SSEparser {SSEparser}

Parse a Server Sent Event

Description

This class can help you parse a single server sent event or a stream of them. You can inherit the class for a custom application. The parse_sse() function wraps this class for a more functional approach.

Details

The HTML specification tells us that event streams are composed by chunks (also called blocks, or messages) and lines. A single new line character (⁠\n⁠) states the end of a line, and two consecutive new line characters (⁠\n\n⁠) state the end of a chunk.

This means that, in practice, an event can be composed of one or more chunks, and a chunk can be composed of one or more lines.

data: This is the first chunk, it has one line

data: This is the second chunk
extra: It has two lines

data: This is the third chunk, it has an id field. This is common.
id: 123

: Lines that start with a colon are comments, they will be ignored
data: This is the forth chunk, it has a comment

data: This is the fifth chunk. Normally you will receive a data field
custom: But the server can send custom field names. SSEparser parses them too.

Typically, an event stream will send a single chunk for event, but it is important to understand that event != chunk because SSEparser$events will be a list of all the chunks received as it makes a more consistent output.

Value

An object with R6 class SSEparser

Public fields

events

List that contains all the events parsed. When the class is initialized, is just an empty list.

Methods

Public methods

• SSEparser$append_parsed_sse()

• SSEparser$parse_sse()

• SSEparser$new()

• SSEparser$clone()

Method append_parsed_sse()

Takes a parsed event and appends it to the events field. You can overwrite this method if you decide to extend this class.

Usage

SSEparser$append_parsed_sse(parsed_event)

Arguments

parsed_event

Event to append to the events field.

Method parse_sse()

Takes a string that comes from a server sent event and parses it to an R list. You should never overwrite this method.

Usage

SSEparser$parse_sse(event)

Arguments

event

A length 1 string containing a server sent event as specified in the HTML spec.

Method new()

Create a new SSE parser

Usage

SSEparser$new()

Method clone()

The objects of this class are cloneable with this method.

Usage

SSEparser$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Examples

example_event <- 
"data: This is the first chunk, it has one line

data: This is the second chunk
extra: It has two lines

data: This is the third chunk, it has an id field. This is common.
id: 123

: Lines that start with a colon are comments, they will be ignored
data: This is the fourth chunk, it has a comment

data: This is the fifth chunk. Normally you will receive a data field
custom: But the server can send custom field names. SSEparser parses them too."
 
parser <- SSEparser$new()
parser$parse_sse(example_event)
 
str(parser$events)