NIP-105
======

API Service Marketplace
-------------------------------

`draft` `optional` `author:coachchuckff` `author:unclejim21` `author:cmdruid`

This NIP defines `kind:31402` (a _parameterized replaceable event_) for broadcasting API services, endpoints and their costs in mSats. API services are offered ala carte to be paid via lightning invoices.

API service providers will issue a `kind:31402` event as an API service offering. Clients can fetch `s` (service) tag offerings, call their endpoints, and pay per use. Creating an API service marketplace.

## Protocol flow

1. API Service provider creates and hosts API service offerings, they then issue a `kind:31402` event for each `s` ( service ) tag.
2. Client fetches API offerings by `s` tag.
3. Client chooses a provider(s) and POSTs to their `endpoint`. The POST body should match exactly what is required by the underlying API less the API key. ( Or following the note's `schema` )
4. The service provider should validate their request and return a lightning invoice with a `successAction` url. The `successAction` url should be formatted as such: `<endpoint>/<invoice_hash>/get_result`
5. The client pays.
6. The client will poll the `successAction` until the service provider has returned the result(s) matching exactly what the underlying API will produce ( Or following the note's `outputSchema` ).

## Server Functions
### Create Invoice

Initally, the client will make a POST request to the `endpoint`. The POST body should be exactly what the underlying API is expecting less the API key. This information should also be represented in the `schema` portion of the `content` field.

The service provider will then do the following:

1. Validate their API request
2. Issue a lightning invoice

The issued lightning invoice will contain a `successAction` url formatted as so:

```typescript
{
      tag: "url",
      url: `https://example.api/chat/${paymentHash}/get_result`,
      description: "Open to get the confirmation code for your purchase."
}
```

From here the service provider can either listen and execute their API request "on-payment" or wait until the client calls `get_results`.

### Get Results

Once the client has gotten the `successAction` url, they can issue a GET request. The service provider should respond in one of three ways:

1. 200 ( DONE ) - the service provider returns the results of the API as if it was coming from the product itself ( Errors included ) 
2. 202 ( WORKING ) - the service provider returns a status that indicates the results are not ready yet.
3. 402 ( NOT PAID YET ) - the service provider should respond with a 402 error if the client has not paid yet.

It is up to the Client to poll the `successAction` until a terminal result is reached.

## Event Reference and Examples

### Offering Event

`kind:31402`

`.content` should be a JSON stringified version of the following JSON:
```typescript
  enum OfferingStatus {
    up = 'UP',
    down = 'DOWN',
    closed = 'CLOSED'
  }

  interface OfferingContent = {
    endpoint: string,          // The POST endpoint you call to pay/fetch
    status: OfferingStatus,    // UP/DOWN/CLOSED
    cost: number,              // The cost per call in mSats
    schema?: Object,           // Reccomended - JSON schema for the POST body of the endpoint
    outputSchema?: Object,     // Reccomended - JSON schema for the response of the call
    description?: string       // Optional - Description for the end user
  }
```

`.tag` MUST include the following:

- `s`, the service tag should simply be the underlying API endpoint of the service provided. For example if you are offering a ChatGPT service, you would set `s` = `https://api.openai.com/v1/chat/completions`. This way the service they are buying is implicit.
- `d`, following **parameterized replaceable events** in [NIP-01](https://github.com/nostr-protocol/nips/blob/master/01.md), this tag allows this event to be replaceable. Since there should only be one service per pubkey, the `d` tag should match the `s` tag.

### Example Service Event

```typescript

const content = {
  endpoint: "https://example.api/chat/",
  status: "UP",
  cost: 5000,
  schema: {...},
  outputSchema: {...},
  description: "This will call the ChatGPT endpoint"
}

const event = {
  "kind": 31402,
  "created_at": 1675642635,
  "content": JSON.stringify(content),
  "tags": [
    ["s", "https://api.openai.com/v1/chat/completions"]
    ["d", "https://api.openai.com/v1/chat/completions"],
  ],
  "pubkey": "<pubkey>",
  "id": "<id>"
}
```

### Example Schema

The following is for the `gpt-3.5-turbo` input schema:

```json
{
    "type": "object",
    "properties": {
        "model": {
            "type": "string",
            "enum": ["gpt-3.5-turbo"]
        },
        "messages": {
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "role": {
                        "type": "string",
                        "enum": ["system", "user"]
                    },
                    "content": {
                        "type": "string"
                    }
                },
                "required": ["role", "content"]
            },
            "minItems": 1
        }
    },
    "required": ["model", "messages"]
}
```

The following is for the `gpt-3.5-turbo` output schema:

```json
{
    "type": "object",
    "required": ["id", "object", "created", "model", "choices", "usage"],
    "properties": {
      "id": {
        "type": "string",
        "pattern": "^chatcmpl-[a-zA-Z0-9-]+$"
      },
      "object": {
        "type": "string",
        "enum": ["chat.completion"]
      },
      "created": {
        "type": "integer"
      },
      "model": {
        "type": "string"
      },
      "choices": {
        "type": "array",
        "items": {
          "type": "object",
          "required": ["index", "message"],
          "properties": {
            "index": {
              "type": "integer"
            },
            "message": {
              "type": "object",
              "required": ["role", "content"],
              "properties": {
                "role": {
                  "type": "string",
                  "enum": ["assistant"]
                },
                "content": {
                  "type": "string"
                }
              }
            },
            "finish_reason": {
              "type": "string",
              "enum": ["stop"]
            }
          }
        }
      },
      "usage": {
        "type": "object",
        "required": ["prompt_tokens", "completion_tokens", "total_tokens"],
        "properties": {
          "prompt_tokens": {
            "type": "integer"
          },
          "completion_tokens": {
            "type": "integer"
          },
          "total_tokens": {
            "type": "integer"
          }
        }
      }
    }
  }
```
### Safey

It is not mandatory, but to raise the barrier to entry, clients should screen service provider's NIP-05 identifier. The domain used in their NIP-05, should be the same domain used for their endpoint.

Clients may wish to create a whitelist of trusted service providers once tested.

### Problems

- No data integrity - service providers can store/redistribute any data passed to them
- Service providers could take payment and never return the product
- Service providers are not gaurenteed to call the endpoint specified in the `s` tag
- No recourse for errored API fetches
- The `cost` field may not match the actual final price
- No proof of purchase

### Example Implementations

- [Server](https://github.com/Team-Pleb-TabConf-2023/nip-105-server)
- [Client](https://github.com/Team-Pleb-TabConf-2023/nip-105-client)