Documentation for default funcs #896

liamzebedee · 2018-06-14T16:43:03Z

- What I did

Fixes: #892.

Documented new default function usage.

- How I did it

Read the source changes, researched a bit about the EVM execution sematics to communicate a stronger understanding.

- How to verify it

Generate docs and visit structure-of-a-contract.html

- Description for the changelog

Documented default functions of contracts (fallback funcs).

- Cute Animal Picture

liamzebedee · 2018-06-14T16:43:24Z

Fixes #892

fubuloubu · 2018-06-14T17:08:25Z

docs/structure-of-a-contract.rst

+
+A contract can also have a default function, which is executed on a call to the contract if no other functions match the given function identifier (or if none was supplied at all, such as through someone sending it Eth). It is the same construct as fallback functions `in Solidity <https://solidity.readthedocs.io/en/latest/contracts.html?highlight=fallback#fallback-function>`_. 
+
+This function is always named `__default__` and must be annotated with `@public` and `@payable`. It cannot have arguments and cannot return anything.


I think @payable is optional, confirm @jacqueswww?

Ah woops! Will fix that.

I'm not 💯, wait for confirmation from @jacqueswww unless you found in the code/tests where this is allowed.

@fubuloubu Haha I found the test, I just misread the failure condition initially.

https://github.com/ethereum/vyper/blob/master/tests/parser/functions/test_default_function.py#L34

Yes payable is optional, depending on the use case ;)

fubuloubu · 2018-06-14T17:14:43Z

docs/structure-of-a-contract.rst

+Default function
+----------------
+
+A contract can also have a default function, which is executed on a call to the contract if no other functions match the given function identifier (or if none was supplied at all, such as through someone sending it Eth). It is the same construct as fallback functions `in Solidity <https://solidity.readthedocs.io/en/latest/contracts.html?highlight=fallback#fallback-function>`_. 


"if no other functions match the given function identifier" I am pretty sure this is the behavior we have, but I don't actually like this behavior now that I think about it. The default function should not have any call data associated with it (aka fails if call data is provided) and I think in general if the function signature switch falls through, the contract should revert by default. We can keep this behavior in place for the fallback function, since that will check that call data is zero if no function signatures match.

@jacqueswww Please confirm current behavior matches this documentation, and also comment on my suggestion for modifying the behavior of the default function. This should be compatible with any contracts created by Solidity. In fact, do we have a test case for one contract sending another Eth internally?

@fubuloubu this is the current behaviour.

And therefore I think it's fine to leave it as is (in the docs). However we can definitely scope a VIP for splitting default function into 2 cases:
1.) Receive funds
2.) Function Not Found (404)
I saw this on solidity something similar is being discussed. ethereum/solidity#3198 (comment)

fubuloubu · 2018-06-14T17:16:03Z

docs/structure-of-a-contract.rst

+
+::
+
+    Sent: event({sender: indexed(address)})


Suggestion: maybe add amount to this event, so if someone tries to run it you can see the amount you sent in the event.

fubuloubu · 2018-06-14T17:23:29Z

docs/structure-of-a-contract.rst

+- Calling an external function which consumes a large amount of gas
+- Sending Ether
+
+Since global variables are still accessible, you can pass data to the default function through the raw byte buffer provided to EVM's CALL (`msg.data`).


See above, I think we should disallow this behavior

haydenadams · 2018-06-15T10:42:09Z

docs/structure-of-a-contract.rst

+
+Unlike Solidity, Vyper generates a default function is one isn't found, in the form of a REVERT call. Note that this still `generates an exception <https://github.com/ethereum/wiki/wiki/Subtleties>`_ and thus will not succeed in receiving funds. 
+
+Send calls to the contract give it a maximum stipend of 2300 gas, leaving not much room to perform other operations except basic logging. The following operations will consume more gas than the 2300 gas stipend:


You can still choose to include a higher gas amount when you send ETH to an address, which allows more complex fallback functions that will automatically fail unless extra gas is included. At least thats how it is with Solidity fallbacks, hoping its the same here.

Many ICOs allowed purchasing by sending ETH to the fallback and including ~200,000 gas. I have even heard of MEW automatically s the higher gas amount when it detected a user sending to a known ICO with a fallback.

