feat(compress): move static CDict gating into Rust

Move public ZSTD_initStaticCDict alignment, null, workspace-size, and callback
dispatch into Rust. Keep C static workspace construction and dictionary
initialization behind a private callback.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml --release init_static_cdict -- --nocapture
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml --release
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --release --all-targets -- -D warnings
- ulimit -v 41943040; make -B -C programs -j1 zstd
- ulimit -v 41943040; make -C tests -j1 test-zstream ZSTREAM_TESTTIME=-T1s

lib/compress/zstd_compress.c

@@ -387,6 +387,27 @@ typedef char ZSTD_rust_free_cdict_state_layout[
                 == 3 * sizeof(void*)
          && sizeof(ZSTD_rust_freeCDictState) == 4 * sizeof(void*))
         ? 1 : -1];
+typedef void* (*ZSTD_rust_initStaticCDictInit_f)(void* context);
+typedef struct {
+    void* callbackContext;
+    void* workspace;
+    size_t workspaceSize;
+    size_t neededSize;
+    ZSTD_rust_initStaticCDictInit_f init;
+} ZSTD_rust_initStaticCDictState;
+void* ZSTD_rust_initStaticCDict(const ZSTD_rust_initStaticCDictState* state);
+typedef char ZSTD_rust_init_static_cdict_state_layout[
+        (offsetof(ZSTD_rust_initStaticCDictState, callbackContext) == 0
+         && offsetof(ZSTD_rust_initStaticCDictState, workspace)
+                == sizeof(void*)
+         && offsetof(ZSTD_rust_initStaticCDictState, workspaceSize)
+                == 2 * sizeof(void*)
+         && offsetof(ZSTD_rust_initStaticCDictState, neededSize)
+                == 3 * sizeof(void*)
+         && offsetof(ZSTD_rust_initStaticCDictState, init)
+                == 4 * sizeof(void*)
+         && sizeof(ZSTD_rust_initStaticCDictState) == 5 * sizeof(void*))
+        ? 1 : -1];
 typedef void (*ZSTD_rust_resetCCtxClearAllDicts_f)(void* context);
 typedef size_t (*ZSTD_rust_resetCCtxResetParams_f)(void* context);
 typedef struct {
@@ -5602,6 +5623,47 @@ size_t ZSTD_freeCDict(ZSTD_CDict* cdict)
  *  Note : there is no corresponding "free" function.
  *         Since workspace was allocated externally, it must be freed externally.
  */
+typedef struct {
+    void* workspace;
+    size_t workspaceSize;
+    const void* dict;
+    size_t dictSize;
+    ZSTD_dictLoadMethod_e dictLoadMethod;
+    ZSTD_dictContentType_e dictContentType;
+    ZSTD_compressionParameters cParams;
+    ZSTD_ParamSwitch_e useRowMatchFinder;
+} ZSTD_rust_initStaticCDictContext;
+
+static void* ZSTD_rust_initStaticCDict_init(void* opaque)
+{
+    ZSTD_rust_initStaticCDictContext* const context =
+            (ZSTD_rust_initStaticCDictContext*)opaque;
+    ZSTD_cwksp ws;
+    ZSTD_CDict* cdict;
+    ZSTD_CCtx_params params;
+
+    ZSTD_cwksp_init(&ws, context->workspace, context->workspaceSize,
+                    ZSTD_cwksp_static_alloc);
+    cdict = (ZSTD_CDict*)ZSTD_cwksp_reserve_object(&ws, sizeof(ZSTD_CDict));
+    if (cdict == NULL) return NULL;
+    ZSTD_cwksp_move(&cdict->workspace, &ws);
+
+    ZSTD_CCtxParams_init(&params, 0);
+    params.cParams = context->cParams;
+    params.useRowMatchFinder = context->useRowMatchFinder;
+    cdict->useRowMatchFinder = context->useRowMatchFinder;
+    cdict->compressionLevel = ZSTD_NO_CLEVEL;
+
+    if (ZSTD_isError( ZSTD_initCDict_internal(cdict,
+                                              context->dict, context->dictSize,
+                                              context->dictLoadMethod,
+                                              context->dictContentType,
+                                              params) ))
+        return NULL;
+
+    return cdict;
+}
+
 const ZSTD_CDict* ZSTD_initStaticCDict(
                                  void* workspace, size_t workspaceSize,
                            const void* dict, size_t dictSize,
@@ -5617,35 +5679,24 @@ const ZSTD_CDict* ZSTD_initStaticCDict(
                                : ZSTD_cwksp_alloc_size(ZSTD_cwksp_align(dictSize, sizeof(void*))))
                             + ZSTD_cwksp_alloc_size(HUF_WORKSPACE_SIZE)
                             + matchStateSize;
-    ZSTD_CDict* cdict;
-    ZSTD_CCtx_params params;
+    ZSTD_rust_initStaticCDictContext context;
+    ZSTD_rust_initStaticCDictState state;
 
