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How to charge percentage of transaction cost?

1

Example:

uint public createPostCost = 0.0003 ether;

function createPost(bytes32 _post) 
 public payable 
 require(msg.value >= createPostCost);
 Post memory newPost;
 newPost.post = _post;
 

Within a discussion forum dapp, the current implementation charges users a set fee per post created. I would like the charge to be dynamic, say 10% of the gas cost of the transaction. Is this possible to implement in the contract? Or is this something for front-end web3 to handle?

solidity web3js contract-development gas gas-limit

share|improve this question

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

add a comment | 

1

Example:

uint public createPostCost = 0.0003 ether;

function createPost(bytes32 _post) 
 public payable 
 require(msg.value >= createPostCost);
 Post memory newPost;
 newPost.post = _post;
 

Within a discussion forum dapp, the current implementation charges users a set fee per post created. I would like the charge to be dynamic, say 10% of the gas cost of the transaction. Is this possible to implement in the contract? Or is this something for front-end web3 to handle?

solidity web3js contract-development gas gas-limit

share|improve this question

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

add a comment | 

Example:

uint public createPostCost = 0.0003 ether;

function createPost(bytes32 _post) 
 public payable 
 require(msg.value >= createPostCost);
 Post memory newPost;
 newPost.post = _post;
 

Within a discussion forum dapp, the current implementation charges users a set fee per post created. I would like the charge to be dynamic, say 10% of the gas cost of the transaction. Is this possible to implement in the contract? Or is this something for front-end web3 to handle?

solidity web3js contract-development gas gas-limit

share|improve this question

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

uint public createPostCost = 0.0003 ether;

function createPost(bytes32 _post) 
 public payable 
 require(msg.value >= createPostCost);
 Post memory newPost;
 newPost.post = _post;
 

share|improve this question

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

share|improve this question

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

edited 7 hours ago

shane

2,4524832

edited 7 hours ago

shane

2,4524832

asked 7 hours ago

Jaren LJaren L

335

asked 7 hours ago

Jaren LJaren L

335

1 Answer
1

active

oldest

votes

3

Yes, you can let the charge be a function of the gas of the transaction. You would do something like this:

uint256 charge = gasleft() / 10;

This is sensitive and you should know that gasleft() returns the amount of gas available at that point in the execution. Therefore, if you call gasleft() at the beginning of a function, the number will be higher than at the end of the function.

Additionally, someone may send a lot of unnecessary gas, so they could end up paying a lot.

My opinion is that it is best to handle this on the front-end.

Edit

If you are trying to take into account the gasPrice, you can use tx.gasprice. See here for more information.

share|improve this answer

edited 7 hours ago

answered 7 hours ago

shaneshane

2,4524832

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Psst, msg.gas has been removed and replaced by gasleft as per solidity.readthedocs.io/en/latest/…
  
  – Lauri Peltonen
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ahh yes. Thank you.
  
  – shane
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah that makes sense. If I made a require to check the msg.value >= 10% of tx.gasprice, would that work? Would there be discrepancies between generating the web3 function call price + value and the contract value?
  
  – Jaren L
  4 hours ago
  
  

  
  
  
  

add a comment | 

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3

Yes, you can let the charge be a function of the gas of the transaction. You would do something like this:

uint256 charge = gasleft() / 10;

This is sensitive and you should know that gasleft() returns the amount of gas available at that point in the execution. Therefore, if you call gasleft() at the beginning of a function, the number will be higher than at the end of the function.

Additionally, someone may send a lot of unnecessary gas, so they could end up paying a lot.

My opinion is that it is best to handle this on the front-end.

Edit

If you are trying to take into account the gasPrice, you can use tx.gasprice. See here for more information.

share|improve this answer

edited 7 hours ago

answered 7 hours ago

shaneshane

2,4524832

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Psst, msg.gas has been removed and replaced by gasleft as per solidity.readthedocs.io/en/latest/…
  
  – Lauri Peltonen
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ahh yes. Thank you.
  
  – shane
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah that makes sense. If I made a require to check the msg.value >= 10% of tx.gasprice, would that work? Would there be discrepancies between generating the web3 function call price + value and the contract value?
  
  – Jaren L
  4 hours ago
  
  

  
  
  
  

add a comment | 

3

Yes, you can let the charge be a function of the gas of the transaction. You would do something like this:

uint256 charge = gasleft() / 10;

This is sensitive and you should know that gasleft() returns the amount of gas available at that point in the execution. Therefore, if you call gasleft() at the beginning of a function, the number will be higher than at the end of the function.

Additionally, someone may send a lot of unnecessary gas, so they could end up paying a lot.

My opinion is that it is best to handle this on the front-end.

Edit

If you are trying to take into account the gasPrice, you can use tx.gasprice. See here for more information.

share|improve this answer

edited 7 hours ago

answered 7 hours ago

shaneshane

2,4524832

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Psst, msg.gas has been removed and replaced by gasleft as per solidity.readthedocs.io/en/latest/…
  
  – Lauri Peltonen
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ahh yes. Thank you.
  
  – shane
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah that makes sense. If I made a require to check the msg.value >= 10% of tx.gasprice, would that work? Would there be discrepancies between generating the web3 function call price + value and the contract value?
  
  – Jaren L
  4 hours ago
  
  

  
  
  
  

add a comment | 

Yes, you can let the charge be a function of the gas of the transaction. You would do something like this:

uint256 charge = gasleft() / 10;

This is sensitive and you should know that gasleft() returns the amount of gas available at that point in the execution. Therefore, if you call gasleft() at the beginning of a function, the number will be higher than at the end of the function.

Additionally, someone may send a lot of unnecessary gas, so they could end up paying a lot.

My opinion is that it is best to handle this on the front-end.

Edit

If you are trying to take into account the gasPrice, you can use tx.gasprice. See here for more information.

share|improve this answer

edited 7 hours ago

answered 7 hours ago

shaneshane

2,4524832

share|improve this answer

edited 7 hours ago

answered 7 hours ago

shaneshane

2,4524832

answered 7 hours ago

shaneshane

2,4524832

answered 7 hours ago

shaneshane

2,4524832