Repeatablely Read Message from Servlet Request

4 분 소요

1. Problem Context

HMAC 인증 필터를 구현하면서 다음 에러를 만났습니다.

실행 후 런타임에서 발생하는 에러 메시지

java.lang.IllegalStateException: getReader() has already been called for this request
    at org.apache.catalina.connector.Request.getInputStream(Request.java:1024) ~[tomcat-embed-core-10.1.10.jar:10.1.10]
    at org.apache.catalina.connector.RequestFacade.getInputStream(RequestFacade.java:298) ~[tomcat-embed-core-10.1.10.jar:10.1.10]
    at org.springframework.http.server.ServletServerHttpRequest.getBody(ServletServerHttpRequest.java:206) ~[spring-web-6.0.10.jar:6.0.10]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver$EmptyBodyCheckingHttpInputMessage.<init>(AbstractMessageConverterMethodArgumentResolver.java:323) ~[spring-webmvc-6.0.10.jar:6.0.10]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:172) ~[spring-webmvc-6.0.10.jar:6.0.10]
    ... 

테스트 실행 시 발생하는 에러 메시지

Request processing failed: java.lang.IllegalStateException: Cannot call getInputStream() after getReader() has already been called for the current request
jakarta.servlet.ServletException: Request processing failed: java.lang.IllegalStateException: Cannot call getInputStream() after getReader() has already been called for the current request
    at app//org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1019)
    at app//org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:914)
    ...

로그에서 볼 수 있듯이 요청(request) 객체에서 getReader() 메소드를 여러번 호출하여 에러가 발생합니다. HMAC 필터에서 application/json 형식의 데이터를 추출하는 작업을 수행했기 때문입니다.

@Component
public class HmacFilter extends OncePerRequestFilter {

    // ...

    private String getMessage(HttpServletRequest request) {
        try (BufferedReader reader = request.getReader()) {
            StringBuilder stringBuilder = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                stringBuilder.append(line);
            }
            return stringBuilder.toString();
        } catch (IOException ioException) {
            throw new RuntimeException(ioException);
        }
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request,
                                    HttpServletResponse response,
                                    FilterChain filterChain) throws ServletException, IOException {

        var message = getMessage(request);

        // ...

        filterChain.doFilter(request, response);
    }
}

getReader() 메소드를 호출하지 않게 우회하더라도 문제가 발생합니다.

InputStream 객체는 메시지를 읽을 때 인덱스를 사용해 바이트 배열의 읽은 위치를 지나가기 때문에 다시 읽지 못 합니다.
요청 객체에 담긴 메시지가 필터에서 소비되어 컨트롤러 영역까지 전달되지 못합니다.
- 요청 핸들러(request handler)에서 메시지가 누락되었다는 예외를 발생시킵니다.

@Component
public class HmacFilter extends OncePerRequestFilter {

    // ...

    private String getMessage(HttpServletRequest request) {
        try (
                OutputStream outputStream = new ByteArrayOutputStream();
                InputStream inputStream = request.getInputStream()
        ) {
            inputStream.transferTo(outputStream);
            return outputStream.toString();
        } catch (IOException ioException) {
            throw new RuntimeException(ioException);
        }
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request,
                                    HttpServletResponse response,
                                    FilterChain filterChain) throws ServletException, IOException {

        var message = getMessage(request);

        // ...

        filterChain.doFilter(request, response);
    }
}

요청 메시지를 필터에서 소비하기 때문에 서블릿 컨테이너에서 메시지를 보내지 않았다는 bad request(400)가 발생합니다.

$ ccurl -X POST http://localhost:8080/todos\
   -H 'Content-Type: application/json'\
   -d '{"content":"Hello World"}' | jq .

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   121    0    96  100    25    866    225 --:--:-- --:--:-- --:--:--  1163
{
  "timestamp": "2023-07-01T14:01:04.009+00:00",
  "status": 400,
  "error": "Bad Request",
  "path": "/todos"
}

테스트 실행 시 동일하게 bad request(400)가 발생합니다.

