一、背景
在本打算写一篇关于identityserver4 的文章时候，却发现自己对endpoint -终结点路由还不是很了解，故暂时先放弃了identityserver4 的研究和编写；所以才产生了今天这篇关于endpoint (终结点路由) 的文章。
还是跟往常一样，打开电脑使用强大的google 和百度搜索引擎查阅相关资料，以及打开asp.net core 3.1 的源代码进行拜读，同时终于在我的实践及测试中对endpoint 有了不一样的认识，说到这里更加敬佩微软对asp.net core 3.x 的框架中管道模型的设计。
我先来提出以下几个问题：
- 当访问一个web 应用地址时，asp.net core 是怎么执行到
controller的action的呢？ endpoint跟普通路由又存在着什么样的关系？userouting()、useauthorization()、userendpoints()这三个中间件的关系是什么呢？- 怎么利用
endpoint终结者路由来拦截action 的执行并且记录相关操作日志？(时间有限，下一篇文章再来分享整理)
二、拜读源码解惑
startup 代码
我们先来看一下startup中简化版的代码，代码如下：
public void configureservices(iservicecollection services)
{
services.addcontrollers();
}
public void configure(iapplicationbuilder app, iwebhostenvironment env)
{
app.userouting();
app.useauthorization();
app.useendpoints(endpoints =>
{
endpoints.mapcontrollers();
});
}
程序启动阶段：
- 第一步：执行services.addcontrollers()
将controller的核心服务注册到容器中去 - 第二步：执行app.userouting()
将endpointroutingmiddleware中间件注册到http管道中 - 第三步：执行app.useauthorization()
将authorizationmiddleware中间件注册到http管道中 - 第四步：执行app.useendpoints(encpoints=>endpoints.mapcontrollers())
有两个主要的作用：
调用endpoints.mapcontrollers()将本程序集定义的所有controller和action转换为一个个的endpoint放到路由中间件的配置对象routeoptions中
将endpointmiddleware中间件注册到http管道中
app.userouting() 源代码如下：
public static iapplicationbuilder userouting(this iapplicationbuilder builder)
{
if (builder == null)
{
throw new argumentnullexception(nameof(builder));
}
verifyroutingservicesareregistered(builder);
var endpointroutebuilder = new defaultendpointroutebuilder(builder);
builder.properties[endpointroutebuilder] = endpointroutebuilder;
return builder.usemiddleware<endpointroutingmiddleware>(endpointroutebuilder);
}
endpointroutingmiddleware 中间件代码如下：
internal sealed class endpointroutingmiddleware
{
private const string diagnosticsendpointmatchedkey = "microsoft.aspnetcore.routing.endpointmatched";
private readonly matcherfactory _matcherfactory;
private readonly ilogger _logger;
private readonly endpointdatasource _endpointdatasource;
private readonly diagnosticlistener _diagnosticlistener;
private readonly requestdelegate _next;
private task<matcher> _initializationtask;
public endpointroutingmiddleware(
matcherfactory matcherfactory,
ilogger<endpointroutingmiddleware> logger,
iendpointroutebuilder endpointroutebuilder,
diagnosticlistener diagnosticlistener,
requestdelegate next)
{
if (endpointroutebuilder == null)
{
throw new argumentnullexception(nameof(endpointroutebuilder));
}
_matcherfactory = matcherfactory ?? throw new argumentnullexception(nameof(matcherfactory));
_logger = logger ?? throw new argumentnullexception(nameof(logger));
_diagnosticlistener = diagnosticlistener ?? throw new argumentnullexception(nameof(diagnosticlistener));
_next = next ?? throw new argumentnullexception(nameof(next));
_endpointdatasource = new compositeendpointdatasource(endpointroutebuilder.datasources);
}
public task invoke(httpcontext httpcontext)
{
// there's already an endpoint, skip maching completely
var endpoint = httpcontext.getendpoint();
if (endpoint != null)
{
log.matchskipped(_logger, endpoint);
return _next(httpcontext);
}
// there's an inherent race condition between waiting for init and accessing the matcher
// this is ok because once `_matcher` is initialized, it will not be set to null again.
