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Operations

Operation verb

Section titled “Operation verb”

Default behavior:

  • If @post operation has a request body
  • @get otherwise

Configure:

You can use one of the verb decorators: @get, @put, etc.

Route

Section titled “Route”

An operation route can be specified using the @route decorator.

@route("/pets") op list(): Pet[];

Route path parameters are declared using {}. Providing @path on the model property with the matching name is optional.

@route("/pets/{petId}") op get(petId: string): Pet;
// or explicit @path
@route("/pets/{petId}") op get(@path petId: string): Pet;

Route can be specified on a parent namespace or interface. In that case all the operations, interfaces and namespaces underneath will be prefixed with it.

@route("/store")
namespace PetStore {
  op hello(): void; // `/store`
  @route("ping") op ping(): void; // `/store/ping`


  @route("/pets")
  interface Pets {
    list(): Pet[]; // `/store/pets`
    @route("{petId}") read(petId: string): Pet; // `/store/pets/{petId}`
  }
}

Path and query parameters

Section titled “Path and query parameters”

Model properties and parameters which should be passed as path and query parameters use the @path and @query parameters respectively. Let’s modify our list operation to support pagination, and add a read operation to our Pets resource:

@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): Pet[];
  op read(@path petId: int32): Pet;
}

Path parameters are appended to the URL unless a substitution with that parameter name exists on the resource path. For example, we might define a sub-resource using the following TypeSpec. Note how the path parameter for our sub-resource’s list operation corresponds to the substitution in the URL.

@route("/pets/{petId}/toys")
namespace PetToys {
  op list(@path petId: int32): Toy[];
}

Request & response bodies

Section titled “Request & response bodies”

Request and response bodies can be declared explicitly using the @body decorator. Let’s add an endpoint to create a pet. Let’s also use this decorator for the responses, although this doesn’t change anything about the API.

@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): {
    @body pets: Pet[];
  };
  op read(@path petId: int32): {
    @body pet: Pet;
  };
  @post
  op create(@body pet: Pet): {};
}

Implicit body resolution

Section titled “Implicit body resolution”

Note that in the absence of explicit @body:

  1. The set of parameters that are not marked @header, @query, or @path form the request body.
  2. The set of properties of the return model that are not marked @header or @statusCode form the response body.
  3. If the return type is not a model, then it defines the response body.

This is how we were able to return Pet and Pet[] bodies without using @body for list and read. We can actually write create in the same terse style by spreading the Pet object into the parameter list like this:

See also metadata for more advanced details.

@route("/pets")
namespace Pets {
  @post
  op create(...Pet): {};
}

@body vs @bodyRoot

Section titled “@body vs @bodyRoot”

The @body decorator applies to a request parameter or model property. The type of that decorated property or parameter will be exactly the http request or response body. If the body type is a Model, annotating any property in that model with applicable metadata (@header, @path, @query for request and @header, @statusCode for response) will be ignored and log a warning. The @bodyRoot decorator similarly applies to a property or parameter. The type of that decorated property or parameter is similarly used to define the request or response body. If the body type is not a model, the behavior is identical to @body. If the body type is a model, instead of exactly defining only the body, the model may also contain properties annotated as applicable http metadata. Such properties will be treated as http metadata, will not be included in the request or response body, and will not result in a warning.

Nesting @body and @bodyRoot, while mostly pointless, can happen when using templates to build operations. A warning will be emitted if nesting happens inline. The meaning when nesting them is as follow:

  • As soon as @body is reached the content is exactly the body which means any nested @bodyRoot or @body will be ignored.
  • if @bodyRoot is reached before any occurrence of @body, it will keep looking for nested properties decorated with @body or @bodyRoot and if found the deepest one will be used to determine the body.

