/*
    * Copyright 2023 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.codec.http;
  
  import io.netty.handler.codec.DefaultHeaders.NameValidator;
  import io.netty.handler.codec.DefaultHeaders.ValueValidator;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * A builder of {@link HttpHeadersFactory} instances, that itself implements {@link HttpHeadersFactory}.
   * The builder is immutable, and every {@code with-} method produce a new, modified instance.
   * <p>
   * The default builder you most likely want to start with is {@link DefaultHttpHeadersFactory#headersFactory()}.
   */
  public final class DefaultHttpHeadersFactory implements HttpHeadersFactory {
      private static final NameValidator<CharSequence> DEFAULT_NAME_VALIDATOR = new NameValidator<CharSequence>() {
          @Override
          public void validateName(CharSequence name) {
              if (name == null || name.length() == 0) {
                  throw new IllegalArgumentException("empty headers are not allowed [" + name + ']');
              }
              int index = HttpHeaderValidationUtil.validateToken(name);
              if (index != -1) {
                  throw new IllegalArgumentException("a header name can only contain \"token\" characters, " +
                          "but found invalid character 0x" + Integer.toHexString(name.charAt(index)) +
                          " at index " + index + " of header '" + name + "'.");
              }
          }
      };
      private static final ValueValidator<CharSequence> DEFAULT_VALUE_VALIDATOR = new ValueValidator<CharSequence>() {
          @Override
          public void validate(CharSequence value) {
              int index = HttpHeaderValidationUtil.validateValidHeaderValue(value);
              if (index != -1) {
                  throw new IllegalArgumentException("a header value contains prohibited character 0x" +
                          Integer.toHexString(value.charAt(index)) + " at index " + index + '.');
              }
          }
      };
      private static final NameValidator<CharSequence> DEFAULT_TRAILER_NAME_VALIDATOR =
              new NameValidator<CharSequence>() {
                  @Override
                  public void validateName(CharSequence name) {
                      DEFAULT_NAME_VALIDATOR.validateName(name);
                      if (HttpHeaderNames.CONTENT_LENGTH.contentEqualsIgnoreCase(name)
                              || HttpHeaderNames.TRANSFER_ENCODING.contentEqualsIgnoreCase(name)
                              || HttpHeaderNames.TRAILER.contentEqualsIgnoreCase(name)) {
                          throw new IllegalArgumentException("prohibited trailing header: " + name);
                      }
                  }
              };
  
      @SuppressWarnings("unchecked")
      private static final NameValidator<CharSequence> NO_NAME_VALIDATOR = NameValidator.NOT_NULL;
      @SuppressWarnings("unchecked")
      private static final ValueValidator<CharSequence> NO_VALUE_VALIDATOR =
              (ValueValidator<CharSequence>) ValueValidator.NO_VALIDATION;
  
      private static final DefaultHttpHeadersFactory DEFAULT =
              new DefaultHttpHeadersFactory(DEFAULT_NAME_VALIDATOR, DEFAULT_VALUE_VALIDATOR, false);
      private static final DefaultHttpHeadersFactory DEFAULT_TRAILER =
              new DefaultHttpHeadersFactory(DEFAULT_TRAILER_NAME_VALIDATOR, DEFAULT_VALUE_VALIDATOR, false);
      private static final DefaultHttpHeadersFactory DEFAULT_COMBINING =
              new DefaultHttpHeadersFactory(DEFAULT.nameValidator, DEFAULT.valueValidator, true);
      private static final DefaultHttpHeadersFactory DEFAULT_NO_VALIDATION =
              new DefaultHttpHeadersFactory(NO_NAME_VALIDATOR, NO_VALUE_VALIDATOR, false);
  
      private final NameValidator<CharSequence> nameValidator;
      private final ValueValidator<CharSequence> valueValidator;
      private final boolean combiningHeaders;
  
