tests: replace cbor with more-recently-deprecated serde_cbor

The `cbor` crate has been unmaintained for several years, and depends on
the ancient `rustc_serialize` crate which (a) doesn't build on WASM, and
(b) doesn't build when we use a minimal-dep Cargo.lock. (The latter is
because cbor specifies rustc_serialize 0.3.0 when it should specify 0.3.1,
but there is nothing we can do to fix that when cbor is unmaintained.)

This changes a hardcoded value in a regression test, but it's because
we're replacing the serialization engine rather than changing our code,
so this is not actually a change.

Author: apoelstra

Cargo.toml

@@ -47,14 +47,10 @@ rand = { version = "0.8", default-features = false, optional = true }
 
 [dev-dependencies]
 rand_core = "0.6"
+serde_cbor = "0.10.0"
 serde_test = "1.0"
 bincode = "1.3.3"
 
-# cbor does not build on WASM, we use it in a single trivial test (an example of when
-# fixed-width-serde breaks down). Just run the test when on an x86_64 machine.
-[target.'cfg(target_arch = "x86_64")'.dev-dependencies]
-cbor = "0.4.1"
-
 [target.wasm32-unknown-unknown.dev-dependencies]
 wasm-bindgen-test = "0.3"
 getrandom = { version = "0.2", features = ["js"] }

tests/serde.rs

@@ -1,8 +1,7 @@
 #![cfg(feature = "serde")]
 
 extern crate bincode;
-#[cfg(target_arch = "x86_64")]
-extern crate cbor;
+extern crate serde_cbor;
 extern crate secp256k1;
 
 #[cfg(feature = "global-context")]
@@ -77,15 +76,12 @@ fn bincode_x_only_public_key() {
     assert_eq!(ser, XONLY_PK_BYTES);
 }
 
-// cbor adds an additional byte of metadata to certain byte values (byte_value < 24).
 #[test]
-#[cfg(target_arch = "x86_64")]
 fn cbor() {
     let sk = secret_key();
-
-    let mut e = cbor::Encoder::from_memory();
-    e.encode(sk.as_ref()).unwrap();
-
-    // 52 because there are 22 bytes in the key for which cbor adds metadata.
-    assert_eq!(e.as_bytes().len(), 52);
+    let e = serde_cbor::to_vec(&sk).unwrap();
+    // Secret key is 32 bytes. CBOR adds a byte of metadata for 20 of these bytes,
+    // (Apparently, any byte whose value is <24 gets an extra byte.)
+    // It also adds a 1-byte length prefix and a byte of metadata for the whole vector.
+    assert_eq!(e.len(), 54);
 }