Examples

```
Code Example Payload 
op case1(
  @header foo: string, //
  name: string,
  age: int32,
): void;
 
POST /
Foo: bar
{
  "name": "Rex",
  "age": 3
}
 
op case2(
  body: {
    @header foo: string;
    name: string;
    age: int32;
  },
): void;
 
POST /
Foo: bar
{
  "body": {
    "name": "Rex",
    "age": 3
  }
}
 
op case3(
  @body body: {
    @header foo: string; // warning: `@header` is ignored
    name: string;
    age: int32;
  },
): void;
 
POST /
{
  "name": "Rex",
  "age": 3
}
 
op case4(
  @bodyRoot body: {
    @header foo: string;
    name: string;
    age: int32;
  },
): void;
 
POST /
Foo: bar
{
  "name": "Rex",
  "age": 3
}
 
op case5(
  // This bodyRoot is a noop and will log a warning
  @bodyRoot body: {
    @bodyRoot reallyBody: {
      @header foo: string;
      name: string;
      age: int32;
    };
  },
): void;
 
POST /
Foo: bar
{
  "name": "Rex",
  "age": 3
}

Headers

Section titled “Headers”

Model properties and parameters that should be passed in a header use the @header decorator. The decorator takes the header name as a parameter. If a header name is not provided, it is inferred from the property or parameter name. Let’s add etag support to our pet store’s read operation.

@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): {
    @body pets: Pet[];
  };
  op read(@path petId: int32, @header ifMatch?: string): {
    @header eTag: string;
    @body pet: Pet;
  };
  @post
  op create(@body pet: Pet): {};
}

Status codes

Section titled “Status codes”

Default behavior:

  • 4xx,5xx if response is marked with @error
  • 200 otherwise

Configure:

Use the @statusCode decorator on a property to declare a status code for a response. Generally, setting this to just int32 isn’t particularly useful. Instead, use number literal types to create a discriminated union of response types. Let’s add status codes to our responses, and add a 404 response to our read endpoint.

@route("/pets")
namespace Pets {
  @error
  model Error {
    code: string;
  }


  op list(@query skip: int32, @query top: int32): {
    @body pets: Pet[]; // statusCode: 200 Implicit
  };
  op read(@path petId: int32, @header ifMatch?: string): {
    @statusCode statusCode: 200;
    @header eTag: string;
    @body pet: Pet;
  } | {
    @statusCode statusCode: 404;
  };
  op create(@body pet: Pet): {
    @statusCode statusCode: 204;
  } | Error; //statusCode: 4xx,5xx as Error use `@error` decorator
}

Content type

Section titled “Content type”

See the documentation of Content-Types.

Built-in response shapes

Section titled “Built-in response shapes”

Since status codes are so common for REST APIs, TypeSpec comes with some built-in types for common status codes so you don’t need to declare status codes so frequently.

There is also a Body<T> type, which can be used as a shorthand for { @body body: T } when an explicit body is required.

Lets update our sample one last time to use these built-in types:

model ETag {
  @header eTag: string;
}
@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): OkResponse & Body<Pet[]>;
  op read(@path petId: int32, @header ifMatch?: string): (OkResponse &
    Body<Pet> &
    ETag) | NotFoundResponse;
  @post
  op create(...Pet): NoContentResponse;
}

Note that the default status code is 200 for non-empty bodies and 204 for empty bodies. Similarly, explicit Body<T> is not required when T is known to be a model. So the following terser form is equivalent:

@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): Pet[];
  op read(@path petId: int32, @header ifMatch?: string): (Pet & ETag) | NotFoundResponse;
  @post
  op create(...Pet): {};
}

Finally, another common style is to make helper response types that are shared across a larger service definition. In this style, you can be entirely explicit while also keeping operation definitions concise.

For example, we could write :

model ListResponse<T> {
  ...OkResponse;
  ...Body<T[]>;
}


model ReadSuccessResponse<T> {
  ...OkResponse;
  ...ETag;
  ...Body<T>;
}


alias ReadResponse<T> = ReadSuccessResponse<T> | NotFoundResponse;


model CreateResponse {
  ...NoContentResponse;
}


@route("/pets")
namespace Pets {
  op list(@query skip: int32, @query top: int32): ListResponse<Pet>;
  op read(@path petId: int32, @header ifMatch?: string): ReadResponse<Pet>;
  @post
  op create(...Pet): CreateResponse;
}

Handling files

Section titled “Handling files”

@typespec/http provides a special model TypeSpec.Http.File for handling file uploads and downloads in HTTP operations. When working with files, emitters need to implement special handling due to their binary nature.

For more information about HTTP file bodies and how to configure them, see [the documentation on Files][http-files].

[http-files][./files.md]

Basic File Handling

Section titled “Basic File Handling”

When the model Http.File (or any model that extends Http.File) is the exact body of an HTTP request, emitters must treat this model with special care:

  • The contentType property should be used as the value for the Content-Type header in requests and vice-versa for responses.
