/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.filter;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

import org.springframework.http.HttpInputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.FormHttpMessageConverter;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;

Filter that parses form data for HTTP PUT, PATCH, and DELETE requests and exposes it as Servlet request parameters. By default the Servlet spec only requires this for HTTP POST. 
Author:
Rossen Stoyanchev
Since:
5.1/**
 * {@code Filter} that parses form data for HTTP PUT, PATCH, and DELETE requests
 * and exposes it as Servlet request parameters. By default the Servlet spec
 * only requires this for HTTP POST.
 *
 * @author Rossen Stoyanchev
 * @since 5.1
 */
public class FormContentFilter extends OncePerRequestFilter {

	private static final List<String> HTTP_METHODS = Arrays.asList("PUT", "PATCH", "DELETE");

	private FormHttpMessageConverter formConverter = new AllEncompassingFormHttpMessageConverter();


	
Set the converter to use for parsing form content.
By default this is an instance of AllEncompassingFormHttpMessageConverter. /**
	 * Set the converter to use for parsing form content.
	 * <p>By default this is an instance of {@link AllEncompassingFormHttpMessageConverter}.
	 */
	public void setFormConverter(FormHttpMessageConverter converter) {
		Assert.notNull(converter, "FormHttpMessageConverter is required");
		this.formConverter = converter;
	}

	
The default character set to use for reading form data.
This is a shortcut for:
 getFormConverter.setCharset(charset). /**
	 * The default character set to use for reading form data.
	 * This is a shortcut for:<br>
	 * {@code getFormConverter.setCharset(charset)}.
	 */
	public void setCharset(Charset charset) {
		this.formConverter.setCharset(charset);
	}


	@Override
	protected void doFilterInternal(
			HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		MultiValueMap<String, String> params = parseIfNecessary(request);
		if (!CollectionUtils.isEmpty(params)) {
			filterChain.doFilter(new FormContentRequestWrapper(request, params), response);
		}
		else {
			filterChain.doFilter(request, response);
		}
	}

	@Nullable
	private MultiValueMap<String, String> parseIfNecessary(HttpServletRequest request) throws IOException {
		if (!shouldParse(request)) {
			return null;
		}

		HttpInputMessage inputMessage = new ServletServerHttpRequest(request) {
			@Override
			public InputStream getBody() throws IOException {
				return request.getInputStream();
			}
		};
		return this.formConverter.read(null, inputMessage);
	}

	private boolean shouldParse(HttpServletRequest request) {
		if (!HTTP_METHODS.contains(request.getMethod())) {
			return false;
		}
		try {
			MediaType mediaType = MediaType.parseMediaType(request.getContentType());
			return MediaType.APPLICATION_FORM_URLENCODED.includes(mediaType);
		}
		catch (IllegalArgumentException ex) {
			return false;
		}
	}


	private static class FormContentRequestWrapper extends HttpServletRequestWrapper {

		private MultiValueMap<String, String> formParams;

		public FormContentRequestWrapper(HttpServletRequest request, MultiValueMap<String, String> params) {
			super(request);
			this.formParams = params;
		}

		@Override
		@Nullable
		public String getParameter(String name) {
			String queryStringValue = super.getParameter(name);
			String formValue = this.formParams.getFirst(name);
			return (queryStringValue != null ? queryStringValue : formValue);
		}

		@Override
		public Map<String, String[]> getParameterMap() {
			Map<String, String[]> result = new LinkedHashMap<>();
			Enumeration<String> names = getParameterNames();
			while (names.hasMoreElements()) {
				String name = names.nextElement();
				result.put(name, getParameterValues(name));
			}
			return result;
		}

		@Override
		public Enumeration<String> getParameterNames() {
			Set<String> names = new LinkedHashSet<>();
			names.addAll(Collections.list(super.getParameterNames()));
			names.addAll(this.formParams.keySet());
			return Collections.enumeration(names);
		}

		@Override
		@Nullable
		public String[] getParameterValues(String name) {
			String[] parameterValues = super.getParameterValues(name);
			List<String> formParam = this.formParams.get(name);
			if (formParam == null) {
				return parameterValues;
			}
			if (parameterValues == null || getQueryString() == null) {
				return StringUtils.toStringArray(formParam);
			}
			else {
				List<String> result = new ArrayList<>(parameterValues.length + formParam.size());
				result.addAll(Arrays.asList(parameterValues));
				result.addAll(formParam);
				return StringUtils.toStringArray(result);
			}
		}
	}

}