Back to top
Smart Contracts

Type conversions

MultiBaas provides users with the ability to, on a per-method per-input/output parameter basis, adjust how the value is interpreted on its..

16

MultiBaas provides users with the ability to, on a per-method per-input/output parameter basis, adjust how the value is interpreted on its way to the blockchain, or adjust the return value on its way back from the blockchain.

One example would be to dynamically insert a decimal point into a smart contract method that returns an amount of type uint256. As exact decimal numbers are not supported by Solidity, the standard way of handling this situation is to use an integer and shift it by a fixed number of decimal places.

In the popular ERC20 token standard, a decimals() method provides the number of decimals place to shift the uint256 (unsigned integer) values for other methods input/output parameters that relate to token balances. For example, if decimals() returns 3, then the return value of the totalSupply() method should be shifted by 3 decimal places to the left.

We start by querying the totalSupply() method for the “autotoken” instance (an alias for the address of a smart contract deployed on the Ethereum blockchain).

Request

POST .../chains/ethereum/addresses/autotoken/contracts/mltitoken/methods/totalSupply
Response

{
   "status": 200,
   "message": "Success",
   "result": {
       "output": "123000",
       "summarizedInputs": []
   }
}

The total supply is therefore 123,000. If we query the contract’s decimals() method:

Request

POST .../chains/ethereum/addresses/autotoken/contracts/mltitoken/methods/decimals
Response

{
   "status": 200,
   "message": "Success",
   "result": {
       "output": 3,
       "summarizedInputs": []
   }
}

Therefore, the result of totalSupply(), along with all other balance/amount method input/output parameters should be shifted by 3 decimal places to the left.

Note that the return value of totalSupply() was automatically enclosed in quotations by MultiBaas. This is done because it is a uint256 value and could overflow JavaScript’s 32-bit limit on integer sizes. The application would have to handle this as a JavaScript big number or string, as appropriate. The return value of the decimals() function, on the other hand, is of type uint8 (maximum decimal 256), and is automatically left unquoted by MultiBaas, so that the application could use it directly as a JavaScript number.

We could instruct MultiBaas to automatically shift the result of the totalSupply() function by 3 places:

Request

POST .../contracts/mltitoken/1.0/methods/totalSupply




   "outputs": [
      {
         "typeConversion": {
            "mode": "decimals",
            "decimalsAbsolute": 3
         }
      }
   ]
}
Response

{
   "status": 200,
   "message": "Success"
}

We can also instruct MultiBaas to use the output of another function to specify the number of decimals. In this way we can support a varying number of decimals across smart contract instances with a single configuration setup of MultiBaas.

This decimals function must satisfy the following requirements:

  • Take no parameters
  • Return a single integer value
  • Be constant (i.e., not modify the blockchain state at all)

Making another request to MultiBaas to use the output of decimals() for the number of decimals of the totalSupply() method:

Request

POST .../contracts/mltitoken/1.0/methods/totalSupply



{
   "outputs": [
      {
         "typeConversion": {
            "mode": "decimals",
            "decimalsFunction": "decimals"
         }
      }
   ]
}
Response

{
   "status": 200,
   "message": "Success"
}

Again calling the totalSupply() method:

Request

POST .../chains/ethereum/addresses/autotoken/contracts/mltitoken/methods/totalSupply
Response

{
   "status": 200,
   "message": "Success",
   "result": {
       "output": "123.000",
       "summarizedInputs": []
   }
}

The total supply is therefore 123.000, with the decimal place shifted three places to the left.

Type Conversion Previews

Type conversions can be previewed by running their inputs or outputs through a temporary, non-persisted type conversion. This is done to generate a preview of what the converted type will look like for presentation in a UI.

The API request and response to preview a type conversion is as follows.

Request

POST .../chains/ethereum/addresses/typesrest/contracts/typesrest/methods/sendBytesAndReturnBytes




{
    "preview": {
        "inputs": [
            {
                "typeConversion": {
                    "mode": "base64Bytes"
                }
            }
        ],
        "outputs": [
            {
                "typeConversion": {
                    "mode": "base64Bytes"
                }
            }
        ]
    },
    "args": [
        "qxI="
    ]
}
Response

{
    "status": 200,
    "message": "Success",
    "result": {
        "input": [
            "0xab12"
        ],
        "output": "qxI="
    }
}

Web UI

From the UI you can also update the type conversion settings.

  1. Select Contracts from the main menu
  2. Select a specific contract then contract instance from the side menu
  3. Click Settings at the top of either the Details section or Methods section of the contract page to reveal the pencil icon next to each detail or method name
  4. Click the pencil icon of the field you wish to edit to reveal its type conversion settings
  5. Depending on the method's input and output types you will be prompted to select an applicable type conversion
  6. Select a type conversion and, if necessary, the type conversion settings
  7. Observe the preview and, if applicable, enter sample input or output to confirm the settings are correct
  8. Click Update to apply the changes
  9. Note the changes will apply immediately!
  10. Click Done at the top of the section (Details or Methods) that you were editing to hide the pencil icon next to each detail or method name

‍

Next document
Previous document
1
Introduction to MultiBaas

MultiBaas is a blockchain middleware that allows you to build decentralized applications quickly and easily.