  • The filename property should be used in the Content-Disposition header in responses and vice-versa for multipart requests (filename cannot be sent in a non-multipart HTTP request because Content-Disposition is only valid for responses and multipart requests).
  • The file content should be treated as the raw body of the request/response without any additional parsing.

See isHttpFile for a helper that emitters/libraries can use to detect instances of Http.File.

Examples

Section titled “Examples”

Uploading and downloading files

Section titled “Uploading and downloading files”
// Uploading and downloading
@route("/files")
interface Files {
  @post
  upload(@body file: Http.File): {
    @statusCode statusCode: 201;
  };


  download(@path fileId: string): Http.File;
}

Custom file types

Section titled “Custom file types”

If you want to declare specific types of files that are accepted, but still treated as binary files, declare the content types by extending the Http.File model and overriding the contentType field.

// Custom file type for images
model ImageFile extends Http.File {
  contentType: "image/jpeg" | "image/png" | "image/gif";
}


@route("/images")
interface Images {
  @post
  upload(@body image: ImageFile): {
    @statusCode statusCode: 201;
  };


  download(@path imageId: string): ImageFile;
}

Automatic visibility

Section titled “Automatic visibility”

The @typespec/rest library understands Lifecycle Visibility and provides functionality for emitters to apply visibility transforms based on whether a model represents a request or response and on HTTP method usage as detailed in the table below.

See handling visibility and metadata for details on how to incorporate this information into an emitter implementation.

ModifierVisible in
Lifecycle.ReadAny response
Lifecycle.QueryGET or HEAD request
Lifecycle.CreatePOST or PUT request
Lifecycle.UpdatePATCH or PUT request
Lifecycle.DeleteDELETE request

This allows a single logical TypeSpec model to be used as in the following example:

model User {
  name: string;
  @visibility(Lifecycle.Read) id: string;
  @visibility(Lifecycle.Create) password: string;
}


@route("/users")
interface Users {
  @post create(@path id: string, ...User): User;
  @get get(@path id: string): User;
}

There is a single logical user entity represented by the single TypeSpec type User, but the HTTP payload for this entity varies based on context. When returned in a response, the id property is included, but when sent in a request, it is not. Similarly, the password property is only included in create requests, but not present in responses.

The OpenAPI v3 emitter will apply these visibilities automatically, without explicit use of @withVisibility, and it will generate separate schemas suffixed by visibility when necessary. @visibility(Lifecycle.Read) can be expressed in OpenAPI without generating additional schema by specifying readOnly: true and the OpenAPI v3 emitter will leverage this a an optimization, but other visibilities will generate additional schemas. For example, @visibility(Lifecycle.Create) applied to a model property of a type named Widget will generate a WidgetCreate schema.

Another emitter such as one generating client code can see and preserve a single logical type and deal with these HTTP payload differences by means other than type proliferation.

Modeling with logical entities rather than HTTP-specific shapes also keeps the TypeSpec spec decoupled from HTTP and REST and can allow the same spec to be used with multiple protocols.

Metadata

Section titled “Metadata”

The properties that designate content for the HTTP envelope (@header, @path, @query, @statusCode) rather than the content in an HTTP payload are often called “metadata”.

Metadata is determined to be applicable or inapplicable based on the context that it is used:

ContextApplicability
@queryrequest only
@pathrequest only
@statusCoderesponse only
@headerrequest or response

Additionally metadata that appears in an array element type always inapplicable.

When metadata is deemed “inapplicable”, for example, if a @path property is seen in a response, it becomes part of the payload instead unless the @includeInapplicableMetadataInPayload decorator is used and given a value of false.

The handling of metadata applicability furthers the goal of keeping a single logical model in TypeSpec. For example, this defines a logical User entity that has a name, ID and password, but further annotates that the ID is sent in the HTTP path and the HTTP body in responses. Also, using automatic visibility as before, we further indicate that the password is only present in create requests.

model User {
  name: string;
  @path id: string;
  @visibility(Lifecycle.Create) password: string;
}

Then, we can write operations in terms of the logical entity:

@route("/users")
interface Users {
  @post create(...User): User;
}

Abstractly, this expresses that a create operation that takes and returns a user. But concretely, at the HTTP protocol level, a create request and response look like this:

