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A parser is responsible for decoding the raw body content of a request into a list of arguments that can be mapped to endpoint function arguments. For instance, parser_json() parse content-type application/json.


register_parser(alias, parser, fixed = NULL, regex = NULL, verbose = TRUE)




An alias to map parser from the @parser plumber tag to the global parsers list.


The parser function to be added. This build the parser function. See Details for more information.


A character vector of fixed string to be matched against a request content-type to use parser.


A character vector of regex string to be matched against a request content-type to use parser.


Logical value which determines if a warning should be displayed when alias in map are overwritten.


When parser is evaluated, it should return a parser function. Parser matching is done first by content-type header matching with fixed then by using regular expressions with regex. Note that plumber strips ; charset* from content-type header before matching.

Plumber will try to use parser_json() (if available) when no content-type header is found and the request body starts with { or [.

Functions signature should include value, ... and possibly content_type, filename. Other parameters may be provided if you want to use the headers from webutils::parse_multipart().

Parser function structure is something like below.

function(parser_arguments_here) {
  # return a function to parse a raw value
  function(value, ...) {
    # do something with raw value


  • registered_parsers(): Return all registered parsers


# `content-type` header is mostly used to look up charset and adjust encoding
parser_dcf <- function(...) {
  function(value, content_type = "text/x-dcf", ...) {
    charset <- get_character_set(content_type)
    value <- rawToChar(value)
    Encoding(value) <- charset
    read.dcf(value, ...)

# Could also leverage existing parsers
parser_dcf <- function(...) {
  parser_read_file(function(tmpfile) {
    read.dcf(tmpfile, ...)

# Register the newly created parser
if (FALSE) register_parser("dcf", parser_dcf, fixed = "text/x-dcf")