     DEBUGLOG(4, "ZSTD_initStaticCDict (dictSize==%u)", (unsigned)dictSize);
-    if ((size_t)workspace & 7) return NULL;  /* 8-aligned */
-
-    {
-        ZSTD_cwksp ws;
-        ZSTD_cwksp_init(&ws, workspace, workspaceSize, ZSTD_cwksp_static_alloc);
-        cdict = (ZSTD_CDict*)ZSTD_cwksp_reserve_object(&ws, sizeof(ZSTD_CDict));
-        if (cdict == NULL) return NULL;
-        ZSTD_cwksp_move(&cdict->workspace, &ws);
-    }
-
-    if (workspaceSize < neededSize) return NULL;
-
-    ZSTD_CCtxParams_init(&params, 0);
-    params.cParams = cParams;
-    params.useRowMatchFinder = useRowMatchFinder;
-    cdict->useRowMatchFinder = useRowMatchFinder;
-    cdict->compressionLevel = ZSTD_NO_CLEVEL;
-
-    if (ZSTD_isError( ZSTD_initCDict_internal(cdict,
-                                              dict, dictSize,
-                                              dictLoadMethod, dictContentType,
-                                              params) ))
-        return NULL;
-
-    return cdict;
+    context.workspace = workspace;
+    context.workspaceSize = workspaceSize;
+    context.dict = dict;
+    context.dictSize = dictSize;
+    context.dictLoadMethod = dictLoadMethod;
+    context.dictContentType = dictContentType;
+    context.cParams = cParams;
+    context.useRowMatchFinder = useRowMatchFinder;
+    state.callbackContext = &context;
+    state.workspace = workspace;
+    state.workspaceSize = workspaceSize;
+    state.neededSize = neededSize;
+    state.init = ZSTD_rust_initStaticCDict_init;
+    return (const ZSTD_CDict*)ZSTD_rust_initStaticCDict(&state);
 }
 
 ZSTD_compressionParameters ZSTD_getCParamsFromCDict(const ZSTD_CDict* cdict)

rust/src/zstd_compress_dictionary.rs

@@ -42,6 +42,7 @@ const ZSTD_MAGIC_DICTIONARY: u32 = 0xEC30_A437;
 const ZSTD_DCT_AUTO: c_int = 0;
 const ZSTD_DCT_RAW_CONTENT: c_int = 1;
 const ZSTD_DCT_FULL_DICT: c_int = 2;
+const ZSTD_STATIC_WORKSPACE_ALIGNMENT: usize = 8;
 
 /// C keeps match-state/content insertion private because it depends on the
 /// configuration-sensitive `ZSTD_MatchState_t`, `ldmState_t`, workspace, and
@@ -479,6 +480,50 @@ pub unsafe extern "C" fn ZSTD_rust_freeCDict(state: *const ZSTD_rust_freeCDictSt
     0
 }
 
+type InitStaticCDictFn = unsafe extern "C" fn(*mut c_void) -> *mut c_void;
+
+/// Explicit projection for the public `ZSTD_initStaticCDict` wrapper.
+///
+/// Rust owns workspace pointer/alignment validation, minimum-size validation,
+/// and callback ordering. C retains the private static-workspace layout and
+/// dictionary initialization behind one callback.
+#[repr(C)]
+pub struct ZSTD_rust_initStaticCDictState {
+    callback_context: *mut c_void,
+    workspace: *mut c_void,
+    workspace_size: usize,
+    needed_size: usize,
+    init: InitStaticCDictFn,
+}
+
+const _: () = {
+    assert!(offset_of!(ZSTD_rust_initStaticCDictState, callback_context) == 0);
+    assert!(offset_of!(ZSTD_rust_initStaticCDictState, workspace) == size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_initStaticCDictState, workspace_size) == 2 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_initStaticCDictState, needed_size) == 3 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_initStaticCDictState, init) == 4 * size_of::<usize>());
+    assert!(size_of::<ZSTD_rust_initStaticCDictState>() == size_of::<[usize; 5]>());
+};
+
+/// Validate static CDict workspace ownership before entering the C leaf.
+#[no_mangle]
+pub unsafe extern "C" fn ZSTD_rust_initStaticCDict(
+    state: *const ZSTD_rust_initStaticCDictState,
+) -> *mut c_void {
+    if state.is_null() {
+        return ptr::null_mut();
+    }
+    let state = unsafe { &*state };
+    if state.callback_context.is_null()
+        || state.workspace.is_null()
+        || (state.workspace as usize) & (ZSTD_STATIC_WORKSPACE_ALIGNMENT - 1) != 0
+        || state.workspace_size < state.needed_size
+    {
+        return ptr::null_mut();
+    }
+    unsafe { (state.init)(state.callback_context) }
+}
+
 type CompressBeginUsingDictBeginFn =
     unsafe extern "C" fn(*mut c_void, *const c_void, usize, *const c_void, u64) -> usize;
 
