Lazarus-openapi

OpenAPI support in lazarus

FPC has OpenAPI support in trunk.

Lazarus contains initial support for OpenAPI. It offers mainly the same interface as the openapi2pas tool provided with Free Pascal.

lazopenapi package

The OpenAPI support is provided by the lazopenapi package. It can be compiled with FPC 3.3.1, but also with FPC 3.2.2

If you compile lazarus with the development version of FPC (3.3.1), then you can compile and install it in the usual manner: all the openapi and json-schema units are available.

If you compile Lazarus with the release version of FPC (3.2.2) then you can still install the package: the openapi support and JSON-schema units are coded in such a way that they will compile with version 3.2.2 (in fact, they are developed using FPC 3.2.2).

To compile the lazopenapi"" package, you must first copy the files with JSON-Schema and OpenAPI support to the ver_3_2_2 subdirectory of the packages' lazarus/components/openapi directory.

The following files must be copied from FPC's main branch in gitlab:

1. All files under packages/fcl-jsonschema/src', which you can find at

https://gitlab.com/freepascal.org/fpc/source/-/tree/main/packages/fcl-jsonschema/src

1. All files under packages/fcl-openapi/src , which you can find at

https://gitlab.com/freepascal.org/fpc/source/-/tree/main/packages/fcl-openapi/src

1. From packages/fcl-json/src , you also need the jsonwriter file, you can find it at

https://gitlab.com/freepascal.org/fpc/source/-/blob/main/packages/fcl-json/src/jsonwriter.pp

Once you copied all these files to the ver_3_2_2 subdirectory of the package, the lazopenapi package can be compiled and installed in the IDE.

The OpenAPI file generation wizard

The package will install a menu item OpenAPI code generator... under the Tools menu.

Clicking it will show a dialog where you can select the OpenAPI description file, and set the available options. At the bottom you can set the base filename. It serves as the base for all generated filenames.

The wizard will always generate the data (.Dto) and serializer unit (.Serializer)

Generate client

Check this option to generate a client service interface and proxy implementation

Generate server

Check this option to generate a server service implementation

Open files in IDE

Check this to open all generated units in the IDE

Add to project

Check this to add all generated units to the current project opened in the IDE

Note that files will be overwritten without warning.

The code generation options are divided over various tabs, where the first one has some general options.

General tab

General code generation options

Delphi code

generate code for Dto/Serializer that can be compiled with Delphi.

verbose header

When checked, adds the used command-line options to the header of the unit.

use enumerated types

When checked, enums will be used instead of strings when the OpenAPI indicates there is an enumeration.

Unit name suffix template

This is the template that is used to generate the unit names if they are not explicitly specified:

the kind' is replaced with the kind of unit (Dto, Serialize, Service.Intf etc.). The result is then appended to the base output name.

Unit name extension

The file extension for the generated units.

Service name suffix

The service names will have this suffix appended.

Service name prefix

The service names will have this prefix prepended.

Data tab

Data (Dto) code generation options

Client tab

Client service code generation options

Asynchrone service calls

Generate calls that use a callback to return the result. You can use this if your HTTP requests are run in another thread, or in pas2js.

Generate \CancelRequest

When checked, adds a CancelRequest method to the interface: the calls return a unique ID that can be used to cancel the HTTP request.

Client service parent class

The parent class for the service proxy classes: you can put the name of any descendant of TFPOpenAPIServiceClient

here, or any other class which implements the same methods as that class.

Client service parent unit

The unit in which the parent class for the service proxy class is defined.

Client service interface unit name

the unit name for the client service interface definition: by default this is the base name appended with .Service.Intf.

Client service proxy implementation unit name

the unit name for the client service proxy implementation: by default this is the base name appended with .Service.Impl.

Server tab

Server service code generation options

Generate abstract service calls in HTTP handler module

All service calls will be marked 'abstract' in the handler module, and moves the generation to the implementation unit

Skip implementation unit

Check this if you are re-generating the definitions and do not wish to overwrite your implementation file.

Server service parent class

The parent class for the service HTTP handler module classes: you can put the name of any descendant of TFPOpenAPIModule

here, or any other class which implements the same methods as that class.

Server service parent unit

The unit in which the parent class for the service HTTP handler module class is defined.

Server handler unit name

the unit name for the service HTTP handler module: by default this is the base name appended with .Module.Handler.

This unit is not generated when Generate abstract service calls is checked.

Server implementation unit name

the unit name for the server actual service implementation: by default this is the base name appended with .Module.Impl.

This unit is not generated when Generate abstract service calls and Skip implementation unit are checked.

GUID map tab

On this page, you can edit the UUID map contents: the map makes sure that whenever interfaces (such as the service interfaces) are regenerated, they have the same UUID. In the first column, you can set the interface name, in the second, the UUID to use.

Service name Map tab

On this page, you can edit the service map contents: this maps operationId s or verb:URLEndpoint to servicename:methodname , allowing you full control over the generated service interfaces and method names. In the first column, you can set the operationId as specified in the OpenAPI file or a verb:URLEndpoint pair. In the second column, you can edit the ServiceName.Methodname pair.

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From the Free Pascal wiki, page "Lazarus-openapi", as the Internet Archive kept it on 2026-01-07, last changed on 2024-11-22. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.