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Add skeleton for new websockets stream api docs #1074

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label: Websockets Stream API
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---
title: List subscriptions request message format
sidebar_label: Listing subscriptions
sidebar_position: 4
---

# List subscriptions message format

List subscriptions requests must be sent as JSON in text frames, one request per frame.
This message is different from other as it doesn't require you to provide subscription ID.
Thus, the response for this message is different too.

### Example of request

```json
{
"action": "list_subscriptions"
}
```

### Example of response

```json
{
"subscriptions": [
{
"subscription_id": "uuid-1",
"topic": "blocks",
"parameters": {
"start_block_height": "123456789"
}
},
{
"subscription_id": "uuid-2",
"topic": "events",
"parameters": {}
}
]
}
```

If there are no active subscriptions, `subscriptions` array will be empty.

### Request fields

| Name | Type | Required | Description |
|----------|--------|----------|-----------------------------------------------------------------------------------------|
| `action` | STRING | YES | Action to perform. Must be `list_subscriptions` to initiate a list subscription request |
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---
title: Overview
sidebar_label: Overview
sidebar_position: 1
---

# Websockets Stream API

## Overview

The Stream API allows clients to receive real-time updates from the Flow blockchain via WebSocket connections. It
supports subscribing to various topics, such as blocks, events, and transactions, enabling low-latency access to live
data.

### Important Information

- **Endpoint**: The WebSocket server is available at:
```
wss://rest-mainnet.onflow.org/ws
```
- **Limits**:
- Each connection supports up to 20 concurrent subscriptions. Exceeding this limit will result in an error.
- Each subscription may provide up to 20 responses per second.
- After 1 minute of inactivity (no data is sent to/read from connection) connection is closed.
- **Supported Topics**:
- `blocks`
- `block_headers`
- `block_digests`
- `events`
- `transaction_statuses`
- `account_statuses`
- **Notes**: Always handle errors gracefully and close unused subscriptions to maintain efficient connections.

---

## Setting Up a WebSocket Connection

Use any WebSocket client library to connect to the endpoint. Below is an example using JavaScript:

```javascript
const ws = new WebSocket('wss://rest-mainnet.onflow.org/ws');

ws.onopen = () => {
console.log('Connected to WebSocket server');
};

ws.onclose = () => {
console.log('Disconnected from WebSocket server');
};

ws.onerror = (error) => {
console.error('WebSocket error:', error);
};
```

---

## Subscribing to Topics

To receive data from a specific topic, send a subscription request in JSON format over the WebSocket connection.

### Request Format

```json
{
"subscription_id": "some-id-42",
"action": "subscribe",
"topic": "blocks",
"arguments": {
"start_block_height": "123456789"
}
}
```

- **`subscription_id`**: A unique identifier for the subscription (string with max len constraint). If omitted, the server generates one.
- **`action`**: The action to perform. Supported actions include: `subscribe`, `unsubscribe`, `list_subscriptions`.
- **`topic`**: The topic to subscribe to. See the supported topics in the Overview.
- **`arguments`**: Additional arguments for subscriptions, such as `start_block_height`, `start_block_id`, and others.

### Response Format

```json
{
"subscription_id": "some-id-42",
"action": "subscribe"
}
```

---

## Unsubscribing from Topics

To stop receiving data from a specific topic, send an unsubscribe request.

### Request Format

```json
{
"subscription_id": "some-id-42",
"action": "unsubscribe"
}
```

### Response Format

```json
{
"subscription_id": "some-id-42",
"action": "unsubscribe"
}
```

---

## Listing Active Subscriptions

You can retrieve a list of all active subscriptions for the current WebSocket connection.

### Request Format

```json
{
"action": "list_subscriptions"
}
```

### Response Format

```json
{
"subscriptions": [
{
"subscription_id": "some-id-1",
"topic": "blocks",
"arguments": {
"start_block_height": "123456789"
}
},
{
"subscription_id": "some-id-2",
"topic": "events",
"arguments": {}
}
]
}
```

---

## Errors Example

If a request is invalid or cannot be processed, the server responds with an error message.

### OK Response

```json
{
"subscription_id": "some-id-42",
"payload": {
"id": "0x1234...",
"height:": "123456789",
"timestamp": "2025-01-02T10:00:00Z"
}
}
```

### Error Response

```json
{
"subscription_id": "some-id-42",
"error": {
"code": 500,
"message": "Access Node failed"
}
}
```

### Common Error Codes

- **400**: Invalid message format or arguments
- **404**: Subscription not found
- **500**: Internal server error

### Asynchronous environments

If you're working in an asynchronous environment, the Streaming API ensures **first-in first-out** message processing,
so responses will be returned in the same order the requests were received over the connection.
You can leverage this feature to simplify your code and maintain consistency.

Additionally, you can specify your own `subscription_id` in the subscribe request to easily identify the correct response.
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---
title: Subscribe request message format
sidebar_label: Subscribing to topic
sidebar_position: 2
---

# Subscribe request format

Subscribe requests must be sent as JSON in text frames, one request per frame.

### Example of subscribe request

```json
{
"subscription_id": "some-id-1",
"action": "subscribe",
"topic": "block_digests",
"parameters": {
"start_block_height": "99,416,580"
}
}
```

### Example of successful response

```json
{
"subscription_id": "some-id-1",
"action": "subscribe"
}
```

### Example of failed response

```json
{
"subscription_id": "some-id-1",
"error": {
"code": 400,
"message": "invalid message"
}
}
```

### Example of messages provided by subscription (if successful)

```json
{
"subscription_id": "some-id-1",
"payload": {
"id": "0x1234...",
"height:": "123456789",
"timestamp": "2025-01-02T10:00:00Z"
}
}
```

### Example of messages provided by subscription (if error)

```json
{
"subscription_id": "some-id-1",
"error": {
"code": 500,
"message": "internal error"
}
}
```

### Request fields:

| Name | Type | Required | Description |
|-------------------|--------|----------|-----------------------------------------------------------------------------------------------------------------------------------|
| `subscription_id` | STRING | NO | Optional unique identifier for the subscription. Max length of ID generated by client is 20. Server will generate UUID if omitted |
| `action` | STRING | YES | Action to perform. Must be `subscribe` to initiate a subscription |
| `topic` | STRING | YES | The topic to subscribe to, such as `blocks`, `block_digests`, etc. |
| `arguments` | STRING | NO | Additional topic specific parameters for the subscription, such as `start_block_id`, `start_block_height` or other. |

You can use `subscription_id` as a client-generated identifier to track responses asynchronously.
If you don't provide `subscription_id`, the server will generate one and include it in the response.
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---
title: Unsubscribe request message format
sidebar_label: Unsubscribing from topic
sidebar_position: 3
---

# Unsubscribe message format

Unsubscribe requests must be sent as JSON in text frames, one request per frame.

### Example of unsubscribe request

```json
{
"subscription_id": "some-id-1",
"action": "unsubscribe"
}
```

### Example of successful response

```json
{
"subscription_id": "some-id-1",
"action": "unsubscribe"
}
```

### Example of error response

```json
{
"error": {
"code": 404,
"message": "subscription not found"
}
}
```

### Request fields

| Name | Type | Required | Description |
|-------------------|--------|----------|-----------------------------------------------------------------------|
| `subscription_id` | STRING | YES | Unique identifier of the subscription |
| `action` | STRING | YES | Action to perform. Must be `unsubscribe` to initiate a unsubscription |
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