/*
    * Copyright (C) 2009-2010, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.http.server;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static org.eclipse.jgit.util.HttpSupport.ENCODING_GZIP;
  import static org.eclipse.jgit.util.HttpSupport.ENCODING_X_GZIP;
  import static org.eclipse.jgit.util.HttpSupport.HDR_ACCEPT_ENCODING;
  import static org.eclipse.jgit.util.HttpSupport.HDR_CONTENT_ENCODING;
  import static org.eclipse.jgit.util.HttpSupport.HDR_ETAG;
  import static org.eclipse.jgit.util.HttpSupport.TEXT_PLAIN;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.security.MessageDigest;
  import java.text.MessageFormat;
  import java.util.zip.GZIPInputStream;
  import java.util.zip.GZIPOutputStream;
  
  import javax.servlet.ServletRequest;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.Repository;
  
  /**
   * Common utility functions for servlets.
   */
  public final class ServletUtils {
  	/** Request attribute which stores the {@link Repository} instance. */
  	public static final String ATTRIBUTE_REPOSITORY = "org.eclipse.jgit.Repository";
  
  	/** Request attribute storing either UploadPack or ReceivePack. */
  	public static final String ATTRIBUTE_HANDLER = "org.eclipse.jgit.transport.UploadPackOrReceivePack";
  
  	/**
  	 * Get the selected repository from the request.
  	 *
  	 * @param req
  	 *            the current request.
  	 * @return the repository; never null.
  	 * @throws IllegalStateException
  	 *             the repository was not set by the filter, the servlet is
  	 *             being invoked incorrectly and the programmer should ensure
  	 *             the filter runs before the servlet.
  	 * @see #ATTRIBUTE_REPOSITORY
  	 */
  	public static Repository getRepository(ServletRequest req) {
  		Repository db = (Repository) req.getAttribute(ATTRIBUTE_REPOSITORY);
  		if (db == null)
  			throw new IllegalStateException(HttpServerText.get().expectedRepositoryAttribute);
  		return db;
  	}
  
  	/**
  	 * Open the request input stream, automatically inflating if necessary.
  	 * <p>
  	 * This method automatically inflates the input stream if the request
  	 * {@code Content-Encoding} header was set to {@code gzip} or the legacy
  	 * {@code x-gzip}.
  	 *
  	 * @param req
  	 *            the incoming request whose input stream needs to be opened.
  	 * @return an input stream to read the raw, uncompressed request body.
  	 * @throws IOException
  	 *             if an input or output exception occurred.
  	 */
  	public static InputStream getInputStream(HttpServletRequest req)
  			throws IOException {
  		InputStream in = req.getInputStream();
  		final String enc = req.getHeader(HDR_CONTENT_ENCODING);
  		if (ENCODING_GZIP.equals(enc) || ENCODING_X_GZIP.equals(enc))
  			in = new GZIPInputStream(in);
  		else if (enc != null)
  			throw new IOException(MessageFormat.format(HttpServerText.get().encodingNotSupportedByThisLibrary
  					, HDR_CONTENT_ENCODING, enc));
  		return in;
  	}
  
  	/**
  	 * Consume the entire request body, if one was supplied.
  	 *
  	 * @param req
  	 *            the request whose body must be consumed.
  	 */
  	public static void consumeRequestBody(HttpServletRequest req) {
  		if (0 < req.getContentLength() || isChunked(req)) {
 			try {
 				consumeRequestBody(req.getInputStream());
 			} catch (IOException e) {
 				// Ignore any errors obtaining the input stream.
 			}
 		}
 	}
 
 	static boolean isChunked(HttpServletRequest req) {
 		return "chunked".equals(req.getHeader("Transfer-Encoding"));
 	}
 
 	/**
 	 * Consume the rest of the input stream and discard it.
 	 *
 	 * @param in
 	 *            the stream to discard, closed if not null.
 	 */
 	public static void consumeRequestBody(InputStream in) {
 		if (in == null)
 			return;
 		try {
 			while (0 < in.skip(2048) || 0 <= in.read()) {
 				// Discard until EOF.
 			}
 		} catch (IOException err) {
 			// Discard IOException during read or skip.
 		} finally {
 			try {
 				in.close();
 			} catch (IOException err) {
 				// Discard IOException during close of input stream.
 			}
 		}
 	}
 
