Add from_program_json_and_class_hash (#836)

* Add from_program_json_and_class_hash

* Use include_str

* Remove unused reference

* Add docs

* Update docs

---------

Co-authored-by: Juan Bono <juanbono94@gmail.com>

Author: matias-gonz

src/services/api/contract_class_errors.rs

@@ -13,4 +13,8 @@ pub enum ContractClassError {
     NotACasmContractClass,
     #[error("Not a deprecated contract class")]
     NotADeprecatedContractClass,
+    #[error("Parse error")]
+    ParseError,
+    #[error("Program error: {0}")]
+    ProgramError(String),
 }

src/services/api/contract_classes/deprecated_contract_class.rs

@@ -128,6 +128,36 @@ impl ContractClass {
         })
     }
 
+    /// Parses a [`ContractClass`] from a compiled Cairo 0 program's JSON and a class hash.
+    ///
+    /// This constructor avoids the need to recompute the class hash from the program JSON,
+    /// but it does not verify that the given class hash is correct.
+    ///
+    /// This could return a wrong [`ContractClass`] if the given class hash is wrong.
+    ///
+    /// # Parameters
+    /// - `program_json`: The JSON of the compiled Cairo 0 program.
+    /// - `hinted_class_hash`: The class hash of the program.
+    ///
+    /// # Returns
+    /// A [`ContractClass`] parsed from the given JSON and class hash.
+    pub fn from_program_json_and_class_hash(
+        program_json: &str,
+        hinted_class_hash: Felt252,
+    ) -> Result<Self, ContractClassError> {
+        let contract_class: starknet_api::deprecated_contract_class::ContractClass =
+            serde_json::from_str(program_json).map_err(|_| ContractClassError::ParseError)?;
+        let program = to_cairo_runner_program(contract_class.program)
+            .map_err(|e| ContractClassError::ProgramError(e.to_string()))?;
+        let entry_points_by_type = convert_entry_points(contract_class.entry_points_by_type);
+        Ok(ContractClass {
+            hinted_class_hash,
+            program,
+            entry_points_by_type,
+            abi: contract_class.abi,
+        })
+    }
+
     /// Parses a [`ContractClass`] from a compiled Cairo 0 program's JSON
     /// at the given file path.
     pub fn from_path<F>(path: F) -> Result<Self, ProgramError>
@@ -393,4 +423,22 @@ mod tests {
 
         res.expect("should be able to read file");
     }
+
+    #[test]
+    fn test_from_program_json_and_class_hash_should_equal_from_path() {
+        let program_json = include_str!("../../../../starknet_programs/fibonacci.json");
+        let contract_class_from_path = ContractClass::from_path("starknet_programs/fibonacci.json")
+            .expect("should be able to read file");
+
+        let contract_class_from_program_json_and_class_hash =
+            ContractClass::from_program_json_and_class_hash(
+                program_json,
+                contract_class_from_path.hinted_class_hash.clone(),
+            )
+            .expect("should be able to read file");
+        assert_eq!(
+            contract_class_from_path,
+            contract_class_from_program_json_and_class_hash
+        );
+    }
 }