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ffigen

README.md

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Binding generator for FFI bindings.

Note: ffigen only supports parsing C headers, not C++ headers.

This bindings generator can be used to call C code -- or code in another language that compiles to C modules that follow the C calling convention -- such as Go or Rust. For more details, see: https://dart.dev/guides/libraries/c-interop

ffigen also has experimental support for calling ObjC and Swift code; for details see: https://dart.dev/guides/libraries/objective-c-interop

Example

For some header file example.h:

int sum(int a, int b);

Add configurations to Pubspec File:

ffigen:
  output: 'generated_bindings.dart'
  headers:
    entry-points:
      - 'example.h'

Output (generated_bindings.dart).

import 'dart:ffi' as ffi;
class NativeLibrary {
  final ffi.Pointer<T> Function<T extends ffi.NativeType>(String symbolName)
      _lookup;
  NativeLibrary(ffi.DynamicLibrary dynamicLibrary)
      : _lookup = dynamicLibrary.lookup;
  NativeLibrary.fromLookup(
      ffi.Pointer<T> Function<T extends ffi.NativeType>(String symbolName)
          lookup)
      : _lookup = lookup;

  int sum(int a, int b) {
    return _sum(a, b);
  }

  late final _sumPtr = _lookup<ffi.NativeFunction<ffi.Int Function(ffi.Int, ffi.Int)>>('sum');
  late final _sum = _sumPtr.asFunction<int Function(int, int)>();
}
}

Using this package

  • Add ffigen under dev_dependencies in your pubspec.yaml (run dart pub add -d ffigen).
  • Add package:ffi under dependencies in your pubspec.yaml (run dart pub add ffi).
  • Install LLVM (see Installing LLVM).
  • Configurations must be provided in pubspec.yaml or in a custom YAML file (see configurations).
  • Run the tool- dart run ffigen.

Jump to FAQ.

Installing LLVM

package:ffigen uses LLVM. Install LLVM (9+) in the following way.

Linux

  1. Install libclangdev.

    With apt-get: sudo apt-get install libclang-dev.

    With dnf: sudo dnf install clang-devel.

Windows

  1. Install Visual Studio with C++ development support.
  2. Install LLVM or winget install -e --id LLVM.LLVM.

MacOS

  1. Install Xcode.
  2. Install Xcode command line tools - xcode-select --install.

Configurations

Configurations can be provided in 2 ways-

  1. In the project's pubspec.yaml file under the key ffigen.
  2. Via a custom YAML file, then specify this file while running - dart run ffigen --config config.yaml

The following configuration options are available-

Key Explaination Example
output
(Required)		 Output path of the generated bindings. 
output: 'generated_bindings.dart'

or

output:
  bindings: 'generated_bindings.dart'
  ...
llvm-path Path to llvm folder.
ffigen will sequentially search for `lib/libclang.so` on linux, `lib/libclang.dylib` on macOs and `bin\libclang.dll` on windows, in the specified paths.

Complete path to the dynamic library can also be supplied.
Required if ffigen is unable to find this at default locations.		 
llvm-path:
  - '/usr/local/opt/llvm'
  - 'C:\Program Files\llvm`
  - '/usr/lib/llvm-11'
  # Specify exact path to dylib
  - '/usr/lib64/libclang.so'
headers
(Required)		 The header entry-points and include-directives. Glob syntax is allowed.
If include-directives are not specified ffigen will generate everything directly/transitively under the entry-points.		 
headers:
  entry-points:
    - 'folder/**.h'
    - 'folder/specific_header.h'
  include-directives:
    - '**index.h'
    - '**/clang-c/**'
    - '/full/path/to/a/header.h'
name
(Prefer)		 Name of generated class. 
name: 'SQLite'
description
(Prefer)		 Dart Doc for generated class. 
description: 'Bindings to SQLite'
compiler-opts Pass compiler options to clang. You can also pass these via the command line tool. 
compiler-opts:
  - '-I/usr/lib/llvm-9/include/'

and/or via the command line -

dart run ffigen --compiler-opts "-I/headers
-L 'path/to/folder name/file'"
compiler-opts-automatic.macos.include-c-standard-library Tries to automatically find and add C standard library path to compiler-opts on macos.
Default: true 
compiler-opts-automatic:
  macos:
    include-c-standard-library: false
functions

structs

unions

enums

unnamed-enums

macros

globals 		Filters for declarations.
Default: all are included.

