Internal Functions

Introduction

Huawei Cloud IoTDA provides multiple internal functions to use in templates. This section introduces these functions, including the input parameter type, parameter length, and return value type.

• The entire function must be in valid JSON format.
• In a function, the variable placeholders (${}) or the Ref function can be used to reference the value defined by the input parameter.
• The parameters used by the function must be declared in the template.
• A function with a single input parameter is followed by a parameter, for example, "Fn::Base64Decode": "${iotda::mqtt::username}".
• A function with multiple input parameters is followed by an array, for example, "Fn::HmacSHA256": ["${iotda::mqtt::username}", "${iotda::device::secret}"].
• Functions can be nested. That is, the parameter of a function can be another function. Note that the return value of a nested function must match its parameter type in the outer function, for example, {"Fn::HmacSHA256": ["${iotda::mqtt::username}", {"Fn::Base64Encode": "${iotda::device::secret}"}]}.
• The hash function (Fn::HmacSHA256) can be used twice at most in an authentication template.
• The total number of Base64 functions (Fn::Base64Decode and Fn::Base64Encode) in an authentication template cannot exceed 2.
• After applying the HmacSHA256 function to the password in the authentication template, the functions Fn::Split, Fn::SplitSelect, Fn::SubStringAfter, and Fn::SubStringBefore cannot be executed.

Fn::ArraySelect

The internal function Fn::ArraySelect returns a string element whose index is index in a string array.

Fn::Base64Decode

The internal function Fn::Base64Decode decodes a string into a byte array using Base64.

JSON

{ "Fn::Base64Decode" : "content" }

Example:

{
	"Fn::Base64Decode": "123456"]
}
return: d76df8e7 // The value is converted into a hexadecimal string for display.

Fn::Base64Encode

The internal function Fn::Base64Encode encodes a string using Base64.

JSON

{"Fn::Base64Encode": "content"}

Example:

{
	"Fn::Base64Encode": "testvalue"
}
return: "dGVzdHZhbHVl"

Fn::GetBytes

The internal function Fn::GetBytes returns a byte array encoded from a string using UTF-8.

JSON

{"Fn::GetBytes": "content"}

Example:

{
	"Fn::GetBytes": "testvalue"
}
return: "7465737476616c7565" // The value is converted into a hexadecimal string for display.

Fn::HmacSHA256

The internal function Fn::HmacSHA256 encrypts a string using the HmacSHA256 algorithm based on a given secret.

JSON

{"Fn::HmacSHA256": ["content", "secret"]}

Example:

{
	"Fn::HmacSHA256": ["testvalue", "123456"]
}
return: "0f9fb47bd47449b6ffac1be951a5c18a7eff694940b1a075b973ff9054a08be3"

Fn::Join

The internal function Fn::Join can concatenate up to 10 strings into one string.

JSON

{"Fn::Join": ["element", "element"...]}

Example:

{
	"Fn::Join": ["123", "456", "789"]
}
return: "123456789"

Fn::MathAdd

The internal function Fn::MathAdd performs mathematical addition on two integers.

JSON

{"Fn::MathAdd": [X, Y]}

Example:

{
	"Fn::MathAdd": [1, 1]
}
return: 2

Fn::MathDiv

The internal function Fn::MathDiv performs a mathematical division on two integers.

JSON

{"Fn::MathDiv": [X, Y]}

Example:

{
	"Fn::MathDiv": [10, 2]
}
return: 5

{
	"Fn::MathDiv": [10, 3]
}
return: 3

Fn::MathMod

The internal function Fn::MathMod performs the mathematical modulo on two integers.

JSON

{"Fn::MathMod": [X, Y]}

Example:

{
	"Fn::MathMod": [10, 3]
}
return: 1

Fn::MathMultiply

The internal function Fn::MathMultiply performs mathematical multiplication on two integers.

JSON

{"Fn::MathMultiply": [X, Y]}

Example:

{
	"Fn::MathMultiply": [3, 3]
}
return: 9

Fn::MathSub

The internal function Fn::MathSub performs mathematical subtraction on two integers.

JSON

{"Fn::MathSub": [X, Y]}

Example:

{
	"Fn::MathSub": [9, 3]
}
return: 6

Fn::ParseLong

The internal function Fn::ParseLong converts a numeric string into an integer.

JSON

{"Fn::ParseLong": "String"}

Example:

{
	"Fn::ParseLong": "123"
}
return: 123

Fn::Split

The internal function Fn::Split splits a string into a string array based on the specified separator.

JSON

{ "Fn::Split" : ["String", "Separator"] }

Example:

{
	"Fn::Split": ["a|b|c", "|"]
}
return: ["a", "b", "c"]

Fn::SplitSelect

The internal function Fn::SplitSelect splits a string into a string array based on the specified separator, and then returns the elements of the specified index in the array.

JSON

{ "Fn::SplitSelect" : ["String", "Separator", index] }

Example:

{
	"Fn::SplitSelect": ["a|b|c", "|", 1]
}
return: "b"

Fn::Sub

The internal function Fn::Sub replaces variables in an input string with specified values. You can use this function in a template to construct a dynamic string.

JSON

{ "Fn::Sub" : [ "String", { "Var1Name": Var1Value, "Var2Name": Var2Value } ] }

Example:

{
	"Fn::Sub": ["${token};hmacsha256", {
		"token": {
			"Fn::HmacSHA256": ["${iotda::mqtt::username}", {
				"Fn::Base64Decode": "${iotda::mqtt::client_id}"
			}]
		}
	}]
}
If:
${iotda::mqtt::username}="test_device_username"
${iotda::device::client_id}="OozqTPlCWTTJjEH/5s+T6w=="
return: "0773c4fd6c92902a1b2f4a45fdcdec416b6fc2bc6585200b496e460e2ef31c3d"

Fn::SubStringAfter

The internal function Fn::SubStringAfter extracts a substring after a specified separator.

JSON

{ "Fn::SubStringAfter" : ["content", "separator"] }

Example:

{
	"Fn::SubStringAfter": ["content:123456", ":"]
]
return: "123456"

Fn::SubStringBefore

The internal function Fn::SubStringBefore extracts a substring before a specified separator.

JSON

{ "Fn::SubStringBefore" : ["content", "separator"] }

Example:

{
	"Fn::SubStringBefore": ["content:123456", ":"]
]
return: "content"

Fn::ToLowerCase

The internal function Fn::ToLowerCase converts a string to the lowercase format.

JSON

{ "Fn::ToLowerCase" : content }

Example:

{
	"Fn::ToLowerCase": "ABC"
]
return: "abc"

Fn::ToUpperCase

The internal function Fn::ToUpperCase converts a string to the uppercase format.

JSON

{ "Fn::ToUpperCase" : content }

Example:

{
	"Fn::ToUpperCase": "abc"
]
return: "ABC"

Ref

The internal function Ref returns the value of the specified referenced parameter. The referenced parameter must be declared in the template.

JSON

{ "Ref" : "paramName" }

Example:

{
	"Ref": "iotda::mqtt::username"
}
If iotda::mqtt::username="device_123"
return: "device_123"