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详解http报文（2）-web容器是如何解析http报文的

方丈的寺院

发布于 2019-10-13 14:41:02

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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 closed        CLOSED  // 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/response            if (_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 response                if (_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

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 CHUNKEDCONTENT -> CHUNKSIZE -> 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GET            final 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path            handlePath(buffer, currentState, builder);           // 处理版本            if (failed) {                handleHttpVersion(buffer, currentState, builder);                handleAfterVersion(buffer, currentState);            }            // 处理header            while (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);    }