Merge pull request #42 from nixops4/store-path-binding

Add `StorePath::from_parts(hash, name)`

Cargo.lock

@@ -132,6 +132,12 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0cc23270f6e1808e30a928bdc84dea0b9b4136a8bc82338574f23baf47bbd280"
 
+[[package]]
+name = "hex-literal"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6fe2267d4ed49bc07b63801559be28c718ea06c4738b7a03c94df7386d2cde46"
+
 [[package]]
 name = "home"
 version = "0.5.11"
@@ -301,12 +307,14 @@ version = "0.2.1"
 dependencies = [
  "anyhow",
  "ctor",
+ "hex-literal",
  "lazy_static",
  "nix-bindings-store-sys",
  "nix-bindings-util",
  "nix-bindings-util-sys",
  "pkg-config",
  "tempfile",
+ "zerocopy",
 ]
 
 [[package]]
@@ -316,6 +324,7 @@ dependencies = [
  "bindgen",
  "nix-bindings-util-sys",
  "pkg-config",
+ "zerocopy",
 ]
 
 [[package]]
@@ -611,3 +620,23 @@ name = "wit-bindgen"
 version = "0.46.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f17a85883d4e6d00e8a97c586de764dabcc06133f7f1d55dce5cdc070ad7fe59"
+
+[[package]]
+name = "zerocopy"
+version = "0.8.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ea879c944afe8a2b25fef16bb4ba234f47c694565e97383b36f3a878219065c"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.8.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf955aa904d6040f70dc8e9384444cb1030aed272ba3cb09bbc4ab9e7c1f34f5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]

nix-bindings-store-sys/Cargo.toml

@@ -13,6 +13,7 @@ path = "src/lib.rs"
 
 [dependencies]
 nix-bindings-util-sys = { path = "../nix-bindings-util-sys", version = "0.2.1" }
+zerocopy = { version = "0.8", features = ["derive"] }
 
 [build-dependencies]
 bindgen = "0.69"

nix-bindings-store-sys/build.rs

@@ -9,6 +9,22 @@ impl bindgen::callbacks::ParseCallbacks for StripNixPrefix {
     }
 }
 
+#[derive(Debug)]
+struct AddZerocopyDerives {}
+impl bindgen::callbacks::ParseCallbacks for AddZerocopyDerives {
+    fn add_derives(&self, info: &bindgen::callbacks::DeriveInfo<'_>) -> Vec<String> {
+        if info.name == "store_path_hash_part" {
+            vec![
+                "zerocopy::FromBytes".to_string(),
+                "zerocopy::IntoBytes".to_string(),
+                "zerocopy::Immutable".to_string(),
+            ]
+        } else {
+            vec![]
+        }
+    }
+}
+
 fn main() {
     println!("cargo:rerun-if-changed=include/nix-c-store.h");
     println!("cargo:rustc-link-lib=nixstorec");
@@ -29,6 +45,7 @@ fn main() {
         .clang_args(args)
         .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
         .parse_callbacks(Box::new(StripNixPrefix))
+        .parse_callbacks(Box::new(AddZerocopyDerives {}))
         // Blocklist symbols from nix-bindings-util-sys
         .blocklist_file(".*nix_api_util\\.h")
         .generate()

nix-bindings-store/Cargo.toml

@@ -17,9 +17,11 @@ nix-bindings-util = { path = "../nix-bindings-util", version = "0.2.1" }
 nix-bindings-util-sys = { path = "../nix-bindings-util-sys", version = "0.2.1" }
 nix-bindings-store-sys = { path = "../nix-bindings-store-sys", version = "0.2.1" }
 lazy_static = "1.4"
+zerocopy = "0.8"
 
 [dev-dependencies]
 ctor = "0.2"
+hex-literal = "0.4"
 tempfile = "3.10"
 
 [build-dependencies]

nix-bindings-store/src/path.rs

@@ -1,15 +1,24 @@
 use std::ptr::NonNull;
 
-use anyhow::Result;
+use anyhow::{Context as _, Result};
 use nix_bindings_store_sys as raw;
+#[cfg(nix_at_least = "2.33")]
+use nix_bindings_util::{check_call, context::Context};
 use nix_bindings_util::{
     result_string_init,
     string_return::{callback_get_result_string, callback_get_result_string_data},
 };
 
+/// The size of a store path hash in bytes (20 bytes, decoded from nix32).
+pub const STORE_PATH_HASH_SIZE: usize = 20;
+
+#[cfg(nix_at_least = "2.33")]
+const _: () = assert!(std::mem::size_of::<raw::store_path_hash_part>() == STORE_PATH_HASH_SIZE);
+
 pub struct StorePath {
     raw: NonNull<raw::StorePath>,
 }
+
 impl StorePath {
     /// Get the name of the store path.
     ///
@@ -26,6 +35,43 @@ impl StorePath {
         }
     }
 
+    /// Get the hash part of the store path.
+    ///
+    /// This returns the decoded hash (not the nix32-encoded string).
+    #[cfg(nix_at_least = "2.33")]
+    pub fn hash(&self) -> Result<[u8; STORE_PATH_HASH_SIZE]> {
+        let mut result = [0u8; STORE_PATH_HASH_SIZE];
+        let hash_part: &mut raw::store_path_hash_part = zerocopy::transmute_mut!(&mut result);
+
+        let mut ctx = Context::new();
+
+        unsafe {
+            check_call!(raw::store_path_hash(&mut ctx, self.as_ptr(), hash_part))?;
+        }
+        Ok(result)
+    }
+
+    /// Create a StorePath from hash and name components.
+    #[cfg(nix_at_least = "2.33")]
+    pub fn from_parts(hash: &[u8; STORE_PATH_HASH_SIZE], name: &str) -> Result<Self> {
+        let hash_part: &raw::store_path_hash_part = zerocopy::transmute_ref!(hash);
+
+        let mut ctx = Context::new();
+
+        let out_path = unsafe {
+            check_call!(raw::store_create_from_parts(
+                &mut ctx,
+                hash_part,
+                name.as_ptr() as *const i8,
+                name.len()
+            ))?
+        };
+
+        NonNull::new(out_path)
+            .map(|ptr| unsafe { Self::new_raw(ptr) })
+            .context("store_create_from_parts returned null")
+    }
+
     /// This is a low level function that you shouldn't have to call unless you are developing the Nix bindings.
     ///
     /// Construct a new `StorePath` by first cloning the C store path.
@@ -81,6 +127,9 @@ impl Drop for StorePath {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
+    use hex_literal::hex;
+
     #[test]
     #[cfg(nix_at_least = "2.26" /* get_storedir */)]
     fn store_path_name() {
@@ -91,4 +140,18 @@ mod tests {
         let store_path = store.parse_store_path(store_path_string.as_str()).unwrap();
         assert_eq!(store_path.name().unwrap(), "bash-interactive-5.2p26");
     }
+
+    #[test]
+    #[cfg(nix_at_least = "2.33")]
+    fn store_path_round_trip() {
+        let original_hash: [u8; STORE_PATH_HASH_SIZE] =
+            hex!("0123456789abcdef0011223344556677deadbeef");
+        let original_name = "foo.drv";
+
+        let store_path = StorePath::from_parts(&original_hash, original_name).unwrap();
+
+        // Round trip gets back what we started with
+        assert_eq!(store_path.hash().unwrap(), original_hash);
+        assert_eq!(store_path.name().unwrap(), original_name);
+    }
 }