[FIXED] set content range in spring

Issue

I have many resting api in my spring boot application.

@GetMapping("lc/all")
    List<LC> getAll()
    {
        return lcRepository.findAll();
    }

Mainly they are sending list.

Now for some reason, I have to receive the length of the response. Changing for each and every method would be tedious.

How can I set Content-Range for each method automatically.

I have modified the CORS:

    @Bean
    public WebMvcConfigurer corsConfigurer() {
        return new WebMvcConfigurer() {
            @Override
            public void addCorsMappings(CorsRegistry registry) {
                registry
                        .addMapping("/**")
                        .allowedOrigins("http://localhost:5000")
                        .exposedHeaders("Content-Range");
            }
        };
    }

Solution

First you need a filter that writes only the requested range part as a response when range header is present.

package com.example.contentrange;

import static java.nio.charset.StandardCharsets.UTF_8;
import static javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT;
import static javax.servlet.http.HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE;

import java.io.IOException;
import java.util.Arrays;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.http.HttpRange;
import org.springframework.web.util.ContentCachingResponseWrapper;

@WebFilter("/*")
public class AddResponseHeaderFilter implements Filter {

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    HttpServletRequest httpServletRequest = (HttpServletRequest) request;

    var rangeHeader = httpServletRequest.getHeader("Range");

    // if there is no range request in the header than do the "normal" filtering
    if (rangeHeader == null) {
      chain.doFilter(request, response);
      return;
    }

    HttpRange range = HttpRange.parseRanges(rangeHeader).get(0);

    ContentCachingResponseWrapper responseWrapper =
        new ContentCachingResponseWrapper((HttpServletResponse) response);

    try {
      chain.doFilter(request, responseWrapper);
    } finally {
      byte[] copy = responseWrapper.getContentAsByteArray();
      int size = responseWrapper.getContentSize();
      int lower = (int) range.getRangeStart(size);
      int upper = (int) range.getRangeEnd(size);
      if (lower <= size) {
        responseWrapper.setStatus(SC_PARTIAL_CONTENT);
        byte[] subArray = Arrays.copyOfRange(copy, lower, upper + 1);
        String newContent = new String(subArray, UTF_8);
        responseWrapper.reset();
        responseWrapper.setHeader(
            "Content-Range", String.format("bytes %d-%d/%d", lower, upper, size));
        responseWrapper.setContentLength(newContent.length());
        responseWrapper.getWriter().write(newContent);
        responseWrapper.getWriter().flush();
        responseWrapper.flushBuffer();
        responseWrapper.copyBodyToResponse();
      } else {
        responseWrapper.setStatus(SC_REQUESTED_RANGE_NOT_SATISFIABLE);
      }
    }
  }
}

Second you need to add org.springframework.boot.web.servlet.ServletComponentScan annotation to your application class.

@ServletComponentScan
@SpringBootApplication
public class ContentRangeApplication {

    public static void main(String[] args) {
        SpringApplication.run(ContentRangeApplication.class, args);
    }

}

For more info on Range: https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests

Answered By - balazs
Answer Checked By - Pedro (JavaFixing Volunteer)