Options -
- Include/Exclude declarations.
- Rename declarations.
- Rename enum, struct, and union members, function parameters, and ObjC interface and protocol methods and properties.
- Expose symbol-address for functions and globals.
 
functions:
  include: # 'exclude' is also available.
    # Matches using regexp.
    - [a-z][a-zA-Z0-9]*
    # '.' matches any character.
    - prefix.*
    # Matches with exact name
    - someFuncName
    # Full names have higher priority.
    - anotherName
  rename:
    # Regexp groups based replacement.
    'clang_(.*)': '$1'
    'clang_dispose': 'dispose'
    # Removes '_' from beginning.
    '_(.*)': '$1'
  symbol-address:
    # Used to expose symbol address.
    include:
      - myFunc
structs:
  rename:
    # Removes prefix underscores
    # from all structures.
    '_(.*)': '$1'
  member-rename:
    '.*': # Matches any struct.
      # Removes prefix underscores
      # from members.
      '_(.*)': '$1'
enums:
  rename:
    # Regexp groups based replacement.
    'CXType_(.*)': '$1'
  member-rename:
    '(.*)': # Matches any enum.
      # Removes '_' from beginning
      # enum member name.
      '_(.*)': '$1'
    # Full names have higher priority.
    'CXTypeKind':
      # $1 keeps only the 1st
      # group i.e only '(.*)'.
      'CXType(.*)': '$1'
  as-int:
    # These enums will be generated as Dart integers instead of Dart enums
    include:
      - MyIntegerEnum
globals:
  exclude:
    - aGlobal
  rename:
    # Removes '_' from
    # beginning of a name.
    '_(.*)': '$1'
typedefs Filters for referred typedefs.

Options -
- Include/Exclude (referred typedefs only).
- Rename typedefs.

Note: By default, typedefs that are not referred to anywhere will not be generated. 
typedefs:
  exclude:
    # Typedefs starting with `p` are not generated.
    - 'p.*'
  rename:
    # Removes '_' from beginning of a typedef.
    '_(.*)': '$1'
include-unused-typedefs Also generate typedefs that are not referred to anywhere.
Default: false 
include-unused-typedefs: true
functions.expose-typedefs Generate the typedefs to Native and Dart type of a function
Default: Inline types are used and no typedefs to Native/Dart type are generated. 
functions:
  expose-typedefs:
    include:
      # Match function name.
      - 'myFunc'
       # Do this to expose types for all function.
      - '.*'
    exclude:
      # If you only use exclude, then everything
      # not excluded is generated.
      - 'dispose'
functions.leaf Set isLeaf:true for functions.
Default: all functions are excluded. 
functions:
  leaf:
    include:
      # Match function name.
      - 'myFunc'
       # Do this to set isLeaf:true for all functions.
      - '.*'
    exclude:
      # If you only use exclude, then everything
      # not excluded is generated.
      - 'dispose'
functions.variadic-arguments Generate multiple functions with different variadic arguments.
Default: var args for any function are ignored. 
functions:
  variadic-arguments:
    myfunc:
      // Native C types are supported
      - [int, unsigned char, long*, float**]
      // Common C typedefs (stddef.h) are supported too
      - [uint8_t, intptr_t, size_t, wchar_t*]
      // Structs/Unions/Typedefs from generated code or a library import can be referred too.
      - [MyStruct*, my_custom_lib.CustomUnion]
structs.pack Override the @Packed(X) annotation for generated structs.

Options - none, 1, 2, 4, 8, 16
You can use RegExp to match with the generated names.

