Wordpress endpoint for upload file to s3

client.js

(function () {
  const TARGET_CONTAINER = '.upload-input-target';
  const ERROR_MESSAGE_ID = 'upload-error-message';
  const FILE_INPUT_ID = 'resume-input';
  const UPLOAD_ENDPOINT = 'https://example.com/wp-json/api/upload';
  const ERROR_CLASS = 'error';
  const LOADING_CLASS = 'loading';
  const LABEL_TEXT = 'Upload'
  const FALLBACK_ERROR_MESSAGE = 'Something wrong. Please use Intercom for contact with us';

  const targetEl = document.querySelector(TARGET_CONTAINER);
  if (!targetEl) {
    console.warn('Input container missing');
    return;
  }

  const setLoading = (isLoading) =>
    isLoading
      ? targetEl.classList.add(LOADING_CLASS)
      : targetEl.classList.remove(LOADING_CLASS);

  const linkInputEl = targetEl.querySelector('input');
  if (!linkInputEl) {
    console.warn('Input missing');
    return;
  }

  const saveLink = (link) => {
    linkInputEl.value = link;
  };

  const errorMessageEl = document.createElement('div');
  errorMessageEl.id = ERROR_MESSAGE_ID;

  const setErrorMessage = (e) => {
    errorMessageEl.innerHTML = e;
    errorMessageEl.hidden = false;
    targetEl.classList.add(ERROR_CLASS);
  };

  const removeErrorMessage = () => {
    targetEl.classList.remove(ERROR_CLASS);
    errorMessageEl.hidden = true;
    while (errorMessageEl.firstChild) {
      errorMessageEl.removeChild(errorMessageEl.firstChild);
    }
  };

  const fileInputEl = document.createElement('input');
  fileInputEl.id = FILE_INPUT_ID;
  fileInputEl.type = 'file';
  fileInputEl.hidden = true;

  const labelInputEl = document.createElement('label');
  labelInputEl.setAttribute('for', fileInputEl.id);
  labelInputEl.innerText = LABEL_TEXT;

  class ValidationError extends Error {}

  fileInputEl.addEventListener('change', function(e) {
    removeErrorMessage();

    const data = new FormData();
    if (this.files === null) return;
    if (this.files[0] === undefined) return;
    data.append('file', this.files[0]);
    setLoading(true);
    fetch(UPLOAD_ENDPOINT, {
        method: 'POST',
        body: data,
      })
      .then((r) => Promise.all([r.ok, r.json()]))
      .then(([ok, json]) => {
        if (ok) saveLink(json.ObjectURL);
        else throw new ValidationError(json.message)
      })
      .catch((e) => {
        e instanceof ValidationError ?
          setErrorMessage(e.message) :
          setErrorMessage(FALLBACK_ERROR_MESSAGE)
      })
      .finally(() => setLoading(false));
  });

  targetEl.appendChild(fileInputEl);
  targetEl.appendChild(labelInputEl);
  targetEl.appendChild(errorMessageEl);
})();

functions.php

<?php
// cd http_public
// curl -sS https://getcomposer.org/installer | php
// php composer.phar require aws/aws-sdk-php
require $_SERVER['DOCUMENT_ROOT'] . '/vendor/autoload.php'; 
use Aws\S3\S3Client;

// Amazon S3 API settings 
$bucket = 'YOUR_BUCKET'; 
$s3 = new S3Client([ 
  'version' => 'latest', 
  'region'  => 'YOUR_REGION', 
  'credentials' => [ 
    'key'    => 'YOUR_KEY', 
    'secret' => 'YOUR_SECRET', 
  ] 
]); 

// Add rule to router
// https://example.com/wp-json/api/upload
add_action('rest_api_init', function () {
  register_rest_route('api', '/upload', 
    array(
      'methods' => 'POST',
      'callback' => 'uploadFile',
    ) 
  );
});

function uploadFile($request) {
    global $s3, $bucket;
    $params = $request->get_file_params();
    // File to upload
    $file = $params["file"];
    $file_name = uniqid('YOUR_NAMESPACE-', true) . '-' . basename($file["name"]);
    $file_type = pathinfo($file_name, PATHINFO_EXTENSION);
    $allowed_types = ["pdf", "doc", "docx", "txt", "rtf"];

    if (!in_array($file_type, $allowed_types)) {
        return new WP_Error("wrong_type", "File type not allowed ({$file_type})", [
            "status" => 400,
        ]);
    }

    try {
        $file_temp_src = $file["tmp_name"];
        $result = $s3->putObject([
            "Bucket" => $bucket,
            "Key" => $file_name,
            "ACL" => "public-read",
            "SourceFile" => $file_temp_src,
        ]);
		
        $result_arr = $result->toArray();
        if (!empty($result_arr["ObjectURL"])) {
            return $result_arr;
        } else {
            return new WP_Error("url_missing", "Upload failed", [
                "status" => 500,
            ]);
        }
    } catch (Exception | Aws\S3\Exception\S3Exception $e) {
        debug_log($e);
        return new WP_Error(
            "storage_servise_error",
            ($api_error = $e->getMessage()),
            ["status" => 500]
        );
    }
}