POST /Users/TypeSpecFan42 HTTP/1.1
Content-Type: application/json
{
  "name": "TypeSpec Fan",
  "password": "Y0uW1llN3v3rGu3ss!"
}


HTTP/1.1 200 OK
Content-Type: application/json
{
  name: "TypeSpec Fan",
  id: "TypeSpecFan42
}

Visibility vs. Metadata applicability

Section titled “Visibility vs. Metadata applicability”

Metadata properties are filtered based on visibility as described above. This is done independently before applicability is considered. If a a metadata property is not visible then it is neither part of the envelope nor the HTTP payload, irrespective of its applicability.

Nested metadata

Section titled “Nested metadata”

Metadata properties are not required to be top-level. They can also be nested deeper in a parameter or response model type. For example:

model Thing {
  headers: {
    @header example: string;
  };
  name: string;
}

Note that nesting in this sense does not require the use of anonymous models. This is equivalent:

model Thing {
  headers: Headers;
  name: string;
}
model Headers {
  @header example: string;
}

In the event that this nesting introduces duplication, then the least nested property with a given name is preferred and the duplicate metadata properties are ignored.

model Thing {
  headers: {
    @header example: string; // preferred
    more: {
      @header example: string; // ignored
    };
  };
}

JSON Merge-Patch

Section titled “JSON Merge-Patch”

RFC 7396 describes a standard for interpreting a Patch request body using content-type application/merge-patch+jsonto update an existing resource. The TypeSpec Http library provides Model templates MergePatchUpdate and MergePatchCreateOrUpdate for specifying a JSON merge-patch request body. The templates recursively apply the merge-patch transformation rules to a TypeSpec resource Model, taking into account the structure and characteristics of the resource Model.

For example, given a resource model like this:

model Resource {
  id: string;
  name?: string;
  quantity?: safeint;
  color: "blue" | "green" | "red" = "blue";
  flavor?: "vanilla" | "chocolate" | "strawberry" = "vanilla";
  related?: Record<Resource>;
  tags?: string[];
}

A JSON Merge-Patch request updating this resource would have the following behavior:

  • id may or may not occur in the request, if it does occur, the resource value can be updated to a new string, but cannot be erased by sending null.
  • name may or may not occur in the request, if it does occur, the resource value can be updated to a new string or erased by sending null.
  • quantity may or ay not occur in the request, if it does occur, the resource value can be updated to a new integer value or erased by sending null.
  • color may or may not occur in the request, if it does occur, the resource value can be updated to one of the appropriate values. If set to null it is returned to its default value (blue)
  • flavor may or may not occur in the request, if it does occur, the resource value can be updated to one of the appropriate values. If set to null it is returned to its default value (vanilla)
  • related may or may not occur in the request, if it does occur, the resource value can be updated or erased (set to {}) by sending null.
    • Since related is a keyed type (Object), each key/value pair in the request will be treated as follows:
    • If the key exists in the ‘related’ field of the resource, the value is merged with the existing value.
    • If the key does not exist in the ‘related’ field of the resource, the key/value pair is added.
  • tags may or may not occur in the request, if it does occur, the resource can be replaced by a new array, or erased by sending null.

The MergePatch Transform

Section titled “The MergePatch Transform”

Generalizing these rules creates a type transform of the resource Model into a Model defining the corresponding Patch request body. The properties of a resource define the allowed properties and their types in a Patch request body for that resource as follows:

  • The type of a property indicates the allowed type of the corresponding property in a Patch request.
  • Required properties without a default value are optional in a Patch request, but if present, the value cannot be null.
  • Optional properties are optional in a Patch request, and, if present, can contain any valid value or null.
  • Properties with a default value are optional in a Patch request, but have no default value in the request body. If present, they can contain any valid value or null. A null value will not erase the property, but set it back to its default value.
  • Model and Record typed properties, when present in a Patch request are merged with the existing resource value in accordance with the merge-patch algorithm: this transformation is recursively applied to these values.
  • Array typed properties, when present in a Patch request replace the existing resource value in accordance with the merge-patch algorithm. This transformation is not recursively applied to these values.
