Question

我处于一个HTTP POST端点/render的位置，该端点返回PDF文档，并希望向用户显示一个按钮/链接，该按钮/链接将导致将此文档下载并保存到文件，而无需离开Elm应用程序。

理想情况下，POST将接受具有自定义格式的text/plain正文，但是我可以重做端点以接受multipart/form-data或application/x-www-form-urlencoded。

我可以按如下所示将原始数据成功下载到Elm应用程序，但是我对如何将文件保存到磁盘一无所知。

import Http

render : String -> Http.Request String
render body =
  Http.request
    { method = "POST"
    , headers = []
    , url = "/render"
    , body = Http.stringBody "text/plain" body
    , expect = expectString
    , timeout = Nothing
    , withCredentials = False
    }

Answer 1

我是用expectBytes而不是expectString来做的所以我的代码是

import Bytes exposing (Bytes)
import File.Download as Download

Msg = .. | FormUploaded (Result Http.Error Bytes)

Http.post
        { url = "/passports"
        , body =
            Http.multipartBody...
        , expect = Http.expectBytesResponse FormUploaded (resolve Ok)
        }


downloadPdf : Bytes -> Cmd msg
downloadPdf pdfContent =
    Download.bytes "form.pdf" "application/pdf" pdfContent

update : Msg -> Model -> ( Model, Cmd Msg )
update model =
...
    FormUploaded (Ok response) ->
            ( model, downloadPdf response )
    FormUploaded (Err err) ->
            ( model, Cmd.none )

-- this helper function copied from https://github.com/elm/http/blob/2.0.0/src/Http.elm#L514-L521
resolve : (body -> Result String a) -> Http.Response body -> Result Http.Error a
resolve toResult response =
    case response of
        BadUrl_ url ->
            Err (BadUrl url)

        Timeout_ ->
            Err Timeout

        NetworkError_ ->
            Err NetworkError

        BadStatus_ metadata _ ->
            Err (BadStatus metadata.statusCode)

        GoodStatus_ _ body ->
            Result.mapError BadBody (toResult body)

这不是理想的方法，但是有效

PS：我从Elm Slack频道https://elmlang.slack.com/

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使用Elm从POST请求下载文件

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