c_no_std binding to show use in C freestanding environments. (#238)

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/c-nostd/CMakeLists.txt

@@ -0,0 +1,41 @@
+# Copyright (c) Microsoft
+# Licensed under the MIT License.
+
+cmake_minimum_required(VERSION 3.12 FATAL_ERROR)
+include(FetchContent)
+
+FetchContent_Declare(
+    Corrosion
+    GIT_REPOSITORY https://github.com/corrosion-rs/corrosion.git
+    GIT_TAG v0.4 # Optionally specify a commit hash, version tag or branch here
+)
+FetchContent_MakeAvailable(Corrosion)
+
+project("regorus-test")
+
+corrosion_import_crate(
+  # Path to <regorus-source-folder>/bindings/ffi/Cargo.toml
+  MANIFEST_PATH "../ffi/Cargo.toml"
+  # Always build regorus in Release mode.
+  PROFILE "release"
+  # Only build the "regorus-ffi" crate.
+  CRATES "regorus-ffi"
+  
+  # Turn off std support in regorus-ffi.
+  NO_DEFAULT_FEATURES
+  NO_STD
+
+  # custom_allocator allows using a custom memory allocator.
+  # To use malloc/free remove custom_allocator below.
+  # Additionally, select specific features in regorus.
+  # See regorus/opa_no_std
+  FEATURES "custom_allocator,regorus/semver"
+
+  # Link statically
+  CRATE_TYPES staticlib FLAGS --crate-type=staticlib
+  )
+
+add_executable(regorus_test_nostd main.c)
+# Add path to <regorus-source-folder>/bindings/ffi
+target_include_directories(regorus_test_nostd PRIVATE "../ffi")
+target_link_libraries(regorus_test_nostd regorus-ffi)

bindings/c-nostd/main.c

@@ -0,0 +1,96 @@
+#include <stdio.h>
+#include "regorus.h"
+
+
+// Regorus has been built for no_std and cannot access files.
+char*  file_to_string(const char* file) {
+    char * buffer = 0;
+    long length;
+    FILE * f = fopen (file, "rb");
+    
+    if (f)
+    {
+	fseek (f, 0, SEEK_END);
+	length = ftell (f);
+	fseek (f, 0, SEEK_SET);
+	buffer = malloc (length);
+	if (buffer)
+	{
+	    fread (buffer, 1, length, f);
+	}
+	fclose (f);
+    }
+
+    return buffer;
+}
+
+// If regorus is built with custom-allocator, then provide implementation.
+uint8_t* regorus_aligned_alloc(size_t alignment, size_t size) {
+    printf("%ld %ld\n", size, alignment);
+    fflush(stdout);
+    return aligned_alloc(alignment, size);
+}
+
+void regorus_free(uint8_t* ptr) {
+    free(ptr);
+}
+
+
+int main() {
+    // Create engine.
+    RegorusEngine* engine = regorus_engine_new();
+    RegorusResult r;
+    char* buffer = NULL;
+
+    // Load policies.
+    r = regorus_engine_add_policy(engine, "framework.rego", (buffer = file_to_string("../../../tests/aci/framework.rego")));
+    free(buffer);
+    if (r.status != RegorusStatusOk)
+	goto error;
+    regorus_result_drop(r);
+
+    r = regorus_engine_add_policy(engine, "api.rego", (buffer = file_to_string("../../../tests/aci/api.rego")));
+    free(buffer);
+    if (r.status != RegorusStatusOk)
+	goto error;
+    regorus_result_drop(r);
+    
+    r = regorus_engine_add_policy(engine, "policy.rego", (buffer = file_to_string("../../../tests/aci/policy.rego")));
+    free(buffer);
+    if (r.status != RegorusStatusOk)
+	goto error;
+    regorus_result_drop(r);
+
+    // Add data
+    r = regorus_engine_add_data_json(engine, (buffer = file_to_string("../../../tests/aci/data.json")));
+    free(buffer);
+    if (r.status != RegorusStatusOk)
+	goto error;
+    regorus_result_drop(r);
+
+    // Set input
+    r = regorus_engine_set_input_json(engine, (buffer = file_to_string("../../../tests/aci/input.json")));
+    free(buffer);
+    if (r.status != RegorusStatusOk)
+	goto error;
+    regorus_result_drop(r);
+
+    // Eval query
+    r = regorus_engine_eval_query(engine, "data.framework.mount_overlay=x");
+    if (r.status != RegorusStatusOk)
+	goto error;
+
+    // Print output
+    printf("%s", r.output);
+    regorus_result_drop(r);
+    
+    
+    // Free the engine.
+    regorus_engine_drop(engine);
+
+    return 0;
+error:
+    printf("%s", r.error_message);
+	
+    return 1;
+}