FredericRezeau / tiny-soroban

Is it the tiniest smart contract?

65 Bytes Soroban Smart Contract

For those who prefer to get straight to the point, here's my WAT:

(module
  (func (export "") (result i64)
    i64.const 2))

Binary:

0061736d010000000105016000017e030201000704010000000a0601040042020b
001e11636f6e7472616374656e766d6574617630000000000000001400000000

Upload/Invoke Transactions (mainnet):

Tx 938c6619dd407eaf303eb79687585fc793c47b6c6aa19ba14e5708e9f6041d1d
Tx f4c1d2abf2a777d44304a6c89df1a69d0ecb805d22618ffd77382f295ca12a55
Tx 21dd674460387f0e0775a42e73401d508d31751d8a1d8b9c27d72ba6f8e5a907

Tiny Soroban challenge

This morning I came across this post from @tyvdh in the Stellar Developer discord server and decided to take on the challenge for the weekend:

kalepail > Fun over-Christmas challenge. Can you beat my smallest invokable soroban contract high score of 66 bytes? https://futurenet.steexp.com/contract/CC4QBKSZKUJNVHMAOYRV4SSE24WRFQ3VAL4IX6PONPBSOFHQFC5F6IDB/code-wat

The WAT looks like this:

(module
  (type (;0;) (func (result i64)))
  (func (;0;) (type 0) (result i64)
    i64.const 2)
  (export "r" (func 0)))

Looking at it closely, it seemed there was no room for compacting the module further: one export, one function, mandatory return type for an invokable contract and 1 byte length function name.

WASM binary generated: 34 bytes.

[magic:4][version:4][type_sec:7][func_sec:5][export_sec:6][code_sec:8]

So, I first tried to strip the custom sections but the smart contract was rejected with the following error:

0: [Diagnostic Event] topics:[error, Error(WasmVm, InvalidInput)], data:"contract missing metadata section"

Then, I found this in the reference Soroban documentation:

https://soroban.stellar.org/docs/reference

Contracts must contain a Wasm custom section with name contractenvmetav0 and containing a serialized SCEnvMetaEntry

The minimum size for this section alone is 32 bytes. The only way to reduce the binary size, given these current Soroban specifications, was to find a way to shrink the module code.

Solution

Here is what the wasm spec says:

name ::= char∗ (if|utf8(char∗)|<2^32)

Function names (utf8(char∗)) can have a length of zero. So hypothetically, we could take one byte off the 34 bytes (export section).

So, the WAT can be written more compactly like this, resulting in the same output except for the export section, which can now be one byte shorter:

(module
  (func (export "") (result i64)
    i64.const 2))

And the generated binary:

0061736d010000000105016000017e030201000704010000000a0601040042020b

[magic:4][version:4][type_sec:7][func_sec:5][export_sec:5][code_sec:7]

Appending the meta section, we get:

0061736d010000000105016000017e030201000704010000000a0601040042020b
001e11636f6e7472616374656e766d6574617630000000000000001400000000

When you build the transaction, just specify an empty string for the contract call.

   new Contract(StrKey.encodeContract(
    Address.fromScAddress(
    response.returnValue.address()).toBuffer()))
    .call("")

Upload and Invoke it

If you want to experiment further, you can write your WAT code directly at the top of the script. It will convert it to WASM binary and append the contractenvmetav0 section, so no need to use external tools.

// Try some new WAT here:
const wat = `
(module
  (func (export "") (result i64)
    i64.const 2))`;

Install and Run it

Install:

$ npm install

Run:

$ node index.js

Merry Xmas! 🎄🎅