/*
    * Copyright 2022 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.ssl.ocsp;
  
  import io.netty.bootstrap.Bootstrap;
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelInitializer;
  import io.netty.channel.ChannelOption;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.EventLoop;
  import io.netty.channel.socket.SocketChannel;
  import io.netty.handler.codec.http.DefaultFullHttpRequest;
  import io.netty.handler.codec.http.FullHttpRequest;
  import io.netty.handler.codec.http.HttpClientCodec;
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpObjectAggregator;
  import io.netty.resolver.dns.DnsNameResolver;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.FutureListener;
  import io.netty.util.concurrent.GenericFutureListener;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  import org.bouncycastle.asn1.DEROctetString;
  import org.bouncycastle.asn1.x509.AccessDescription;
  import org.bouncycastle.asn1.x509.AuthorityInformationAccess;
  import org.bouncycastle.asn1.x509.Extension;
  import org.bouncycastle.asn1.x509.Extensions;
  import org.bouncycastle.cert.X509CertificateHolder;
  import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
  import org.bouncycastle.cert.jcajce.JcaX509CertificateHolder;
  import org.bouncycastle.cert.ocsp.BasicOCSPResp;
  import org.bouncycastle.cert.ocsp.CertificateID;
  import org.bouncycastle.cert.ocsp.OCSPException;
  import org.bouncycastle.cert.ocsp.OCSPReqBuilder;
  import org.bouncycastle.cert.ocsp.OCSPResp;
  import org.bouncycastle.operator.ContentVerifierProvider;
  import org.bouncycastle.operator.DigestCalculatorProvider;
  import org.bouncycastle.operator.OperatorCreationException;
  import org.bouncycastle.operator.jcajce.JcaContentVerifierProviderBuilder;
  import org.bouncycastle.operator.jcajce.JcaDigestCalculatorProviderBuilder;
  
  import java.net.InetAddress;
  import java.net.URL;
  import java.security.InvalidAlgorithmParameterException;
  import java.security.NoSuchAlgorithmException;
  import java.security.SecureRandom;
  import java.security.cert.CertPathBuilder;
  import java.security.cert.CertPathBuilderException;
  import java.security.cert.CertPathBuilderResult;
  import java.security.cert.CertStore;
  import java.security.cert.CertificateEncodingException;
  import java.security.cert.CertificateException;
  import java.security.cert.CollectionCertStoreParameters;
  import java.security.cert.PKIXBuilderParameters;
  import java.security.cert.TrustAnchor;
  import java.security.cert.X509CertSelector;
  import java.security.cert.X509Certificate;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  
  import static io.netty.handler.codec.http.HttpMethod.POST;
  import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
  import static io.netty.handler.ssl.ocsp.OcspHttpHandler.OCSP_REQUEST_TYPE;
  import static io.netty.handler.ssl.ocsp.OcspHttpHandler.OCSP_RESPONSE_TYPE;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  import static org.bouncycastle.asn1.ocsp.OCSPObjectIdentifiers.id_pkix_ocsp_nonce;
  import static org.bouncycastle.asn1.x509.X509ObjectIdentifiers.id_ad_ocsp;
  import static org.bouncycastle.cert.ocsp.CertificateID.HASH_SHA1;
  
  final class OcspClient {
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(OcspClient.class);
  
      private static final SecureRandom SECURE_RANDOM = new SecureRandom();
      private static final int OCSP_RESPONSE_MAX_SIZE = SystemPropertyUtil.getInt(
              "io.netty.ocsp.responseSize", 1024 * 10);
      public static final String OID_OCSP_SIGNING = "1.3.6.1.5.5.7.3.9";
  
      static {
          logger.debug("-Dio.netty.ocsp.responseSize: {} bytes", OCSP_RESPONSE_MAX_SIZE);
     }
 
