dream-html 2.1.0 · OCaml Package

Constructing HTML. Detailed explanation in https://github.com/yawaramin/dream-html.

Let's adapt the example from the Dream home page:

let hello who =
  let open Dream_html in
  let open HTML in
  html [] [body [] [h1 [] [txt "Hello, %s!" who]]]

let () =
  Dream.run
  @@ Dream.logger
  @@ Dream.router [Dream.get "/" (fun _ -> Dream_html.respond (hello "world"))]

More examples shown below.

Core types

These are the types of the final values which get rendered.

type attr

E.g. id="toast".

type node

Either a tag, a comment, or text data in the markup.

Output

val to_string : node -> string

val pp : Stdlib.Format.formatter -> node -> unit

val respond : 
  ?status:[< Dream.status ] ->
  ?code:int ->
  ?headers:(string * string) list ->
  node ->
  Dream.response Dream.promise

val set_body : Dream.response -> node -> unit

Type-safe wrapper for Dream.set_body. Sets the body to the given node and sets the Content-Type header to text/html.

val write : Dream.stream -> node -> unit Dream.promise

Type-safe wrapper for Dream.write.

Constructing nodes and attributes

type 'a to_attr = 'a -> attr

Attributes can be created from typed values.

type 'a string_attr = ('a, unit, string, attr) Stdlib.format4 -> 'a

Special handling for string-value attributes so they can use format strings i.e. string interpolation.

type std_tag = attr list -> node list -> node

A 'standard' tag with attributes and children.

type void_tag = attr list -> node

A 'void element': https://developer.mozilla.org/en-US/docs/Glossary/Void_element with no children.

type 'a text_tag = attr list -> ('a, unit, string, node) Stdlib.format4 -> 'a

Tags which can have attributes but can contain only text. The text can be formatted.

val attr : string -> attr

attr name is a new attribute which does not carry any payload. E.g.

let required = attr "required"

since 0.1.0.

val string_attr : string -> ?raw:bool -> _ string_attr

string_attr name fmt is a new string-valued attribute which allows formatting i.e. string interpolation of the value. Note, the fmt argument is required due to the value restriction.

parameter raw
(default false) whether to inject the raw text or to escape it. Note that Dream does not support escaping inline JavaScript nor CSS, so neither does dream-html: https://github.com/aantron/dream/tree/master/example/7-template#security.

val uri_attr : string -> _ string_attr

Convenience for attributes whose values should be URIs. Takes care of URI- encoding.

a [href "/blog?tags=iamsafe\"></a><script>alert('Pwned')</script>"] [txt "Tags: tag1 | tag2"]

Output:

<a href="/blog?tags=iamsafe%22%3E%3C/a%3E%3Cscript%3Ealert('Pwned')%3C/script%3E">Tags: tag1 | tag2</a>

val bool_attr : string -> bool to_attr

val float_attr : string -> float to_attr

val int_attr : string -> int to_attr

val std_tag : string -> std_tag

val void_tag : string -> void_tag

val text_tag : string -> ?raw:bool -> _ text_tag

Build a tag which can contain only text.

parameter raw
(default false) whether to inject the raw text or to escape it. Note that Dream does not support escaping inline JavaScript nor CSS, so neither does dream-html: https://github.com/aantron/dream/tree/master/example/7-template#security.

val txt : ?raw:bool -> ('a, unit, string, node) Stdlib.format4 -> 'a

A text node inside the DOM e.g. the 'hi' in <b>hi</b>. Allows string interpolation using the same formatting features as Printf.sprintf:

b [] [txt "Hello, %s!" name]

Or without interpolation:

b [] [txt "Bold of you."]

HTML-escapes the text value using Dream.html_escape. You can use the ~raw param to bypass escaping:

let user_input = "<script>alert('I like HTML injection')</script>" in
txt ~raw:true "%s" user_input

val comment : string -> node

A comment that will be embedded in the rendered HTML, i.e. . The text is HTML-escaped.

val csrf_tag : Dream.request -> node

Convenience to add a CSRF token generated by Dream into your form. Type-safe wrapper for Dream.csrf_tag.

form
  [action "/foo"]
  [csrf_tag req; input [name "bar"]; input [type_ "submit"]]

Accessors for tags

val (+@) : node -> attr -> node

Add an attribute to a tag.