      /**
       * Create a header builder with the given settings.
       *
       * @param nameValidator The name validator to use, not null.
       * @param valueValidator The value validator to use, not null.
       * @param combiningHeaders {@code true} if multi-valued headers should be combined into single lines.
       */
      private DefaultHttpHeadersFactory(
              NameValidator<CharSequence> nameValidator,
              ValueValidator<CharSequence> valueValidator,
              boolean combiningHeaders) {
          this.nameValidator = checkNotNull(nameValidator, "nameValidator");
          this.valueValidator = checkNotNull(valueValidator, "valueValidator");
          this.combiningHeaders = combiningHeaders;
     }
 
     /**
      * Get the default implementation of {@link HttpHeadersFactory} for creating headers.
      * <p>
      * This {@link DefaultHttpHeadersFactory} creates {@link HttpHeaders} instances that has the
      * recommended header validation enabled.
      */
     public static DefaultHttpHeadersFactory headersFactory() {
         return DEFAULT;
     }
 
     /**
      * Get the default implementation of {@link HttpHeadersFactory} for creating trailers.
      * <p>
      * This {@link DefaultHttpHeadersFactory} creates {@link HttpHeaders} instances that has the
      * validation enabled that is recommended for trailers.
      */
     public static DefaultHttpHeadersFactory trailersFactory() {
         return DEFAULT_TRAILER;
     }
 
     @Override
     public HttpHeaders newHeaders() {
         if (isCombiningHeaders()) {
             return new CombinedHttpHeaders(getNameValidator(), getValueValidator());
         }
         return new DefaultHttpHeaders(getNameValidator(), getValueValidator());
     }
 
     @Override
     public HttpHeaders newEmptyHeaders() {
         if (isCombiningHeaders()) {
             return new CombinedHttpHeaders(getNameValidator(), getValueValidator(), 2);
         }
         return new DefaultHttpHeaders(getNameValidator(), getValueValidator(), 2);
     }
 
     /**
      * Create a new builder that has HTTP header name validation enabled or disabled.
      * <p>
      * <b>Warning!</b> Setting {@code validation} to {@code false} will mean that Netty won't
      * validate & protect against user-supplied headers that are malicious.
      * This can leave your server implementation vulnerable to
      * <a href="https://cwe.mitre.org/data/definitions/113.html">
      *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
      * </a>.
      * When disabling this validation, it is the responsibility of the caller to ensure that the values supplied
      * do not contain a non-url-escaped carriage return (CR) and/or line feed (LF) characters.
      *
      * @param validation If validation should be enabled or disabled.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withNameValidation(boolean validation) {
         return withNameValidator(validation ? DEFAULT_NAME_VALIDATOR : NO_NAME_VALIDATOR);
     }
 
     /**
      * Create a new builder that with the given {@link NameValidator}.
      * <p>
      * <b>Warning!</b> If the given validator does not check that the header names are standards compliant, Netty won't
      * validate & protect against user-supplied headers that are malicious.
      * This can leave your server implementation vulnerable to
      * <a href="https://cwe.mitre.org/data/definitions/113.html">
      *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
      * </a>.
      * When disabling this validation, it is the responsibility of the caller to ensure that the values supplied
      * do not contain a non-url-escaped carriage return (CR) and/or line feed (LF) characters.
      *
      * @param validator The HTTP header name validator to use.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withNameValidator(NameValidator<CharSequence> validator) {
         if (nameValidator == checkNotNull(validator, "validator")) {
             return this;
         }
         if (validator == DEFAULT_NAME_VALIDATOR && valueValidator == DEFAULT_VALUE_VALIDATOR) {
             return combiningHeaders ? DEFAULT_COMBINING : DEFAULT;
         }
         return new DefaultHttpHeadersFactory(validator, valueValidator, combiningHeaders);
     }
 
     /**
      * Create a new builder that has HTTP header value validation enabled or disabled.
      * <p>
      * <b>Warning!</b> Setting {@code validation} to {@code false} will mean that Netty won't
      * validate & protect against user-supplied headers that are malicious.
      * This can leave your server implementation vulnerable to
      * <a href="https://cwe.mitre.org/data/definitions/113.html">
      *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
      * </a>.
      * When disabling this validation, it is the responsibility of the caller to ensure that the values supplied
      * do not contain a non-url-escaped carriage return (CR) and/or line feed (LF) characters.
      *
      * @param validation If validation should be enabled or disabled.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withValueValidation(boolean validation) {
         return withValueValidator(validation ? DEFAULT_VALUE_VALIDATOR : NO_VALUE_VALIDATOR);
     }
 
