How do I compile a Solidity contract with an import to standalone byte code?

Question

I am trying to compile the MetaCoin contract (part of the Truffle Init Webpack). I need to get the byte code as hex numbers so that I can use it with Nethereum. The MetaCoin contains an import to ConvertLib.sol:

pragma solidity ^0.4.4;

import "./ConvertLib.sol";

contract MetaCoin {
    ...

When I compile it (using either Truffle from the command line or the Solidity extension for VS Code), the byte code I get is:

0x6060 ... 0073__ConvertLib____________________________6396 ... 0029

This is obviously a reference the ConvertLib library. When I use Nethereum to try and deploy the contract:

...
var ByteCode = 
    "0x6060 ... 0073__ConvertLib____________________________6396 ... 0029";
var transactionHash = await web3.Eth.DeployContract.SendRequestAsync(
    Abi, ByteCode, Address, Gas, GasPrice);

I get the error message:

System.InvalidOperationException: Character '_' at index '604' is not valid alphanumeric character.

Clearly, it does not like the "ConvertLib" reference in the middle of the byte code. I could just include the library code in the MetaCoin contract and remove the import, but I would like to sort this problem out properly.

How can I compile the MetaCoin contract so that it includes the ConvertLib library in the byte code?

Answer 1

What you are looking for is

solc --optimize --bin MetaCoin.sol | solc --link --libraries ConvertLib:<address>

In order for this to work ConvertLib has to be deployed first, the linking will then replace the placeholders like 0073__ConvertLib____________________________6396 with the actual addresses.

To quote the relevant part of the documentation:

If your contracts use libraries, you will notice that the bytecode contains substrings of the form __LibraryName______. You can use solc as a linker meaning that it will insert the library addresses for you at those points:

Either add --libraries "Math:0x12345678901234567890 Heap:0xabcdef0123456" to your command to provide an address for each library or store the string in a file (one library per line) and run solc using --libraries fileName.

If solc is called with the option --link, all input files are interpreted to be unlinked binaries (hex-encoded) in the __LibraryName____-format given above and are linked in-place (if the input is read from stdin, it is written to stdout). All options except --libraries are ignored (including -o) in this case.