Note: Ffigen can only reliably identify packing specified using __attribute__((__packed__)). However, structs packed using `#pragma pack(...)` or any other way could potentially be incorrect in which case you can override the generated annotations. 
structs:
  pack:
    # Matches with the generated name.
    'NoPackStruct': none # No packing
    '.*': 1 # Pack all structs with value 1
comments Extract documentation comments for declarations.
The style and length of the comments recognized can be specified with the following options-
style: doxygen(default) | any
length: brief | full(default)
If you want to disable all comments you can also pass
comments: false. 
comments:
  style: any
  length: full
structs.dependency-only

unions.dependency-only 		If `opaque`, generates empty `Opaque` structs/unions if they were not included in config (but were added since they are a dependency) and only passed by reference(pointer).
Options - full(default) | opaque
 
structs:
  dependency-only: opaque
unions:
  dependency-only: opaque
sort Sort the bindings according to name.
Default: false, i.e keep the order as in the source files. 
sort: true
use-supported-typedefs Should automatically map typedefs, E.g uint8_t => Uint8, int16_t => Int16, size_t => Size etc.
Default: true 
use-supported-typedefs: true
use-dart-handle Should map `Dart_Handle` to `Handle`.
Default: true 
use-dart-handle: true
ignore-source-errors Where to ignore compiler warnings/errors in source header files.
Default: false 
ignore-source-errors: true

and/or via the command line -

dart run ffigen --ignore-source-errors
silence-enum-warning Where to silence warning for enum integer type mimicking.
The integer type used for enums is implementation-defined, and not part of the ABI. FFIgen tries to mimic the integer sizes chosen by the most common compilers for the various OS and architecture combinations.
Default: false 
silence-enum-warning: true
exclude-all-by-default When a declaration filter (eg `functions:` or `structs:`) is empty or unset, it defaults to including everything. If this flag is enabled, the default behavior is to exclude everything instead.
Default: false 
exclude-all-by-default: true
preamble Raw header of the file, pasted as-it-is. 
preamble: |
  // ignore_for_file: camel_case_types, non_constant_identifier_names
library-imports Specify library imports for use in type-map.

Note: ffi (dart:ffi) is already available as a predefined import. 
library-imports:
  custom_lib: 'package:some_pkg/some_file.dart'
type-map Map types like integers, typedefs, structs, unions to any other type.

Sub-fields - typedefs, structs, unions, ints

lib must be specified in library-imports or be one of a predefined import. 
type-map:
  'native-types': # Targets native types.
    'char':
      'lib': 'pkg_ffi' # predefined import.
      'c-type': 'Char'
      # For native-types dart-type can be be int, double or float
      # but same otherwise.
      'dart-type': 'int'
    'int':
      'lib': 'custom_lib'
      'c-type': 'CustomType4'
      'dart-type': 'int'
  'typedefs': # Targets typedefs.
    'my_type1':
      'lib': 'custom_lib'
      'c-type': 'CustomType'
      'dart-type': 'CustomType'
  'structs': # Targets structs.
    'my_type2':
      'lib': 'custom_lib'
      'c-type': 'CustomType2'
      'dart-type': 'CustomType2'
  'unions': # Targets unions.
    'my_type3':
      'lib': 'custom_lib'
      'c-type': 'CustomType3'
      'dart-type': 'CustomType3'
ffi-native WARNING: Native support is EXPERIMENTAL. The API may change in a breaking way without notice.

Generate `@Native` bindings instead of bindings using `DynamicLibrary` or `lookup`. 
ffi-native:
  asset-id: 'myasset' # Optional, was assetId in previous versions
language WARNING: Other language support is EXPERIMENTAL. The API may change in a breaking way without notice.

Choose the input langauge. Must be one of 'c', or 'objc'. Defaults to 'c'. 
language: 'objc'
output.objc-bindings Choose where the generated ObjC code (if any) is placed. The default path is `'${output.bindings}.m'`, so if your Dart bindings are in `generated_bindings.dart`, your ObjC code will be in `generated_bindings.dart.m`.

This ObjC file will only be generated if it's needed. If it is generated, it must be compiled into your package, as part of a flutter plugin or build.dart script. If your package already has some sort of native build, you can simply add this generated ObjC file to that build. 
output:
  ...
  objc-bindings: 'generated_bindings.m'
output.symbol-file Generates a symbol file yaml containing all types defined in the generated output. 
output:
  ...
  symbol-file:
    # Although file paths are supported here, prefer Package Uri's here
    # so that other pacakges can use them.
    output: 'package:some_pkg/symbols.yaml'
    import-path: 'package:some_pkg/base.dart'
import.symbol-files Import symbols from a symbol file. Used for sharing type definitions from other pacakges. 
import:
  symbol-files:
    # Both package Uri and file paths are supported here.
    - 'package:some_pkg/symbols.yaml'
    - 'path/to/some/symbol_file.yaml'
external-versions Interfaces, methods, and other API elements may be marked with deprecation annotations that indicate which platform version they were deprecated in. If external-versions is set, APIs that were deprecated as of the minimum version will be omitted from the generated bindings.

