Merge rust-bitcoin#737: Deprecate from_slice methods in favor of arrays

537b85b Deprecate and replace `from_slice` (Jamil Lambert, PhD)
1661f57 Add `from_byte_array` functions (Jamil Lambert, PhD)

Pull request description:

  As brought up in issue rust-bitcoin/rust-bitcoin#3102 support for Rust arrays is now much better so slice-accepting methods that require a fixed length can be replaced with a method that accepts an array.

  `from_slice()` methods have been deprecated and calls to it from within the crate have been changed to use the equivalent array method.

ACKs for top commit:
  apoelstra:
    ACK 537b85b successfully ran local tests
  tcharding:
    ACK 537b85b
  Kixunil:
    ACK 537b85b

Tree-SHA512: 8f8f807af0032130b64a93ff86cae0df1ccee83de052603968be9e30751c27dfc763a6128472e6d0f3a5c2016e7da8e4d06eefc86d8310bdaacc6be0f8fe3822

src/ecdh.rs

@@ -64,6 +64,7 @@ impl SharedSecret {
     pub fn from_bytes(bytes: [u8; SHARED_SECRET_SIZE]) -> SharedSecret { SharedSecret(bytes) }
 
     /// Creates a shared secret from `bytes` slice.
+    #[deprecated(since = "TBD", note = "Use `from_bytes` instead.")]
     #[inline]
     pub fn from_slice(bytes: &[u8]) -> Result<SharedSecret, Error> {
         match bytes.len() {

src/key.rs

@@ -115,7 +115,7 @@ impl str::FromStr for SecretKey {
     fn from_str(s: &str) -> Result<SecretKey, Error> {
         let mut res = [0u8; constants::SECRET_KEY_SIZE];
         match from_hex(s, &mut res) {
-            Ok(constants::SECRET_KEY_SIZE) => SecretKey::from_slice(&res),
+            Ok(constants::SECRET_KEY_SIZE) => SecretKey::from_byte_array(&res),
             _ => Err(Error::InvalidSecretKey),
         }
     }
@@ -138,7 +138,7 @@ impl str::FromStr for SecretKey {
 /// use secp256k1::{SecretKey, Secp256k1, PublicKey};
 ///
 /// let secp = Secp256k1::new();
-/// let secret_key = SecretKey::from_slice(&[0xcd; 32]).expect("32 bytes, within curve order");
+/// let secret_key = SecretKey::from_byte_array(&[0xcd; 32]).expect("32 bytes, within curve order");
 /// let public_key = PublicKey::from_secret_key(&secp, &secret_key);
 /// # }
 /// ```
@@ -168,9 +168,13 @@ impl str::FromStr for PublicKey {
     fn from_str(s: &str) -> Result<PublicKey, Error> {
         let mut res = [0u8; constants::UNCOMPRESSED_PUBLIC_KEY_SIZE];
         match from_hex(s, &mut res) {
-            Ok(constants::PUBLIC_KEY_SIZE) =>
-                PublicKey::from_slice(&res[0..constants::PUBLIC_KEY_SIZE]),
-            Ok(constants::UNCOMPRESSED_PUBLIC_KEY_SIZE) => PublicKey::from_slice(&res),
+            Ok(constants::PUBLIC_KEY_SIZE) => {
+                let bytes: [u8; constants::PUBLIC_KEY_SIZE] =
+                    res[0..constants::PUBLIC_KEY_SIZE].try_into().unwrap();
+                PublicKey::from_byte_array_compressed(&bytes)
+            }
+            Ok(constants::UNCOMPRESSED_PUBLIC_KEY_SIZE) =>
+                PublicKey::from_byte_array_uncompressed(&res),
             _ => Err(Error::InvalidPublicKey),
         }
     }
@@ -203,33 +207,43 @@ impl SecretKey {
         SecretKey(data)
     }
 
-    /// Converts a `SECRET_KEY_SIZE`-byte slice to a secret key.
+    /// Converts a 32-byte slice to a secret key.
     ///
     /// # Examples
     ///
     /// ```
     /// use secp256k1::SecretKey;
     /// let sk = SecretKey::from_slice(&[0xcd; 32]).expect("32 bytes, within curve order");
     /// ```
+    #[deprecated(since = "TBD", note = "Use `from_byte_array` instead.")]
     #[inline]
     pub fn from_slice(data: &[u8]) -> Result<SecretKey, Error> {
         match <[u8; constants::SECRET_KEY_SIZE]>::try_from(data) {
-            Ok(data) => {
-                unsafe {
-                    if ffi::secp256k1_ec_seckey_verify(
-                        ffi::secp256k1_context_no_precomp,
-                        data.as_c_ptr(),
-                    ) == 0
-                    {
-                        return Err(InvalidSecretKey);
-                    }
-                }
-                Ok(SecretKey(data))
-            }
+            Ok(data) => Self::from_byte_array(&data),
             Err(_) => Err(InvalidSecretKey),
         }
     }
 
+    /// Converts a 32-byte array to a secret key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use secp256k1::SecretKey;
+    /// let sk = SecretKey::from_byte_array(&[0xcd; 32]).expect("32 bytes, within curve order");
+    /// ```
+    #[inline]
+    pub fn from_byte_array(data: &[u8; constants::SECRET_KEY_SIZE]) -> Result<SecretKey, Error> {
+        unsafe {
+            if ffi::secp256k1_ec_seckey_verify(ffi::secp256k1_context_no_precomp, data.as_c_ptr())
+                == 0
+            {
+                return Err(InvalidSecretKey);
+            }
+        }
+        Ok(SecretKey(*data))
+    }
+
     /// Creates a new secret key using data from BIP-340 [`Keypair`].
     ///
     /// # Examples
@@ -353,7 +367,7 @@ impl SecretKey {
 impl<T: ThirtyTwoByteHash> From<T> for SecretKey {
     /// Converts a 32-byte hash directly to a secret key without error paths.
     fn from(t: T) -> SecretKey {
-        SecretKey::from_slice(&t.into_32()).expect("failed to create secret key")
+        SecretKey::from_byte_array(&t.into_32()).expect("failed to create secret key")
     }
 }
 
