Explain HTTP message (2) - how web container parses HTTP message

Abbot's temple 2020-11-13 05:41:10
explain http message web container


stay Detailed explanation http message In the article , In detail http The text structure of the message . So as a server ,web How does the container parse http What about the message ? This article takes jetty and undertow Container as an example , Parsing web How does the container handle http The message .

We can learn from the overview in the previous article ,http A message is a regular string , So parse them , It's parsing strings , See if you are satisfied http The rules of the agreement .

start-line: Start line , Basic information describing the request or response
*( header-field CRLF ): head
[message-body]: news body, Data actually transmitted


The following code is jetty9.4.12 edition

How to parse such a long string ,jetty It is realized by state machine . You can look at it org.eclipse.jetty.http.HttpParse class

 public enum State
CLOSE, // The associated stream/endpoint should be closed
CLOSED // The associated stream/endpoint is at EOF

It's divided into 21 States , And then the flow of States . stay parseNext Method for the starting line -> header -> body content Resolve separately

public boolean parseNext(ByteBuffer buffer)
// Start a request/response
if (_state==State.START)
// Quick judgment
if (quickStart(buffer))
return true;
// Request/response line transformation
if (_state.ordinal()>= State.START.ordinal() && _state.ordinal()<State.HEADER.ordinal())
if (parseLine(buffer))
return true;
// headers transformation
if (_state== State.HEADER)
if (parseFields(buffer))
return true;
// content transformation
if (_state.ordinal()>= State.CONTENT.ordinal() && _state.ordinal()<State.TRAILER.ordinal())
// Handle HEAD response
if (_responseStatus>0 && _headResponse)
return handleContentMessage();
if (parseContent(buffer))
return true;
return false;

Overall process

As a whole, there are three paths

  1. Start -> start-line -> header -> end
  2. Start -> start-line -> header -> content -> end
  3. Start -> start-line -> header -> chunk-content -> end

Start line

start-line = request-line( Request start line )/( Response start line )status-line

  1. Request message parsing state migration
    Request line :START -> METHOD -> SPACE1 -> URI -> SPACE2 -> REQUEST_VERSION

  2. Response message parsing state migration

header head

HEADER There is only one state , stay jetty There is also a distinction between HEADER_IN_NAM, HEADER_VALUE, HEADER_IN_VALUE etc. ,9.4 All of them have been removed . In order to improve the matching efficiency ,jetty Used Trie Tree quick match header head .

CACHE.put(new HttpField(HttpHeader.CONNECTION,HttpHeaderValue.CLOSE));
CACHE.put(new HttpField(HttpHeader.CONNECTION,HttpHeaderValue.KEEP_ALIVE));
// A lot of generalities are omitted below header head


Request body :

  1. CONTENT -> END, This is a normal belt Content-Length Header message ,HttpParser Has been running CONTENT state , Until the last ContentLength Reached the specified number , entering END state
  2. chunked Data transmitted in blocks


undertow It's another kind of web Containers , How it's handled and jetty What's the difference
There are different kinds of state machines ,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;

The specific processing flow is HttpRequestParser In an abstract class

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
// Rapid processing 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);
currentState.state = ParseState.PATH;
} else {
try {
handleHttpVerb(buffer, currentState, builder);
} catch (IllegalArgumentException e) {
throw new BadRequestException(e);
// Handle path
handlePath(buffer, currentState, builder);
// Processing version
if (failed) {
handleHttpVersion(buffer, currentState, builder);
handleAfterVersion(buffer, currentState);
// Handle header
while (currentState.state != ParseState.PARSE_COMPLETE && buffer.hasRemaining()) {
handleHeader(buffer, currentState, builder);
if (currentState.state == ParseState.HEADER_VALUE) {
handleHeaderValue(buffer, currentState, builder);
handleStateful(buffer, currentState, builder);

And jetty The difference is right content To deal with , stay header After processing , Place data in io.undertow.server.HttpServerExchange, Then according to the type , Different content Read mode , For example, deal with fixed length ,FixedLengthStreamSourceConduit.

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Reference resources





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