libstore-c: Organize, and flesh out API

- Move some things to their own headers (in a backwards compatible way).

- Add more derivation functions.

Co-authored-by: Tristan Ross <tristan.ross@determinate.systems>

src/libstore-c/meson.build

@@ -35,6 +35,8 @@ include_dirs = [ include_directories('.') ]
 
 headers = files(
   'nix_api_store.h',
+  'nix_api_store/derivation.h',
+  'nix_api_store/store_path.h',
 )
 
 # TODO don't install this once tests don't use it and/or move the header into `libstore`, non-`c`

src/libstore-c/nix_api_store.cc

@@ -10,6 +10,10 @@
 #include "nix/store/local-fs-store.hh"
 
 #include "nix/store/globals.hh"
+#include "nix/util/base-nix-32.hh"
+
+#include <cstring>
+#include <span>
 
 extern "C" {
 
@@ -218,6 +222,44 @@ StorePath * nix_store_path_clone(const StorePath * p)
     return new StorePath{p->path};
 }
 
+nix_store_path_hash_path nix_store_path_hash(const StorePath * store_path)
+{
+    auto hashPart = store_path->path.hashPart();
+    // Decode from Nix32 (base32) encoding to raw bytes
+    auto decoded = nix::BaseNix32::decode(hashPart);
+
+    nix_store_path_hash_path result;
+    assert(decoded.size() == 20);
+    std::memcpy(result.bytes, decoded.data(), 20);
+    return result;
+}
+
+StorePath * nix_store_create_from_parts(
+    nix_c_context * context, const nix_store_path_hash_path * hash, const char * name, size_t name_len)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        // Encode the 20 raw bytes to Nix32 (base32) format
+        auto hashStr =
+            nix::BaseNix32::encode(std::span<const std::byte>(reinterpret_cast<const std::byte *>(hash->bytes), 20));
+
+        // Construct the store path basename: <hash>-<name>
+        std::string baseName;
+        baseName += hashStr;
+        baseName += "-";
+        baseName += std::string_view{name, name_len};
+
+        return new StorePath{nix::StorePath(std::move(baseName))};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_derivation * nix_derivation_clone(const nix_derivation * d)
+{
+    return new nix_derivation{d->drv};
+}
+
 nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store, const char * json)
 {
     if (context)
@@ -228,6 +270,20 @@ nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store
     NIXC_CATCH_ERRS_NULL
 }
 
+nix_err nix_derivation_to_json(
+    nix_c_context * context, const nix_derivation * drv, nix_get_string_callback callback, void * userdata)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto result = static_cast<nlohmann::json>(drv->drv).dump();
+        if (callback) {
+            callback(result.data(), result.size(), userdata);
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
 StorePath * nix_add_derivation(nix_c_context * context, Store * store, nix_derivation * derivation)
 {
     if (context)
@@ -252,4 +308,73 @@ nix_err nix_store_copy_closure(nix_c_context * context, Store * srcStore, Store
     NIXC_CATCH_ERRS
 }
 
+nix_err nix_store_drv_from_path(
+    nix_c_context * context,
+    Store * store,
+    const StorePath * path,
+    void (*callback)(void * userdata, const nix_derivation * drv),
+    void * userdata)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::Derivation drv = store->ptr->derivationFromPath(path->path);
+        if (callback) {
+            const nix_derivation tmp{drv};
+            callback(userdata, &tmp);
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_store_query_path_info(
+    nix_c_context * context,
+    Store * store,
+    const StorePath * store_path,
+    void * userdata,
+    nix_get_string_callback callback)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto info = store->ptr->queryPathInfo(store_path->path);
+        if (callback) {
+            auto result = info->toJSON(&*store->ptr, true).dump();
+            callback(result.data(), result.size(), userdata);
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_store_build_paths(
+    nix_c_context * context,
+    Store * store,
+    const StorePath ** store_paths,
+    unsigned int num_store_paths,
+    void (*callback)(void * userdata, const char * path, const char * result),
+    void * userdata)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::span<const StorePath * const> paths_span(store_paths, num_store_paths);
+
+        std::vector<nix::DerivedPath> derived_paths;
+        for (const StorePath * store_path : paths_span) {
+            derived_paths.push_back(nix::SingleDerivedPath::Opaque{store_path->path});
+        }
+
+        auto results = store->ptr->buildPathsWithResults(derived_paths);
+        for (auto & result : results) {
+            if (callback) {
+                callback(
+                    userdata,
+                    result.path.to_string(store->ptr->config).c_str(),
+                    static_cast<nlohmann::json>(result).dump().c_str());
+            }
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
 } // extern "C"