@haydenadams yes it is I believe, created an issue to demonstrate this as a tests.
@liamzebedee please make it clear that one can still send more gas to a default function, if you don't use send. for example raw_call / CALL allows you to send as much gas as you like.

liamzebedee · 2018-06-25T11:32:26Z

Ready for another review!

liamzebedee · 2018-07-03T19:02:03Z

Ping @fubuloubu

fubuloubu

Some updates, but it's looking good.

fubuloubu · 2018-07-04T04:17:14Z

docs/structure-of-a-contract.rst

+- Calling an external function which consumes a large amount of gas
+- Sending Ether
+
+Since global variables are still accessible, you can pass data to the default function through the raw byte buffer provided to EVM's CALL (``msg.data``).


I think accessing msg.data is discouraged behavior. Please mention that, or skip this section. You could perhaps mention accessing msg.sender instead.

+1 a block mentioning that when using msg.data care should be taking.

fubuloubu · 2018-07-04T04:18:19Z

docs/structure-of-a-contract.rst

+Considerations
+~~~~~~~~~~~~~~
+
+Unlike Solidity, Vyper generates a default function is one isn't found, in the form of a REVERT call. Note that this still `generates an exception <https://github.com/ethereum/wiki/wiki/Subtleties>`_ and thus will not succeed in receiving funds. 


Typo: "... generates a default function if one isn't found"

fubuloubu · 2018-07-04T04:28:01Z

docs/structure-of-a-contract.rst

+
+Unlike Solidity, Vyper generates a default function is one isn't found, in the form of a REVERT call. Note that this still `generates an exception <https://github.com/ethereum/wiki/wiki/Subtleties>`_ and thus will not succeed in receiving funds. 
+
+Ethereum specifies that the operations will be rolled back if the contract runs out of gas in execution. ``send`` calls to the contract come with a free stipend of 2300 gas, which does not leave much room to perform other operations except basic logging. **However**, if the sender includes a higher gas amount through a ``call`` instead of ``send``, then more complex functionality can be run.


This is more nuanced than your description. I can call a default/fallback directly from a raw transaction (in a contract or from an EOA) and the gas stipend is more than 2300. This stipend only holds when when an address.transfer(uint) is called, as implemented by Solidity and Vyper compilers as a mitigation against excessive gas usage.

It is therefore considered a best practice to ensure your payable default function is compatible with the 2300 gas stipend. If it is currently an error, then overusing the gas stipend should be a warning instead. There are legitimate use cases for a default that exceeds this amount. Lots of nuance here.

@jacqueswww, do you agree?

jacqueswww · 2018-07-10T16:10:12Z

@liamzebedee looking good, make above changes and we are good to go!
Also make sure your ethereum address set in your openbounty profile.

liamzebedee · 2018-07-16T23:28:29Z

RE: global variables that are accessible, I scraped this list from expr.py of what we can currently access in contracts:

msg.sender
msg.value
msg.gas
block.difficulty
block.timestamp
block.coinbase
block.number
block.prevhash
tx.origin

Would be worth adding this later on :)

liamzebedee · 2018-07-16T23:31:37Z

👍 take a peek!

jacqueswww · 2018-07-27T17:40:03Z

@liamzebedee sorry for only getting back to you now, slipped past my radar. I think it's ready to merge. Thanks :)

jacqueswww · 2018-07-31T13:55:07Z

@liamzebedee do you have a payout address set in openbounty.status.im? There is a bounty on this issue, and I want to pay it out 😄

liamzebedee · 2018-08-07T15:31:31Z

@jacqueswww sure am :)

pablanopete · 2018-08-14T15:39:17Z

@liamzebedee sorry for the slow response on bounty payout, could you drop your wallet address here so I can send you the bounty amount Out of Band while we wait on a dashboard fix in Status Open Bounty.

If you don't feel comfortable putting it here in the comment could you email a ERC20 compatible wallets address to me? chris.hutchinson@status.im

liamzebedee · 2018-08-15T20:06:08Z

Cheers @pablanopete :)

0xf87de2add59a3c23ab6365f8addfc5db9c86b3b9

pablanopete · 2018-08-17T03:55:16Z

Sent thanks! https://etherscan.io/tx/0xaecb732bfeaaa32adcf080038aafc5d8c60e11320ec520b102473eee74286833