     /**
      * Query the certificate status using OCSP
      *
      * @param x509Certificate       Client {@link X509Certificate} to validate
      * @param issuer                {@link X509Certificate} issuer of client certificate
      * @param validateResponseNonce Set to {@code true} to enable OCSP response validation
      * @param ioTransport           {@link IoTransport} to use
      * @param responsePromise      {@link Promise} of {@link BasicOCSPResp}
      */
     static void query(final X509Certificate x509Certificate,
                                         final X509Certificate issuer, final boolean validateResponseNonce,
                                         final IoTransport ioTransport, final DnsNameResolver dnsNameResolver,
                                         final Promise<BasicOCSPResp> responsePromise) {
         final EventLoop eventLoop = ioTransport.eventLoop();
         eventLoop.execute(new Runnable() {
             @Override
             public void run() {
                 try {
                     DigestCalculatorProvider digestCalculatorProvider = new JcaDigestCalculatorProviderBuilder()
                             .build();
 
                     CertificateID certificateID = new CertificateID(digestCalculatorProvider.get(HASH_SHA1),
                             new JcaX509CertificateHolder(issuer),
                             x509Certificate.getSerialNumber());
 
                     // Initialize OCSP Request Builder and add CertificateID into it.
                     OCSPReqBuilder builder = new OCSPReqBuilder();
                     builder.addRequest(certificateID);
 
                     // Generate 16-bytes (octets) of nonce and add it into OCSP Request builder.
                     // Because as per RFC-8954#2.1:
                     //
                     //   OCSP responders MUST accept lengths of at least
                     //   16 octets and MAY choose to ignore the Nonce extension for requests
                     //   where the length of the nonce is less than 16 octets.
                     byte[] nonce = new byte[16];
                     SECURE_RANDOM.nextBytes(nonce);
                     final DEROctetString derNonce = new DEROctetString(nonce);
                     builder.setRequestExtensions(new Extensions(new Extension(id_pkix_ocsp_nonce, false, derNonce)));
 
                     // Get OCSP URL from Certificate and query it.
                     URL uri = new URL(parseOcspUrlFromCertificate(x509Certificate));
 
                     // Find port
                     int port = uri.getPort();
                     if (port == -1) {
                         port = uri.getDefaultPort();
                     }
 
                     // Configure path
                     String path = uri.getPath();
                     if (path.isEmpty()) {
                         path = "/";
                     } else {
                         if (uri.getQuery() != null) {
                             path = path + '?' + uri.getQuery();
                         }
                     }
 
                     Promise<OCSPResp> ocspResponsePromise = query(eventLoop,
                             Unpooled.wrappedBuffer(builder.build().getEncoded()),
                             uri.getHost(), port, path, ioTransport, dnsNameResolver);
 
                     // Validate OCSP response
                     ocspResponsePromise.addListener((GenericFutureListener<Future<OCSPResp>>) future -> {
                         // If Future was successful then we have received OCSP response
                         // We will now validate it.
                         if (future.isSuccess()) {
                             final Object responseObject;
                             try {
                                 responseObject = future.getNow().getResponseObject();
                             } catch (OCSPException e) {
                                 responsePromise.setFailure(future.cause());
                                 return;
                             }
                             if (responseObject instanceof BasicOCSPResp) {
                                 validateResponse(x509Certificate, digestCalculatorProvider, responsePromise,
                                         (BasicOCSPResp) responseObject, derNonce, issuer, validateResponseNonce);
                             } else {
                                 responsePromise.tryFailure(new OCSPException("Unsupported OCSP response type: "
                                         + (responseObject == null ? null : responseObject.getClass())));
                             }
                         } else {
                             responsePromise.tryFailure(future.cause());
                         }
                     });
                 } catch (Exception ex) {
                     responsePromise.tryFailure(ex);
                 }
             }
         });
     }
 
