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Description
Fn::ArraySelect
Fn::Base64Decode
Fn::Base64Encode
Fn::GetBytes
Fn::HmacSHA256
Fn::Join
Fn::MathAdd
Fn::MathDiv
Fn::MathMod
Fn::MathMultiply
Fn::MathSub
Fn::ParseLong
Fn::Split
Fn::SplitSelect
Fn::Sub
Fn::SubStringAfter
Fn::SubStringBefore
Ref

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Help Center/ IoT Device Access/ User Guide/ Device Access/ Device Authentication/ MQTT(S) Custom Template Authentication/ Internal Functions

Internal Functions

Updated on 2024-11-06 GMT+08:00

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Description

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.

NOTE:

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}"}]}.

Fn::ArraySelect

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

JSON

{"Fn::ArraySelect": [index, [StringArray]]}

**Table 1** Parameters
Parameter	Type	Description
index	int	Index of an array element. The value is an integer and starts from 0.
StringArray	String[]	String array element.
Return values	String	Element whose index is index.

Example:

{
	"Fn::ArraySelect": [1, ["123", "456", "789"]]
}
return: "456"

Fn::Base64Decode

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

JSON

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

**Table 2** Parameters
Parameter	Type	Description
content	String	String to be decoded.
Return Values	byte[]	Base64-decoded byte array.

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"}

**Table 3** Parameters
Parameter	Type	Description
content	String	String to be encoded.
Return Values	String	Base64-encoded string.

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"}

**Table 4** Parameters
Parameter	Type	Description
content	String	String to be encoded.
Return Values	byte[]	Byte array converted from a string encoded using UTF-8.

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"]}

**Table 5** Parameters
Parameter	Type	Description
content	String	String to be encrypted.
secret	String or byte[]	Secret key, which can be a string or byte array.
Return Values	String	Value encrypted using the HMACSHA256 algorithm.

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"...]}

**Table 6** Parameters
Parameter	Type	Description
element	String	String to be concatenated.
Return Values	String	String obtained by concatenating substrings.

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]}

**Table 7** Parameters
Parameter	Type	Description
X	long	Augend.
Y	long	Addend.
Return Values	long	Sum of X and 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]}

**Table 8** Parameters
Parameter	Type	Description
X	long	Dividend.
Y	long	Divisor.
Return Values	long	Value of X divided by 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]}

**Table 9** Parameters
Parameter	Type	Description
X	long	Dividend.
Y	long	Divisor.
Return Values	long	Residue of X modulo 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]}

**Table 10** Parameters
Parameter	Type	Description
X	long	Multiplicand.
Y	long	Multiplier.
Return Values	long	Value of X multiplied by 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]}

**Table 11** Parameters
Parameter	Type	Description
X	long	Minuend.
Y	long	Subtrahend.
Return Values	long	Value of X minus Y.

Example:

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

Fn::ParseLong

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

JSON

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

**Table 12** Parameters
Parameter	Type	Description
String	String	String to be converted.
Return Values	long	Value obtained after a string is converted into an integer.

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"] }

**Table 13** Parameters
Parameter	Type	Description
String	String	String to be split.
Separator	String	Separator.
Return Values	String[]	String array obtained after String is split by 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] }

**Table 14** Parameters
Parameter	Type	Description
String	String	String to be split.
Separator	String	Separator.
index	int	Index value of the target element in the array, starting from 0.
Return Values	String	Substring of the specified index after a string is split by the specified separator.

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 } ] }

**Table 15** Parameters
Parameter	Type	Description
String	String	A string that contains variables. Variables are defined using placeholders (${}).
VarName	String	Variable name, which must be defined in the String parameter.
VarValue	String	Variable value. Function nesting is supported.
Return Values	String	Value of string after replacement in the original String parameter

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 truncates the substring after the specified separator in a string.

JSON

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

**Table 16** Parameters
Parameter	Type	Description
content	String	String to be truncated.
separator	String	Separator.
Return Values	String	Substring after the specified separator that separates the string.

Example:

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

Fn::SubStringBefore

The internal function Fn::SubStringBefore truncates the substring before the specified separator in a string.

JSON

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

**Table 17** Parameters
Parameter	Type	Description
content	String	String to be truncated.
separator	String	Separator.
Return Values	String	Substring before the specified separator that separates the string.

Example:

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

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" }

**Table 18** Parameters
Parameter	Type	Description
paramName	String	Name of the referenced parameter.
Return Values	String	Value of the referenced parameter.

Example:

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

Parent topic: MQTT(S) Custom Template Authentication

Previous topic: Examples

Next topic: Open Protocol Access

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