Implement a sortedmulti_a descriptor

This is the starting point of implementing a sortedmulti_a descriptor
valid for taproot descriptors.

Author: Harshit933

src/descriptor/mod.rs

@@ -34,6 +34,7 @@ mod segwitv0;
 mod sh;
 mod sortedmulti;
 mod tr;
+mod sortedmulti_a;
 
 // Descriptor Exports
 pub use self::bare::{Bare, Pkh};

src/descriptor/sortedmulti_a.rs

@@ -0,0 +1,172 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::str::FromStr;
+
+use bitcoin::script;
+
+use crate::miniscript::context::ScriptContext;
+use crate::miniscript::decode::Terminal;
+use crate::miniscript::limits::MAX_PUBKEYS_PER_MULTISIG;
+use crate::miniscript::satisfy::{Placeholder, Satisfaction};
+use crate::plan::AssetProvider;
+use crate::prelude::*;
+use crate::{
+    errstr, expression, Error, ForEachKey, Miniscript, MiniscriptKey,
+    Satisfier, ToPublicKey, TranslateErr, Translator,
+};
+
+/// Contents of a "sortedmultiA" descriptor
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct SortedMultiAVec<Pk: MiniscriptKey, Ctx: ScriptContext> {
+    /// signatures required
+    pub k: usize,
+    /// public keys inside sorted Multi
+    pub pks: Vec<Pk>,
+    /// The current ScriptContext for sortedmultiA
+    pub(crate) phantom: PhantomData<Ctx>,
+}
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> SortedMultiAVec<Pk, Ctx> {
+    /// Create a new instance of `SortedMultiVecA` given a list of keys and the threshold
+    pub fn new(k: usize, pks: Vec<Pk>) -> Result<Self, Error> {
+        if pks.len() > MAX_PUBKEYS_PER_MULTISIG {
+            return Err(Error::BadDescriptor("Too many public keys".to_string()));
+        }
+
+        let term: Terminal<Pk, Ctx> = Terminal::MultiA(k, pks.clone());
+        let ms = Miniscript::from_ast(term)?;
+
+        Ctx::check_local_validity(&ms)?;
+
+        Ok(Self { k, pks, phantom: PhantomData })
+    }
+
+    /// Parse an expression tree into a SortedMultiVec
+    #[allow(dead_code)]
+    pub fn from_tree(tree: &expression::Tree) -> Result<Self, Error>
+    where
+        Pk: FromStr,
+        <Pk as FromStr>::Err: ToString,
+    {
+        if tree.args.is_empty() {
+            return Err(errstr("no arguments given for sortedmulti_a"));
+        }
+        let k = expression::parse_num(tree.args[0].name)?;
+        if k > (tree.args.len() - 1) as u32 {
+            return Err(errstr("higher threshold than there were keys in sortedmulti_a"));
+        }
+        let pks: Result<Vec<Pk>, _> = tree.args[1..]
+            .iter()
+            .map(|sub| expression::terminal(sub, Pk::from_str))
+            .collect();
+
+        pks.map(|pks| SortedMultiAVec::new(k as usize, pks))?
+    }
+
+    #[allow(dead_code)]
+    pub fn translate_pk<T, Q, FuncError>(
+        &self,
+        t: &mut T,
+    ) -> Result<SortedMultiAVec<Q, Ctx>, TranslateErr<FuncError>>
+    where
+        T: Translator<Pk, Q, FuncError>,
+        Q: MiniscriptKey,
+    {
+        let pks: Result<Vec<Q>, _> = self.pks.iter().map(|pk| t.pk(pk)).collect();
+        let res = SortedMultiAVec::new(self.k, pks?).map_err(TranslateErr::OuterError)?;
+        Ok(res)
+    }
+}
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> ForEachKey<Pk> for SortedMultiAVec<Pk, Ctx> {
+    fn for_each_key<'a, F: FnMut(&'a Pk) -> bool>(&'a self, pred: F) -> bool {
+        self.pks.iter().all(pred)
+    }
+}
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> SortedMultiAVec<Pk, Ctx> {
+    /// utility function to sanity a sorted multi vec
+    #[allow(dead_code)]
+    pub fn sanity_check(&self) -> Result<(), Error> {
+        let ms: Miniscript<Pk, Ctx> =
+            Miniscript::from_ast(Terminal::MultiA(self.k, self.pks.clone()))
+                .expect("Must typecheck");
+        // '?' for doing From conversion
+        ms.sanity_check()?;
+        Ok(())
+    }
+}
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> SortedMultiAVec<Pk, Ctx> {
+    /// Create Terminal::Multi containing sorted pubkeys
+    #[allow(dead_code)]
+    pub fn sorted_node(&self) -> Terminal<Pk, Ctx>
+    where
+        Pk: ToPublicKey,
+    {
+        let mut pks = self.pks.clone();
+        pks.sort_by(|a, b| {
+            a.to_public_key()
+                .inner
+                .serialize()
+                .partial_cmp(&b.to_public_key().inner.serialize())
+                .unwrap()
+        });
+        Terminal::MultiA(self.k, pks)
+    }
+
+    /// Encode as a Bitcoin script
+    #[allow(dead_code)]
+    pub fn encode(&self) -> script::ScriptBuf
+    where
+        Pk: ToPublicKey,
+    {
+        self.sorted_node()
+            .encode(script::Builder::new())
+            .into_script()
+    }
+
+    #[allow(dead_code)]
+    pub fn satisfy<S>(&self, satisfier: S) -> Result<Vec<Vec<u8>>, Error>
+    where
+        Pk: ToPublicKey,
+        S: Satisfier<Pk>,
+    {
+        todo!("Unimplemented")
+    }
+
+    #[allow(dead_code)]
+    pub fn build_template<P>(&self, provider: &P) -> Satisfaction<Placeholder<Pk>>
+    where
+        Pk: ToPublicKey,
+        P: AssetProvider<Pk>,
+    {
+        todo!("Unimplemented")
+    }
+
+    #[allow(dead_code)]
+    pub fn script_size(&self) -> usize {
+        todo!("Unimplemented")
+    }
+
+    #[allow(dead_code)]
+    pub fn max_satisfaction_witness_elements(&self) -> usize { self.pks.len() }
+
+    #[allow(dead_code)]
+    pub fn max_satisfaction_size(&self) -> usize { (1 + 65) * self.k + (self.pks.len() - self.k) }
+}
+
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> fmt::Debug for SortedMultiAVec<Pk, Ctx> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Display::fmt(self, f) }
+}
+
+impl<Pk: MiniscriptKey, Ctx: ScriptContext> fmt::Display for SortedMultiAVec<Pk, Ctx> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "sortedmulti_a({}", self.k)?;
+        for k in &self.pks {
+            write!(f, ",{}", k)?;
+        }
+        f.write_str(")")
+    }
+}