Question

ImageResizer文档中的扩展点页面提到插件可以“修改HTTP标头”，但是它们没有任何方向或示例。我创建了一个同时实现IPlugin和IChache接口的插件来添加HTTP标头，但感觉不正确，原因是：

我不想实现或创建“备用缓存系统”
如果我没有在current.RemapHandler(New NoCacheHandler(e))方法的末尾添加代码Process()，它将无法正常工作（该图像不会显示/显示为空白图像）。我不知道这行在做什么，或者不知道重新映射处理程序的含义

这是我当前的实现方式

web.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    ...
    <resizer>
        <plugins>
            <add name="MyNamespace.CorsHeadersPlugin" />
            <add name="Watermark" />
            <add name="MvcRoutingShim" />
            <add name="PsdReader" />
            <add name="WicDecoder" />
            <add name="WicEncoder" />
            <add name="WicBuilder" />
        </plugins>
    </resizer>
    ...
</configuration>

CorsHeadersPlugin

Imports ImageResizer.Caching
Imports ImageResizer.Configuration
Imports ImageResizer.Plugins
Imports ImageResizer.Plugins.Basic

Public Class CorsHeadersPlugin
    Implements IPlugin
    Implements ICache

    Private ReadOnly AllowedDomains As String()

    Public Sub New()
        AllowedDomains = {"http://allowthisdomain.com"}

#If DEBUG Then
        AllowedDomains = AllowedDomains.Union({"http://localhost", "https://localhost"}).ToArray
#End If
    End Sub

    Public Function CanProcess(current As HttpContext, e As IResponseArgs) As Boolean Implements ICache.CanProcess
        Return True
    End Function

    Public Sub Process(current As HttpContext, e As IResponseArgs) Implements ICache.Process
        Dim origin = current.Request.Url.GetLeftPart(UriPartial.Authority)

        If AllowedDomains.Contains(origin) Then
            current.Response.Headers.Add("Access-Control-Allow-Origin", origin)
        End If

        current.RemapHandler(New NoCacheHandler(e))
    End Sub

    Public Function Install(c As Config) As IPlugin Implements IPlugin.Install
        c.Plugins.add_plugin(Me)
        Return Me
    End Function

    Public Function Uninstall(c As Config) As Boolean Implements IPlugin.Uninstall
        c.Plugins.remove_plugin(Me)
        Return True
    End Function
End Class

Answer 1

事件处理程序ImageResizer.Config.Current.Pipeline.PreHandleImage and .PreHandleImageAsync允许您修改响应头。确保在AppStart期间仅注册一次处理程序。

Answer 2

更新，有效的实施方式

Imports ImageResizer.Caching
Imports ImageResizer.Configuration
Imports ImageResizer.Plugins

Public Class CorsHeadersPlugin
    Implements IPlugin

    Private ReadOnly AllowedDomains As String()

    Public Sub New()
        AllowedDomains = {"http://allowthisdomain.com"}

#If DEBUG Then
        AllowedDomains = AllowedDomains.Union({"http://localhost:3416", "https://localhost:3416"}).ToArray
#End If
    End Sub

    Public Function Install(c As Config) As IPlugin Implements IPlugin.Install
        AddHandler c.Pipeline.PreHandleImage, AddressOf ModifyHttpHeaders
        c.Plugins.add_plugin(Me)
        Return Me
    End Function

    Public Function Uninstall(c As Config) As Boolean Implements IPlugin.Uninstall
        RemoveHandler c.Pipeline.PreHandleImage, AddressOf ModifyHttpHeaders
        c.Plugins.remove_plugin(Me)
        Return True
    End Function

    Private Sub ModifyHttpHeaders(sender As IHttpModule, context As HttpContext, e As IResponseArgs)
        Dim origin = GetRequestOrigin(context.Request)

        If origin IsNot Nothing AndAlso AllowedDomains.Contains(origin) Then
            context.Response.Headers.Add("Access-Control-Allow-Origin", origin)
        End If
    End Sub

    Private Function GetRequestOrigin(request As HttpRequest) As String
        If request.Headers("Origin") IsNot Nothing Then
            Return request.Headers("Origin")
        ElseIf request.UrlReferrer IsNot Nothing Then
            Return request.UrlReferrer.GetLeftPart(UriPartial.Authority)
        End If

        Return Nothing
    End Function
End Class

如何使用ImageResizer插件添加Access-Control-Allow-Origin标头

2 个答案: