capi: has_start_function check

include/fizzy/fizzy.h

@@ -200,6 +200,12 @@ bool fizzy_module_has_memory(const FizzyModule* module);
 bool fizzy_find_exported_function_index(
     const FizzyModule* module, const char* name, uint32_t* out_func_idx);
 
+/// Check whether module has a start function.
+///
+/// @param  module          Pointer to module. Cannot be NULL.
+/// @return                 true if module has a start function, false otherwise.
+bool fizzy_module_has_start_function(const FizzyModule* module);
+
 /// Instantiate a module.
 ///
 /// The instance takes ownership of the module, i.e. fizzy_free_module must not be called on the

lib/fizzy/capi.cpp

@@ -404,6 +404,11 @@ bool fizzy_find_exported_global(
     return true;
 }
 
+bool fizzy_module_has_start_function(const FizzyModule* module)
+{
+    return unwrap(module)->startfunc.has_value();
+}
+
 FizzyInstance* fizzy_instantiate(const FizzyModule* module,
     const FizzyExternalFunction* imported_functions, size_t imported_functions_size,
     const FizzyExternalTable* imported_table, const FizzyExternalMemory* imported_memory,

test/unittests/capi_test.cpp

@@ -388,6 +388,32 @@ TEST(capi, find_exported_global)
     fizzy_free_instance(instance);
 }
 
+TEST(capi, has_start_function)
+{
+    /* wat2wasm
+      (module)
+    */
+    const auto wasm_no_start = from_hex("0061736d01000000");
+    const auto module_no_start = fizzy_parse(wasm_no_start.data(), wasm_no_start.size());
+    ASSERT_NE(module_no_start, nullptr);
+
+    EXPECT_FALSE(fizzy_module_has_start_function(module_no_start));
+
+    fizzy_free_module(module_no_start);
+
+    /* wat2wasm
+      (func)
+      (start 0)
+    */
+    const auto wasm_start = from_hex("0061736d01000000010401600000030201000801000a040102000b");
+    const auto module_start = fizzy_parse(wasm_start.data(), wasm_start.size());
+    ASSERT_NE(module_start, nullptr);
+
+    EXPECT_TRUE(fizzy_module_has_start_function(module_start));
+
+    fizzy_free_module(module_start);
+}
+
 TEST(capi, instantiate)
 {
     uint8_t wasm_prefix[]{0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00};