 	/**
 	 * Send a plain text response to a {@code GET} or {@code HEAD} HTTP request.
 	 * <p>
 	 * The text response is encoded in the Git character encoding, UTF-8.
 	 * <p>
 	 * If the user agent supports a compressed transfer encoding and the content
 	 * is large enough, the content may be compressed before sending.
 	 * <p>
 	 * The {@code ETag} and {@code Content-Length} headers are automatically set
 	 * by this method. {@code Content-Encoding} is conditionally set if the user
 	 * agent supports a compressed transfer. Callers are responsible for setting
 	 * any cache control headers.
 	 *
 	 * @param content
 	 *            to return to the user agent as this entity's body.
 	 * @param req
 	 *            the incoming request.
 	 * @param rsp
 	 *            the outgoing response.
 	 * @throws IOException
 	 *             the servlet API rejected sending the body.
 	 */
 	public static void sendPlainText(final String content,
 			final HttpServletRequest req, final HttpServletResponse rsp)
 			throws IOException {
 		final byte[] raw = content.getBytes(UTF_8);
 		rsp.setContentType(TEXT_PLAIN);
 		rsp.setCharacterEncoding(UTF_8.name());
 		send(raw, req, rsp);
 	}
 
 	/**
 	 * Send a response to a {@code GET} or {@code HEAD} HTTP request.
 	 * <p>
 	 * If the user agent supports a compressed transfer encoding and the content
 	 * is large enough, the content may be compressed before sending.
 	 * <p>
 	 * The {@code ETag} and {@code Content-Length} headers are automatically set
 	 * by this method. {@code Content-Encoding} is conditionally set if the user
 	 * agent supports a compressed transfer. Callers are responsible for setting
 	 * {@code Content-Type} and any cache control headers.
 	 *
 	 * @param content
 	 *            to return to the user agent as this entity's body.
 	 * @param req
 	 *            the incoming request.
 	 * @param rsp
 	 *            the outgoing response.
 	 * @throws IOException
 	 *             the servlet API rejected sending the body.
 	 */
 	public static void send(byte[] content, final HttpServletRequest req,
 			final HttpServletResponse rsp) throws IOException {
 		content = sendInit(content, req, rsp);
 		try (OutputStream out = rsp.getOutputStream()) {
 			out.write(content);
 			out.flush();
 		}
 	}
 
 	private static byte[] sendInit(byte[] content,
 			final HttpServletRequest req, final HttpServletResponse rsp)
 			throws IOException {
 		rsp.setHeader(HDR_ETAG, etag(content));
 		if (256 < content.length && acceptsGzipEncoding(req)) {
 			content = compress(content);
 			rsp.setHeader(HDR_CONTENT_ENCODING, ENCODING_GZIP);
 		}
 		rsp.setContentLength(content.length);
 		return content;
 	}
 
 	static boolean acceptsGzipEncoding(HttpServletRequest req) {
 		return acceptsGzipEncoding(req.getHeader(HDR_ACCEPT_ENCODING));
 	}
 
 	static boolean acceptsGzipEncoding(String accepts) {
 		if (accepts == null)
 			return false;
 
 		int b = 0;
 		while (b < accepts.length()) {
 			int comma = accepts.indexOf(',', b);
 			int e = 0 <= comma ? comma : accepts.length();
 			String term = accepts.substring(b, e).trim();
 			if (term.equals(ENCODING_GZIP))
 				return true;
 			b = e + 1;
 		}
 		return false;
 	}
 
 	private static byte[] compress(byte[] raw) throws IOException {
 		final int maxLen = raw.length + 32;
 		final ByteArrayOutputStream out = new ByteArrayOutputStream(maxLen);
 		final GZIPOutputStream gz = new GZIPOutputStream(out);
 		gz.write(raw);
 		gz.finish();
 		gz.flush();
 		return out.toByteArray();
 	}
 
 	private static String etag(byte[] content) {
 		final MessageDigest md = Constants.newMessageDigest();
 		md.update(content);
 		return ObjectId.fromRaw(md.digest()).getName();
 	}
 
 	static String identify(Repository git) {
 		String identifier = git.getIdentifier();
 		if (identifier == null) {
 			return "unknown";
 		}
 		return identifier;
 	}
 
 	private ServletUtils() {
 		// static utility class only
 	}
 }