2
Getting started: creating a MultiBaas deployment

To use MultiBaas you will need to create a new deployment. To do that you will first create an account on our management portal

3
Create an account

Go to the Sign Up page to create a new account. You will need to enter

4
Deploy a MultiBaas instance

After creating a new account you will be directed to the New Deployment page. You can also reach this page by the following actions:

5
Multilingual support

The MultiBaas UI is designed in English but has limited support for the following languages...

6
The MultiBaas API

MultiBaas takes smart contract source code and dynamically constructs a REST API that users can use to interact with smart contracts ...

7
Generate API keys

API keys belong to individual user accounts and inherit the same permissions as the associated account. If you want to your API key to ...

8
Using curl

Curl is a free, open source command line utility that can be used to interact with URLs including those defined in the MultiBaas API.

9
Getting started: smart contracts

MultiBaas currently supports Ethereum smart contracts written in the Solidity programming language, although support for additional ...

10
Prepare a smart contract for upload

Due to the compilation process, it is currently required to combine your contracts into a single file before uploading.

11
Upload a smart contract

MultiBaas compiles the smart contract server-side and provides feedback as to what sub-contracts are present in the source code.

12
Deploy a smart contract

After uploading a solidity file containing one or more smart contracts, you will be prompted to deploy or link the compiled contracts to a..

13
Link a deployed smart contract instance

Besides deploying a smart contract to a new address, you can also link a smart contract to an existing instance.

14
Contracts, versions, and instances

Contracts, contract meta-data, deployed instances, and blockchain addresses have a number of user-defined attributes in order to help you...

15
Interact with a smart contract

Once you have uploaded and deployed or linked a smart contract you can then interact with it through either the UI or the API.

16
Type conversions

MultiBaas provides users with the ability to, on a per-method per-input/output parameter basis, adjust how the value is interpreted on its..

17
Multi-signature (multisig) wallet smart contracts

Multisignature (multisig) wallets are smart contracts that allow multiple signers to review and agree on an action on the blockchain ...

18
Sample smart contracts

MultiBaas comes with a number of sample smart contracts pre-installed. They may be linked to deployed contracts on the blockchain or just...

19
Overview of the blockchain

A blockchain is a distributed database that uses a decentralized consensus algorithm to agree on the current state of the world.

20
Connect to geth

Coming soon...

21
ABIs: enhanced ABI and raw ABI

MultiBaas generates its own stable ABI that provides a stable platform to build DApps on. The MultiBaas ABI, along with the rest of the...

22
Addresses

thereum addresses are represented by 40 hexadecimal digits prefixed with "0x". An address can refer to an account controlled by an ...

23
OMG Network

Plasma is a "layer 2" blockchain scaling solution designed by Joseph Poon and Vitalik Buterin.

24
Role based access control

MultiBaas uses a rudimentary three part role based access control (RBAC) model for controlling access to MultiBaas resources.

25
RBAC model: users, groups, and roles

There are four pre-defined Groups in MultiBaas...

26
Assign roles to groups

As explained in the previous section 13.1 RBAC model: users, groups, and roles, there are four pre-defined Groups and five pre-defined...

27
Assign groups to users

You can assign one or more groups to a user when creating or editing a user. A common scenario where you might do this is when giving ...

28
Users

Users of MultiBaas are identified by their email address and can perform various actions within the system. Primarily user accounts are...

29
Create, edit, and delete users

Users can be created interactively using the UI or by uploading a CSV file...

30
MultiBaas users vs. console.curvegrid.com users

console.curvegrid.com is the deployment management and billing portal from where you will launch instances of the MultiBaas software ...

31
Reset passwords

If you forget your password for either console.curvegrid.com or for your MultiBaas deployment you can request a password reset link.

32
Two factor authentication

Curvegrid supports two factor authentication using time based one time passwords.

33
Events and Event Queries

The Ethereum blockchain has a concept called events, also referred to as transaction logs, which are used to indicate that a specific ...

34
Event summaries per contract instance

In MultiBaas event monitoring persistence is enabled on a per-smart contract per-address basis when a smart contract is linked ...

35
Events page

he Events page shows a preview of the events of all contracts being monitored by MultiBaas. To navigate to the Events page

36
Event queries

One of the challenges of interacting with smart contracts is computing the current state of a contract.

37
MultiBaas Spreadsheet

MultiBaas Spreadsheet is an add-on for Google Sheets. It provides an easy way to interact with the blockchain via custom ...

38
Install add-on

Installing the Google Sheets add-on.

39
Set API key in add-on

To set the API key in the add-on, navigate to your MultiBaas deployment in a web browser. Login, and go to Admin > API Keys or Account ...

40
Set deployment ID in add-on

To set the deployment ID, navigate to your MultiBaas deployment. Copy the URL from your browser's URL bar.

41
Spreadsheet Functions

Retrieve the details of a blockchain address.