multipartkit - v0.14.0

multipartkit/infer

Types

Inferer

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A pair of content-type inferers that callers can wire into form.add_file_auto_with.

from_filename is consulted first; if it returns None, from_bytes is tried next; if both return None, the host falls back to application/octet-stream.

Two ready-made inferers are provided: default_inferer (a no-op that always returns None, so add_file_auto falls through to application/octet-stream) and builtin_inferer (backed by the built-in content_type_from_filename / content_type_from_bytes, which resolve well-known extensions and magic-byte signatures via nao1215/mimetype). Pass whichever you want to form.add_file_auto_with, or supply your own:

import multipartkit/form
import multipartkit/infer

pub fn upload(form_value, filename, bytes) {
  // Resolve image/png, application/pdf, etc. out of the box.
  form.add_file_auto_with(form_value, "upload", filename, bytes, infer.builtin_inferer())
}

pub type Inferer {
  Inferer(
    from_filename: fn(String) -> option.Option(String),
    from_bytes: fn(BitArray) -> option.Option(String),
  )
}

Constructors

Values

builtin_inferer

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pub fn builtin_inferer() -> Inferer

Inferer backed by the built-in content_type_from_filename and content_type_from_bytes helpers (which delegate to nao1215/mimetype).

Pass this to form.add_file_auto_with to get content-type inference for well-known extensions and magic-byte signatures without writing the mimetype wiring yourself:

form.add_file_auto_with(my_form, "upload", "photo.png", bytes, infer.builtin_inferer())
// -> the part's Content-Type is image/png

content_type_from_bytes

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pub fn content_type_from_bytes(
  body: BitArray,
) -> option.Option(String)

Infer a content type from a body’s leading bytes (magic-number signature).

Delegates to nao1215/mimetype’s detector: returns Some(mime) for a recognised signature (for example the 8-byte PNG header -> Some("image/png"), <<0xFF, 0xD8, 0xFF, ...>> -> Some("image/jpeg"), "%PDF-..." -> Some("application/pdf")) and None for the empty BitArray or input whose bytes match no supported signature. Note mimetype’s detector classifies arbitrary printable-ASCII input as Some("text/plain"), so a text body with no stronger signature resolves to text/plain rather than None.

As with content_type_from_filename, this is a convenience over the mimetype dependency; wire it into the form builder with form.add_file_auto_with(form, ..., builtin_inferer()).

content_type_from_filename

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pub fn content_type_from_filename(
  filename: String,
) -> option.Option(String)

Infer a content type from a filename’s extension.

Delegates to nao1215/mimetype’s extension database: returns Some(mime) for a recognised extension (for example "photo.png" -> Some("image/png"), "doc.pdf" -> Some("application/pdf"), "data.json" -> Some("application/json")) and None when the path has no usable extension ("", "README") or the extension is not in the database ("a.zzznosuch").

This is a convenience over the mimetype dependency; for the form builder, wire it in with form.add_file_auto_with(form, ..., builtin_inferer()) (or build your own Inferer).

default_inferer

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pub fn default_inferer() -> Inferer

Inferer that always returns None.

add_file_auto uses this and therefore always emits application/octet-stream unless the host swaps in a real inferer via add_file_auto_with (for example builtin_inferer, or one of your own). Keeping the default a no-op means add_file_auto never changes the content type implicitly — inference is always something the caller opts into.

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