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Overview

The publish endpoint is a protected mutation procedure that publishes a chat message to a specified channel. It includes content validation, rate limiting, and support for reply threads.

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Procedure Type

Mutation - Protected procedure (authentication required)

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Authentication

This endpoint requires a valid JWT token. The authenticated user’s information (from ctx.user) is automatically attached to the published message.

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Input Parameters

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content
string
required
The message content to publish. Will be trimmed before validation.
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channel
string
required
The channel identifier to publish the message to
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replyToId
string | null
Optional message ID to reply to. Use null or omit for top-level messages.

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Response Structure

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id
string
Unique identifier for the message (UUID v4)
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author
JwtUser
The authenticated user who sent the message
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author.robloxUserId
string
User’s Roblox user ID
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author.username
string
User’s Roblox username
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author.displayName
string
User’s Roblox display name
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author.picture
string
URL to user’s profile picture
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content
string
The trimmed message content that was published
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replyToId
string | null
Message ID this message is replying to, or null if not a reply

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Validation Rules

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Empty Message Check

After trimming whitespace, the content must not be empty. Error: BAD_REQUEST - “Message cannot be empty.”

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Message Length Validation

The message content length must not exceed the maxMessageLength limit for the channel. Error: BAD_REQUEST - “Message exceeds characters.”

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Rate Limiting

Rate limiting is enforced per user (by robloxUserId) per channel. The limits are retrieved using getChatLimitsForChannel(input.channel):
  • Limit Count: rateLimitCount messages
  • Window: rateLimitWindowMs milliseconds
When the rate limit is exceeded: Error: TOO_MANY_REQUESTS - “Rate limit hit. Try again in s.” The error message includes the retry-after time in seconds.

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Message Broadcasting

Successfully published messages are broadcast to all subscribers on the channel using the global pub/sub system (globalPubSub.emit).

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Example Usage

import { trpc } from './trpc';

// Publish a simple message
const message = await trpc.chat.publish.mutate({
  content: 'Hello, world!',
  channel: 'global'
});

console.log(`Message published with ID: ${message.id}`);

// Publish a reply to another message
const reply = await trpc.chat.publish.mutate({
  content: 'Thanks for the help!',
  channel: 'support',
  replyToId: 'abc123-def456-789'
});

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Example Response

{
  "id": "550e8400-e29b-41d4-a716-446655440000",
  "author": {
    "robloxUserId": "123456789",
    "username": "johndoe",
    "displayName": "John Doe",
    "picture": "https://tr.rbxcdn.com/..."
  },
  "content": "Hello, world!",
  "replyToId": null
}

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Error Handling

try {
  const message = await trpc.chat.publish.mutate({
    content: '   ',  // Empty after trim
    channel: 'global'
  });
} catch (error) {
  if (error.data?.code === 'BAD_REQUEST') {
    console.error('Validation error:', error.message);
  } else if (error.data?.code === 'TOO_MANY_REQUESTS') {
    console.error('Rate limited:', error.message);
  }
}

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Implementation Details

The publish endpoint is implemented at chat.ts:19-68 and uses:
  • getChatLimitsForChannel for retrieving channel limits (line 28)
  • ratelimit service for rate limit enforcement (lines 45-50)
  • crypto.randomUUID() for message ID generation (line 59)
  • globalPubSub.emit for broadcasting messages (line 65)

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