Add Descriptor::max_satisfaction_weight function

bdk-ffi/src/bdk.udl

@@ -475,6 +475,9 @@ interface Descriptor {
   [Name=new_bip84_public]
   constructor(DescriptorPublicKey public_key, string fingerprint, KeychainKind keychain, Network network);
 
+  [Throws=BdkError]
+  u32 max_satisfaction_weight();
+
   string as_string();
 
   string as_string_private();

bdk-ffi/src/descriptor.rs

@@ -10,6 +10,7 @@ use bdk::template::{
     Bip44, Bip44Public, Bip49, Bip49Public, Bip84, Bip84Public, DescriptorTemplate,
 };
 use bdk::KeychainKind;
+use std::convert::TryFrom;
 use std::ops::Deref;
 use std::str::FromStr;
 use std::sync::Arc;
@@ -183,6 +184,22 @@ impl Descriptor {
         }
     }
 
+    /// Computes an upper bound on the weight of a satisfying witness to the
+    /// transaction.
+    ///
+    /// Assumes all ec-signatures are 73 bytes, including push opcode and
+    /// sighash suffix. Includes the weight of the VarInts encoding the
+    /// scriptSig and witness stack length.
+    ///
+    /// # Errors
+    /// When the descriptor is impossible to satisfy (ex: sh(OP_FALSE)).
+    pub(crate) fn max_satisfaction_weight(&self) -> Result<u32, BdkError> {
+        self.extended_descriptor
+            .max_satisfaction_weight()
+            .map(|w| u32::try_from(w).unwrap())
+            .map_err(BdkError::Miniscript)
+    }
+
     pub(crate) fn as_string_private(&self) -> String {
         let descriptor = &self.extended_descriptor;
         let key_map = &self.key_map;