Consider using stringi as dependency

[DyfanJones]

json_convert_string <- function(string) {
  replace <- list(
    c("\\", "\\\\"),
    c('"', '\\"'),
    c("\b", "\\b"),
    c("\f", "\\f"),
    c("\r", "\\r"),
    c("\t", "\\t"),
    c("\n", "\\n")
  )
  for (elem in replace) {
    string <- gsub(elem[1], elem[2], string, fixed = TRUE)
  }
  string <- json_escape_unicode(string)
  string <- sprintf('"%s"', string)
  return(string)
}

json_escape_unicode <- function(string) {
  from <- intToUtf8(1:31, multiple = T)
  to <- paste0("\\u00", format(as.hexmode(1:31), width = 2))
  for (i in 1:31) {
    string <- gsub(from[i], to[i], string, fixed = TRUE)
  }
  return(string)
}

json_convert_string_stringi <- function(string) {
  from <- c("\\", '"', "\b", "\f", "\r", "\t", "\n")
  to <- c("\\\\", '\\"', "\\b", "\\f", "\\r", "\\t", "\\n")
  string <- stringi::stri_replace_all_fixed(string, from, to, vectorize_all =F)
  string <- json_escape_unicode_stringi(string)
  string <- sprintf('"%s"', string)
  return(string)
}

json_escape_unicode_stringi <- function(string) {
  from <- intToUtf8(1:31, multiple = T)
  to <- paste0("\\u00", format(as.hexmode(1:31), width = 2))
  string <- stringi::stri_replace_all_fixed(string, from, to, vectorize_all = F)
  return(string)
}

unicode <- c(intToUtf8(1:31, multiple = T), c("\\", '"', "\b", "\f", "\r", "\t", "\n"))

x <- c(1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6)
bms <- lapply(x, \(i) {
  string <- paste0(sample(c(letters, LETTERS, unicode), i, replace = T), collapse = "")
  bm <- bench::mark(
    paws = paws.common:::json_escape_unicode(string),
    new_mthd = json_escape_unicode(string),
    stringi = json_escape_unicode_stringi(string)
  )
  bm$id <- i
  return(bm)
})

do.call(rbind, bms) |> ggplot2::autoplot() + 
  ggplot2::facet_wrap("id", labeller = ggplot2::label_both, scales = "free_x")

^{Created on 2024-02-26 with reprex v2.1.0}

stringi has some significant performance enhancements. Alternatively move some of the looping gsub to cpp, however cpp isn't my forte so will need help regarding that option :)

[DyfanJones]

Found Rcpp solutions developed from: https://stackoverflow.com/questions/25609174/fast-escaping-deparsing-of-character-vectors-in-r

remotes::install_github("dyfanjones/paws/paws.common", ref="json_escape")

json_escape_unicode <- function(string) {
  from <- intToUtf8(1:31, multiple = TRUE)
  to <- paste0("\\u00", format(as.hexmode(1:31), width = 2))
  for (i in 1:31) {
    string <- gsub(from[i], to[i], string, fixed = TRUE)
  }
  return(string)
}

json_convert_string <- function(string) {
  replace <- list(
    c("\\", "\\\\"),
    c('"', '\\"'),
    c("\b", "\\b"),
    c("\f", "\\f"),
    c("\r", "\\r"),
    c("\t", "\\t"),
    c("\n", "\\n")
  )
  for (elem in replace) {
    string <- gsub(elem[1], elem[2], string, fixed = TRUE)
  }
  string <- json_escape_unicode(string)
  string <- sprintf('"%s"', string)
  return(string)
}

json_convert_string_stringi <- function(string) {
  from <- c("\\", '"', "\b", "\f", "\r", "\t", "\n")
  to <- c("\\\\", '\\"', "\\b", "\\f", "\\r", "\\t", "\\n")
  string <- stringi::stri_replace_all_fixed(string, from, to, vectorize_all =F)
  string <- json_escape_unicode_stringi(string)
  string <- sprintf('"%s"', string)
  return(string)
}

json_escape_unicode_stringi <- function(string) {
  from <- intToUtf8(1:31, multiple = T)
  to <- paste0("\\u00", format(as.hexmode(1:31), width = 2))
  string <- stringi::stri_replace_all_fixed(string, from, to, vectorize_all = F)
  return(string)
}

unicode <- c(intToUtf8(1:31, multiple = T), "\\", '"', "\b", "\f", "\r", "\t", "\n")
x <- c(1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6)
bms <- lapply(x, \(i) {
  string <- paste0(sample(c(letters, LETTERS, unicode), i, replace = T), collapse = "")
  bm <- bench::mark(
    old_paws = json_convert_string(string),
    stringi = json_convert_string_stringi(string),
    new_paws = paws.common:::json_convert_string(string)
  )
  bm$id <- i
  return(bm)
})

^{Created on 2024-02-27 with reprex v2.1.0}

From this we have significant performance improvement.