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

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

.gitignore

@@ -13,4 +13,7 @@ Cargo.lock
 .vscode/
 
 # worktrees
-worktrees/
+worktrees/
+
+# build folders
+**/build

Cargo.toml

@@ -121,7 +121,7 @@ jsonwebtoken = { version = "9.2.0", optional = true }
 itertools = { version = "0.12.1", default-features = false, optional = true }
 
 serde_yaml = {version = "0.9.16", default-features = false, optional = true }
-rand = { version = "0.8.5", default-features = false, optional = true } 
+rand = { version = "0.8.5", default-features = false, optional = true }
 
 [dev-dependencies]
 anyhow = "1.0.45"

README.md

@@ -8,6 +8,7 @@
 
 Regorus is also
   - *cross-platform* - Written in platform-agnostic Rust.
+  - *no_std compatible* - Regorus can be used in `no_std` environments too. Most of the builtins are supported.
   - *current* - We strive to keep Regorus up to date with latest OPA release. Regorus supports `import rego.v1`.
   - *compliant* - Regorus is mostly compliant with the latest [OPA release v0.64.0](https://github.com/open-policy-agent/opa/releases/tag/v0.64.0). See [OPA Conformance](#opa-conformance) for details. Note that while we behaviorally produce the same results, we don't yet support all the builtins.
   - *extensible* - Extend the Rego language by implementing custom stateful builtins in Rust.
@@ -85,7 +86,7 @@ Regorus is designed with [Confidential Computing](https://confidentialcomputing.
 it is important to be able to control exactly what is being run. Regorus allows enabling and disabling various components using cargo
 features. By default all features are enabled.
 