src/libstore-c/nix_api_store.h

@@ -12,6 +12,8 @@
  */
 
 #include "nix_api_util.h"
+#include "nix_api_store/store_path.h"
+#include "nix_api_store/derivation.h"
 #include <stdbool.h>
 
 #ifdef __cplusplus
@@ -21,10 +23,6 @@ extern "C" {
 
 /** @brief Reference to a Nix store */
 typedef struct Store Store;
-/** @brief Nix store path */
-typedef struct StorePath StorePath;
-/** @brief Nix Derivation */
-typedef struct nix_derivation nix_derivation;
 
 /**
  * @brief Initializes the Nix store library
@@ -108,7 +106,7 @@ nix_err
 nix_store_get_storedir(nix_c_context * context, Store * store, nix_get_string_callback callback, void * user_data);
 
 /**
- * @brief Parse a Nix store path into a StorePath
+ * @brief Parse a Nix store path that includes the store dir into a StorePath
  *
  * @note Don't forget to free this path using nix_store_path_free()!
  * @param[out] context Optional, stores error information
@@ -118,30 +116,6 @@ nix_store_get_storedir(nix_c_context * context, Store * store, nix_get_string_ca
  */
 StorePath * nix_store_parse_path(nix_c_context * context, Store * store, const char * path);
 
-/**
- * @brief Get the path name (e.g. "name" in /nix/store/...-name)
- *
- * @param[in] store_path the path to get the name from
- * @param[in] callback called with the name
- * @param[in] user_data arbitrary data, passed to the callback when it's called.
- */
-void nix_store_path_name(const StorePath * store_path, nix_get_string_callback callback, void * user_data);
-
-/**
- * @brief Copy a StorePath
- *
- * @param[in] p the path to copy
- * @return a new StorePath
- */
-StorePath * nix_store_path_clone(const StorePath * p);
-
-/** @brief Deallocate a StorePath
- *
- * Does not fail.
- * @param[in] p the path to free
- */
-void nix_store_path_free(StorePath * p);
-
 /**
  * @brief Check if a StorePath is valid (i.e. that corresponding store object and its closure of references exists in
  * the store)
@@ -214,6 +188,12 @@ nix_store_get_version(nix_c_context * context, Store * store, nix_get_string_cal
 /**
  * @brief Create a `nix_derivation` from a JSON representation of that derivation.
  *
+ * @note Unlike `nix_derivation_to_json`, this needs a `Store`. This is because
+ * over time we expect the internal representation of derivations in Nix to
+ * differ from accepted derivation formats. The store argument is here to help
+ * any logic needed to convert from JSON to the internal representation, in
+ * excess of just parsing.
+ *
  * @param[out] context Optional, stores error information.
  * @param[in] store nix store reference.
  * @param[in] json JSON of the derivation as a string.
@@ -229,14 +209,6 @@ nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store
  */
 StorePath * nix_add_derivation(nix_c_context * context, Store * store, nix_derivation * derivation);
 
-/**
- * @brief Deallocate a `nix_derivation`
- *
- * Does not fail.
- * @param[in] drv the derivation to free
- */
-void nix_derivation_free(nix_derivation * drv);
-
 /**
  * @brief Copy the closure of `path` from `srcStore` to `dstStore`.
  *
@@ -276,6 +248,61 @@ nix_err nix_store_get_fs_closure(
     void * userdata,
     void (*callback)(nix_c_context * context, void * userdata, const StorePath * store_path));
 
