feat(c+go): implement API for obtaining the total number of rules

Implements the new function `yrx_rules_count()` in the C API, and the new method `Rules.Count()` in the Golang API.

capi/include/yara_x.h

@@ -209,6 +209,11 @@ enum YRX_RESULT yrx_rules_iterate(struct YRX_RULES *rules,
                                   YRX_RULE_CALLBACK callback,
                                   void *user_data);
 
+// Returns the total number of rules.
+//
+// Returns -1 in case of error.
+int yrx_rules_count(struct YRX_RULES *rules);
+
 // Destroys a [`YRX_RULES`] object.
 void yrx_rules_destroy(struct YRX_RULES *rules);
 

capi/src/lib.rs

@@ -48,10 +48,10 @@ cargo cinstall -p yara-x-capi --release
 
 The command above will put the library and header files in the correct path
 in your system (usually `/usr/local/lib` and `/usr/local/include` for Linux
-and MacOS users), and will generate a `.pc` file so that `pkg-config` knows
+and macOS users), and will generate a `.pc` file so that `pkg-config` knows
 about the library.
 
-In Linux and MacOS you can check if everything went fine by compiling a simple
+In Linux and macOS you can check if everything went fine by compiling a simple
 test program, like this:
 
 ```text
@@ -94,7 +94,7 @@ includes:
 #![allow(clippy::not_unsafe_ptr_arg_deref)]
 
 use std::cell::RefCell;
-use std::ffi::{c_char, c_void, CStr, CString};
+use std::ffi::{c_char, c_int, c_void, CStr, CString};
 use std::mem::ManuallyDrop;
 use std::ptr::slice_from_raw_parts_mut;
 use std::slice;
@@ -432,6 +432,18 @@ pub unsafe extern "C" fn yrx_rules_iterate(
     }
 }
 
+/// Returns the total number of rules.
+///
+/// Returns -1 in case of error.
+#[no_mangle]
+pub unsafe extern "C" fn yrx_rules_count(rules: *mut YRX_RULES) -> c_int {
+    if let Some(rules) = rules.as_ref() {
+        rules.0.iter().len() as c_int
+    } else {
+        -1
+    }
+}
+
 /// Destroys a [`YRX_RULES`] object.
 #[no_mangle]
 pub unsafe extern "C" fn yrx_rules_destroy(rules: *mut YRX_RULES) {

go/compiler_test.go

@@ -155,11 +155,13 @@ func TestRulesIter(t *testing.T) {
 	c.AddSource("rule test_2 { condition: true }")
 	assert.NoError(t, err)
 
-	rules := c.Build().Slice()
+  rules := c.Build()
+  assert.Equal(t, 2, rules.Count())
 
-	assert.Len(t, rules, 2)
-	assert.Equal(t, rules[0].Identifier(), "test_1")
-	assert.Equal(t, rules[1].Identifier(), "test_2")
+	slice := rules.Slice()
+	assert.Len(t, slice, 2)
+	assert.Equal(t, "test_1", slice[0].Identifier())
+	assert.Equal(t, "test_2", slice[1].Identifier())
 }
 
 func TestWarnings(t *testing.T) {

go/main.go

@@ -131,6 +131,15 @@ func (r *Rules) Slice() []*Rule {
 	return rules
 }
 
+// Count returns the total number of rules.
+//
+// This is more a more efficient alternative to len(rules.Slice()).
+func (r *Rules) Count() int {
+	count := C.yrx_rules_count(r.cRules)
+	runtime.KeepAlive(r)
+	return int(count)
+}
+
 // Rule represents a YARA rule.
 type Rule struct {
 	namespace  string