How does solidity online compiler link libraries?

Question

Suppose I have this code:

import "github.com/Arachnid/solidity-stringutils/strings.sol";

contract Contract {
    using strings for *;

    // ...
}

For this solidity online compiler generates this byte code:

60606040523415600b57fe5b5b60338060196000396000f30060606040525bfe00a165627a7a723058207a17f097139e731ad961366b8214b226041a3cd4427248c94ea39ee29bafface0029

Here I don't see any placeholder to add the library address. But when I deploy the byte code it creates a contract successfully.

So how does solidity online compiler find the address of the library?

And how does it know where to deploy the library i.e., mainnet or testnet. I am able to use the same byte code in both mainnet and testnet but the library address may be different in both networks. There are private networks also too.

Answer 1

In this case, the "strings" library only has functions with internal visibility therefore all the functions from the library are copied to the Contract contract therefore "strings" library was never deployed and so there isn't any placeholder to add the "strings" library address in the bytecode of Contract.

To know why it was copied read this http://solidity.readthedocs.io/en/develop/contracts.html#libraries

Answer 2

I assume you're using https://ethereum.github.io/browser-solidity/ when you're referring to the "solidity online compiler".

If that's the case, here's what happens when you "create" your Contract:

1. The import generates a library from the github source, compiles it, deploys it, and keeps the address in memory.
2. The compiler compiles your Contract, and then links the resulting bytecode to the address of the library's address.
3. The linked bytecode is then deployed to the blockchain.

Hope that clarifies it. I'm a bit out of date on the internals of the browser-solidity project, so hopefully I'm not leading you astray.