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Kafka Compatible Schema Registry
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/**
 * 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 io.streamnative.pulsar.handlers.kop.schemaregistry;

import static io.netty.handler.codec.http.HttpResponseStatus.NOT_FOUND;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpHeaderNames;
import io.netty.util.CharsetUtil;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import lombok.extern.slf4j.Slf4j;

@Slf4j
@ChannelHandler.Sharable
public class SchemaRegistryHandler extends SimpleChannelInboundHandler {

    private final List processors = new ArrayList<>();

    public SchemaRegistryHandler addProcessor(HttpRequestProcessor processor) {
        this.processors.add(processor);
        return this;
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.flush();
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) {
        if (log.isDebugEnabled()) {
            log.debug("SchemaRegistry at {} request {}", ctx.channel().localAddress(), request);
        }
        log.info("SchemaRegistry {} {} from {}", request.method(), request.uri(), ctx.channel().localAddress());

        HttpRequestProcessor processor = null;
        for (HttpRequestProcessor p : processors) {
            if (p.acceptRequest(request)) {
                processor = p;
                break;
            }
        }
        if (processor == null) {
            String body = "{\n"
                    + "  \"message\" : \"Not found\",\n"
                    + "  \"error_code\" : 404\n"
                    + "}";
            FullHttpResponse httpResponse = new DefaultFullHttpResponse(HTTP_1_1,
                    NOT_FOUND,
                    Unpooled.copiedBuffer(body, CharsetUtil.UTF_8));
            httpResponse.headers().set(HttpHeaderNames.CONTENT_TYPE, "application/vnd.schemaregistry.v1+json");
            httpResponse.headers().set(HttpHeaderNames.CONTENT_LENGTH, body.length());
            HttpRequestProcessor.addCORSHeaders(httpResponse);
            log.info("not found {} {} from {}", request.method(), request.uri(), ctx.channel().localAddress());
            if (log.isDebugEnabled()) {
                log.debug("SchemaRegistry at {} request {} response {}", ctx.channel().localAddress(), request,
                        httpResponse);
            }
            ctx.writeAndFlush(httpResponse);
            return;
        }

        CompletableFuture fullHttpResponse = processor.processRequest(request);
        fullHttpResponse.thenAccept(resp -> {
            if (log.isDebugEnabled()) {
                log.debug("SchemaRegistry at {} request {} response {}", ctx.channel().localAddress(), request,
                        resp);
            }
            log.info("SchemaRegistry {} {} from {} response {} {}", request.method(), request.uri(),
                    ctx.channel().localAddress(),
                    resp.status().code(), resp.status().reasonPhrase());
            ctx.writeAndFlush(resp);
        }).exceptionally(err -> {
            FullHttpResponse resp = HttpRequestProcessor.buildJsonErrorResponse(err);
            if (log.isDebugEnabled()) {
                log.debug("SchemaRegistry at {} request {} response {}", ctx.channel().localAddress(), request,
                        resp);
            }
            log.info("SchemaRegistry {} {} from {} response {} {}", request.method(), request.uri(),
                    ctx.channel().localAddress(),
                    resp.status().code(), resp.status().reasonPhrase());
            ctx.writeAndFlush(resp);
            return null;
        });
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        log.error("Unhandled error, closing connection to {}", ctx.channel(), cause);
        ctx.close();
    }
}