Added a new struct for the DER serialized signature

src/lib.rs

@@ -156,6 +156,7 @@ pub mod key;
 pub use key::SecretKey;
 pub use key::PublicKey;
 use core::marker::PhantomData;
+use core::ops::Deref;
 
 /// A tag used for recovering the public key from a compact signature
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
@@ -165,6 +166,13 @@ pub struct RecoveryId(i32);
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub struct Signature(ffi::Signature);
 
+/// A DER serialized Signature
+#[derive(Copy, Clone)]
+pub struct SerializedSignature {
+    data: [u8; 72],
+    len: usize,
+}
+
 impl fmt::Debug for Signature {
 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
     fmt::Display::fmt(self, f)
@@ -231,6 +239,40 @@ pub fn to_i32(self) -> i32 {
 }
 }
 
+impl SerializedSignature {
+    /// Get a pointer to the underlying data with the specified capacity.
+    pub(crate) fn get_data_mut_ptr(&mut self) -> *mut u8 {
+        self.data.as_mut_ptr()
+    }
+
+    /// Get the capacity of the underlying data buffer.
+    pub fn capacity(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Get the len of the used data.
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Set the length of the object.
+    pub(crate) fn set_len(&mut self, len: usize) {
+        self.len = len;
+    }
+
+    /// Convert the serialized signature into the Signature struct.
+    /// (This DER deserializes it)
+    pub fn to_signature(&self) -> Result<Signature, Error> {
+        Signature::from_der(&self)
+    }
+
+    /// Create a SerializedSignature from a Signature.
+    /// (this DER serializes it)
+    pub fn from_signature(sig: &Signature) -> SerializedSignature {
+        sig.serialize_der()
+    }
+}
+
 impl Signature {
 #[inline]
     /// Converts a DER-encoded byte slice to a signature
@@ -337,18 +379,18 @@ impl Signature {
 
     #[inline]
     /// Serializes the signature in DER format
-    pub fn serialize_der(&self) -> Vec<u8> {
+    pub fn serialize_der(&self) -> SerializedSignature {
-        let mut ret = Vec::with_capacity(72);
+        let mut ret = SerializedSignature::default();
-        let mut len: usize = ret.capacity() as usize;
+        let mut len: usize = ret.capacity();
         unsafe {
             let err = ffi::secp256k1_ecdsa_signature_serialize_der(
                 ffi::secp256k1_context_no_precomp,
-                ret.as_mut_ptr(),
+                ret.get_data_mut_ptr(),
                 &mut len,
                 self.as_ptr(),
             );
             debug_assert!(err == 1);
-            ret.set_len(len as usize);
+            ret.set_len(len);
         }
         ret
     }
@@ -590,6 +632,36 @@ impl<C> PartialEq for Secp256k1<C> {
     fn eq(&self, _other: &Secp256k1<C>) -> bool { true }
 }
 
+impl Default for SerializedSignature {
+    fn default() -> SerializedSignature {
+        SerializedSignature {
+            data: [0u8; 72],
+            len: 0,
+        }
+    }
+}
+
+impl PartialEq for SerializedSignature {
+    fn eq(&self, other: &SerializedSignature) -> bool {
+        &self.data[..self.len] == &other.data[..other.len]
+    }
+}
+
+impl AsRef<[u8]> for SerializedSignature {
+    fn as_ref(&self) -> &[u8] {
+        &self.data[..self.len]
+    }
+}
+
+impl Deref for SerializedSignature {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        &self.data[..self.len]
+    }
+}
+
+impl Eq for SerializedSignature {}
+
 impl<C> Eq for Secp256k1<C> { }
 
 impl<C> Drop for Secp256k1<C> {