如何在Squeak FFI中处理typedef？对接HDF5库的适配问题

Got it, let's walk through how to handle HDF5's typedef-heavy structs and functions in Squeak FFI—this is a common pain point when moving between Smalltalk implementations, so I’ll break it down step by step using your H5L_info_t example:

Step 1: Map HDF5's Custom Typedefs to Squeak FFI Types #

First, you need to tell Squeak what each HDF5 typedef corresponds to in its FFI system. Most of these are just aliases for standard C types, so we'll register them using FFITypeAlias:

-- Register basic typedef aliases
FFITypeAlias new
    typeName: #H5L_type_t;
    baseType: #long;  -- H5L_type_t is an enum, which maps to long in Squeak
    register.

FFITypeAlias new
    typeName: #hbool_t;
    baseType: #uchar;  -- HDF5's hbool_t is typically an unsigned char
    register.

FFITypeAlias new
    typeName: #int64_t;
    baseType: #longlong;
    register.

FFITypeAlias new
    typeName: #H5T_cset_t;
    baseType: #long;  -- Another enum type
    register.

FFITypeAlias new
    typeName: #haddr_t;
    baseType: #longlong;  -- 64-bit address type
    register.

FFITypeAlias new
    typeName: #size_t;
    baseType: #ulong;
    register.

Note: Double-check HDF5's platform-specific definitions for types like haddr_t—if you're on a 32-bit system, you might use #ulong instead of #longlong.

Step 2: Define the H5L_info_t Struct (Including the Union) #

Squeak FFI supports both structs and unions. For the union in your example, we'll define it as a separate sub-struct first, then embed it in the main struct:

First, the union H5L_info_u

FFIStructure subclass: #H5L_info_u
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'HDF5-Bindings'

H5L_info_u class >> fieldsDesc
    -- Unions share memory, so both fields occupy the same space
    ^ #(
        haddr_t address;
        size_t val_size;
    )

Then the main H5L_info_t struct

FFIStructure subclass: #H5L_info_t
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'HDF5-Bindings'

H5L_info_t class >> fieldsDesc
    -- Match the exact order of fields from the C definition!
    ^ #(
        H5L_type_t type;
        hbool_t corder_valid;
        int64_t corder;
        H5T_cset_t cset;
        H5L_info_u u;
    )

Step 3: Bind HDF5 Functions That Use These Types #

Let's use H5Lget_info as an example—its C prototype is:

herr_t H5Lget_info(hid_t loc_id, const char *name, H5L_info_t *info, hid_t lapl_id);

Here's how to bind it in Squeak:

FFILibrary subclass: #HDF5Library
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'HDF5-Bindings'

HDF5Library class >> ffiLibraryName
    -- Use the correct library name for your platform: 'hdf5' (Unix) or 'hdf5.dll' (Windows)
    ^ 'hdf5'

HDF5Library >> H5Lget_info: loc_id name: name info: info lapl_id: lapl_id
    -- Squeak FFI automatically handles struct pointers when you pass a struct instance
    ^ self ffiCall: #(int H5Lget_info(int loc_id, const char *name, H5L_info_t *info, int lapl_id))

Step 4: Validate and Test #

• Check struct size: Verify that H5L_info_t instanceSize matches the C sizeof(H5L_info_t)—if not, you've got a type mapping or alignment error.
• Test field access: After calling H5Lget_info, you can read fields directly like:

  | info |
  info := H5L_info_t new.
  hdf5Lib H5Lget_info: someLocId name: '/my/link' info: info lapl_id: 0.
  Transcript show: 'Link type: ', info type asString; cr.
  Transcript show: 'Hard link address: ', (info u address) asString; cr.
  

• Add enum constants: For readability, define constants for HDF5 enum values in your struct class:

  H5L_info_t class >> H5L_TYPE_HARD
      ^ 0
  H5L_info_t class >> H5L_TYPE_SOFT
      ^ 1
  

内容的提问来源于stack exchange，提问作者aka.nice