nacos中DistroFilter的作用是什么

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CanDistro

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/web/CanDistro.java

@Retention(RetentionPolicy.RUNTIME)
public @interface CanDistro {
}

• CanDistro用于标识一个方法需要判断是否应该根据distro被重定向

DistroFilter

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/web/DistroFilter.java

public class DistroFilter implements Filter {

    private static final int PROXY_CONNECT_TIMEOUT = 2000;
    private static final int PROXY_READ_TIMEOUT = 2000;

    @Autowired
    private DistroMapper distroMapper;

    @Autowired
    private SwitchDomain switchDomain;

    @Autowired
    private FilterBase filterBase;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;

        String urlString = req.getRequestURI();

        if (StringUtils.isNotBlank(req.getQueryString())) {
            urlString += "?" + req.getQueryString();
        }

        try {
            String path = new URI(req.getRequestURI()).getPath();
            String serviceName = req.getParameter(CommonParams.SERVICE_NAME);
            // For client under 0.8.0:
            if (StringUtils.isBlank(serviceName)) {
                serviceName = req.getParameter("dom");
            }
            Method method = filterBase.getMethod(req.getMethod(), path);

            if (method == null) {
                throw new NoSuchMethodException(req.getMethod() + " " + path);
            }

            String groupName = req.getParameter(CommonParams.GROUP_NAME);
            if (StringUtils.isBlank(groupName)) {
                groupName = Constants.DEFAULT_GROUP;
            }

            // use groupName@@serviceName as new service name:
            String groupedServiceName = serviceName;
            if (StringUtils.isNotBlank(serviceName) && !serviceName.contains(Constants.SERVICE_INFO_SPLITER)) {
                groupedServiceName = groupName + Constants.SERVICE_INFO_SPLITER + serviceName;
            }

            // proxy request to other server if necessary:
            if (method.isAnnotationPresent(CanDistro.class) && !distroMapper.responsible(groupedServiceName)) {

                String userAgent = req.getHeader("User-Agent");

                if (StringUtils.isNotBlank(userAgent) && userAgent.contains(UtilsAndCommons.NACOS_SERVER_HEADER)) {
                    // This request is sent from peer server, should not be redirected again:
                    Loggers.SRV_LOG.error("receive invalid redirect request from peer {}", req.getRemoteAddr());
                    resp.sendError(HttpServletResponse.SC_BAD_REQUEST,
                        "receive invalid redirect request from peer " + req.getRemoteAddr());
                    return;
                }

                List headerList = new ArrayList<>(16);
                Enumeration headers = req.getHeaderNames();
                while (headers.hasMoreElements()) {
                    String headerName = headers.nextElement();
                    headerList.add(headerName);
                    headerList.add(req.getHeader(headerName));
                }
                HttpClient.HttpResult result =
                    HttpClient.request("http://" + distroMapper.mapSrv(groupedServiceName) + urlString, headerList,
                        StringUtils.isBlank(req.getQueryString()) ? HttpClient.translateParameterMap(req.getParameterMap()) : new HashMap<>(2)
                        , PROXY_CONNECT_TIMEOUT, PROXY_READ_TIMEOUT, "UTF-8", req.getMethod());

                try {
                    resp.setCharacterEncoding("UTF-8");
                    resp.getWriter().write(result.content);
                    resp.setStatus(result.code);
                } catch (Exception ignore) {
                    Loggers.SRV_LOG.warn("[DISTRO-FILTER] request failed: " + distroMapper.mapSrv(groupedServiceName) + urlString);
                }
                return;
            }

            OverrideParameterRequestWrapper requestWrapper = OverrideParameterRequestWrapper.buildRequest(req);
            requestWrapper.addParameter(CommonParams.SERVICE_NAME, groupedServiceName);
            filterChain.doFilter(requestWrapper, resp);
        } catch (AccessControlException e) {
            resp.sendError(HttpServletResponse.SC_FORBIDDEN, "access denied: " + UtilsAndCommons.getAllExceptionMsg(e));
            return;
        } catch (NoSuchMethodException e) {
            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, "no such api: " + e.getMessage());
            return;
        } catch (Exception e) {
            resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
                "Server failed," + UtilsAndCommons.getAllExceptionMsg(e));
            return;
        }

    }

    @Override
    public void destroy() {

    }
}

• DistroFilter实现了servlet的Filter接口；其doFilter方法会从servletRequest中读取serviceName、method、groupName等，然后判断method是否标注CanDistro，如果是而且distroMapper不负责该service则构建http请求然后将结果写回Filter；如果不需要重定向则继续filterChain.doFilter

HttpClient.request

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/misc/HttpClient.java

public class HttpClient {
    private static final int TIME_OUT_MILLIS = 10000;
    private static final int CON_TIME_OUT_MILLIS = 5000;

    private static AsyncHttpClient asyncHttpClient;

    private static CloseableHttpClient postClient;

    //......

    public static HttpResult request(String url, List headers, Map paramValues, int connectTimeout, int readTimeout, String encoding, String method) {
        HttpURLConnection conn = null;
        try {
            String encodedContent = encodingParams(paramValues, encoding);
            url += (null == encodedContent) ? "" : ("?" + encodedContent);

            conn = (HttpURLConnection) new URL(url).openConnection();
            conn.setConnectTimeout(connectTimeout);
            conn.setReadTimeout(readTimeout);
            conn.setRequestMethod(method);

            conn.addRequestProperty("Client-Version", UtilsAndCommons.SERVER_VERSION);
            conn.addRequestProperty("User-Agent", UtilsAndCommons.SERVER_VERSION);
            setHeaders(conn, headers, encoding);
            conn.connect();

            return getResult(conn);
        } catch (Exception e) {
            Loggers.SRV_LOG.warn("Exception while request: {}, caused: {}", url, e);
            return new HttpResult(500, e.toString(), Collections.emptyMap());
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
    }

    private static HttpResult getResult(HttpURLConnection conn) throws IOException {
        int respCode = conn.getResponseCode();

        InputStream inputStream;
        if (HttpURLConnection.HTTP_OK == respCode) {
            inputStream = conn.getInputStream();
        } else {
            inputStream = conn.getErrorStream();
        }

        Map respHeaders = new HashMap(conn.getHeaderFields().size());
        for (Map.Entry> entry : conn.getHeaderFields().entrySet()) {
            respHeaders.put(entry.getKey(), entry.getValue().get(0));
        }

        String gzipEncoding = "gzip";

        if (gzipEncoding.equals(respHeaders.get(HttpHeaders.CONTENT_ENCODING))) {
            inputStream = new GZIPInputStream(inputStream);
        }

        HttpResult result = new HttpResult(respCode, IOUtils.toString(inputStream, getCharset(conn)), respHeaders);
        inputStream.close();

        return result;
    }

    public static class HttpResult {
        final public int code;
        final public String content;
        final private Map respHeaders;

        public HttpResult(int code, String content, Map respHeaders) {
            this.code = code;
            this.content = content;
            this.respHeaders = respHeaders;
        }

        public String getHeader(String name) {
            return respHeaders.get(name);
        }
    }

    //......
}

• HttpClient的request方法直接使用jdk的HttpURLConnection进行请求，返回结果封装为HttpResult，其content即为响应的body

小结

DistroFilter实现了servlet的Filter接口；其doFilter方法会从servletRequest中读取serviceName、method、groupName等，然后判断method是否标注CanDistro，如果是而且distroMapper不负责该service则构建http请求然后将结果写回Filter；如果不需要重定向则继续filterChain.doFilter

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