2be4678a098"
 "checksum rayon-core 1.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "08a89b46efaf957e52b18062fb2f4660f8b8a4dde1807ca002690868ef2c85a9"
 "checksum redox_syscall 0.1.56 (registry+https://github.com/rust-lang/crates.io-index)" = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
@@ -1496,6 +1515,7 @@ dependencies = [
 "checksum sha-1 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f7d94d0bede923b3cea61f3f1ff57ff8cdfd77b400fb8f9998949e0cf04163df"
 "checksum signal-hook-registry 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "94f478ede9f64724c5d173d7bb56099ec3e2d9fc2774aac65d34b8b890405f41"
 "checksum slab 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
+"checksum smallvec 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)" = "f7b0758c52e15a8b5e3691eae6cc559f08eee9406e548a4477ba4e67770a82b6"
 "checksum smallvec 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5c2fb2ec9bcd216a5b0d0ccf31ab17b5ed1d627960edff65bbe95d3ce221cefc"
 "checksum strsim 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
 "checksum structopt 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "df136b42d76b1fbea72e2ab3057343977b04b4a2e00836c3c7c0673829572713"

Cargo.toml

@@ -18,6 +18,7 @@ log = "0.4"
 rmp-serde = "0.14"
 fswatcher = { git = "https://github.com/mgottschlag/fswatcher-rs.git" }
 url = "*"
+range-set = "*"
 
 [dev-dependencies]
 criterion = "0.3"

src/network/idalloc.rs

@@ -0,0 +1,70 @@
+use range_set::RangeSet;
+use std::ops::RangeInclusive;
+
+/// Allocator for packet IDs.
+pub struct IdAllocator {
+    free_ids: RangeSet<[RangeInclusive<u32>; 4]>,
+}
+
+impl IdAllocator {
+    /// Creates a new allocator for IDs in the range between 0 and 1<<31-1.
+    pub fn new() -> IdAllocator {
+        IdAllocator {
+            free_ids: RangeSet::<[RangeInclusive<u32>; 4]>::from(0..=(1 << 31) - 1),
+        }
+    }
+
+    /// Allocates an ID.
+    ///
+    /// The ID needs to be manually freed by calling `free(id)` once the server
+    /// has sent a response..
+    pub fn alloc(&mut self) -> u32 {
+        assert!(!self.free_ids.is_empty());
+        let id = self.free_ids.iter().next().unwrap();
+        self.free_ids.remove(id);
+        id
+    }
+
+    /// Frees an ID to allow reuse.
+    pub fn free(&mut self, id: u32) {
+        assert!(id < 1 << 31);
+        let inserted = self.free_ids.insert(id);
+        if !inserted {
+            panic!("free() called for invalid packet ID.");
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_alloc() {
+        let mut ids = IdAllocator::new();
+        assert_eq!(ids.alloc(), 0);
+        assert_eq!(ids.alloc(), 1);
+        assert_eq!(ids.alloc(), 2);
+        assert_eq!(ids.alloc(), 3);
+        assert_eq!(ids.alloc(), 4);
+        ids.free(2);
+        ids.free(3);
+        assert_eq!(ids.alloc(), 2);
+        assert_eq!(ids.alloc(), 3);
+        assert_eq!(ids.alloc(), 5);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_invalid_free() {
+        let mut ids = IdAllocator::new();
+        ids.free(42);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_invalid_free2() {
+        let mut ids = IdAllocator::new();
+        ids.free(1 << 31);
+    }
+}

src/network/mod.rs

@@ -1,4 +1,5 @@
 pub mod client;
+pub mod idalloc;
 pub mod packet;
 pub mod server;
 pub mod websocket;