HttpRule defines the mapping of an RPC method to one or more HTTP REST APIs. The mapping determines what portions of the request message are populated from the path, query parameters, or body of the HTTP request. The mapping is typically specified as an google.api.http annotation, see "google/api/annotations.proto" for details.

The mapping consists of a field specifying the path template and method kind. The path template can refer to fields in the request message, as in the example below which describes a REST GET operation on a resource collection of messages: service Messaging { rpc GetMessage(GetMessageRequest) returns (Message) { option (google.api.http).get = "/v1/messages/{message_id}/{sub.subfield}"; } } message GetMessageRequest { message SubMessage { string subfield = 1; } string message_id = 1; // mapped to the URL SubMessage sub = 2; // sub.subfield is url-mapped } message Message { string text = 1; // content of the resource } The same http annotation can alternatively be expressed inside the GRPC API Configuration YAML file. http: rules: - selector: .Messaging.GetMessage get: /v1/messages/{message_id}/{sub.subfield} This definition enables an automatic, bidrectional mapping of HTTP JSON to RPC. Example: HTTP | RPC -----|----- GET /v1/messages/123456/foo | GetMessage(message_id: "123456" sub: SubMessage(subfield: "foo")) In general, not only fields but also field paths can be referenced from a path pattern. Fields mapped to the path pattern cannot be repeated and must have a primitive (non-message) type. Any fields in the request message which are not bound by the path pattern automatically become (optional) HTTP query parameters. Assume the following definition of the request message: message GetMessageRequest { message SubMessage { string subfield = 1; } string message_id = 1; // mapped to the URL int64 revision = 2; // becomes a parameter SubMessage sub = 3; // sub.subfield becomes a parameter } This enables a HTTP JSON to RPC mapping as below: HTTP | RPC -----|----- GET /v1/messages/123456?revision=2&sub.subfield=foo | GetMessage(message_id: "123456" revision: 2 sub: SubMessage(subfield: "foo")) Note that fields which are mapped to HTTP parameters must have a primitive type or a repeated primitive type. Message types are not allowed. In the case of a repeated type, the parameter can be repeated in the URL, as in ...?param=A&param=B. For HTTP method kinds which allow a request body, the body field specifies the mapping. Consider a REST update method on the message resource collection: service Messaging { rpc UpdateMessage(UpdateMessageRequest) returns (Message) { option (google.api.http) = { put: "/v1/messages/{message_id}" body: "message" }; } } message UpdateMessageRequest { string message_id = 1; // mapped to the URL Message message = 2; // mapped to the body } The following HTTP JSON to RPC mapping is enabled, where the representation of the JSON in the request body is determined by protos JSON encoding: HTTP | RPC -----|----- PUT /v1/messages/123456 { "text": "Hi!" } | UpdateMessage(message_id: "123456" message { text: "Hi!" }) The special name * can be used in the body mapping to define that every field not bound by the path template should be mapped to the request body. This enables the following alternative definition of the update method: service Messaging { rpc UpdateMessage(Message) returns (Message) { option (google.api.http) = { put: "/v1/messages/{message_id}" body: "*" }; } } message Message { string message_id = 1; string text = 2; } The following HTTP JSON to RPC mapping is enabled: HTTP | RPC -----|----- PUT /v1/messages/123456 { "text": "Hi!" } | UpdateMessage(message_id: "123456" text: "Hi!") Note that when using * in the body mapping, it is not possible to have HTTP parameters, as all fields not bound by the path end in the body. This makes this option more rarely used in practice of defining REST APIs. The common usage of * is in custom methods which don't use the URL at all for transferring data. It is possible to define multiple HTTP methods for one RPC by using the additional_bindings option. Example: service Messaging { rpc GetMessage(GetMessageRequest) returns (Message) { option (google.api.http) = { get: "/v1/messages/{message_id}" additional_bindings { get: "/v1/users/{user_id}/messages/{message_id}" } }; } } message GetMessageRequest { string message_id = 1; string user_id = 2; } This enables the following two alternative HTTP JSON to RPC mappings:

Rules for HTTP mapping

The rules for mapping HTTP path, query parameters, and body fields to the request message are as follows: 1. The body field specifies either * or a field path, or is omitted. If omitted, it assumes there is no HTTP body. 2. Leaf fields (recursive expansion of nested messages in the request) can be classified into three types: (a) Matched in the URL template. (b) Covered by body (if body is *, everything except (a) fields; else everything under the body field) (c) All other fields. 3. URL query parameters found in the HTTP request are mapped to (c) fields. 4. Any body sent with an HTTP request can contain only (b) fields. The syntax of the path template is as follows: Template = "/" Segments [ Verb ] ; Segments = Segment { "/" Segment } ; Segment = "*" | "**" | LITERAL | Variable ; Variable = "{" FieldPath [ "=" Segments ] "}" ; FieldPath = IDENT { "." IDENT } ; Verb = ":" LITERAL ; The syntax * matches a single path segment. It follows the semantics of RFC 6570 Section 3.2.2 Simple String Expansion. The syntax ** matches zero or more path segments. It follows the semantics of RFC 6570 Section 3.2.3 Reserved Expansion. NOTE: it must be the last segment in the path except the Verb. The syntax LITERAL matches literal text in the URL path. The syntax Variable matches the entire path as specified by its template; this nested template must not contain further variables. If a variable matches a single path segment, its template may be omitted, e.g. {var} is equivalent to {var=*}. NOTE: the field paths in variables and in the body must not refer to repeated fields or map fields. Use CustomHttpPattern to specify any HTTP method that is not included in the pattern field, such as HEAD, or "*" to leave the HTTP method unspecified for a given URL path rule. The wild-card rule is useful for services that provide content to Web (HTML) clients.

Protobuf type Google\Api\HttpRule