The minimum version is specified per platform, and an API will be generated if it is available on *any* of the targeted platform versions. If a version is not specified for a particular platform, the API's inclusion will be based purely on the platforms that have a specified minimum version.

Current support OS keys are ios and macos. If you have a use case for version checking on other OSs, please file an issue. 
external-versions:
  # See https://docs.flutter.dev/reference/supported-platforms.
  ios:
    min: 12.0.0
  macos:
    min: 10.14.0

Objective-C config options

Key Explaination Example
objc-interfaces

objc-protocols

objc-categories 		Filters for Objective C interface, protocol, and category declarations. This option works the same as other declaration filters like `functions` and `structs`. 
objc-interfaces:
  include:
    # Includes a specific interface.
    - 'MyInterface'
    # Includes all interfaces starting with "NS".
    - 'NS.*'
  exclude:
    # Override the above NS.* inclusion, to exclude NSURL.
    - 'NSURL'
  rename:
    # Removes '_' prefix from interface names.
    '_(.*)': '$1'
objc-protocols:
  include:
    # Generates bindings for a specific protocol.
    - MyProtocol
objc-category:
  include:
    # Generates bindings for a specific category.
    - MyCategory
objc-interfaces.module

objc-protocols.module 		Adds a module prefix to the interface/protocol name when loading it from the dylib. This is only relevent for ObjC headers that are generated wrappers for a Swift library. See example/swift for more information.

This is not necessary for objc-categories. 
headers:
  entry-points:
    # Generated by swiftc to wrap foo_lib.swift.
    - 'foo_lib-Swift.h'
objc-interfaces:
  include:
    # Eg, foo_lib contains a set of classes prefixed with FL.
    - 'FL.*'
  module:
    # Use 'foo_lib' as the module name for all the FL.* classes.
    # We don't match .* here because other classes like NSString
    # shouldn't be given a module prefix.
    'FL.*': 'foo_lib'
objc-interfaces.member-filter

objc-protocols.member-filter

objc-categories.member-filter 		Filters interface and protocol methods and properties. This is a map from interface name to a list of method include and exclude rules. The interface name can be a regexp. The include and exclude rules work exactly like any other declaration. See below for more details. 
objc-interfaces:
  member-filter:
    MyInterface:
      include:
        - "someMethod:withArg:"
      # Since MyInterface has an include rule, all other methods
      # are excluded by default.
objc-protocols:
  member-filter:
    NS.*:  # Matches all protocols starting with NS.
      exclude:
        - copy.*  # Remove all copy methods from these protocols.
objc-categories:
  member-filter:
    MyCategory:
      include:
        - init.*  # Include all init methods.
include-transitive-objc-interfaces

include-transitive-objc-protocols 		By default, Objective-C interfaces and protocols that are not directly included by the inclusion rules, but are transitively depended on by the inclusions, are not fully code genned. Transitively included interfaces are generated as stubs, and transitive protocols are omitted.

If these flags are enabled, transitively included interfaces and protocols are fully code genned.

Default: false 
include-transitive-objc-interfaces: true
include-transitive-objc-protocols: true
include-transitive-objc-categories By default, if an Objective-C interface is included in the bindings, all the categories that extend it are also included. To filter them, set this flag to false, then use objc-categories to include/exclude particular categories.

Transitive categories are generated by default because it's not always obvious from the Apple documentation which interface methods are declared directly in the interface, and which are declared in categories. So it may appear that the interface is missing methods, when in fact those methods are part of a category. This would be a difficult problem to diagnose if transitive categories were not generated by default.

Default: true 
include-transitive-objc-categories: false

Trying out examples

  1. cd examples/<example_u_want_to_run>, Run dart pub get.
  2. Run dart run ffigen.