+/**
+ * @brief Returns the derivation associated with the store path
+ *
+ * @note The callback borrows the Derivation only for the duration of the call.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store The nix store
+ * @param[in] path The nix store path
+ * @param[in] callback The callback to call
+ * @param[in] userdata The userdata to pass to the callback
+ */
+nix_err nix_store_drv_from_path(
+    nix_c_context * context,
+    Store * store,
+    const StorePath * path,
+    void (*callback)(void * userdata, const nix_derivation * drv),
+    void * userdata);
+
+/**
+ * @brief Queries for the nix store path info JSON.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] path A store path
+ * @param[in] userdata The data to pass to the callback
+ * @param[in] callback Called for when the path info is resolved
+ */
+nix_err nix_store_query_path_info(
+    nix_c_context * context,
+    Store * store,
+    const StorePath * store_path,
+    void * userdata,
+    nix_get_string_callback callback);
+
+/**
+ * @brief Builds the paths, if they are a derivation then they get built.
+ *
+ * @note Path and result for the callback only exist for the lifetime of
+ * the call. Result is a string containing the build result in JSON.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] store_paths Pointer to list of nix store paths
+ * @param[in] num_store_paths Number of nix store paths
+ * @param[in] callback The callback to trigger for build results
+ * @param[in] userdata User data to pass to the callback
+ */
+nix_err nix_store_build_paths(
+    nix_c_context * context,
+    Store * store,
+    const StorePath ** store_paths,
+    unsigned int num_store_paths,
+    void (*callback)(void * userdata, const char * path, const char * result),
+    void * userdata);
+
 // cffi end
 #ifdef __cplusplus
 }

src/libstore-c/nix_api_store/derivation.h

@@ -0,0 +1,57 @@
+#ifndef NIX_API_STORE_DERIVATION_H
+#define NIX_API_STORE_DERIVATION_H
+/**
+ * @defgroup libstore_derivation Derivation
+ * @ingroup libstore
+ * @brief Derivation operations that don't require a Store
+ * @{
+ */
+/** @file
+ * @brief Derivation operations
+ */
+
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @brief Nix Derivation */
+typedef struct nix_derivation nix_derivation;
+
+/**
+ * @brief Copy a `nix_derivation`
+ *
+ * @param[in] d the derivation to copy
+ * @return a new `nix_derivation`
+ */
+nix_derivation * nix_derivation_clone(const nix_derivation * d);
+
+/**
+ * @brief Deallocate a `nix_derivation`
+ *
+ * Does not fail.
+ * @param[in] drv the derivation to free
+ */
+void nix_derivation_free(nix_derivation * drv);
+
+/**
+ * @brief Gets the derivation as a JSON string
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] drv The derivation
+ * @param[in] callback Called with the JSON string
+ * @param[in] userdata Arbitrary data passed to the callback
+ */
+nix_err nix_derivation_to_json(
+    nix_c_context * context, const nix_derivation * drv, nix_get_string_callback callback, void * userdata);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/**
+ * @}
+ */
+#endif // NIX_API_STORE_DERIVATION_H