     /**
      * Create a new builder that with the given {@link ValueValidator}.
      * <p>
      * <b>Warning!</b> If the given validator does not check that the header values are standards compliant, Netty won't
      * validate & protect against user-supplied headers that are malicious.
      * This can leave your server implementation vulnerable to
      * <a href="https://cwe.mitre.org/data/definitions/113.html">
      *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
      * </a>.
      * When disabling this validation, it is the responsibility of the caller to ensure that the values supplied
      * do not contain a non-url-escaped carriage return (CR) and/or line feed (LF) characters.
      *
      * @param validator The HTTP header name validator to use.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withValueValidator(ValueValidator<CharSequence> validator) {
         if (valueValidator == checkNotNull(validator, "validator")) {
             return this;
         }
         if (nameValidator == DEFAULT_NAME_VALIDATOR && validator == DEFAULT_VALUE_VALIDATOR) {
             return combiningHeaders ? DEFAULT_COMBINING : DEFAULT;
         }
         return new DefaultHttpHeadersFactory(nameValidator, validator, combiningHeaders);
     }
 
     /**
      * Create a new builder that has HTTP header validation enabled or disabled.
      * <p>
      * <b>Warning!</b> Setting {@code validation} to {@code false} will mean that Netty won't
      * validate & protect against user-supplied headers that are malicious.
      * This can leave your server implementation vulnerable to
      * <a href="https://cwe.mitre.org/data/definitions/113.html">
      *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
      * </a>.
      * When disabling this validation, it is the responsibility of the caller to ensure that the values supplied
      * do not contain a non-url-escaped carriage return (CR) and/or line feed (LF) characters.
      *
      * @param validation If validation should be enabled or disabled.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withValidation(boolean validation) {
         if (this == DEFAULT && !validation) {
             return DEFAULT_NO_VALIDATION;
         }
         if (this == DEFAULT_NO_VALIDATION && validation) {
             return DEFAULT;
         }
         return withNameValidation(validation).withValueValidation(validation);
     }
 
     /**
      * Create a new builder that will build {@link HttpHeaders} objects that either combine
      * multi-valued headers, or not.
      *
      * @param combiningHeaders {@code true} if multi-valued headers should be combined, otherwise {@code false}.
      * @return The new builder.
      */
     public DefaultHttpHeadersFactory withCombiningHeaders(boolean combiningHeaders) {
         if (this.combiningHeaders == combiningHeaders) {
             return this;
         }
         return new DefaultHttpHeadersFactory(nameValidator, valueValidator, combiningHeaders);
     }
 
     /**
      * Get the currently configured {@link NameValidator}.
      * <p>
      * This method will be used by the {@link #newHeaders()} method.
      *
      * @return The configured name validator.
      */
     public NameValidator<CharSequence> getNameValidator() {
         return nameValidator;
     }
 
     /**
      * Get the currently configured {@link ValueValidator}.
      * <p>
      * This method will be used by the {@link #newHeaders()} method.
      *
      * @return The configured value validator.
      */
     public ValueValidator<CharSequence> getValueValidator() {
         return valueValidator;
     }
 
     /**
      * Check whether header combining is enabled or not.
      *
      * @return {@code true} if header value combining is enabled, otherwise {@code false}.
      */
     public boolean isCombiningHeaders() {
         return combiningHeaders;
     }
 
     /**
      * Check whether header name validation is enabled.
      *
      * @return {@code true} if header name validation is enabled, otherwise {@code false}.
      */
     public boolean isValidatingHeaderNames() {
         return nameValidator != NO_NAME_VALIDATOR;
     }
 
     /**
      * Check whether header value validation is enabled.
      *
      * @return {@code true} if header value validation is enabled, otherwise {@code false}.
      */
     public boolean isValidatingHeaderValues() {
         return valueValidator != NO_VALUE_VALIDATOR;
     }
 }