当SpringCloud中使用open feign调用其他服务时出现IO Exception too many bytes written的问题，

首先通过查看源码知道

HttpURLConnection#StreamingOutputStream

具体的报错地方：
@Override
        public void write (byte[] b, int off, int len) throws IOException {
            checkError();
            written += len;
            // 异常是由此处抛出的，主要是written的值大于期望的值。
            if (expected != -1L && written > expected) {
                out.close ();
                throw new IOException ("too many bytes written");
            }
            out.write (b, off, len);
        }

解决方案是实现RequestInterceptor接口，进行获取header的Content-Length，并特殊处理。

代码如下：

package com.example.integration.config;

import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;
import java.util.Enumeration;

/**
 * <p>
 *  feign透传header
 * </p>
 * @author example
 * @date 2021-05-26 22:16
 */
@Configuration
public class FeignConfiguration implements RequestInterceptor {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public void apply(RequestTemplate template) {
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder
                .getRequestAttributes();
        HttpServletRequest request = attributes.getRequest();
        Enumeration<String> headerNames = request.getHeaderNames();
        if (headerNames != null) {
            while (headerNames.hasMoreElements()) {
                String name = headerNames.nextElement();
                String values = request.getHeader(name);

				// 跳过 content-length，解决too many bites written的问题
				if (name.equalsIgnoreCase("content-length")){
					continue;
				}
				template.header(name, values);
            }
            logger.info("feign interceptor header:{}",template);
        }
    }
}

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