Parse a Server Sent Event

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.

Value

An object with R6 class SSEparser

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.

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()

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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.

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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.

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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)
#> List of 5
#>  $ :List of 1
#>   ..$ data: chr "This is the first chunk, it has one line"
#>  $ :List of 2
#>   ..$ data : chr "This is the second chunk"
#>   ..$ extra: chr "It has two lines"
#>  $ :List of 2
#>   ..$ data: chr "This is the third chunk, it has an id field. This is common."
#>   ..$ id  : chr "123"
#>  $ :List of 1
#>   ..$ data: chr "This is the fourth chunk, it has a comment"
#>  $ :List of 2
#>   ..$ data  : chr "This is the fifth chunk. Normally you will receive a data field"
#>   ..$ custom: chr "But the server can send custom field names. SSEparser parses them too."