  • Properties required to deserialize a request (for example, discriminators) are required in a Patch request body.

Constraints

Section titled “Constraints”

Because JSON merge-patch only describes the request body of an http request, the merge-patch transform in TypeSpec does not allow http envelope property metadata like @query, @path, @header, @cookie, and @statusCode in http requests.

The merge-patch templates will emit an error diagnostic if a model containing Http metadata properties is passed in. For example:

model ResourceWithMetadata {
  @path id: string;
  @header eTag: string;
  description: string;
}


// THIS WILL RESULT IN AN ERROR
@patch op update(...MergePatchUpdate<ResourceWithMetadata>): ResourceWithMetadata;

Patch Behavior of Nested Models

Section titled “Patch Behavior of Nested Models”

Model types may be nested beneath the top level of a resource. The characteristics of the ModelProperty that references a nested Model type determines the valid values for that nested model in the Patch request. Here is how the valid values are determined for each of the model property types that might reference a nested model (also depicted in the following tables):

  • The property type is a (simple) Model or an intersection of models
    • if the property is optional, the MergePatch transform applies, and the visibility is CreateOrUpdate. This is because, in an update, the property may or may not exist if the resource exists, so might need to be created or updated.
    • if the property is required, the MergePatch transform applies and the visibility matches the input visibility. This is because, in an update, the property must exist if the resource exists, so it can only be updated. In a CreateOrUpdate, it could also be created with the resource.
  • The property type is an array (sequence) of model type items
    • For required or optional arrays: The MergePatch transform does not apply and the visibility is Create
  • The property type is a Record (keyed collection) of model type values
    • For required or optional keyed collections, the MergePatch transform applies, and the visibility is create or update.
  • The property type is a union of model type values
    • The MergePatch transform applies to each of the union variants, and because switching between variants is possible, CreateOrUpdate visibility is applied regardless of the optionality of the property. If the union is discriminated, the discriminator remains ‘required’ so the service can understand which variant the request was intended to apply to.

Treatment of Nested Keyed Types in Patch Request with Update Visibility Filter

Section titled “Treatment of Nested Keyed Types in Patch Request with Update Visibility Filter”
Property TypeOptionalityExampleApply MergePatch transform?Visibility Filter
SimpleRequiredfooProp: FooYesUpdate
SimpleOptionalfooProp?: FooYesCreateOrUpdate
ReplaceOnlyRequired@replaceOnly fooProp: FooNoCreate
ReplaceOnlyOptional@replaceOnly fooProp?: FooNoCreate
Array*fooProp?: Foo[]NoCreate
Record*fooProp?: Record<Foo>YesCreateOrUpdate
Union*fooProp?: Foo | BarYesCreateOrUpdate

Treatment of Nested Keyed Types in Patch Request with CreateOrUpdate Visibility Filter

Section titled “Treatment of Nested Keyed Types in Patch Request with CreateOrUpdate Visibility Filter”
Property TypeOptionalityExampleApply MergePatch transform?Visibility Filter
SimpleRequiredfooProp: FooYesCreateOrUpdate
SimpleOptionalfooProp?: FooYesCreateOrUpdate
ReplaceOnlyRequired@replaceOnly fooProp: FooNoCreate
ReplaceOnlyOptional@replaceOnly fooProp?: FooNoCreate
Array*fooProp?: Foo[]NoCreate
Record*fooProp?: Record<Foo>YesCreateOrUpdate
Union*fooProp?: Foo | BarYesCreateOrUpdate

Examples

Section titled “Examples”

Update

Section titled “Update”

A JSON Merge Patch update operation for a Widget resource using @body.

// A Json merge-patch operation to update a 'Widget' resource
// and return the updated Widget.
@patch op update(@body request: MergePatchUpdate<Widget>): Widget;

A JSON Merge Patch update operation for a Widget resource using the spread operator.

// A Json merge-patch operation to update a 'Widget' resource
// and return the updated Widget.
@patch op update(...MergePatchUpdate<Widget>): Widget;

Create or Update

Section titled “Create or Update”

A JSON Merge Patch create or update operation for a Widget resource using @body.

// A Json merge-patch operation to update a 'Widget' resource
// or create it if it does not exist and return the updated Widget.
@patch op update(@body request: MergePatchCreateOrUpdate<Widget>): Widget;

A JSON Merge Patch create or update operation for a Widget resource using the spread operator.

// A Json merge-patch operation to update a 'Widget' resource
// or create it if it does not exist and return the updated Widget.
@patch op update(...MergePatchCreateOrUpdate<Widget>): Widget;

Emitter resources

Section titled “Emitter resources”

See Handling metadata and visibility in emitters for REST API for information on how to handle metadata applicability and automatic visibility in a custom emitter.