MockHttpServletRequest:
      HTTP Method = POST
      Request URI = /todos
       Parameters = {}
          Headers = [Content-Type:"application/json;charset=UTF-8", Content-Length:"32"]
             Body = {"id":0,"content":"Hello World"}
    Session Attrs = {}

Handler:
             Type = action.in.blog.TodoController
           Method = action.in.blog.TodoController#createTodo(Todo)

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = org.springframework.http.converter.HttpMessageNotReadableException

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 400
    Error message = null
          Headers = []
     Content type = null
             Body = 
    Forwarded URL = null
   Redirected URL = null
          Cookies = []

Status expected:<200> but was:<400>
Expected :200
Actual   :400

2. Solve the problem

문제 해결을 위해 HttpServletRequestWrapper 클래스를 상속 받은 요청 클래스를 생성합니다.

객체 생성시 메시지 인코딩 방법과 InputStream 객체에 저장된 원장(origin) 데이터를 필드에 저장합니다.
클라이언트(client)가 InputStream 객체나 Reader 객체를 요청하면 원장 데이터를 담은 객체를 전달합니다.

package action.in.blog;

import io.micrometer.common.util.StringUtils;
import jakarta.servlet.ReadListener;
import jakarta.servlet.ServletInputStream;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletRequestWrapper;

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

public class RepeatableReadRequest extends HttpServletRequestWrapper {

    private final Charset encoding;
    private final byte[] rawBytes;

    public RepeatableReadRequest(HttpServletRequest request) {
        super(request);
        String characterEncoding = request.getCharacterEncoding();
        if (StringUtils.isBlank(characterEncoding)) {
            characterEncoding = StandardCharsets.UTF_8.name();
        }
        encoding = Charset.forName(characterEncoding);
        try {
            rawBytes = request.getInputStream().readAllBytes();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        var byteInputStream = new ByteArrayInputStream(rawBytes);
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener listener) {
            }

            @Override
            public int read() throws IOException {
                return byteInputStream.read();
            }
        };
    }

    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(this.getInputStream(), this.encoding));
    }
}

위 요청 객체를 래핑할 수 있는 클래스를 필터에서 사용합니다.

요청 객체를 위에서 생성한 RepeatableReadRequest 클래스로 감쌉니다.
래핑된 객체를 사용해 메시지를 추출합니다.
래핑된 객체를 필터 체인(filter chain)에 전달합니다.

@Component
public class HmacFilter extends OncePerRequestFilter {

    // ...

    private String getMessage(HttpServletRequest request) {
        try (
                OutputStream outputStream = new ByteArrayOutputStream();
                InputStream inputStream = request.getInputStream()
        ) {
            inputStream.transferTo(outputStream);
            return outputStream.toString();
        } catch (IOException ioException) {
            throw new RuntimeException(ioException);
        }
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request,
                                    HttpServletResponse response,
                                    FilterChain filterChain) throws ServletException, IOException {
        var wrappedRequest = new RepeatableReadRequest(request);
        var message = getMessage(wrappedRequest);

        // ...

        filterChain.doFilter(wrappedRequest, response);
    }
}

Result

위 방법으로 해당 문제를 해결하면 정상적으로 요청 메시지가 전달됩니다.

$ curl -X POST http://localhost:8080/todos\
   -H 'Content-Type: application/json'\
   -d '{"content":"Hello World"}' | jq .

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    60    0    35  100    25   4490   3207 --:--:-- --:--:-- --:--:-- 30000
{
  "id": 1000,
  "content": "Hello World"
}

CLOSING

전체 구현 코드를 확인하시려면 HMAC(Hash-based Message Authentication Code) 포스트를 참고하시길 바랍니다.

TEST CODE REPOSITORY

https://github.com/Junhyunny/blog-in-action/tree/master/2023-06-28-hmac

HMAC(Hash-based Message Authentication Code)

REFERENCE

Twitter Facebook LinkedIn

강준현

Repeatablely Read Message from Servlet Request

1. Problem Context

2. Solve the problem

Result

CLOSING

TEST CODE REPOSITORY

REFERENCE

공유하기

댓글남기기

참고

Memory leak by detached DOM elements in React

Mark-and-sweep algorithm for garbage collect

Reference counting algorithm for garbage collect

Socket Identificaiton

강준현

1. Problem Context

2. Solve the problem

Result

CLOSING

TEST CODE REPOSITORY

RECOMMEND NEXT POSTS

REFERENCE

공유하기

댓글남기기

참고

Memory leak by detached DOM elements in React

Mark-and-sweep algorithm for garbage collect

Reference counting algorithm for garbage collect

Socket Identificaiton