     /**
      * Query the OCSP responder for certificate status using HTTP/1.1
      *
      * @param eventLoop   {@link EventLoop} for HTTP request execution
      * @param ocspRequest {@link ByteBuf} containing OCSP request data
      * @param host        OCSP responder hostname
      * @param port        OCSP responder port
      * @param path        OCSP responder path
      * @param ioTransport {@link IoTransport} to use
      * @return Returns {@link Promise} containing {@link OCSPResp}
      */
     private static Promise<OCSPResp> query(final EventLoop eventLoop, final ByteBuf ocspRequest,
                                            final String host, final int port, final String path,
                                            final IoTransport ioTransport, final DnsNameResolver dnsNameResolver) {
         final Promise<OCSPResp> responsePromise = eventLoop.newPromise();
 
         try {
             final Bootstrap bootstrap = new Bootstrap()
                     .group(ioTransport.eventLoop())
                     .option(ChannelOption.TCP_NODELAY, true)
                     .channelFactory(ioTransport.socketChannel())
                     .attr(OcspServerCertificateValidator.OCSP_PIPELINE_ATTRIBUTE, Boolean.TRUE)
                     .handler(new Initializer(responsePromise, 10 * 1000));
             dnsNameResolver.resolve(host).addListener((FutureListener<InetAddress>) future -> {
 
                 // If Future was successful then we have successfully resolved OCSP server address.
                 // If not, mark 'responsePromise' as failure.
                 if (future.isSuccess()) {
                     // Get the resolved InetAddress
                     InetAddress hostAddress = future.getNow();
                     final ChannelFuture channelFuture = bootstrap.connect(hostAddress, port);
                     channelFuture.addListener(f -> {
                         // If Future was successful then connection to OCSP responder was successful.
                         // We will send a OCSP request now
                         if (f.isSuccess()) {
                             FullHttpRequest request = new DefaultFullHttpRequest(HTTP_1_1, POST, path,
                                     ocspRequest);
                             request.headers().add(HttpHeaderNames.HOST, host);
                             request.headers().add(HttpHeaderNames.USER_AGENT, "Netty OCSP Client");
                             request.headers().add(HttpHeaderNames.CONTENT_TYPE, OCSP_REQUEST_TYPE);
                             request.headers().add(HttpHeaderNames.ACCEPT_ENCODING, OCSP_RESPONSE_TYPE);
                             request.headers().add(HttpHeaderNames.CONTENT_LENGTH, ocspRequest.readableBytes());
 
                             // Send the OCSP HTTP Request
                             channelFuture.channel().writeAndFlush(request);
                         } else {
                             responsePromise.tryFailure(new IllegalStateException(
                                     "Connection to OCSP Responder Failed", f.cause()));
                         }
                     });
                 } else {
                     responsePromise.tryFailure(future.cause());
                 }
             });
         } catch (Exception ex) {
             responsePromise.tryFailure(ex);
         }
 
         return responsePromise;
     }
 
     private static void validateResponse(
             X509Certificate x509Certificate, DigestCalculatorProvider digestCalculatorProvider,
             Promise<BasicOCSPResp> responsePromise, BasicOCSPResp basicResponse,
             DEROctetString derNonce, X509Certificate issuer, boolean validateNonce) {
         try {
             // Validate number of responses. We only requested for 1 certificate
             // so number of responses must be 1. If not, we will throw an error.
             int responses = basicResponse.getResponses().length;
             if (responses != 1) {
                 responsePromise.tryFailure(
                         new IllegalArgumentException("Expected number of responses was 1 but got: " + responses));
                 return;
             }
 
             CertificateID respCertId = basicResponse.getResponses()[0].getCertID();
             if (!respCertId.matchesIssuer(new JcaX509CertificateHolder(issuer), digestCalculatorProvider)
                     || !respCertId.getSerialNumber().equals(x509Certificate.getSerialNumber())) {
                 responsePromise.tryFailure(
                         new CertificateException("OCSP response CertID does not match queried certificate"));
                 return;
             }
 
             if (validateNonce) {
                 validateNonce(basicResponse, derNonce);
             }
             validateSignature(basicResponse, issuer);
             responsePromise.trySuccess(basicResponse);
         } catch (Exception ex) {
             responsePromise.tryFailure(ex);
         }
     }
 
