web3j | Lightweight Java and Android library | Blockchain library

I was able to figure this out finally. My initial understanding was incorrect. I was not supposed to attempt to decrypt the message to retrieve the nonce. Rather I needed to use the nonce to see if I can retrieve the public key of the private key used to sign the message and see if that public key retrieved matches the wallet ID.

1. Receive the signed message and the wallet ID from the client
2. Retrieve the nonce sent to the client with the same wallet ID
3. Generate the hash of the nonce
4. Generate the signature data from the message. This basically retrieves the V, R and S and. R and S are the outputs of the ECDSA Signature and V is the Recovery ID.
5. Using the ECDSA Signature and Hash of the Nonce, generate the possible public Key that was used to sign the message. At max, one will be able to generate 4 possible public keys for this message.
6. Check if any of the generated keys match public wallet ID that the client sent. If it matches, then we have a positive match. Generate the JWT and respond to the client. If not, we know that the nonce was not signed by the Metamask wallet we expected.

Here is a sample code for UI (JavaScript and HTML):

From the comments, you seem to be using some less common libraries. Sometimes, those kinds of libraries are not updated to be compatible with the Java Platform Module System. I think it is probably safe to assume that unless you know otherwise.

Defining a non-modular project

The easiest way to deal with such dependencies is to make your project non-modular: delete the module-info.java.

But JavaFX itself is only supported as modules. So, even though your project and its dependencies are non-modular, you should still place the JavaFX libraries on the module path.

Using a JDK which includes JavaFX

To accomplish such a setup (non-modular application using JavaFX modules), the easiest way is to rely on a JDK or JRE that includes JavaFX modules, for example, the Zulu JDK FX distribution or the Liberica Full JDK distribution. It is important to use the correct distribution as the base JDK distributions for Zulu and Liberica do not include JavaFX.

Using a base JDK which does not include JavaFX

With a bit more work, you can use OpenJDK. You can do this by sourcing the JavaFX modules from either the maven repository with a build tool, or a manual download of the modules and SDK from Gluon. In all your build and execution steps, you need to ensure that all of those modules are on the module path and declared to the module system via either VM arguments or a module-info.java.

Building with Maven

For a Maven build, you need to add each module to the module path individually, as they are all in separate directories in the local .m2 repository (modern Maven systems and some IDEs, such as Idea, will do that automatically, other IDEs such as VSCode may not).

Building with the SDK

Alternately, don't add dependencies on the JavaFX modules via Maven. Instead, download the JavaFX SDK and add the JavaFX modules there via VM arguments --module-path and --add-modules. This process for adding JavaFX modules to OpenJDK is documented in the getting started documentation at openjfx.io.

A note on openjfx.io Maven archetypes

Note that the openjfx.io getting started documentation around this mentions maven archetypes. My advice is not to use those as they are really difficult to work with if you try to use them from IDEs. Instead, use the Idea new JavaFX project wizard, either keeping the module-info.java it generates for a modular project or removing it and manually specifying JavaFX module VM arguments for a non-modular project.

Issues with your project build

In terms of your actual project, I encountered the same error that duffymo pointed out in the comments:

I can't resolve all the dependencies for web3jm-evm from Maven Central. It's pulling in a bunch of JARs from org.hyperledger.besu that aren't in Maven Central.

So I was unable to build or test it.

The ABI needs to contain just the function and event definitions that are stored in your result property. Without the wrapper object containing status and other properties.

So in your case

Polyfilling the Node globals and modules enables the web3 import to run in the browser:

1. Install the ESBuild plugins that polyfill Node globals/modules:

I found the solution here ethereum.stackexchange Anyone with the same question gets a very detailed answer there.

some contracts actually transfers to recipient specified amount of tokens minus 10% (5% tax fee and 5% liquidity fee) 208940457743532637 - 10% = 188046411969179375 and emits Transfer event. Then, PancakePair _swap function emits Swap event with base value of Amount0Out 208940457743532637

Amount0In is greater than zero because the token contract returns part of tokens as a liquidity pair on Pancake Swap.

Found it in the Ether.js docs:

You're going in the right direction checking the Transfer() event logs. Even though both ERC20 and ERC721 use the same event signature, the ERC721 (NFT) standard defines the 3rd topic (token ID) as indexed, which stores its value in the set of indexed topics. While the ERC20 defines the 3rd topic (amount) as non-indexed, making the total length of indexed topics set just 2.

I picked a random transaction that contains event logs of both ERC20 and ERC721 transfers. Looks like the logic behind it is payment in the form of an ERC20 token to mint a new ERC721 token.

Note: I'm not a Java dev, so I'll use a JS code in my answer that you can hopefully use as a reference to find the correct syntax and methods in the Java implementation of the Web3 library.

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