package topojsone

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Module TopojsoneSource

A library for manipulating large TopoJSON documents without reading the whole document into memory using the Jsone streaming, JSON parser.

module Jsone = Geojsone.Jsone
module Ezjsone = Geojsone.Ezjsone
Sourcemodule Err : sig ... end

Topojsone comes with an implementation of a TopoJSON parser using Ezjsone. This is like Ezjsonm but uses Jsone for providing a non-blocking interface.

Sources and Sinks

Topojsone is intended to be used with a non-blocking IO library using OCaml 5's effect support to provide a direct-style buffer filling and buffer writing functions.

Here's an example using the Eio library:

  let src_of_flow ?(size = 2048) flow =
    let buff = Cstruct.create size in
    fun () ->
      let got = Eio.Flow.(single_read flow buff) in
      let t = Cstruct.sub buff 0 got in
      t

  let with_src cwd f func =
    Eio.Path.(with_open_in (cwd / f)) @@ fun ic -> func @@ src_of_flow ic

  let buffer_to_dst buf bs =
    Eio.Flow.(copy (cstruct_source [ bs ]) (Eio.Flow.buffer_sink buf))

Mapping

Maps are functions that allow you to manipulate common structure in TopoJson objects. These will be written directly back to the destination that you provide.

Sourceval map_object : ((string * Topojson.Geometry.t) -> string * Topojson.Geometry.t) -> Jsone.src -> Jsone.dst -> (unit, Err.t) result

map_object f src dst will apply f to all TopoJson objects. The map will recurse into TopoJson Object. Note for the moment if you have a single geometry object as your document, this will not work.

Folding

Sourceval fold_object : ('acc -> (string * Topojson.Geometry.t) -> 'acc) -> 'acc -> Jsone.src -> ('acc, Err.t) result

fold_object f initial_acc src is much like map_object but allows you to accumulate some result that is then returned to you.