1+ using Microsoft . Extensions . Options ;
2+
3+ namespace ExampleDataApis ;
4+
5+ /// <summary>
6+ /// Options for configuring the UserAgentBlockingMiddleware
7+ /// </summary>
8+ public class UserAgentBlockingOptions
9+ {
10+ /// <summary>
11+ /// List of user agents to block (supports exact matches or substring matches)
12+ /// </summary>
13+ public List < string > BlockedUserAgents { get ; set ; } = [ ] ;
14+
15+ public List < string > BlockedIps { get ; set ; } = [ ] ;
16+
17+ /// <summary>
18+ /// HTTP status code to return when a user agent is blocked (defaults to 403 Forbidden)
19+ /// </summary>
20+ public int BlockedStatusCode { get ; set ; } = StatusCodes . Status403Forbidden ;
21+
22+ /// <summary>
23+ /// Optional message to return in the response body when a user agent is blocked
24+ /// </summary>
25+ public string BlockedMessage { get ; set ; } = "Access denied based on your user agent" ;
26+
27+ /// <summary>
28+ /// If true, will perform case-insensitive matching (defaults to true)
29+ /// </summary>
30+ public bool IgnoreCase { get ; set ; } = true ;
31+
32+ /// <summary>
33+ /// If true, blocked requests will be logged (defaults to true)
34+ /// </summary>
35+ public bool LogBlockedRequests { get ; set ; } = true ;
36+ }
37+
38+ /// <summary>
39+ /// Middleware that blocks requests from specific user agents
40+ /// </summary>
41+ public class UserAgentBlockingMiddleware (
42+ RequestDelegate next ,
43+ IOptions < UserAgentBlockingOptions > options ,
44+ ILogger < UserAgentBlockingMiddleware > logger )
45+ {
46+ UserAgentBlockingOptions Options => options ? . Value ?? throw new ArgumentNullException ( nameof ( options ) ) ;
47+
48+ public async Task InvokeAsync ( HttpContext context )
49+ {
50+ if ( context == null )
51+ {
52+ throw new ArgumentNullException ( nameof ( context ) ) ;
53+ }
54+
55+ // Get the client IP address
56+ var remoteIp = context . Connection . RemoteIpAddress ? . ToString ( ) ;
57+
58+ // Check if the IP should be blocked
59+ if ( ShouldBlockIp ( remoteIp ) )
60+ {
61+ if ( Options . LogBlockedRequests )
62+ {
63+ logger . LogInformation (
64+ "Request blocked from IP: {IPAddress}, Path: {Path}" ,
65+ remoteIp ,
66+ context . Request . Path ) ;
67+ }
68+
69+ context . Response . StatusCode = Options . BlockedStatusCode ;
70+ context . Response . ContentType = "text/plain" ;
71+ await context . Response . WriteAsync ( Options . BlockedMessage ) ;
72+ return ;
73+ }
74+
75+ // Get the User-Agent header
76+ string userAgent = context . Request . Headers [ "User-Agent" ] . ToString ( ) ;
77+
78+ // Check if the user agent should be blocked
79+ if ( ShouldBlockUserAgent ( userAgent ) )
80+ {
81+ // Log the blocked request if enabled
82+ if ( Options . LogBlockedRequests )
83+ {
84+ logger . LogInformation (
85+ "Request blocked from user agent: {UserAgent}, IP: {IPAddress}, Path: {Path}" ,
86+ userAgent ,
87+ remoteIp ,
88+ context . Request . Path ) ;
89+ }
90+
91+ // Set the response status code
92+ context . Response . StatusCode = Options . BlockedStatusCode ;
93+ context . Response . ContentType = "text/plain" ;
94+
95+ // Write the blocked message to the response
96+ await context . Response . WriteAsync ( Options . BlockedMessage ) ;
97+ return ;
98+ }
99+
100+ // If not blocked, continue to the next middleware
101+ await next ( context ) ;
102+ }
103+
104+ private bool ShouldBlockUserAgent ( string userAgent )
105+ {
106+ if ( string . IsNullOrEmpty ( userAgent ) )
107+ {
108+ // You might want to block requests with no user agent
109+ // Return true here if you want to block empty user agents
110+ return false ;
111+ }
112+
113+ foreach ( var blockedAgent in Options . BlockedUserAgents )
114+ {
115+ var comparison = Options . IgnoreCase
116+ ? StringComparison . OrdinalIgnoreCase
117+ : StringComparison . Ordinal ;
118+
119+ if ( userAgent . Contains ( blockedAgent , comparison ) )
120+ return true ;
121+ if ( blockedAgent . Contains ( ' ' ) && userAgent . Contains ( blockedAgent . Replace ( " " , "" ) , comparison ) )
122+ return true ;
123+ }
124+
125+ return false ;
126+ }
127+
128+ private bool ShouldBlockIp ( string ? ipAddress )
129+ {
130+ if ( string . IsNullOrEmpty ( ipAddress ) )
131+ return false ;
132+
133+ foreach ( var blockedIp in Options . BlockedIps )
134+ {
135+ // Support partial IP matching (e.g., "114.119" blocks all IPs starting with "114.119")
136+ if ( ipAddress . StartsWith ( blockedIp , StringComparison . Ordinal ) )
137+ return true ;
138+ }
139+
140+ return false ;
141+ }
142+ }
143+
144+ /// <summary>
145+ /// Extension methods for registering the UserAgentBlockingMiddleware
146+ /// </summary>
147+ public static class UserAgentBlockingMiddlewareExtensions
148+ {
149+ /// <summary>
150+ /// Adds the UserAgentBlockingMiddleware to the application pipeline
151+ /// </summary>
152+ public static IApplicationBuilder UseUserAgentBlocking (
153+ this IApplicationBuilder builder )
154+ {
155+ return builder . UseMiddleware < UserAgentBlockingMiddleware > ( ) ;
156+ }
157+
158+ /// <summary>
159+ /// Adds the UserAgentBlockingMiddleware to the application pipeline with custom options
160+ /// </summary>
161+ public static IApplicationBuilder UseUserAgentBlocking (
162+ this IApplicationBuilder builder ,
163+ Action < UserAgentBlockingOptions > configureOptions )
164+ {
165+ // Create a new options instance
166+ var options = new UserAgentBlockingOptions ( ) ;
167+
168+ // Apply the configuration
169+ configureOptions ( options ) ;
170+
171+ // Use the middleware with the configured options
172+ return builder . UseMiddleware < UserAgentBlockingMiddleware > ( Options . Create ( options ) ) ;
173+ }
174+ }
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