     /**
      * Validate OCSP response nonce
      */
     private static void validateNonce(BasicOCSPResp basicResponse, DEROctetString encodedNonce) throws OCSPException {
         Extension nonceExt = basicResponse.getExtension(id_pkix_ocsp_nonce);
         if (nonceExt != null) {
             DEROctetString responseNonceString = (DEROctetString) nonceExt.getExtnValue();
             if (!responseNonceString.equals(encodedNonce)) {
                 throw new OCSPException("Nonce does not match");
             }
         } else {
             throw new IllegalArgumentException("Nonce is not present");
         }
     }
 
     /**
      * Validate OCSP response signature
      */
     static void validateSignature(BasicOCSPResp resp, X509Certificate issuerCertificate) throws OCSPException {
         try {
             X509CertificateHolder[] certs = resp.getCerts();
             JcaContentVerifierProviderBuilder providerBuilder = new JcaContentVerifierProviderBuilder();
 
             // If responder certificate is included, validate the chain
             if (certs != null && certs.length > 0) {
                 X509Certificate[] certificates = new X509Certificate[certs.length];
                 JcaX509CertificateConverter toCertificateConverter = new JcaX509CertificateConverter();
                 for (int i = 0; i < certs.length; i++) {
                     certificates[i] = toCertificateConverter.getCertificate(certs[i]);
                 }
 
                 // Use the first included certificate to verify the OCSP response signature.
                 X509Certificate responderCertificate = certificates[0];
 
                 if (!isIssuingCa(responderCertificate, issuerCertificate)) {
                     // Original certificate issuer has delegated OCSP signing.
                     // Responder cert must be authorized to sign OCSP responses.
                     try {
                         List<String> extendedKeyUsage = responderCertificate.getExtendedKeyUsage();
                         if (extendedKeyUsage == null ||
                             !extendedKeyUsage.contains(OID_OCSP_SIGNING)) {
                             throw new OCSPException("OCSP Responder is not authorized to sign OCSP responses");
                         }
                     } catch (ClassCastException | IllegalArgumentException e) {
                         throw new OCSPException("Responder has invalid or malformed ExtendedKeyUsage extension", e);
                     }
 
                     // Build chain from responder certificate to issuer using CertPathBuilder
                     validateCertificateChain(responderCertificate, certificates, issuerCertificate);
                 }
 
                 // Verify OCSP response signature using responder cert
                 ContentVerifierProvider responderVerifier = providerBuilder.build(certs[0]);
 
                 if (!resp.isSignatureValid(responderVerifier)) {
                     throw new OCSPException("OCSP response signature is not valid");
                 }
             } else {
                 // Validate signature using issuer certificate
                 ContentVerifierProvider issuerVerifier = providerBuilder.build(issuerCertificate);
 
                 if (!resp.isSignatureValid(issuerVerifier)) {
                     throw new OCSPException("OCSP response signature is not valid");
                 }
             }
         } catch (OperatorCreationException e) {
             throw new OCSPException("Error validating OCSP-Signature", e);
         } catch (CertificateException e) {
             throw new OCSPException("Error while processing certificates for OCSP signature validation", e);
         }
     }
 
     /**
      * <a href="https://datatracker.ietf.org/doc/html/rfc6960#section-4.2.2.2">RFC 6960 4.2.2.2</a>:
      * <blockquote>Is the certificate of the CA that issued the certificate in question</blockquote>
      * The name and the key are compared instead of the encoding, so that a CA certificate that was re-issued or
      * cross-signed with the same name and key still matches.
      */
     private static boolean isIssuingCa(X509Certificate responderCertificate, X509Certificate issuerCertificate) {
         return responderCertificate.getSubjectX500Principal().equals(issuerCertificate.getSubjectX500Principal())
             && responderCertificate.getPublicKey().equals(issuerCertificate.getPublicKey());
     }
 
     /**
      * Validates that a certificate chain can be built from the responder certificate to the issuer.
      * Uses Java's CertPathBuilder to construct and validate the chain.
      */
     private static void validateCertificateChain(X509Certificate responderCertificate,
                                                  X509Certificate[] allCerts,
                                                  X509Certificate issuerCertificate) throws OCSPException {
         try {
             // Create a CertStore with all the certificates from the OCSP response
             CertStore certStore = CertStore.getInstance("Collection",
                     new CollectionCertStoreParameters(Arrays.asList(allCerts)));
 