var matchertask = initializeasync();
if (!matchertask.iscompletedsuccessfully)
{
return awaitmatcher(this, httpcontext, matchertask);
}
var matchtask = matchertask.result.matchasync(httpcontext);
if (!matchtask.iscompletedsuccessfully)
{
return awaitmatch(this, httpcontext, matchtask);
}
return setroutingandcontinue(httpcontext);
// awaited fallbacks for when the tasks do not synchronously complete
static async task awaitmatcher(endpointroutingmiddleware middleware, httpcontext httpcontext, task<matcher> matchertask)
{
var matcher = await matchertask;
await matcher.matchasync(httpcontext);
await middleware.setroutingandcontinue(httpcontext);
}
static async task awaitmatch(endpointroutingmiddleware middleware, httpcontext httpcontext, task matchtask)
{
await matchtask;
await middleware.setroutingandcontinue(httpcontext);
}
}
[methodimpl(methodimploptions.aggressiveinlining)]
private task setroutingandcontinue(httpcontext httpcontext)
{
// if there was no mutation of the endpoint then log failure
var endpoint = httpcontext.getendpoint();
if (endpoint == null)
{
log.matchfailure(_logger);
}
else
{
// raise an event if the route matched
if (_diagnosticlistener.isenabled() && _diagnosticlistener.isenabled(diagnosticsendpointmatchedkey))
{
// we're just going to send the httpcontext since it has all of the relevant information
_diagnosticlistener.write(diagnosticsendpointmatchedkey, httpcontext);
}
log.matchsuccess(_logger, endpoint);
}
return _next(httpcontext);
}
// initialization is async to avoid blocking threads while reflection and things
// of that nature take place.
//
// we've seen cases where startup is very slow if we allow multiple threads to race
// while initializing the set of endpoints/routes. doing cpu intensive work is a
// blocking operation if you have a low core count and enough work to do.
private task<matcher> initializeasync()
{
var initializationtask = _initializationtask;
if (initializationtask != null)
{
return initializationtask;
}
return initializecoreasync();
}
private task<matcher> initializecoreasync()
{
var initialization = new taskcompletionsource<matcher>(taskcreationoptions.runcontinuationsasynchronously);
var initializationtask = interlocked.compareexchange(ref _initializationtask, initialization.task, null);
if (initializationtask != null)
{
// this thread lost the race, join the existing task.
return initializationtask;
}
// this thread won the race, do the initialization.
try
{
var matcher = _matcherfactory.creatematcher(_endpointdatasource);
// now replace the initialization task with one created with the default execution context.
// this is important because capturing the execution context will leak memory in asp.net core.
using (executioncontext.suppressflow())
{
_initializationtask = task.fromresult(matcher);
}
// complete the task, this will unblock any requests that came in while initializing.
initialization.setresult(matcher);
return initialization.task;
}
catch (exception ex)
{
// allow initialization to occur again. since datasources can change, it's possible
// for the developer to correct the data causing the failure.
_initializationtask = null;
// complete the task, this will throw for any requests that came in while initializing.
initialization.setexception(ex);
return initialization.task;
}
}
private static class log
{
private static readonly action<ilogger, string, exception> _matchsuccess = loggermessage.define<string>(
loglevel.debug,
new eventid(1, "matchsuccess"),
"request matched endpoint '{endpointname}'");
private static readonly action<ilogger, exception> _matchfailure = loggermessage.define(
loglevel.debug,
new eventid(2, "matchfailure"),
"request did not match any endpoints");
private static readonly action<ilogger, string, exception> _matchingskipped = loggermessage.define<string>(
loglevel.debug,
new eventid(3, "matchingskipped"),
"endpoint '{endpointname}' already set, skipping route matching.");
public static void matchsuccess(ilogger logger, endpoint endpoint)
{
_matchsuccess(logger, endpoint.displayname, null);
}
public static void matchfailure(ilogger logger)
{
_matchfailure(logger, null);
}
public static void matchskipped(ilogger logger, endpoint endpoint)
{
_matchingskipped(logger, endpoint.displayname, null);
}
}
}
我们从它的源码中可以看到，endpointroutingmiddleware中间件先是创建matcher，然后调用matcher.matchasync(httpcontext)去寻找endpoint，最后通过httpcontext.getendpoint()验证了是否已经匹配到了正确的endpoint并交个下个中间件继续执行！
app.useendpoints() 源代码
public static iapplicationbuilder useendpoints(this iapplicationbuilder builder, action<iendpointroutebuilder> configure)
{
if (builder == null)
{
throw new argumentnullexception(nameof(builder));
}
if (configure == null)
{
throw new argumentnullexception(nameof(configure));
}
verifyroutingservicesareregistered(builder);
verifyendpointroutingmiddlewareisregistered(builder, out var endpointroutebuilder);
configure(endpointroutebuilder);
// yes, this mutates an ioptions. we're registering data sources in a global collection which
// can be used for discovery of endpoints or url generation.
//
// each middleware gets its own collection of data sources, and all of those data sources also
// get added to a global collection.
var routeoptions = builder.applicationservices.getrequiredservice<ioptions<routeoptions>>();
foreach (var datasource in endpointroutebuilder.datasources)
{
routeoptions.value.endpointdatasources.add(datasource);
}
return builder.usemiddleware<endpointmiddleware>();
}
internal class defaultendpointroutebuilder : iendpointroutebuilder
{
public defaultendpointroutebuilder(iapplicationbuilder applicationbuilder)
{
applicationbuilder = applicationbuilder ?? throw new argumentnullexception(nameof(applicationbuilder));
datasources = new list<endpointdatasource>();
}
public iapplicationbuilder applicationbuilder { get; }
public iapplicationbuilder createapplicationbuilder() => applicationbuilder.new();
public icollection<endpointdatasource> datasources { get; }
public iserviceprovider serviceprovider => applicationbuilder.applicationservices;
}
代码中构建了defaultendpointroutebuilder 终结点路由构建者对象，该对象中存储了endpoint的集合数据；同时把终结者路由集合数据存储在了routeoptions 中，并注册了endpointmiddleware 中间件到http管道中；
endpoint对象代码如下：
/// <summary>
/// represents a logical endpoint in an application.
