conditional redirect (404)

The host header is only required for HTTP 1.1. If a client sends an HTTP 1.0 (or even 0.9) request, the Host header value wouldn't necessarily be present, but regardless the $host variable should be set to a zero length string. I'm not sure how the runtime error could be triggered for $host not being defined, as it's set on every HTTP request (even if it's to a null value).

Using the rule below, I did some tests on 9.2.4 using netcat. In every test, checking if the $host value contained a string succeeded without a TCL error. Between this post and a related one on the ProxyPass rule (Click here), I'd suggest opening a case with F5 Support. It seems like this might be a bug.

As a workaround, you could add a check to see if $host exists before trying to check if it contains a string:

  
  when HTTP_REQUEST {   
     set host [HTTP::host]  
     set url  [HTTP::uri]   
  }  
  when HTTP_RESPONSE {   
     if { [HTTP::status] == 404 } {  
        if {[info exists host]}{  
           if {$host contains "abcd" } {  
              HTTP::redirect "http://abcd.otherdomain.com/$url"  
           } elseif {[info exists host] && $host contains "efg" } {  
              HTTP::redirect "http://efg.otherdomain.com/$url"  
           } else {  
              HTTP::redirect "http://anotherone.com/xyz.html"  
           }  
        } else {  
            $host doesn't exist!  
           log local0. "[IP::client_addr]:[TCP::client_port]: \$host was not set!?"  
        }  
     }  
  }  
  

Aaron

Example rule which saves the HTTP::host output and checks the value in HTTP_RESPONSE:

  
  when HTTP_REQUEST {  
    
     set host [HTTP::host]  
       
     log local0. "HTTP version: [HTTP::version], HTTP host: $host, HTTP uri: [HTTP::uri]"  
  }  
  when HTTP_RESPONSE {  
    
     if { $host contains "www" } {  
        log local0. "matched $host"  
     } else {    
        log local0. "didn't match $host"  
     }    
  }  
  

Request with a Host header:

$ nc 192.168.101.40 80

GET /withhost HTTP/1.1

Connection: close

Host: www.example.com

Log output:

Rule log_http_host_rule : HTTP version: 1.1, HTTP host: www.example.com, HTTP uri: /withhost

Rule log_http_host_rule : matched www.example.com

Request without a Host header:

$ nc 192.168.101.40 80

GET /withouthost HTTP/1.0

Log output:

Rule log_http_host_rule : HTTP version: 1.0, HTTP host: , HTTP uri: /withouthost

Rule log_http_host_rule : didn't match

0.9 formatted request:

$ nc 192.168.101.40 80

GET /

Log output:

Rule log_http_host_rule : HTTP version: 0.9, HTTP host: , HTTP uri: /

Rule log_http_host_rule : didn't match

Request with a Host header, but nothing after the colon:

nc 192.168.101.40 80

GET / HTTP/1.0

Host:

Test: value

Log output:

Rule log_http_host_rule : HTTP version: 1.1, HTTP host: Connection: close, HTTP uri: /

Rule log_http_host_rule : didn't match Connection: close

This last one could be considered a bug as well. Apparently the HTTP parser doesn't stop parsing the Host header value at the line terminating CRLF if there isn't a value for the header.

'HTTP::header Host' seems to be more accurate:

 
 when HTTP_REQUEST { 
  
    set http_host [HTTP::host] 
    set http_header_host [HTTP::header Host] 
     
    log local0. "HTTP version: [HTTP::version], HTTP host: $http_host, HTTP header Host: $http_header_host, HTTP uri: [HTTP::uri]" 
 } 
 when HTTP_RESPONSE { 
  
    if { $http_host contains "www" } { 
       log local0. "http_host matched $http_host" 
    } else {   
       log local0. "http_host didn't match $http_host" 
    }   
    if { $http_header_host contains "www" } { 
       log local0. "http_header_host matched $http_header_host" 
    } else {   
       log local0. "http_header_host didn't match $http_header_host" 
    }   
 } 
 

Request:

$ nc 192.168.101.40 80

GET / HTTP/1.0

Host:

Test: value

Log output shows HTTP::host errantly returns the next header name and value, while HTTP::header Host correctly returns nothing:

Rule log_http_host_rule : HTTP version: 1.0, HTTP host: Test: value, HTTP header Host: , HTTP uri: /

Rule log_http_host_rule : http_host didn't match Test: value

Rule log_http_host_rule : http_header_host didn't match