-The default build of regorus example program is 6.4M:
+The default build of regorus example program is 6.3M:
 ```bash
 $ cargo build -r --example regorus; strip target/release/examples/regorus; ls -lh target/release/examples/regorus
 -rwxr-xr-x  1 anand  staff   6.3M May 11 22:03 target/release/examples/regorus*
@@ -108,6 +109,7 @@ Regorus can be used from a variety of languages:
 - *C*: C binding is generated using [cbindgen](https://github.com/mozilla/cbindgen).
   [corrosion-rs](https://github.com/corrosion-rs/corrosion) can be used to seamlessly use Regorous
    in your CMake based projects. See [bindings/c](https://github.com/microsoft/regorus/tree/main/bindings/c).
+- *C freestanding*: [bindings/c_no_std](https://github.com/microsoft/regorus/tree/main/bindings/c_no_std) shows how to use Regorus from C environments without a libc.
 - *C++*: C++ binding is generated using [cbindgen](https://github.com/mozilla/cbindgen).
   [corrosion-rs](https://github.com/corrosion-rs/corrosion) can be used to seamlessly use Regorous
    in your CMake based projects. See [bindings/cpp](https://github.com/microsoft/regorus/tree/main/bindings/cpp).

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;
+}

bindings/c/CMakeLists.txt

@@ -18,8 +18,15 @@ corrosion_import_crate(
   MANIFEST_PATH "../ffi/Cargo.toml"
   # Always build regorus in Release mode.
   PROFILE "release"
-  # Only build the "regorusc" crate.
-  CRATES "regorus-ffi")
+  # Only build the "regorus-ffi" crate.
+  CRATES "regorus-ffi"
+
+  # Select specific features in regorus.
+  FEATURES "regorus/semver"
+
+  # Link statically
+  CRATE_TYPES "staticlib"
+  )
 
 add_executable(regorus_test main.c)
 # Add path to <regorus-source-folder>/bindings/ffi

bindings/ffi/Cargo.toml

@@ -5,13 +5,18 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 [lib]
-crate-type = ["cdylib"]
+crate-type = ["cdylib", "staticlib"]
 
 [dependencies]
 anyhow = "1.0"
-regorus = { path  = "../.." }
+regorus = { path  = "../..", default-features = false }
 serde_json = "1.0.113"
 
+[features]
+default = ["std"]
+std = ["regorus/std"]
+custom_allocator = []
+
 [build-dependencies]
 cbindgen = "0.26.0"
 csbindgen = "1.9.0"

bindings/ffi/RegorusFFI.g.cs

@@ -85,4 +85,3 @@ namespace RegorusFFI
 
 
 }
-    

bindings/ffi/cbindgen.toml

@@ -137,9 +137,6 @@ bitflags = false
 
 
 
-
-
-
 ############## Options for How Your Rust library Should Be Parsed ##############
 
 [parse]
@@ -154,5 +151,5 @@ extra_bindings = []
 [parse.expand]
 crates = []
 all_features = false
-default_features = true
+default_features = false
 features = []

bindings/ffi/regorus.ffi.hpp

@@ -90,6 +90,10 @@ RegorusResult regorus_engine_set_input_from_json_file(RegorusEngine *engine, con
 /// * `query`: Rego expression to be evaluate.
 RegorusResult regorus_engine_eval_query(RegorusEngine *engine, const char *query);
 
+extern uint8_t *regorus_aligned_alloc(uintptr_t alignment, uintptr_t size);
+
+extern void regorus_free(uint8_t *ptr);
+
 } // extern "C"
 
 #endif // REGORUS_FFI_HPP

bindings/ffi/regorus.h

@@ -124,4 +124,8 @@ struct RegorusResult regorus_engine_set_input_from_json_file(struct RegorusEngin
  */
 struct RegorusResult regorus_engine_eval_query(struct RegorusEngine *engine, const char *query);
 
+extern uint8_t *regorus_aligned_alloc(uintptr_t alignment, uintptr_t size);
+
+extern void regorus_free(uint8_t *ptr);
+
 #endif /* REGORUS_H */

bindings/ffi/src/lib.rs

@@ -127,7 +127,6 @@ pub extern "C" fn regorus_engine_drop(engine: *mut RegorusEngine) {
 ///
 /// * `path`: A filename to be associated with the policy.
 /// * `rego`: Rego policy.
-
 #[no_mangle]
 pub extern "C" fn regorus_engine_add_policy(
     engine: *mut RegorusEngine,
@@ -141,6 +140,7 @@ pub extern "C" fn regorus_engine_add_policy(
     }())
 }
 
+#[cfg(feature = "std")]
 #[no_mangle]
 pub extern "C" fn regorus_engine_add_policy_from_file(
     engine: *mut RegorusEngine,
@@ -169,6 +169,7 @@ pub extern "C" fn regorus_engine_add_data_json(
     }())
 }
 
+#[cfg(feature = "std")]
 #[no_mangle]
 pub extern "C" fn regorus_engine_add_data_from_json_file(
     engine: *mut RegorusEngine,
@@ -209,6 +210,7 @@ pub extern "C" fn regorus_engine_set_input_json(
     }())
 }
 
+#[cfg(feature = "std")]
 #[no_mangle]
 pub extern "C" fn regorus_engine_set_input_from_json_file(
     engine: *mut RegorusEngine,
@@ -246,3 +248,32 @@ pub extern "C" fn regorus_engine_eval_query(
         Err(e) => to_regorus_result(Err(e)),
     }
 }
+
+#[cfg(feature = "custom_allocator")]
+extern "C" {
+    fn regorus_aligned_alloc(alignment: usize, size: usize) -> *mut u8;
+    fn regorus_free(ptr: *mut u8);
+}
+
+#[cfg(feature = "custom_allocator")]
+mod allocator {
+    use std::alloc::{GlobalAlloc, Layout};
+
+    struct RegorusAllocator {}
+
+    unsafe impl GlobalAlloc for RegorusAllocator {
+        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+            let size = layout.size();
+            let align = layout.align();
+
+            crate::regorus_aligned_alloc(align, size)
+        }
+
+        unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+            crate::regorus_free(ptr)
+        }
+    }
+
+    #[global_allocator]
+    static ALLOCATOR: RegorusAllocator = RegorusAllocator {};
+}