Add global context API

Our API often involves a `Secp256k1` parameter, when users enable the
`global-context` feature they must then pass `SECP256K1` into these
functions. This is kind of clunky since the global is by definition
available everywhere.

Make the API more ergonomic for `global-context` builds by adding
various API functions/methods that use the global context implicitly.

src/ecdsa/mod.rs

@@ -12,6 +12,9 @@ mod recovery;
 #[cfg_attr(docsrs, doc(cfg(feature = "recovery")))]
 pub use self::recovery::{RecoveryId, RecoverableSignature};
 
+#[cfg(feature = "global-context")]
+use SECP256K1;
+
 /// An ECDSA signature
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub struct Signature(pub(crate) ffi::Signature);
@@ -269,6 +272,13 @@ impl Signature {
         }
         ret
     }
+
+    /// Verifies an ECDSA signature for `msg` using `pk` and the global [`SECP256K1`] context.
+    #[cfg(feature = "global-context")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "global-context")))]
+    pub fn verify(&self, msg: &Message, pk: &PublicKey) -> Result<(), Error> {
+        SECP256K1.verify_ecdsa(msg, self, pk)
+    }
 }
 
 impl CPtr for Signature {

src/ecdsa/recovery.rs

@@ -121,6 +121,14 @@ impl RecoverableSignature {
             Signature(ret)
         }
     }
+
+    /// Determines the public key for which this [`Signature`] is valid for `msg`. Requires a
+    /// verify-capable context.
+    #[cfg(feature = "global-context")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "global-context")))]
+    pub fn recover(&self, msg: &Message) -> Result<key::PublicKey, Error> {
+        SECP256K1.recover_ecdsa(msg, self)
+    }
 }
 
 

src/key.rs

@@ -28,6 +28,11 @@ use Verification;
 use constants;
 use ffi::{self, CPtr};
 
+#[cfg(feature = "global-context")]
+use {Message, ecdsa, SECP256K1};
+#[cfg(all(feature  = "global-context", feature = "rand-std"))]
+use schnorr;
+
 /// Secret 256-bit key used as `x` in an ECDSA signature.
 ///
 /// # Examples
@@ -279,6 +284,13 @@ impl SecretKey {
             }
         }
     }
+
+    /// Constructs an ECDSA signature for `msg` using the global [`SECP256K1`] context.
+    #[cfg(feature = "global-context")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "global-context")))]
+    pub fn sign_ecdsa(&self, msg: Message) -> ecdsa::Signature {
+        SECP256K1.sign_ecdsa(&msg, self)
+    }
 }
 
 #[cfg(feature = "serde")]
@@ -832,6 +844,13 @@ impl KeyPair {
     pub fn public_key(&self) -> XOnlyPublicKey {
         XOnlyPublicKey::from_keypair(self)
     }
+
+    /// Constructs an schnorr signature for `msg` using the global [`SECP256K1`] context.
+    #[cfg(all(feature = "global-context", feature = "rand-std"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "global-context")))]
+    pub fn sign_schnorr(&self, msg: Message) -> schnorr::Signature {
+        SECP256K1.sign_schnorr(&msg, self)
+    }
 }
 
 impl From<KeyPair> for SecretKey {

src/schnorr.rs

@@ -13,6 +13,9 @@ use ffi::{self, CPtr};
 use {constants, Secp256k1};
 use {Message, Signing, Verification, KeyPair, XOnlyPublicKey};
 
+#[cfg(all(feature  = "global-context", feature = "rand-std"))]
+use SECP256K1;
+
 /// Represents a Schnorr signature.
 pub struct Signature([u8; constants::SCHNORRSIG_SIGNATURE_SIZE]);
 impl_array_newtype!(Signature, u8, constants::SCHNORRSIG_SIGNATURE_SIZE);
@@ -88,6 +91,13 @@ impl Signature {
             _ => Err(Error::InvalidSignature),
         }
     }
+
+    /// Verifies a schnorr signature for `msg` using `pk` and the global [`SECP256K1`] context.
+    #[cfg(all(feature = "global-context", feature = "rand-std"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "global-context")))]
+    pub fn verify(&self, msg: &Message, pk: &XOnlyPublicKey) -> Result<(), Error> {
+        SECP256K1.verify_schnorr(self, msg, pk)
+    }
 }
 
 impl<C: Signing> Secp256k1<C> {