@@ -2939,6 +2984,103 @@ mod tests {
         assert_eq!(result, 0);
     }
 
+    #[derive(Default)]
+    struct InitStaticCDictProbe {
+        events: Vec<&'static str>,
+        result: *mut c_void,
+    }
+
+    unsafe extern "C" fn init_static_cdict_test_init(context: *mut c_void) -> *mut c_void {
+        let probe = unsafe { &mut *context.cast::<InitStaticCDictProbe>() };
+        probe.events.push("init");
+        probe.result
+    }
+
+    fn init_static_cdict_test_state(
+        probe: &mut InitStaticCDictProbe,
+        workspace: *mut c_void,
+        workspace_size: usize,
+        needed_size: usize,
+    ) -> ZSTD_rust_initStaticCDictState {
+        ZSTD_rust_initStaticCDictState {
+            callback_context: (probe as *mut InitStaticCDictProbe).cast(),
+            workspace,
+            workspace_size,
+            needed_size,
+            init: init_static_cdict_test_init,
+        }
+    }
+
+    #[test]
+    fn init_static_cdict_rejects_an_unaligned_workspace_before_callback() {
+        let mut probe = InitStaticCDictProbe {
+            result: ptr::dangling_mut(),
+            ..Default::default()
+        };
+        let mut workspace = [0usize; 2];
+        let unaligned_workspace = workspace.as_mut_ptr().cast::<u8>().wrapping_add(1).cast();
+        let state = init_static_cdict_test_state(&mut probe, unaligned_workspace, usize::MAX, 0);
+
+        let result = unsafe { ZSTD_rust_initStaticCDict(&state) };
+
+        assert!(result.is_null());
+        assert!(probe.events.is_empty());
+    }
+
+    #[test]
+    fn init_static_cdict_rejects_insufficient_workspace_before_callback() {
+        let mut probe = InitStaticCDictProbe {
+            result: ptr::dangling_mut(),
+            ..Default::default()
+        };
+        let mut workspace = [0usize; 1];
+        let state = init_static_cdict_test_state(
+            &mut probe,
+            workspace.as_mut_ptr().cast(),
+            size_of_val(&workspace),
+            size_of_val(&workspace) + 1,
+        );
+
+        let result = unsafe { ZSTD_rust_initStaticCDict(&state) };
+
+        assert!(result.is_null());
+        assert!(probe.events.is_empty());
+    }
+
+    #[test]
+    fn init_static_cdict_calls_the_initializer_after_workspace_validation() {
+        let mut probe = InitStaticCDictProbe {
+            result: ptr::dangling_mut(),
+            ..Default::default()
+        };
+        let mut workspace = [0usize; 1];
+        let state = init_static_cdict_test_state(
+            &mut probe,
+            workspace.as_mut_ptr().cast(),
+            size_of_val(&workspace),
+            size_of_val(&workspace),
+        );
+
+        let result = unsafe { ZSTD_rust_initStaticCDict(&state) };
+
+        assert_eq!(result, probe.result);
+        assert_eq!(probe.events, ["init"]);
+    }
+
+    #[test]
+    fn init_static_cdict_rejects_a_null_workspace() {
+        let mut probe = InitStaticCDictProbe {
+            result: ptr::dangling_mut(),
+            ..Default::default()
+        };
+        let state = init_static_cdict_test_state(&mut probe, ptr::null_mut(), usize::MAX, 0);
+
+        let result = unsafe { ZSTD_rust_initStaticCDict(&state) };
+
+        assert!(result.is_null());
+        assert!(probe.events.is_empty());
+    }
+
     #[derive(Default)]
     struct CompressBeginUsingDictProbe {
         events: Vec<&'static str>,