add satisfaction checks

Author: sanket1729

src/descriptor/mod.rs

@@ -45,6 +45,7 @@ use miniscript::{decode::Terminal, Legacy, Miniscript, Segwitv0};
 use policy;
 use push_opcode_size;
 use script_num_size;
+use util::witness_to_scriptsig;
 use Bare;
 use Error;
 use MiniscriptKey;
@@ -983,18 +984,6 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
         Pk: ToPublicKey<ToPkCtx>,
         S: Satisfier<ToPkCtx, Pk>,
     {
-        fn witness_to_scriptsig(witness: &[Vec<u8>]) -> Script {
-            let mut b = script::Builder::new();
-            for wit in witness {
-                if let Ok(n) = script::read_scriptint(wit) {
-                    b = b.push_int(n);
-                } else {
-                    b = b.push_slice(wit);
-                }
-            }
-            b.into_script()
-        }
-
         match *self {
             Descriptor::Bare(ref d) => {
                 let wit = match d.satisfy(satisfier, to_pk_ctx) {

src/lib.rs

@@ -119,6 +119,8 @@ pub mod miniscript;
 pub mod policy;
 pub mod psbt;
 
+mod util;
+
 use std::str::FromStr;
 use std::{error, fmt, hash, str};
 

src/miniscript/context.rs

@@ -18,6 +18,7 @@ use miniscript::types::extra_props::{
     MAX_STANDARD_P2WSH_SCRIPT_SIZE, MAX_STANDARD_P2WSH_STACK_ITEMS,
 };
 use std::fmt;
+use util::{witness_size, witness_to_scriptsig};
 use Error;
 use {Miniscript, MiniscriptKey, Terminal};
 /// Error for Script Context
@@ -111,6 +112,18 @@ pub trait ScriptContext:
         _frag: &Terminal<Pk, Ctx>,
     ) -> Result<(), ScriptContextError>;
 
+    /// Check whether the given satisfaction is valid under the ScriptContext
+    /// For example, segwit satisfactions may fail if the witness len is more
+    /// 3600 or number of stack elements are more than 100.
+    fn check_witness<Pk: MiniscriptKey, Ctx: ScriptContext>(
+        _witness: &[Vec<u8>],
+    ) -> Result<(), ScriptContextError> {
+        // Only really need to do this for segwitv0 and legacy
+        // Bare is already restrcited by standardness rules
+        // and would reach these limits.
+        Ok(())
+    }
+
     /// Depending on script context, the size of a satifaction witness may slightly differ.
     fn max_satisfaction_size<Pk: MiniscriptKey, Ctx: ScriptContext>(
         ms: &Miniscript<Pk, Ctx>,
@@ -241,6 +254,17 @@ impl ScriptContext for Legacy {
         }
     }
 
+    fn check_witness<Pk: MiniscriptKey, Ctx: ScriptContext>(
+        witness: &[Vec<u8>],
+    ) -> Result<(), ScriptContextError> {
+        // In future, we could avoid by having a function to count only
+        // len of script instead of converting it.
+        if witness_to_scriptsig(witness).len() > MAX_SCRIPTSIG_SIZE {
+            return Err(ScriptContextError::MaxScriptSigSizeExceeded);
+        }
+        Ok(())
+    }
+
     fn check_global_consensus_validity<Pk: MiniscriptKey, Ctx: ScriptContext>(
         ms: &Miniscript<Pk, Ctx>,
     ) -> Result<(), ScriptContextError> {
@@ -294,6 +318,17 @@ impl ScriptContext for Segwitv0 {
         Ok(())
     }
 
+    fn check_witness<Pk: MiniscriptKey, Ctx: ScriptContext>(
+        witness: &[Vec<u8>],
+    ) -> Result<(), ScriptContextError> {
+        if witness_size(witness) > MAX_STANDARD_P2WSH_SCRIPT_SIZE {
+            return Err(ScriptContextError::MaxScriptSigSizeExceeded);
+        } else if witness.len() > MAX_STANDARD_P2WSH_STACK_ITEMS {
+            return Err(ScriptContextError::MaxWitnessItemssExceeded);
+        }
+        Ok(())
+    }
+
     fn check_global_consensus_validity<Pk: MiniscriptKey, Ctx: ScriptContext>(
         ms: &Miniscript<Pk, Ctx>,
     ) -> Result<(), ScriptContextError> {

src/miniscript/satisfy.rs

@@ -29,6 +29,7 @@ use {MiniscriptKey, ToPublicKey};
 use miniscript::types::extra_props::{
     HEIGHT_TIME_THRESHOLD, SEQUENCE_LOCKTIME_DISABLE_FLAG, SEQUENCE_LOCKTIME_TYPE_FLAG,
 };
+use util::witness_size;
 use Error;
 use Miniscript;
 use NullCtx;
@@ -415,15 +416,6 @@ impl PartialOrd for Witness {
     }
 }
 
-fn varint_len(n: usize) -> usize {
-    bitcoin::VarInt(n as u64).len()
-}
-
-// Helper function to calculate witness size
-fn witness_size(wit: &[Vec<u8>]) -> usize {
-    wit.iter().map(Vec::len).sum::<usize>() + varint_len(wit.len())
-}
-
 impl Ord for Witness {
     fn cmp(&self, other: &Self) -> cmp::Ordering {
         match (self, other) {

src/util.rs

@@ -0,0 +1,23 @@
+use bitcoin;
+use bitcoin::blockdata::script;
+use bitcoin::Script;
+pub(crate) fn varint_len(n: usize) -> usize {
+    bitcoin::VarInt(n as u64).len()
+}
+
+// Helper function to calculate witness size
+pub(crate) fn witness_size(wit: &[Vec<u8>]) -> usize {
+    wit.iter().map(Vec::len).sum::<usize>() + varint_len(wit.len())
+}
+
+pub(crate) fn witness_to_scriptsig(witness: &[Vec<u8>]) -> Script {
+    let mut b = script::Builder::new();
+    for wit in witness {
+        if let Ok(n) = script::read_scriptint(wit) {
+            b = b.push_int(n);
+        } else {
+            b = b.push_slice(wit);
+        }
+    }
+    b.into_script()
+}