limit the number of StatementTmpl in CustomPredicate: (#101)

* limit the number of StatementTmpl in CustomPredicate:

- add constructor method for CustomPredicate
- make size checks at the CustomPredicate creation, so that once instantiated we can assume that contains valid data

This resolves #79

* Update tests to use new interface

---------

Co-authored-by: Ahmad <root@ahmadafuni.com>

src/frontend/custom.rs

@@ -1,8 +1,9 @@
 #![allow(unused)]
+use anyhow::Result;
 use std::sync::Arc;
 
 use crate::middleware::{
-    hash_str, CustomPredicate, CustomPredicateBatch, Hash, HashOrWildcard, NativePredicate,
+    hash_str, CustomPredicate, CustomPredicateBatch, Hash, HashOrWildcard, NativePredicate, Params,
     Predicate, StatementTmpl, StatementTmplArg, ToFields, Value, F,
 };
 
@@ -96,31 +97,34 @@ impl CustomPredicateBatchBuilder {
 
     fn predicate_and(
         &mut self,
+        params: &Params,
         args: &[&str],
         priv_args: &[&str],
         sts: &[StatementTmplBuilder],
-    ) -> Predicate {
-        self.predicate(true, args, priv_args, sts)
+    ) -> Result<Predicate> {
+        self.predicate(params, true, args, priv_args, sts)
     }
 
     fn predicate_or(
         &mut self,
+        params: &Params,
         args: &[&str],
         priv_args: &[&str],
         sts: &[StatementTmplBuilder],
-    ) -> Predicate {
-        self.predicate(false, args, priv_args, sts)
+    ) -> Result<Predicate> {
+        self.predicate(params, false, args, priv_args, sts)
     }
 
     /// creates the custom predicate from the given input, adds it to the
     /// self.predicates, and returns the index of the created predicate
     fn predicate(
         &mut self,
+        params: &Params,
         conjunction: bool,
         args: &[&str],
         priv_args: &[&str],
         sts: &[StatementTmplBuilder],
-    ) -> Predicate {
+    ) -> Result<Predicate> {
         let statements = sts
             .iter()
             .map(|sb| {
@@ -138,13 +142,9 @@ impl CustomPredicateBatchBuilder {
                 StatementTmpl(sb.predicate.clone(), args)
             })
             .collect();
-        let custom_predicate = CustomPredicate {
-            conjunction,
-            statements,
-            args_len: args.len(),
-        };
+        let custom_predicate = CustomPredicate::new(params, conjunction, statements, args.len())?;
         self.predicates.push(custom_predicate);
-        Predicate::BatchSelf(self.predicates.len() - 1)
+        Ok(Predicate::BatchSelf(self.predicates.len() - 1))
     }
 
     fn finish(self) -> Arc<CustomPredicateBatch> {
@@ -174,7 +174,7 @@ mod tests {
     use crate::middleware::{CustomPredicateRef, Params, PodType};
 
     #[test]
-    fn test_custom_pred() {
+    fn test_custom_pred() -> Result<()> {
         use NativePredicate as NP;
         use StatementTmplBuilder as STB;
 
@@ -183,6 +183,7 @@ mod tests {
 
         let mut builder = CustomPredicateBatchBuilder::new("eth_friend".into());
         let _eth_friend = builder.predicate_and(
+            &params,
             // arguments:
             &["src_ori", "src_key", "dst_ori", "dst_key"],
             // private arguments:
@@ -202,7 +203,7 @@ mod tests {
                     .arg(("attestation_pod", literal("attestation")))
                     .arg(("dst_ori", "dst_key")),
             ],
-        );
+        )?;
 
         println!("a.0. eth_friend = {}", builder.predicates.last().unwrap());
         let eth_friend = builder.finish();
@@ -216,6 +217,7 @@ mod tests {
         // >
         let mut builder = CustomPredicateBatchBuilder::new("eth_dos_distance_base".into());
         let eth_dos_distance_base = builder.predicate_and(
+            &params,
             &[
                 // arguments:
                 "src_ori",
@@ -236,7 +238,7 @@ mod tests {
                     .arg(("distance_ori", "distance_key"))
                     .arg(0),
             ],
-        );
+        )?;
         println!(
             "b.0. eth_dos_distance_base = {}",
             builder.predicates.last().unwrap()
@@ -246,6 +248,7 @@ mod tests {
 
         // next chunk builds:
         let eth_dos_distance_ind = builder.predicate_and(
+            &params,
             &[
                 // arguments:
                 "src_ori",
@@ -281,7 +284,7 @@ mod tests {
                     .arg(("intermed_ori", "intermed_key"))
                     .arg(("dst_ori", "dst_key")),
             ],
-        );
+        )?;
 
         println!(
             "b.1. eth_dos_distance_ind = {}",
@@ -289,6 +292,7 @@ mod tests {
         );
 
         let _eth_dos_distance = builder.predicate_or(
+            &params,
             &[
                 "src_ori",
                 "src_key",
@@ -308,7 +312,7 @@ mod tests {
                     .arg(("dst_ori", "dst_key"))
                     .arg(("distance_ori", "distance_key")),
             ],
-        );
+        )?;
 
         println!(
             "b.2. eth_dos_distance = {}",
@@ -318,5 +322,7 @@ mod tests {
         let eth_dos_batch_b = builder.finish();
         let fields = eth_dos_batch_b.to_fields(&params);
         println!("Batch b, serialized: {:?}", fields);
+
+        Ok(())
     }
 }

src/frontend/operation.rs

@@ -1,7 +1,7 @@
 use std::fmt;
 
 use super::{AnchoredKey, SignedPod, Statement, StatementArg, Value};
-use crate::middleware::{hash_str, NativeOperation, NativePredicate, OperationType, Predicate};
+use crate::middleware::{hash_str, NativePredicate, OperationType, Predicate};
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum OperationArg {