Remove rustc-serialize

[workingjubilee]

This crate will have difficulties being updated to future compilers if it continues to depend on rustc-serialize. This PR updates it to remove this dependency. Not all tests pass on my machine but this appears to be due to preexisting unsoundness in the library's test suite:

    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.01s
warning: the following packages contain code that will be rejected by a future version of Rust: grin_secp256k1zkp v0.7.12 (/home/jubilee/rust/rust-secp256k1-zkp)
note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 2`
     Running unittests src/lib.rs (target/debug/deps/secp256k1zkp-6adad85efc3e032c)

running 56 tests
test key::test::test_bad_serde_deserialize ... ok
test ecdh::tests::ecdh ... ok
test key::test::invalid_secret_key ... ok
test key::test::pubkey_from_slice ... ok
test key::test::skey_from_slice ... ok
test key::test::test_debug_output ... ok
test aggsig::tests::test_aggsig_fuzz ... ok
test key::test::skey_clear_on_drop ... ok
thread 'key::test::keypair_slice_round_trip' panicked at library/core/src/panicking.rs:152:5:
unsafe precondition(s) violated: slice::get_unchecked_mut requires that the index is within the slice
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread caused non-unwinding panic. aborting.
error: test failed, to rerun pass `--lib`

Caused by:
  process didn't exit successfully: `/home/jubilee/rust/rust-secp256k1-zkp/target/debug/deps/secp256k1zkp-6adad85efc3e032c` (signal: 6, SIGABRT: process abort signal)

[yeastplume]

Thanks, appreciate you looking at this, and we definitely need to get this library updated soon.

We need to be extremely careful with this though, as we've found binding can have subtle errors that can lead to dangerous issues on the live chain (which we've actually experienced). What's the 'preexisting unsoundness' in the existing test suite? We'd take these kinds of issues in this library very, very seriously.

[dagonharett]

Quite needed indeed. I am already unable to build rust-secp256k1-zkp on rust 1.77.2 due to the dependency on rustc-serialize.

error[E0310]: the parameter type `T` may not live long enough
    --> /home/dagon/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustc-serialize-0.3.24/src/serialize.rs:1155:5
     |
1155 |     fn decode<D: Decoder>(d: &mut D) -> Result<Cow<'static, T>, D::Error> {
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |     |
     |     the parameter type `T` must be valid for the static lifetime...
     |     ...so that the type `T` will meet its required lifetime bounds...
     |
note: ...that is required by this bound
    --> /usr/src/debug/rust/rustc-1.77.2-src/library/alloc/src/borrow.rs:180:30
help: consider adding an explicit lifetime bound
     |
1151 | impl<'a, T: ?Sized + 'static> Decodable for Cow<'a, T>
     |                    +++++++++
For more information about this error, try `rustc --explain E0310`.
error: could not compile `rustc-serialize` (lib) due to 1 previous error

Hope to see this PR in proper shape and merged.

[workingjubilee]

Apologies, I don't get through my entire notification backlog very often. Hm. It seems #83 duplicates this work, so I can close this.

What's the 'preexisting unsoundness' in the existing test suite?

I posted an error message.

thread 'key::test::keypair_slice_round_trip' panicked at library/core/src/panicking.rs:152:5:
unsafe precondition(s) violated: slice::get_unchecked_mut requires that the index is within the slice
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread caused non-unwinding panic. aborting.
error: test failed, to rerun pass `--lib`

We'd take these kinds of issues in this library very, very seriously.

Do you take it seriously enough to read the documentation for the functions your code calls? MaybeUninit::assume_init specifically prohibits this usage:

• rust-secp256k1-zkp/src/key.rs

  Line 319 in 6242b05

  let mut ret: [u8; constants::UNCOMPRESSED_PUBLIC_KEY_SIZE] = mem::MaybeUninit::uninit().assume_init();

• rust-secp256k1-zkp/src/ffi.rs

  Lines 78 to 88 in 6242b05

  	pub struct PublicKey(pub [c_uchar; 64]);
  	impl Copy for PublicKey {}
  	impl_array_newtype!(PublicKey, c_uchar, 64);
  	impl_raw_debug!(PublicKey);
  	impl PublicKey {
  	/// Create a new (zeroed) public key usable for the FFI interface
  	pub fn new() -> PublicKey { PublicKey([0; 64]) }
  	/// Create a new (uninitialized) public key usable for the FFI interface
  	pub unsafe fn blank() -> PublicKey { mem::MaybeUninit::uninit().assume_init() }
  	}

• rust-secp256k1-zkp/src/ffi.rs

  Lines 90 to 132 in 6242b05

  	/// Library-internal representation of a Secp256k1 signature
  	#[repr(C)]
  	pub struct Signature(pub [c_uchar; 64]);
  	impl Copy for Signature {}
  	impl_array_newtype!(Signature, c_uchar, 64);
  	impl_raw_debug!(Signature);
  	/// Library-internal representation of a Secp256k1 signature + recovery ID
  	#[repr(C)]
  	pub struct RecoverableSignature([c_uchar; 65]);
  	impl Copy for RecoverableSignature {}
  	impl_array_newtype!(RecoverableSignature, c_uchar, 65);
  	impl_raw_debug!(RecoverableSignature);
  	/// Library-internal representation of a Secp256k1 aggsig partial signature
  	#[repr(C)]
  	pub struct AggSigPartialSignature([c_uchar; 32]);
  	impl Copy for AggSigPartialSignature {}
  	impl_array_newtype!(AggSigPartialSignature, c_uchar, 32);
  	impl_raw_debug!(AggSigPartialSignature);
  	impl Signature {
  	/// Create a new (zeroed) signature usable for the FFI interface
  	pub fn new() -> Signature { Signature([0; 64]) }
  	/// Create a signature from raw data
  	pub fn from_data(data: [u8; 64]) -> Signature { Signature(data) }
  	/// Create a new (uninitialized) signature usable for the FFI interface
  	pub unsafe fn blank() -> Signature { mem::MaybeUninit::uninit().assume_init() }
  	}
  	impl RecoverableSignature {
  	/// Create a new (zeroed) signature usable for the FFI interface
  	pub fn new() -> RecoverableSignature { RecoverableSignature([0; 65]) }
  	/// Create a new (uninitialized) signature usable for the FFI interface
  	pub unsafe fn blank() -> RecoverableSignature { mem::MaybeUninit::uninit().assume_init() }
  	}
  	impl AggSigPartialSignature {
  	/// Create a new (zeroed) aggsig partial signature usable for the FFI interface
  	pub fn new() -> AggSigPartialSignature { AggSigPartialSignature([0; 32]) }
  	/// Create a new (uninitialized) signature usable for the FFI interface
  	pub unsafe fn blank() -> AggSigPartialSignature { mem::MaybeUninit::uninit().assume_init() }
  	}

• rust-secp256k1-zkp/src/ffi.rs

  Lines 136 to 145 in 6242b05

  	pub struct SharedSecret([c_uchar; 32]);
  	impl_array_newtype!(SharedSecret, c_uchar, 32);
  	impl_raw_debug!(SharedSecret);
  	impl SharedSecret {
  	/// Create a new (zeroed) signature usable for the FFI interface
  	pub fn new() -> SharedSecret { SharedSecret([0; 32]) }
  	/// Create a new (uninitialized) signature usable for the FFI interface
  	pub unsafe fn blank() -> SharedSecret { mem::MaybeUninit::uninit().assume_init() }
  	}