Google's API platform provides a set of common functionality to all Google APIs built using the platform. In order to use and control such functionality, the platform pre-defines a special set of request parameters called system parameters. These parameters are available across all Google REST APIs and gRPC APIs. A system parameter can be specified either using an HTTP query parameter or an HTTP header. For Google gRPC APIs, only HTTP headers are supported.
Most users will not need to use these parameters directly, however they are often used by Google-provided client libraries. If you need to write custom code to access Google APIs directly, the system parameters can be useful in cases such as controlling JSON pretty-printing or specifying API Keys.
HTTP Mapping
For HTTP protocols, the system parameters are mapped to HTTP URL query
parameters and HTTP headers, see below. For example, if you have a system
parameter $foo, it's mapped to ?$foo=xxx in the URL
(URL-encoded on wire as ?%24foo=xxx).
NOTE: the "$" prefix is added to avoid conflicting with normal request
parameters.
gRPC Mapping
For gRPC, the system parameters are sent through normal HTTP request headers. See the table below for more details.
Definitions
The following table lists all system parameters and their definitions.
| URL Query Parameter | HTTP/gRPC Header | Description |
|---|---|---|
access_token,oauth_token |
Authorization | OAuth 2.0 access token. See the Cloud Platform Authentication Guide for more details. |
$alt,alt |
Alternative response format. Supported values are json (default), media, proto (binary protobuf). |
|
$apiFormat,$.xgafv |
JSON error format. Supported values are 1, 2 (default). The error format 1 should only be used by legacy clients. |
|
$callback,callback |
JSONP callback parameter. | |
$ct |
Content-Type | HTTP Content-Type header override. |
$fields,fields |
X-Goog-FieldMask | FieldMask(google.protobuf.FieldMask) used for response filtering. If empty, all fields will be returned. |
$httpMethod |
X-HTTP-Method-Override | The intended HTTP method for the request. Some network proxies don't accept all HTTP methods. |
$key,key |
X-Goog-Api-Key | Google API key, see details at https://developers.google.com/console/help/#generatingdevkeys. |
passwd,password |
Reserved to prevent putting passwords in the URLs. | |
$prettyPrint,prettyPrint |
Pretty-print JSON response. Supported values are true, false. |
|
$outputDefaults |
Force to output proto default values for JSON responses. | |
$unique |
Unique query parameter to disable request caching. | |
| X-Goog-Api-Client | API client identification. The value is a space-separated list of NAME "/" SEMVER strings, where the NAME should only contain lowercase letters, digits, and "-", and the SEMVER should be a semantic version string. For example: X-Goog-Api-Client: python/3.5.0 grpc-google-pubsub-v1/0.1.0-beta2 linux/2.7.0. |
|
$userProject |
X-Goog-User-Project | A user specified project that is responsible for the request quota and billing charges. |