@@ -442,17 +456,50 @@ impl PublicKey {
     /// Creates a public key directly from a slice.
     #[inline]
     pub fn from_slice(data: &[u8]) -> Result<PublicKey, Error> {
-        if data.is_empty() {
-            return Err(Error::InvalidPublicKey);
+        match data.len() {
+            constants::PUBLIC_KEY_SIZE => PublicKey::from_byte_array_compressed(
+                &<[u8; constants::PUBLIC_KEY_SIZE]>::try_from(data).unwrap(),
+            ),
+            constants::UNCOMPRESSED_PUBLIC_KEY_SIZE => PublicKey::from_byte_array_uncompressed(
+                &<[u8; constants::UNCOMPRESSED_PUBLIC_KEY_SIZE]>::try_from(data).unwrap(),
+            ),
+            _ => Err(InvalidPublicKey),
         }
+    }
 
+    /// Creates a public key from a serialized array in compressed format.
+    #[inline]
+    pub fn from_byte_array_compressed(
+        data: &[u8; constants::PUBLIC_KEY_SIZE],
+    ) -> Result<PublicKey, Error> {
         unsafe {
             let mut pk = ffi::PublicKey::new();
             if ffi::secp256k1_ec_pubkey_parse(
                 ffi::secp256k1_context_no_precomp,
                 &mut pk,
                 data.as_c_ptr(),
-                data.len(),
+                constants::PUBLIC_KEY_SIZE,
+            ) == 1
+            {
+                Ok(PublicKey(pk))
+            } else {
+                Err(InvalidPublicKey)
+            }
+        }
+    }
+
+    /// Creates a public key from a serialized array in uncompressed format.
+    #[inline]
+    pub fn from_byte_array_uncompressed(
+        data: &[u8; constants::UNCOMPRESSED_PUBLIC_KEY_SIZE],
+    ) -> Result<PublicKey, Error> {
+        unsafe {
+            let mut pk = ffi::PublicKey::new();
+            if ffi::secp256k1_ec_pubkey_parse(
+                ffi::secp256k1_context_no_precomp,
+                &mut pk,
+                data.as_c_ptr(),
+                constants::UNCOMPRESSED_PUBLIC_KEY_SIZE,
             ) == 1
             {
                 Ok(PublicKey(pk))
@@ -500,7 +547,7 @@ impl PublicKey {
         };
         buf[1..].clone_from_slice(&pk.serialize());
 
-        PublicKey::from_slice(&buf).expect("we know the buffer is valid")
+        PublicKey::from_byte_array_compressed(&buf).expect("we know the buffer is valid")
     }
 
     #[inline]
@@ -1114,8 +1161,7 @@ impl str::FromStr for XOnlyPublicKey {
     fn from_str(s: &str) -> Result<XOnlyPublicKey, Error> {
         let mut res = [0u8; constants::SCHNORR_PUBLIC_KEY_SIZE];
         match from_hex(s, &mut res) {
-            Ok(constants::SCHNORR_PUBLIC_KEY_SIZE) =>
-                XOnlyPublicKey::from_slice(&res[0..constants::SCHNORR_PUBLIC_KEY_SIZE]),
+            Ok(constants::SCHNORR_PUBLIC_KEY_SIZE) => XOnlyPublicKey::from_byte_array(&res),
             _ => Err(Error::InvalidPublicKey),
         }
     }
@@ -1161,12 +1207,25 @@ impl XOnlyPublicKey {
     ///
     /// Returns [`Error::InvalidPublicKey`] if the length of the data slice is not 32 bytes or the
     /// slice does not represent a valid Secp256k1 point x coordinate.
+    #[deprecated(since = "TBD", note = "Use `from_byte_array` instead.")]
     #[inline]
     pub fn from_slice(data: &[u8]) -> Result<XOnlyPublicKey, Error> {
-        if data.is_empty() || data.len() != constants::SCHNORR_PUBLIC_KEY_SIZE {
-            return Err(Error::InvalidPublicKey);
+        match <[u8; constants::SCHNORR_PUBLIC_KEY_SIZE]>::try_from(data) {
+            Ok(data) => Self::from_byte_array(&data),
+            Err(_) => Err(InvalidPublicKey),
         }
+    }
 
+    /// Creates a schnorr public key directly from a byte array.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`Error::InvalidPublicKey`] if the array does not represent a valid Secp256k1 point
+    /// x coordinate.
+    #[inline]
+    pub fn from_byte_array(
+        data: &[u8; constants::SCHNORR_PUBLIC_KEY_SIZE],
+    ) -> Result<XOnlyPublicKey, Error> {
         unsafe {
             let mut pk = ffi::XOnlyPublicKey::new();
             if ffi::secp256k1_xonly_pubkey_parse(

src/schnorr.rs

@@ -78,6 +78,7 @@ impl Signature {
     pub fn from_byte_array(sig: [u8; constants::SCHNORR_SIGNATURE_SIZE]) -> Self { Self(sig) }
 
     /// Creates a `Signature` directly from a slice.
+    #[deprecated(since = "TBD", note = "Use `from_byte_array` instead.")]
     #[inline]
     pub fn from_slice(data: &[u8]) -> Result<Signature, Error> {
         match data.len() {