/// </summary>
public class endpoint
{
/// <summary>
/// creates a new instance of <see cref="endpoint"/>.
/// </summary>
/// <param name="requestdelegate">the delegate used to process requests for the endpoint.</param>
/// <param name="metadata">
/// the endpoint <see cref="endpointmetadatacollection"/>. may be null.
/// </param>
/// <param name="displayname">
/// the informational display name of the endpoint. may be null.
/// </param>
public endpoint(
requestdelegate requestdelegate,
endpointmetadatacollection metadata,
string displayname)
{
// all are allowed to be null
requestdelegate = requestdelegate;
metadata = metadata ?? endpointmetadatacollection.empty;
displayname = displayname;
}
/// <summary>
/// gets the informational display name of this endpoint.
/// </summary>
public string displayname { get; }
/// <summary>
/// gets the collection of metadata associated with this endpoint.
/// </summary>
public endpointmetadatacollection metadata { get; }
/// <summary>
/// gets the delegate used to process requests for the endpoint.
/// </summary>
public requestdelegate requestdelegate { get; }
public override string tostring() => displayname ?? base.tostring();
}
endpoint 对象代码中有两个关键类型属性分别是endpointmetadatacollection 类型和requestdelegate：
- endpointmetadatacollection：存储了
controller和action相关的元素集合，包含action上的attribute特性数据等 requestdelegate：存储了action 也即委托，这里是每一个controller 的action 方法
再回过头来看看endpointmiddleware 中间件和核心代码，endpointmiddleware 的一大核心代码主要是执行endpoint 的requestdelegate 委托，也即controller 中的action 的执行。
public task invoke(httpcontext httpcontext)
{
var endpoint = httpcontext.getendpoint();
if (endpoint?.requestdelegate != null)
{
if (!_routeoptions.suppresscheckforunhandledsecuritymetadata)
{
if (endpoint.metadata.getmetadata<iauthorizedata>() != null &&
!httpcontext.items.containskey(authorizationmiddlewareinvokedkey))
{
throwmissingauthmiddlewareexception(endpoint);
}
if (endpoint.metadata.getmetadata<icorsmetadata>() != null &&
!httpcontext.items.containskey(corsmiddlewareinvokedkey))
{
throwmissingcorsmiddlewareexception(endpoint);
}
}
log.executingendpoint(_logger, endpoint);
try
{
var requesttask = endpoint.requestdelegate(httpcontext);
if (!requesttask.iscompletedsuccessfully)
{
return awaitrequesttask(endpoint, requesttask, _logger);
}
}
catch (exception exception)
{
log.executedendpoint(_logger, endpoint);
return task.fromexception(exception);
}
log.executedendpoint(_logger, endpoint);
return task.completedtask;
}
return _next(httpcontext);
static async task awaitrequesttask(endpoint endpoint, task requesttask, ilogger logger)
{
try
{
await requesttask;
}
finally
{
log.executedendpoint(logger, endpoint);
}
}
}
疑惑解答：
1. 当访问一个web 应用地址时，asp.net core 是怎么执行到controller 的action的呢？
答：程序启动的时候会把所有的controller 中的action 映射存储到routeoptions 的集合中，action 映射成endpoint终结者 的requestdelegate 委托属性，最后通过useendpoints 添加endpointmiddleware 中间件进行执行，同时这个中间件中的endpoint 终结者路由已经是通过routing匹配后的路由。
2. endpoint 跟普通路由又存在着什么样的关系？
答：ednpoint 终结者路由是普通路由map 转换后的委托路由，里面包含了路由方法的所有元素信息endpointmetadatacollection 和requestdelegate 委托。
3. userouting() 、useauthorization()、useendpoints() 这三个中间件的关系是什么呢？
答：userouing 中间件主要是路由匹配，找到匹配的终结者路由endpoint ；useendpoints 中间件主要针对userouting 中间件匹配到的路由进行 委托方法的执行等操作。
useauthorization 中间件主要针对 userouting 中间件中匹配到的路由进行拦截 做授权验证操作等，通过则执行下一个中间件useendpoints(),具体的关系可以看下面的流程图：
上面流程图中省略了一些部分，主要是把userouting 、useauthorization 、useendpoint 这三个中间件的关系突显出来。
最后我们可以在userouting() 和useendpoint() 注册的http 管道之间 注册其他牛逼的自定义中间件，以实现我们自己都有的业务逻辑
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