解析 http 请求 header 错误_详解http报文（2）-web容器是如何解析http报文的

摘要

在详解http报文一文中，详细介绍了http报文的文本结构。那么作为服务端，web容器是如何解析http报文的呢？本文以jetty和undertow容器为例，来解析web容器是如何处理http报文的。

在前文中我们从概览中可以了解到，http报文其实就是一定规则的字符串，那么解析它们，就是解析字符串，看看是否满足http协议约定的规则。

start-line: 起始行,描述请求或响应的基本信息*( header-field CRLF ): 头CRLF[message-body]: 消息body，实际传输的数据

jetty

以下代码都是jetty9.4.12版本

如何解析这么长的字符串呢，jetty是通过状态机来实现的。具体可以看下org.eclipse.jetty.http.HttpParse类

public enum State{START,METHOD,![](https://user-gold-cdn.xitu.io/2019/10/9/16db0a55c99520eb?w=1202&h=630&f=png&s=101034),SPACE1,STATUS,URI,SPACE2,REQUEST_VERSION,REASON,PROXY,HEADER,CONTENT,EOF_CONTENT,CHUNKED_CONTENT,CHUNK_SIZE,CHUNK_PARAMS,CHUNK,TRAILER,END,CLOSE,  // The associated stream/endpoint should be closedCLOSED  // The associated stream/endpoint is at EOF}

总共分成了21种状态，然后进行状态间的流转。在parseNext方法中分别对起始行 -> header -> body content分别解析

public boolean parseNext(ByteBuffer buffer){try{// Start a request/responseif (_state==State.START){// 快速判断if (quickStart(buffer))return true;}// Request/response line 转换if (_state.ordinal()>= State.START.ordinal() && _state.ordinal()<State.HEADER.ordinal()){if (parseLine(buffer))return true;}// headers转换if (_state== State.HEADER){if (parseFields(buffer))return true;}// content转换if (_state.ordinal()>= State.CONTENT.ordinal() && _state.ordinal()<State.TRAILER.ordinal()){// Handle HEAD responseif (_responseStatus>0 && _headResponse){setState(State.END);return handleContentMessage();}else{if (parseContent(buffer))return true;}}return false;}

整体流程

整体有三条路径

开始 -> start-line -> header -> 结束
开始 -> start-line -> header -> content -> 结束
开始 -> start-line -> header -> chunk-content -> 结束

起始行

start-line = request-line(请求起始行）/（响应起始行）status-line

1. 请求报文解析状态迁移请求行：START -> METHOD -> SPACE1 -> URI -> SPACE2 -> REQUEST_VERSION

响应报文解析状态迁移响应行：START -> RESPONSE_VERSION -> SPACE1 -> STATUS -> SPACE2 -> REASON

header 头

HEADER 的状态只有一种了，在jetty的老版本中还区分了HEADER_IN_NAM, HEADER_VALUE, HEADER_IN_VALUE等，9.4中都去除了。为了提高匹配效率，jetty使用了Trie树快速匹配header头。

static{CACHE.put(new HttpField(HttpHeader.CONNECTION,HttpHeaderValue.CLOSE));CACHE.put(new HttpField(HttpHeader.CONNECTION,HttpHeaderValue.KEEP_ALIVE));// 以下省略了很多了通用header头

content

请求体：

CONTENT -> END，这种是普通的带Content-Length头的报文，HttpParser一直运行CONTENT状态，直到最后ContentLength达到了指定的数量，则进入END状态
chunked分块传输的数据 CHUNKED_CONTENT -> CHUNK_SIZE -> CHUNK -> CHUNK_END -> END

undertow

undertow是另一种web容器，它的处理方式与jetty有什么不同呢状态机种类不一样了，io.undertow.util.HttpString.ParseState

public static final int VERB = 0;public static final int PATH = 1;public static final int PATH_PARAMETERS = 2;public static final int QUERY_PARAMETERS = 3;public static final int VERSION = 4;public static final int AFTER_VERSION = 5;public static final int HEADER = 6;public static final int HEADER_VALUE = 7;public static final int PARSE_COMPLETE = 8;

具体处理流程在HttpRequestParser抽象类中

public void handle(ByteBuffer buffer, final ParseState currentState, final HttpServerExchange builder) throws BadRequestException {if (currentState.state == ParseState.VERB) {//fast path, we assume that it will parse fully so we avoid all the if statements// 快速处理GETfinal int position = buffer.position();if (buffer.remaining() > 3&& buffer.get(position) == 'G'&& buffer.get(position + 1) == 'E'&& buffer.get(position + 2) == 'T'&& buffer.get(position + 3) == ' ') {buffer.position(position + 4);builder.setRequestMethod(Methods.GET);currentState.state = ParseState.PATH;} else {try {handleHttpVerb(buffer, currentState, builder);} catch (IllegalArgumentException e) {throw new BadRequestException(e);}}// 处理pathhandlePath(buffer, currentState, builder);// 处理版本if (failed) {handleHttpVersion(buffer, currentState, builder);handleAfterVersion(buffer, currentState);}// 处理headerwhile (currentState.state != ParseState.PARSE_COMPLETE && buffer.hasRemaining()) {handleHeader(buffer, currentState, builder);if (currentState.state == ParseState.HEADER_VALUE) {handleHeaderValue(buffer, currentState, builder);}}return;}handleStateful(buffer, currentState, builder);}

与jetty不同的是对content的处理，在header处理完以后，将数据放到io.undertow.server.HttpServerExchange,然后根据类型，有不同的content读取方式，比如处理固定长度的，FixedLengthStreamSourceConduit。

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参考

http://www.blogjava.net/DLevin/archive/2014/04/19/411673.html

https://www.ph0ly.com/2018/10/06/jetty/connection/http-parser/

https://webtide.com/http-trailers-in-jetty/

http://undertow.io/undertow-docs/undertow-docs-2.0.0/