Running Tests

See test/README.md

FAQ

Can ffigen be used for removing underscores or renaming declarations?

Ffigen supports regexp based renaming, the regexp must be a full match, for renaming you can use regexp groups ($1 means group 1).

E.g - For renaming clang_dispose_string to string_dispose. We can can match it using clang_(.*)_(.*) and rename with $2_$1.

Here's an example of how to remove prefix underscores from any struct and its members.

structs:
  ...
  rename:
    '_(.*)': '$1' # Removes prefix underscores from all structures.
  member-rename:
    '.*': # Matches any struct.
      '_(.*)': '$1' # Removes prefix underscores from members.

How to generate declarations only from particular headers?

The default behaviour is to include everything directly/transitively under each of the entry-points specified.

If you only want to have declarations directly particular header you can do so using include-directives. You can use glob matching to match header paths.

headers:
  entry-points:
    - 'path/to/my_header.h'
  include-directives:
    - '**my_header.h' # This glob pattern matches the header path.

Can ffigen filter declarations by name?

Ffigen supports including/excluding declarations using full regexp matching.

Here's an example to filter functions using names

functions:
  include:
    - 'clang.*' # Include all functions starting with clang.
  exclude:
    - '.*dispose': # Exclude all functions ending with dispose.

This will include clang_help. But will exclude clang_dispose.

Note: exclude overrides include.

How does ffigen handle C Strings?

Ffigen treats char* just as any other pointer,(Pointer<Int8>). To convert these to/from String, you can use package:ffi. Use ptr.cast<Utf8>().toDartString() to convert char* to dart string and "str".toNativeUtf8() to convert string to char*.

How are unnamed enums handled?

Unnamed enums are handled separately, under the key unnamed-enums, and are generated as top level constants.

Here's an example that shows how to include/exclude/rename unnamed enums

unnamed-enums:
  include:
    - 'CX_.*'
  exclude:
    - '.*Flag'
  rename:
    'CXType_(.*)': '$1'

How can I handle unexpected enum values?

Native enums are, by default, generated into Dart enums with int get value and fromValue(int). This works well in the case that your enums values are known in advance and not going to change, and in return, you get the full benefits of Dart enums like exhaustiveness checking.

However, if a native library adds another possible enum value after you generate your bindings, and this new value is passed to your Dart code, this will result in an ArgumentError at runtime. To fix this, you can regenerate the bindings on the new header file, but if you wish to avoid this issue entirely, you can tell ffigen to generate plain Dart integers for your enum instead. To do this, simply list your enum's name in the as-int section of your ffigen config:

enums:
  as-int:
    include:
      - MyIntegerEnum
      - '*IntegerEnum'
    exclude:
      - FakeIntegerEnum

Functions that accept or return these enums will now accept or return integers instead, and it will be up to your code to map integer values to behavior and handle invalid values. But your code will be future-proof against new additions to the enums.

Why are some struct/union declarations generated even after excluded them in config?

This happens when an excluded struct/union is a dependency to some included declaration. (A dependency means a struct is being passed/returned by a function or is member of another struct in some way)

Note: If you supply structs.dependency-only as opaque ffigen will generate these struct dependencies as Opaque if they were only passed by reference(pointer).

structs:
  dependency-only: opaque
unions:
  dependency-only: opaque

How to expose the native pointers?

By default the native pointers are private, but you can use the symbol-address subkey for functions/globals and make them public by matching with its name. The pointers are then accesible via nativeLibrary.addresses.

Example -

functions:
  symbol-address:
    include:
      - 'myFunc' # Match function name.
      - '.*' # Do this to expose all function pointers.
    exclude: # If you only use exclude, then everything not excluded is generated.
      - 'dispose'

How to get typedefs to Native and Dart type of a function?

By default these types are inline. But you can use the expose-typedef subkey for functions to generate them. This will expose the Native and Dart type. E.g - for a function named hello, the generated typedefs are named as NativeHello and DartHello.

Example -

functions:
  expose-typedefs:
    include:
      - 'myFunc' # Match function name.
      - '.*' # Do this to expose types for all function.
    exclude: # If you only use exclude, then everything not excluded is generated.
      - 'dispose'

How are Structs/Unions/Enums that are reffered to via typedefs handled?

