Upload a PDF (debug UI)

#!/usr/bin/env python3
# SPDX-FileCopyrightText: 2019 James R. Barlow
# SPDX-License-Identifier: AGPL-3.0-or-later

"""This is a simple web service/HTTP wrapper for OCRmyPDF

This may be more convenient than the command line tool for some Docker users.
Note that OCRmyPDF uses Ghostscript, which is licensed under AGPLv3+. While
OCRmyPDF is under GPLv3, this file is distributed under the Affero GPLv3+ license,
to emphasize that SaaS deployments should make sure they comply with
Ghostscript's license as well as OCRmyPDF's.
"""

from __future__ import annotations

import os
import shlex
from subprocess import PIPE, run
from tempfile import TemporaryDirectory

from flask import Flask, Response, request, send_from_directory
from werkzeug.utils import secure_filename

app = Flask(__name__)
app.secret_key = "secret"
app.config['MAX_CONTENT_LENGTH'] = 50_000_000
app.config.from_envvar("OCRMYPDF_WEBSERVICE_SETTINGS", silent=True)

ALLOWED_EXTENSIONS = {"pdf"}


def allowed_file(filename):
    return "." in filename and filename.rsplit(".", 1)[1].lower() in ALLOWED_EXTENSIONS


def do_ocrmypdf(file):
    uploaddir = TemporaryDirectory(prefix="ocrmypdf-upload")
    downloaddir = TemporaryDirectory(prefix="ocrmypdf-download")

    filename = secure_filename(file.filename)
    up_file = os.path.join(uploaddir.name, filename)
    file.save(up_file)

    down_file = os.path.join(downloaddir.name, filename)

    cmd_args = [arg for arg in shlex.split(request.form["params"])]
    if "--sidecar" in cmd_args:
        return Response("--sidecar not supported", 501, mimetype='text/plain')

    ocrmypdf_args = ["ocrmypdf", *cmd_args, up_file, down_file]
    proc = run(ocrmypdf_args, capture_output=True, encoding="utf-8")
    if proc.returncode != 0:
        stderr = proc.stderr
        return Response(stderr, 400, mimetype='text/plain')

    return send_from_directory(downloaddir.name, filename)


@app.route("/", methods=["GET", "POST"])
def upload_file():
    if request.method == "POST":
        if "file" not in request.files:
            return Response("No file in POST", 400, mimetype='text/plain')
        file = request.files["file"]
        if file.filename == "":
            return Response("Empty filename", 400, mimetype='text/plain')
        if not allowed_file(file.filename):
            return Response("Invalid filename", 400, mimetype='text/plain')
        if file and allowed_file(file.filename):
            return do_ocrmypdf(file)
        return Response("Some other problem", 400, mimetype='text/plain')

    return """
    <!doctype html>
    <title>OCRmyPDF webservice</title>
    <h1>Upload a PDF (debug UI)</h1>
    <form method=post enctype=multipart/form-data>
      <label for="args">Command line parameters</label>
      <input type=textbox name=params>
      <label for="file">File to upload</label>
      <input type=file name=file>
      <input type=submit value=Upload>
    </form>
    <h4>Notice</h2>
    <div style="font-size: 70%; max-width: 34em;">
    <p>This is a webservice wrapper for OCRmyPDF.</p>
    <p>Copyright 2019 James R. Barlow</p>
    <p>This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
    </p>
    <p>This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    </p>
    <p>
    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see &lt;http://www.gnu.org/licenses/&gt;.
    </p>
    </div>
    """


if __name__ == "__main__":
    app.run(host='0.0.0.0', port=5000)