             // Set up the target certificate selector for the responder certificate
             X509CertSelector targetConstraints = new X509CertSelector();
             targetConstraints.setCertificate(responderCertificate);
 
             // Set up trust anchor with the issuer certificate
             TrustAnchor trustAnchor = new TrustAnchor(issuerCertificate, null);
 
             // Build PKIX parameters
             PKIXBuilderParameters pkixParams = new PKIXBuilderParameters(
                     Collections.singleton(trustAnchor), targetConstraints);
             pkixParams.addCertStore(certStore);
             pkixParams.setRevocationEnabled(false); // Don't check revocation when validating OCSP response
 
             // Build and validate the certificate path
             CertPathBuilder builder = CertPathBuilder.getInstance("PKIX");
             CertPathBuilderResult result = builder.build(pkixParams);
 
             // RFC 6960 https://datatracker.ietf.org/doc/html/rfc6960#section-4.2.2.2
             // "Includes a value of id-kp-OCSPSigning in an extended key usage extension
             // and is issued by the CA that issued the certificate in question as stated above."
             if (result.getCertPath().getCertificates().size() > 1) {
                 throw new OCSPException("OCSP responder certificate was not issued by the certificate issuer: "
                         + issuerCertificate.getSubjectX500Principal());
             }
         } catch (CertPathBuilderException e) {
             throw new OCSPException("OCSP responder certificate is not trusted by issuer: " + e.getMessage(), e);
         } catch (InvalidAlgorithmParameterException | NoSuchAlgorithmException e) {
             throw new OCSPException("Error setting up certificate path validation", e);
         }
     }
 
     /**
      * Parse OCSP endpoint URL from Certificate
      *
      * @param cert Certificate to be parsed
      * @return OCSP endpoint URL
      * @throws NullPointerException     If we couldn't locate OCSP responder URL
      * @throws IllegalArgumentException If we couldn't parse X509Certificate into JcaX509CertificateHolder
      */
     private static String parseOcspUrlFromCertificate(X509Certificate cert) {
         X509CertificateHolder holder;
         try {
             holder = new JcaX509CertificateHolder(cert);
         } catch (CertificateEncodingException e) {
             // Though this should never happen
             throw new IllegalArgumentException("Error while parsing X509Certificate into JcaX509CertificateHolder", e);
         }
 
         AuthorityInformationAccess aiaExtension = AuthorityInformationAccess.fromExtensions(holder.getExtensions());
 
         // Lookup for OCSP responder url
         if (aiaExtension != null) {
             for (AccessDescription accessDescription : aiaExtension.getAccessDescriptions()) {
                 if (accessDescription.getAccessMethod().equals(id_ad_ocsp)) {
                     return accessDescription.getAccessLocation().getName().toASN1Primitive().toString();
                 }
             }
         }
 
         throw new NoOcspResponderException("Unable to find OCSP responder URL in Certificate");
     }
 
     static final class Initializer extends ChannelInitializer<SocketChannel> {
 
         private final Promise<OCSPResp> responsePromise;
         private final long timeoutMillis;
 
         Initializer(Promise<OCSPResp> responsePromise, long timeoutMillis) {
             this.responsePromise = checkNotNull(responsePromise, "responsePromise");
             this.timeoutMillis = ObjectUtil.checkPositive(timeoutMillis, "timeoutMillis");
         }
 
         @Override
         protected void initChannel(SocketChannel socketChannel) {
             ChannelPipeline pipeline = socketChannel.pipeline();
             pipeline.addLast(new HttpClientCodec());
             pipeline.addLast(new HttpObjectAggregator(OCSP_RESPONSE_MAX_SIZE));
             pipeline.addLast(new OcspHttpHandler(responsePromise, timeoutMillis));
         }
     }
 
     private OcspClient() {
         // Prevent outside initialization
     }
 }