Named declarations use their own names even when inside another typedef. However, unnamed declarations inside typedefs take the name of the first typedef that refers to them.

Why are some typedefs not generated?

The following typedefs are not generated -

  • They are not referred to anywhere in the included declarations.
  • They refer to a struct/union having the same name as itself.
  • They refer to a boolean, enum, inline array, Handle or any unsupported type.

How are macros handled?

ffigen uses clang's own compiler frontend to parse and traverse the C header files. ffigen expands the macros using clang's macro expansion and then traverses the expanded code. To do this, ffigen generates temporary files in a system tmp directory.

A custom temporary directory can be specified by setting the TEST_TMPDIR environment variable.

What are these logs generated by ffigen and how to fix them?

Ffigen can sometimes generate a lot of logs, especially when it's parsing a lot of code.

  • SEVERE logs are something you definitely need to address. They can be caused due to syntax errors, or more generally missing header files (which need to be specified using compiler-opts in config)
  • WARNING logs are something you can ignore, but should probably look into. These are mostly indications of declarations ffigen couldn't generate due to limitations of dart:ffi, private declarations (which can be resolved by renaming them via ffigen config) or other minor issues in the config file itself.
  • Everything else can be safely ignored. It's purpose is to simply let you know what ffigen is doing.
  • The verbosity of the logs can be changed by adding a flag with the log level. E.g - dart run ffigen --verbose <level>. Level options are - [all, fine, info (default), warning, severe]. The all and fine will print a ton of logs are meant for debugging purposes only.

How can type definitions be shared?

Ffigen can share type definitions using symbol files.

  • A package can generate a symbol file using the output.symbol-file config.
  • And another package can then import this, using import.symbol-files config.
  • Doing so will reuse all the types such as Struct/Unions, and will automatically exclude generating other types (E.g functions, enums, macros).

Checkout examples/shared_bindings for details.

For manually reusing definitions from another package, the library-imports and type-map config can be used.

How does ObjC method filtering work?

Methods and properties on ObjC interfaces and protocols can be filtered using the member-filter option under objc-interfaces and objc-protocols. For simplicity we'll focus on interface methods, but the same rules apply to properties and protocols. There are two parts to the filtering process: matching the interface, and then filtering the method.

The syntax of member-filter is a YAML map from a pattern to some include/exclude rules, and include and exclude are each a list of patterns.

objc-interfaces:
  member-filter:
    MyInterface:  # Matches an interface.
      include:
        - "someMethod:withArg:"  # Matches a method.
      exclude:
        - someOtherMethod  # Matches a method.

The interface matching logic is the same as the matching logic for the member-rename option:

  • The pattern is compared against the original name of the interface (before any renaming is applied).
  • The pattern may be a string or a regexp, but in either case they must match the entire interface name.
  • If the pattern contains only alphanumeric characters, or _, it is treated as a string rather than a regex.
  • String patterns take precedence over regexps. That is, if an interface matches both a regexp pattern, and a string pattern, it uses the string pattern's include/exclude rules.

The method filtering logic uses the same include/exclude rules as the rest of the config:

  • include and exclude are a list of patterns.
  • The patterns are compared against the original name of the method, before renaming.
  • The patterns can be strings or regexps, but must match the entire method name.
  • The method name is in ObjC selector syntax, which means that the method name and all the external parameter names are concatenated together with : characters. This is the same name you'll see in ObjC's API documentation.
  • NOTE: Since the pattern must match the entire method name, and most ObjC method names end with a :, it's a good idea to surround the pattern with quotes, ". Otherwise YAML will think you're defining a map key.
  • If no include or exclude rules are defined, all methods are included, regardless of the top level exclude-all-by-default rule.
  • If only include rules are defined, all non-matching methods are excluded.
  • If only exclude rules are defined, all non-matching methods are included.
  • If both include and exclude rules are defined, the exclude rules take precedence. That is, if a method name matches both an include rule and an exclude rule, the method is excluded. All non-matching methods are also excluded.

The property filtering rules live in the same objc-interfaces.member-filter option as the methods. There is no distinction between methods and properties in the filters. The protocol filtering rules live in objc-protocols.member-filter.