# Reserved parameters
A requester can pass request parameters either by referencing a template that contains them, or as an argument of the request-making methods of Airnode.sol.
In either case, these parameters are encoded in a bytes-type variable using Airnode ABI.
There are two types of parameters:
- Endpoint parameters mapped to API operation parameters
- Reserved parameters
Reserved parameters signal to the provider to perform a specific operation while fulfilling the request.
Reserved parameter names start with _.
# _type
Can be int256, bool, or bytes32.
Signifies what Solidity type the API response will be typecast to before fulfillment.
See the conversion behavior docs (opens new window) for details.
# _path
Assuming that the API response will be a JSON object, defines the field to be used to fulfill the request using dot notation. For example, if the API returns
{
"field1": {
"fieldA": [
"valueA1",
"valueA2"
],
"fieldB: "valueB"
},
"field2": {
"fieldZ": "valueZ"
}
}
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and _path is field1.fieldA.1, the response will be valueA2.
If the response is a literal value (i.e., not a JSON object) and _path is not provided, Airnode will use the literal value to fulfill the request.
# _times
If _type is int256 and a _times parameter is provided, Airnode multiplies the value returned by the API with the _times parameter before fulfilling the request.
For example, if the API returns:
{
"data": "1.238",
"apiVersion": "1.0.4"
}
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and the reserved parameters are
_type: int256
_path: data
_times: 100
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the request will be fulfilled with the value 123.
Note that the number gets multiplied by 100, and then gets floored.
# _relay_metadata
By setting this reserved parameter to a specific version string then Airnode will attach its metadata as request parameters before performing the API call.
For example v1 will add the following request parameters with their corresponding values:
_airnode_airnode_id: '0x19255a4ec31e89cea54d1f125db7536e874ab4a96b4d4f6438668b6bb10a6adb',
_airnode_client_address: '0xe7f1725E7734CE288F8367e1Bb143E90bb3F0512',
_airnode_designated_wallet: '0x1c5b7e13fe3977a384397b17b060Ec96Ea322dEc',
_airnode_endpoint_id: '0xeddc421714e1b46ef350e8ecf380bd0b38a40ce1a534e7ecdf4db7dbc9319353',
_airnode_requester_index: 10,
_airnode_request_id: '0xd1984b7f40c4b5484b756360f56a41cb7ee164d8acd0e0f18f7a0bbf5a353e65',
_airnode_chain_id: 'N/A',
_airnode_chain_type: 'N/A',
_airnode_airnode_rrp: 'N/A',
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Available values: v1
Note that requests events emitted by the pre-alpha Airnode.sol do not include the chain id.
Therefore, we cannot map chain information of each request with data configured for each provider in config.json.
That is why _airnode_chain_id, _airnode_chain_type and _airnode_airnode_rrp are set to "N/A" by default.
These fields will be populated in the future versions of the protocol