feat: nix_util::settings::set, get

(cherry picked from commit 19ed7bd655e72e10373f1afab5af214f2f47881e)

rust/Cargo.lock

@@ -209,6 +209,7 @@ name = "nix-util"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "ctor",
  "nix-c-raw",
 ]
 

rust/nix-util/Cargo.toml

@@ -8,3 +8,4 @@ edition = "2021"
 [dependencies]
 anyhow = "1.0.79"
 nix-c-raw = { path = "../nix-c-raw" }
+ctor = "0.2.7"

rust/nix-util/src/lib.rs

@@ -1,2 +1,3 @@
 pub mod context;
+pub mod settings;
 pub mod string_return;

rust/nix-util/src/settings.rs

@@ -0,0 +1,71 @@
+use anyhow::Result;
+use nix_c_raw as raw;
+
+use crate::{
+    context,
+    string_return::{callback_get_vec_u8, callback_get_vec_u8_data},
+};
+
+pub fn set(key: &str, value: &str) -> Result<()> {
+    let ctx = context::Context::new();
+    let key = std::ffi::CString::new(key)?;
+    let value = std::ffi::CString::new(value)?;
+    unsafe {
+        raw::setting_set(ctx.ptr(), key.as_ptr(), value.as_ptr());
+    };
+    ctx.check_err()
+}
+
+pub fn get(key: &str) -> Result<String> {
+    let ctx = context::Context::new();
+    let key = std::ffi::CString::new(key)?;
+    let mut raw_buffer: Vec<u8> = Vec::new();
+    unsafe {
+        raw::setting_get(
+            ctx.ptr(),
+            key.as_ptr(),
+            callback_get_vec_u8 as *mut std::ffi::c_void,
+            callback_get_vec_u8_data(&mut raw_buffer),
+        )
+    };
+    ctx.check_err()?;
+    String::from_utf8(raw_buffer).map_err(|e| e.into())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[ctor::ctor]
+    fn setup() {
+        let ctx = context::Context::new();
+        unsafe {
+            nix_c_raw::libstore_init(ctx.ptr());
+        };
+        ctx.check_err().unwrap();
+    }
+
+    #[test]
+    fn set_get() {
+        // Something that shouldn't matter if it's a different value temporarily
+        let key = "user-agent-suffix";
+
+        // Save the old value, in case it's important. Probably not.
+        // If this doesn't work, pick a different setting to test with
+        let old_value = get(key).unwrap();
+
+        let new_value = "just a string that we're storing into some option for testing purposes";
+
+        let res_e = (|| {
+            set(key, new_value)?;
+            get(key)
+        })();
+
+        // Restore immediately; try not to affect other tests (if relevant).
+        set(key, old_value.as_str()).unwrap();
+
+        let res = res_e.unwrap();
+
+        assert_eq!(res, new_value);
+    }
+}