Talk:BIP 0021

Marian on IRC reports: "The BNF [here] is erroneous, regarding the params, it says [ "?" bitcoinparams ] while bitcoinparams is just *bitcoinparam, thus with that BNF there are no separators between the parameters". --Gmaxwell (talk) 23:04, 23 April 2013 (GMT)

Suggesting usability enhancement in BIP 0021 for paying tips in restaurant/bar conveniently

I am suggesting a simple downward compatible enhancement of BIP 0021 to allow effortless tipping in restaurants, bars, pubs, etc.

When watching bitpay's mobile checkout demo video "http://www.youtube.com/watch?v=YZ-pqo0cLcE" it is clear that paying tips is somewhat cumbersome for the customer with today's wallet and merchant solutions. This can be dramatically improved with some support by the client app and a minor enhancement of BIP 0021.

Enhancement proposal:

bitcoinurn     = "bitcoin:" bitcoinaddress [ "?" bitcoinparams ]
bitcoinaddress = base58 *base58
bitcoinparams  = *bitcoinparam
bitcoinparam   = amountparam | labelparam | messageparam | tipparam | otherparam | reqparam
amountparam    = "amount=" *digit [ "." *digit ]
labelparam     = "label=" *pchar
messageparam   = "message=" *pchar
tipparam       = "tip=" [ *digit [ "." *digit ] [ "%" [ "25" ] ] ]
otherparam     = pchar *pchar "=" *pchar
reqparam       = "req-" pchar *pchar "=" *pchar

Actually, "tipparam" is just a special case of "otherparam", hence completely downwards compatible.

The tip can be specified in BTC or in percent of the amount, and it acts as a recommended or default tip setting in the customer's wallet app.

Examples for the following scenario:

Request 0.567 BTC from the customer of a restaurant and make the customer's bitcoin app show an advanced send dialog that allows adding a tip:

Ex. 1) The pre-set tip value in the send dialog is set to zero (or to the client's pre-configured default tip value):

bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=
bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=0

Ex. 2) The pre-set tip value is 15% of 0.567 BTC, i.e. 0.08508 BTC:

bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=0.08505
bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=15%25
  [URI code of the percentage character is "%25"]
bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=15%
  ["lazy" notation, omitting the "25". Actually, this is NOT correct, not URI compiant (RFC 2396), hence such an URI
  should not be generated. But it is proposed that the wallet app that has to decode the URI is implemented to understand
  this "lazy" syntax in the "tip" field anyhow, as safeguard to avoid errors in case that the merchant app generates such
  a "lazy" URI]

Ex. 3) The pre-set tip value is 0.08508 BTC, and the "notes" field in the client app is pre-occupied with the name of the restaurant:

bitcoin:175tWpb8K1S7NmH4Zx6rewF9WQrcZv245W?amount=0.567&tip=15%&message=Charly%27s%20Bar

Explanation:

• The new parameter has no "req-" prefix, i.e. if an old bitcoin client app does not know it, it can safely ignore it.
• Otherwise, the customer's bitcoin client will not open the normal but an enhanced send dialog where the customer can specify a tip that will be added to the bill to be paid. In examples 2 and 3 above the tip shall be pre-configured with the amount specified in the URI, so the customer can most conveniently just accept it by a simple tap, if the client app is well-written.

The details are of course dependent on the client app implementation, a best practice-example is demonstrated in the following images.