Taxonomy of Transaction Fees in Smart Contracts

Protocol Design
6

I found these diagrams a little confusing. Here’s how I think I would draw them; what do you think?

  • Rounded boxes are utxos
  • Square boxes are transactions
  • Green lines emphasise where fee/change amounts come from/go
  • Dashed lines just indicate conflicting txs (due to attempting to spend the same utxo) and are also labelled.
  • If RBFing a previous state, the minimal set of txs that justify the RBF are highlighted in orange. If only one tx is highlighted, it probably works today; if two txs are highlighted, you need to wait for package RBF to be able to do state conflicts.

Endogenous fees, single transaction RBF

flowchart TD
    Pc([contract]) --> P4:::rbf
    Pc --> Pi4
    Pi4[Pay to state y] <-.->|conflicts| P4[Pay to state x\nEndo fees, Single RBF]
    P4 --> Po4([state x balance minus fees])
    
    classDef rbf fill:#f96
    linkStyle 0 stroke-width:4px,stroke:green
    linkStyle 1 stroke-width:4px,stroke:green

Exogenous fees, single transaction RBF

flowchart TD
    Pc([contract]) --> P5:::rbf
    Pc --> Pi5
    Pi5[Pay to state y] <-.->|conflicts| P5[Pay to state x\nExo fees, Single RBF]
    Pi5_2([fee input])--> P5
    P5 --> Po5([state x balance])
    P5 --> Co5([change])
    
    classDef rbf fill:#f96
    linkStyle 3 stroke-width:4px,stroke:green
    linkStyle 5 stroke-width:4px,stroke:green

Endogenous fees, CPFP

This is the same as “endogenous fees, package rbf”, if you note that “Pay to state x” conflicts with some other tx “Pay to state y”, both spending “contract”

flowchart TD
    Pi3([contract]) --> P3[Pay to state x]:::rbf
    Pi3 --> Pc[Pay to state y] <-.->|conflicts| P3
    P3 --> Po3([contract state x])
    Po3 --> C3[Endo fees, CPFP]:::rbf
    C3 --> Co3([state x balance minus fees])
    
    classDef rbf fill:#f96
    linkStyle 0 stroke-width:4px,stroke:green
    linkStyle 3 stroke-width:4px,stroke:green
    linkStyle 4 stroke-width:4px,stroke:green
    linkStyle 5 stroke-width:4px,stroke:green

Exogenous fees, CPFP

Likewise

flowchart TD
    Pi([contract]) --> P[Pay to state x]:::rbf
    Pi --> Pc[Pay to state y] <-.->|conflicts| P
    P --> Po([state x])
    Po --> C[Exo fees, CPFP]:::rbf
    fee([fee input]) --> C
    C --> Co([change plus state x balance])
    
    classDef rbf fill:#f96
    linkStyle 5 stroke-width:4px,stroke:green
    linkStyle 6 stroke-width:4px,stroke:green