Documentation for default funcs

e8dac25

fubuloubu reviewed Jun 14, 2018

View reviewed changes

haydenadams reviewed Jun 15, 2018

View reviewed changes

liamzebedee added 3 commits June 24, 2018 23:34

Fix @payable semantics

aa98645

Add more info on stipend and send/call distinction

433abba

Update structure-of-a-contract.rst

162d218

fubuloubu requested changes Jul 4, 2018

View reviewed changes

liamzebedee added 2 commits July 17, 2018 00:40

Fix typo

02dc2bd

Rewrite default data given

89352e9

Edited about gas stipend

36805f0

jacqueswww merged commit 6c98cab into vyperlang:master Jul 27, 2018

nrryuya mentioned this pull request Dec 17, 2018

[Proxy] Implement proxy contract LayerXcom/verified-vyper-contracts#55

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Documentation for default funcs #896

Documentation for default funcs #896

liamzebedee commented Jun 14, 2018 •

edited by jacqueswww

Loading

liamzebedee commented Jun 14, 2018

fubuloubu Jun 14, 2018

liamzebedee Jun 14, 2018 •

edited

Loading

fubuloubu Jun 14, 2018

liamzebedee Jun 15, 2018

jacqueswww Jun 15, 2018

fubuloubu Jun 14, 2018

jacqueswww Jun 15, 2018

fubuloubu Jun 14, 2018

jacqueswww Jun 15, 2018

fubuloubu Jun 14, 2018

haydenadams Jun 15, 2018

jacqueswww Jun 15, 2018

liamzebedee commented Jun 25, 2018

liamzebedee commented Jul 3, 2018

fubuloubu left a comment

fubuloubu Jul 4, 2018

jacqueswww Jul 10, 2018

fubuloubu Jul 4, 2018

fubuloubu Jul 4, 2018

jacqueswww commented Jul 10, 2018 •

edited

Loading

liamzebedee commented Jul 16, 2018

liamzebedee commented Jul 16, 2018

jacqueswww commented Jul 27, 2018

jacqueswww commented Jul 31, 2018 •

edited

Loading

liamzebedee commented Aug 7, 2018

pablanopete commented Aug 14, 2018

liamzebedee commented Aug 15, 2018

pablanopete commented Aug 17, 2018


		A contract can also have a default function, which is executed on a call to the contract if no other functions match the given function identifier (or if none was supplied at all, such as through someone sending it Eth). It is the same construct as fallback functions `in Solidity <https://solidity.readthedocs.io/en/latest/contracts.html?highlight=fallback#fallback-function>`_.

		This function is always named `__default__` and must be annotated with `@public` and `@payable`. It cannot have arguments and cannot return anything.


		Unlike Solidity, Vyper generates a default function is one isn't found, in the form of a REVERT call. Note that this still `generates an exception <https://github.com/ethereum/wiki/wiki/Subtleties>`_ and thus will not succeed in receiving funds.

		Send calls to the contract give it a maximum stipend of 2300 gas, leaving not much room to perform other operations except basic logging. The following operations will consume more gas than the 2300 gas stipend:


		Unlike Solidity, Vyper generates a default function is one isn't found, in the form of a REVERT call. Note that this still `generates an exception <https://github.com/ethereum/wiki/wiki/Subtleties>`_ and thus will not succeed in receiving funds.

		Ethereum specifies that the operations will be rolled back if the contract runs out of gas in execution. ``send`` calls to the contract come with a free stipend of 2300 gas, which does not leave much room to perform other operations except basic logging. However, if the sender includes a higher gas amount through a ``call`` instead of ``send``, then more complex functionality can be run.

Documentation for default funcs #896

Documentation for default funcs #896

Conversation

liamzebedee commented Jun 14, 2018 • edited by jacqueswww Loading

- What I did

- How I did it

- How to verify it

- Description for the changelog

- Cute Animal Picture

liamzebedee commented Jun 14, 2018

Choose a reason for hiding this comment

liamzebedee Jun 14, 2018 • edited Loading

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

liamzebedee commented Jun 25, 2018

liamzebedee commented Jul 3, 2018

fubuloubu left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

jacqueswww commented Jul 10, 2018 • edited Loading

liamzebedee commented Jul 16, 2018

liamzebedee commented Jul 16, 2018

jacqueswww commented Jul 27, 2018

jacqueswww commented Jul 31, 2018 • edited Loading

liamzebedee commented Aug 7, 2018

pablanopete commented Aug 14, 2018

liamzebedee commented Aug 15, 2018

pablanopete commented Aug 17, 2018

liamzebedee commented Jun 14, 2018 •

edited by jacqueswww

Loading

liamzebedee Jun 14, 2018 •

edited

Loading

jacqueswww commented Jul 10, 2018 •

edited

Loading

jacqueswww commented Jul 31, 2018 •

edited

Loading