RestTemplate 请求转发异常 ERR_CONTENT_DECODING_FAILED 200 (OK)

#1 问题描述

在基于Spring Boot的项目中实现了请求转发（使用 RestTemplate 的 exchange 方法）的功能，忽然在前端报net::ERR_CONTENT_DECODING_FAILED 200 (OK)的错误，后端及上游系统日志均显示请求已完成。

#2 原因探寻

上述错误字面意思为内容解码失败，就是说浏览器拿到后端数据后没办法正常解码。此时我们看看请求响应的编码

可以看到上游系统启用了响应压缩，然后中转系统读取方式为：

restTemplate.exchange(entity, String::class.java)

故当上游系统的响应启用压缩后，中转系统按String读取再返回给前端，浏览器拿到数据后通过响应头识别到是gzip编码则尝试解压，导致前面出现的异常。

#3 修复

要修复其实也很简单，在中转系统中用字节数组格式读取响应即可（兼容上游系统的各种格式的响应），完整代码如下：

class ServiceRoute {val logger = LoggerFactory.getLogger(javaClass)val restTemplate = RestTemplate().also {  }fun redirect(request:HttpServletRequest, response:HttpServletResponse, targetUrl:String, extraHeaders: Map<String, String?>?=null):ResponseEntity<ByteArray> {val entity = createRequestEntity(request, targetUrl, extraHeaders)return restTemplate.exchange(entity, ByteArray::class.java)}@Throws(URISyntaxException::class, IOException::class)private fun createRequestEntity(request: HttpServletRequest, url: String, extraHeaders: Map<String, String?>?): RequestEntity<*> {val httpMethod = HttpMethod.valueOf(request.method)val headers = parseRequestHeader(request)extraHeaders?.forEach { (k, v) -> headers.add(k, v) }//将原始请求转换为字节数组val body = StreamUtils.copyToByteArray(request.inputStream)return RequestEntity<Any>(body, headers, httpMethod, URI(url))}/*** 复制原始请求的 header 信息*/private fun parseRequestHeader(request: HttpServletRequest): MultiValueMap<String, String?> {val headers = HttpHeaders()val headerNames: List<String> = Collections.list(request.headerNames)for (headerName in headerNames) {val headerValues: List<String> = Collections.list(request.getHeaders(headerName))for (headerValue in headerValues) {headers.add(headerName, headerValue)}}return headers}
}

使用示例

@RequestMapping("route/**", name = "转发请求")
fun redirect(response:HttpServletResponse):ResponseEntity<*> {val path = request.servletPath.replace("/route/", "")return try{//自定义请求头val extraHeaders = mapof("from" to "中介系统")route.redirect( request, response, "http://localhost:8080/${path}", extraHeaders ).also {//此处可查看返回内容}}catch (e:Exception) {logger.error("[SERVICE-ROUTE] 转发失败", e)ResponseEntity(e.message, HttpStatus.INTERNAL_SERVER_ERROR)}finally {//此处可以做一些后续操作}
}