CfgPath: Test serialisation round-trip with a binary format

Use MessagePack.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Cargo.lock

@@ -2162,6 +2162,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "paste"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c520e05135d6e763148b6426a837e239041653ba7becd2e538c076c738025fc"
+
 [[package]]
 name = "pathdiff"
 version = "0.2.1"
@@ -2536,6 +2542,28 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "rmp"
+version = "0.8.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44519172358fd6d58656c86ab8e7fbc9e1490c3e8f14d35ed78ca0dd07403c9f"
+dependencies = [
+ "byteorder",
+ "num-traits",
+ "paste",
+]
+
+[[package]]
+name = "rmp-serde"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "25786b0d276110195fa3d6f3f31299900cf71dfbd6c28450f3f58a0e7f7a347e"
+dependencies = [
+ "byteorder",
+ "rmp",
+ "serde",
+]
+
 [[package]]
 name = "rsa"
 version = "0.5.0"
@@ -3296,6 +3324,7 @@ dependencies = [
  "directories",
  "dirs",
  "once_cell",
+ "rmp-serde",
  "serde",
  "serde_json",
  "shellexpand-fork",

crates/tor-config/Cargo.toml

@@ -30,6 +30,7 @@ directories = { version = "4", optional = true }
 [dev-dependencies]
 config = { version = "0.12.0", default-features = false, features = ["toml"] }
 dirs = "4.0.0"
+rmp-serde = "1"
 serde_json = "1.0.50"
 toml = "0.5"
 tracing-test = "0.2"

crates/tor-config/src/path.rs

@@ -420,4 +420,12 @@ mod test_serde {
     fn roundtrip_toml() {
         test_roundtrip_cases(|input| toml::to_string(&input), |toml| toml::from_str(toml));
     }
+
+    #[test]
+    fn roundtrip_mpack() {
+        test_roundtrip_cases(
+            |input| rmp_serde::to_vec(&input),
+            |mpack| rmp_serde::from_slice(mpack),
+        );
+    }
 }