調錯-Nginx代理SpringBoot應用時報400 bad request

測試場景

使用Nginx代理SpringBoot應用，版本如下：
SpringBoot 2.1.3.RELEASE（內嵌tomcat9）
nginx-1.14.0

配置如下：

upstream code_server_pool{
	server 127.0.0.1:63049 weight=10;
   } 
 server{
	listen       80;
	server_name  www.pbteach.com;
   #驗證碼
	location ^~ /checkcode/ {  
		proxy_pass http://code_server_pool/checkcode/;  
	} 
	...

使用postman測試報錯

查看日誌：
nginx日誌：127.0.0.1 - - [08/May/2020:22:57:55 +0800] “POST /checkcode/getToken HTTP/1.1” 400 812 “-” “PostmanRuntime/7.1.1”

SpringBoot日誌如下：

java.lang.IllegalArgumentException: The character [_] is never valid in a domain name.
	at org.apache.tomcat.util.http.parser.HttpParser$DomainParseState.next(HttpParser.java:926)
	at org.apache.tomcat.util.http.parser.HttpParser.readHostDomainName(HttpParser.java:822)
	at org.apache.tomcat.util.http.parser.Host.parse(Host.java:71)
	at org.apache.tomcat.util.http.parser.Host.parse(Host.java:45)
	at org.apache.coyote.AbstractProcessor.parseHost(AbstractProcessor.java:288)
	at org.apache.coyote.http11.Http11Processor.prepareRequest(Http11Processor.java:809)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:384)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)

分析與解決

根據SpringBoot的報錯得知，下劃線字符“_”在域名中無效。
查看org.apache.tomcat.util.http.parser.HttpParser源碼：

 public DomainParseState next(int c) {
            if (HttpParser.isAlpha(c)) {
                return ALPHA;
            } else if (HttpParser.isNumeric(c)) {
                return NUMERIC;
            } else if (c == '.') {
                if (allowsPeriod) {
                    return PERIOD;
                } else {
                    throw new IllegalArgumentException(sm.getString(errorMsg,
                            Character.toString((char) c)));
                }
            } else if (c == ':') {
                if (allowsEnd) {
                    return COLON;
                } else {
                    throw new IllegalArgumentException(sm.getString(errorMsg,
                            Character.toString((char) c)));
                }
            } else if (c == -1) {
                if (allowsEnd) {
                    return END;
                } else {
                    throw new IllegalArgumentException(
                            sm.getString("http.invalidSegmentEndState", this.name()));
                }
            } else if (c == '-') {
                if (allowsHyphen) {
                    return HYPHEN;
                } else {
                    throw new IllegalArgumentException(sm.getString(errorMsg,
                            Character.toString((char) c)));
                }
            } else {
                throw new IllegalArgumentException(sm.getString(
                        "http.illegalCharacterDomain", Character.toString((char) c)));
            }

早期使用SpringBoot低版本時沒有此問題，升級SpringBoot後，內嵌的是Tomcat9版本，對域名的合法性進行校驗中，包含下劃線“_”則拋出異常。

修改nginx配置，將code_server_pool中的下劃線去掉，修改如下：

upstream codeserverpool{
	server 127.0.0.1:63049 weight=10;
   } 
 server{
	listen       80;
	server_name  www.pbteach.com;
   #驗證碼
	location ^~ /checkcode/ {  
		proxy_pass http://codeserverpool/checkcode/;  
	} 
	...

重啓nginx解決此問題。