From c484777f3a7dde9e9fe8f47344fd8a6b30840b78 Mon Sep 17 00:00:00 2001
From: Robin Krahl <robin.krahl@ireas.org>
Date: Tue, 22 Sep 2020 19:09:40 +0200
Subject: Add feature to generate bindings during build

This patch adds the bindgen feature to the crate that allows users to
re-generate the bindings, including layout tests, during the build
instead of using the pre-generated bindings.  Per default, this feature
is disabled.
---
 CHANGELOG.md |  2 ++
 Cargo.toml   |  4 ++++
 Makefile     |  1 +
 README.md    |  7 +++++++
 build.rs     | 32 ++++++++++++++++++++++++++++++++
 src/lib.rs   |  5 +++++
 6 files changed, 51 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8efd48c..5991614 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@
 - Implement `std::fmt::Display` instead of `std::string::ToString` for the
   `Version` enum in `build.rs`.
 - Do not include layout tests in the generated bindings.
+- Add `bindgen` feature that re-generates the bindings during the build,
+  including layout tests.
 - Update to libnitrokey 3.6, causing all following changes.
 - New constants:
   - `NK_device_model_NK_LIBREM` (`NK_device_model` enum)
diff --git a/Cargo.toml b/Cargo.toml
index 068670b..99b2afd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,4 +13,8 @@ build = "build.rs"
 readme = "README.md"
 
 [build-dependencies]
+bindgen = { version = "0.55.1", optional = true }
 cc = "1.0"
+
+[features]
+default = []
diff --git a/Makefile b/Makefile
index b5fec75..b0b5bba 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,7 @@ LIBNITROKEY ?= $(wildcard libnitrokey-v*)
 
 src/ffi.rs: ${LIBNITROKEY}/NK_C_API.h
 	quilt pop -af || true
+	# always keep options in sync with build.rs
 	${BINDGEN} \
 		--whitelist-function "NK_.*" \
 		--whitelist-var "NK_.*" \
diff --git a/README.md b/README.md
index 343b7b5..2646a33 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,13 @@ crate, it links directly against `libnitrokey` instead of building it from
 source.  In this case, `libnitrokey` must be available in the library search
 path.
 
+Per default, this crate uses bindings that have been generated using Rust’s
+`x86_64-unknown-linux-gnu` target.  To the best of our knowledge, these
+bindings are platform-independent.  If you want to generate the bindings,
+including layout tests, specifically for your platform during the build,
+activate the `bindgen` feature.  In this case, you will also need `clang` and
+`libclang` in the default search path.
+
 ## Versioning
 
 The major and minor version of the `nitrokey-sys` crate map to the major and
diff --git a/build.rs b/build.rs
index a6ae9fc..d097021 100644
--- a/build.rs
+++ b/build.rs
@@ -54,6 +54,35 @@ fn prepare_version_source(
     Ok(out)
 }
 
+#[cfg(feature = "bindgen")]
+fn generate_bindings(library_path: &path::Path, out_path: &path::Path) {
+    let header_path = library_path.join("NK_C_API.h");
+    let header_str = header_path
+        .to_str()
+        .expect("Header path contains invalid UTF-8");
+
+    let include_path = library_path.join("libnitrokey");
+    let include_str = include_path
+        .to_str()
+        .expect("Include path contains invalid UTF-8");
+
+    println!("cargo:rerun-if-changed={}", header_str);
+
+    // always keep options in sync with Makefile
+    let bindings = bindgen::Builder::default()
+        .header(header_str)
+        .whitelist_function("NK_.*")
+        .whitelist_var("NK_.*")
+        .whitelist_var("MAXIMUM_STR_REPLY_LENGTH")
+        .derive_default(true)
+        .clang_arg(&format!("-I{}", include_str))
+        .generate()
+        .expect("Unable to generate bindings");
+    bindings
+        .write_to_file(out_path.join("bindings.rs"))
+        .expect("Could not write bindings");
+}
+
 fn main() {
     if env::var("USE_SYSTEM_LIBNITROKEY").is_ok() {
         println!("cargo:rustc-link-lib=nitrokey");
@@ -78,6 +107,9 @@ fn main() {
     let version_source = prepare_version_source(LIBNITROKEY_VERSION, &out_path, &library_path)
         .expect("Could not prepare the version source file");
 
+    #[cfg(feature = "bindgen")]
+    generate_bindings(library_path, &out_path);
+
     cc::Build::new()
         .cpp(true)
         .flag("-std=c++14")
diff --git a/src/lib.rs b/src/lib.rs
index a179da8..81a98bc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,10 +2,15 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
 
+#[cfg(not(feature = "bindgen"))]
 mod ffi;
 
+#[cfg(not(feature = "bindgen"))]
 pub use crate::ffi::*;
 
+#[cfg(feature = "bindgen")]
+include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
+
 #[cfg(test)]
 mod tests {
     use super::*;
-- 
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