src/libstore-c/nix_api_store/store_path.h

@@ -0,0 +1,93 @@
+#ifndef NIX_API_STORE_STORE_PATH_H
+#define NIX_API_STORE_STORE_PATH_H
+/**
+ * @defgroup libstore_storepath StorePath
+ * @ingroup libstore
+ * @brief Store path operations that don't require a Store
+ * @{
+ */
+/** @file
+ * @brief Store path operations
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @brief Nix store path */
+typedef struct StorePath StorePath;
+
+/**
+ * @brief Copy a StorePath
+ *
+ * @param[in] p the path to copy
+ * @return a new StorePath
+ */
+StorePath * nix_store_path_clone(const StorePath * p);
+
+/** @brief Deallocate a StorePath
+ *
+ * Does not fail.
+ * @param[in] p the path to free
+ */
+void nix_store_path_free(StorePath * p);
+
+/**
+ * @brief Get the path name (e.g. "<name>" in /nix/store/<hash>-<name>)
+ *
+ * @param[in] store_path the path to get the name from
+ * @param[in] callback called with the name
+ * @param[in] user_data arbitrary data, passed to the callback when it's called.
+ */
+void nix_store_path_name(const StorePath * store_path, nix_get_string_callback callback, void * user_data);
+
+/**
+ * @brief A store path hash
+ *
+ * Once decoded from "nix32" encoding, a store path hash is 20 raw bytes.
+ */
+typedef struct nix_store_path_hash_path
+{
+    uint8_t bytes[20];
+} nix_store_path_hash_path;
+
+/**
+ * @brief Get the path hash (e.g. "<hash>" in /nix/store/<hash>-<name>)
+ *
+ * The hash is returned as raw bytes, decoded from "nix32" encoding.
+ *
+ * @param[in] store_path the path to get the hash from
+ * @return the decoded hash as 20 raw bytes
+ */
+nix_store_path_hash_path nix_store_path_hash(const StorePath * store_path);
+
+/**
+ * @brief Create a StorePath from its constituent parts (hash and name)
+ *
+ * This function constructs a store path from a hash and name, without needing
+ * a Store reference or the store directory prefix.
+ *
+ * @note Don't forget to free this path using nix_store_path_free()!
+ * @param[out] context Optional, stores error information
+ * @param[in] hash The store path hash (20 raw bytes)
+ * @param[in] name The store path name (the part after the hash)
+ * @param[in] name_len Length of the name string
+ * @return owned store path, NULL on error
+ */
+StorePath * nix_store_create_from_parts(
+    nix_c_context * context, const nix_store_path_hash_path * hash, const char name[/*name_len*/], size_t name_len);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/**
+ * @}
+ */
+#endif // NIX_API_STORE_STORE_PATH_H

src/libstore-tests/nix_api_store.cc

@@ -92,6 +92,63 @@ TEST_F(nix_api_store_test, DoesNotCrashWhenContextIsNull)
     nix_store_path_free(path);
 }
 
+TEST_F(nix_api_store_test, nix_store_path_hash)
+{
+    StorePath * path = nix_store_parse_path(ctx, store, (nixStoreDir + PATH_SUFFIX).c_str());
+    ASSERT_NE(path, nullptr);
+
+    nix_store_path_hash_path hash = nix_store_path_hash(path);
+
+    // Verify it's 20 bytes
+    static_assert(sizeof(hash.bytes) == 20);
+
+    // The hash should be non-zero
+    bool allZero = true;
+    for (int i = 0; i < 20; i++) {
+        if (hash.bytes[i] != 0) {
+            allZero = false;
+            break;
+        }
+    }
+    ASSERT_FALSE(allZero);
+
+    nix_store_path_free(path);
+}
+
+TEST_F(nix_api_store_test, nix_store_create_from_parts_roundtrip)
+{
+    // Parse a path
+    StorePath * original = nix_store_parse_path(ctx, store, (nixStoreDir + PATH_SUFFIX).c_str());
+    EXPECT_NE(original, nullptr);
+
+    // Get its hash
+    nix_store_path_hash_path hash = nix_store_path_hash(original);
+
+    // Get its name
+    std::string name;
+    nix_store_path_name(original, OBSERVE_STRING(name));
+
+    // Reconstruct from parts
+    StorePath * reconstructed = nix_store_create_from_parts(ctx, &hash, name.c_str(), name.size());
+    assert_ctx_ok();
+    ASSERT_NE(reconstructed, nullptr);
+
+    // Should be equal
+    EXPECT_EQ(original->path, reconstructed->path);
+
+    nix_store_path_free(original);
+    nix_store_path_free(reconstructed);
+}
+
+TEST_F(nix_api_store_test, nix_store_create_from_parts_invalid_name)
+{
+    nix_store_path_hash_path hash = {};
+    // Invalid name with spaces
+    StorePath * path = nix_store_create_from_parts(ctx, &hash, "invalid name", 12);
+    ASSERT_EQ(path, nullptr);
+    ASSERT_EQ(nix_err_code(ctx), NIX_ERR_NIX_ERROR);
+}
+
 TEST_F(nix_api_store_test, get_version)
 {
     std::string str;