raises Invalid_argument
if the node is not a tag (i.e. if it is a text or comment node).

since 0.0.3.

val (-@) : node -> string -> node

Remove an attribute from a tag.

raises Invalid_argument
if the node is not a tag (i.e. if it is a text or comment node).

since 0.0.3.

val (.@[]) : node -> string -> string

Get the value of an existing attribute.

let toast = p [id "toast"] [txt "OK."]
let toast_id = toast.@["id"]

raises Invalid_argument
if the node is not a tag (i.e. if it is a text or comment node).

raises Not_found
if the tag does not have the given attribute.

since 0.0.3.

val is_null : node -> bool

Get whether a node is null (empty) or not. Useful for conditional rendering of UIs when you are passed in a node and you don't know if it's empty or not.

since 1.2.0.

val is_null_ : attr -> bool

Get whether an attribute is null (empty) or not.

since 1.2.0.

Standard attributes and tags

module HTML : sig ... end

All standard HTML attributes and tags. Some attributes and tags have the same name, e.g. style. To disambiguate them, attributes have a _ (underscore) suffix.

module SVG : sig ... end

htmx support

module Hx : sig ... end

htmx support https://htmx.org/reference/

Interop example–Markdown to HTML

In this section we show an extended example of interoperability of dream-html with other formats, e.g. the Markdown format defined by the omd library:

open Dream_html
open HTML

let omd_attr (k, opt_v) =
  string_attr k "%s" @@ Option.fold ~none:"" ~some:Fun.id opt_v

let rec omd_node elements = elements |> List.map element_node |> null
and item omd = li [] [omd_node omd]

and element_node = function
  | Omd.H1 omd -> h1 [] [omd_node omd]
  | H2 omd -> h2 [] [omd_node omd]
  | H3 omd -> h3 [] [omd_node omd]
  | H4 omd -> h4 [] [omd_node omd]
  | H5 omd -> h5 [] [omd_node omd]
  | H6 omd -> h6 [] [omd_node omd]
  | Paragraph omd -> p [] [omd_node omd]
  | Text str -> txt "%s" str
  | Emph omd -> em [] [omd_node omd]
  | Bold omd -> b [] [omd_node omd]
  | Ul omds | Ulp omds -> ul [] @@ List.map item omds
  | Ol omds | Olp omds -> ol [] @@ List.map item omds
  | Code (cls, str) -> code [class_ "%s" cls] [txt "%s" str]
  | Code_block (cls, str) ->
    pre [class_ "%s" cls] [code [class_ "%s" cls] [txt "%s" str]]
  | Br -> br []
  | Hr -> hr []
  | NL -> txt "\n"
  | Url (hre, omd, titl) ->
    a
      [ href "%s" hre;
        target "_blank";
        class_ "after:content-['_↗️']";
        title "%s" titl ]
      [omd_node omd]
  | Html ("details", attrs, omd) ->
    details (List.map omd_attr attrs) [omd_node omd]
  | Html ("summary", attrs, omd) ->
    summary (List.map omd_attr attrs) [omd_node omd]
  | Html_block ("details", attrs, omd) ->
    details (List.map omd_attr attrs) [omd_node omd]
  | Html_block ("summary", attrs, omd) ->
    summary (List.map omd_attr attrs) [omd_node omd]
  | Ref (_, _, _, _)
  | Img_ref (_, _, _, _)
  | Html (_, _, _)
  | Html_block (_, _, _)
  | X _ -> null []
  | Html_comment str -> comment str
  | Raw str -> txt ~raw:true "%s" str
  | Raw_block str -> pre [] [txt ~raw:true "%s" str]
  | Blockquote omd -> blockquote [] [omd_node omd]
  | Img (al, sr, titl) -> img [alt "%s" al; src "%s" sr; title "%s" titl]

The entrypoint of the functionality is the omd_node function, which converts from the Omd.t value which can be obtained by, for example, parsing Markdown with the Omd.of_string function, to a type-safe node value.

In the element_node function we traverse the Markdown structure and convert it into specific nodes–tags, comments, etc.. Text is escaped as appropriate and some specific conversions are handled specially:

All hyperlinks are made to open new tabs and suffixed using a Tailwind CSS style class.
We support the <details> and <summary> HTML tags, but no others.

This is just an example, but it shows the idea that we can take various formats and interop with them using type-sdfe HTML generated by dream-html.

package dream-html