Debugging Proxy HTML

MWE for running Apache serving index.html through http://localhost/proxied/, which should rewrite links in HTML so that <link href="/style.css"> becomes <link href="/proxied/style.css>. That is not the case. Why?

Run make to launch apache and one request (which goes through the proxy, so apache proxies the request to python http server, then sends the index.html back through the reverse proxy); the result should have the links modified (but does not). Apache is terminated after a few seconds.

This MWE was tested on Debian, you need apache2 installed, python, and also ccze (for colors). All runs as the current user in the current directory, for a few seconds, does not touch anything else. Port 8080 for apache and 8081 for python http server.

Solved

ProxyHTMLURLMap was missing the R flag for "regex", so ^/ was not matching as literal. After adding R, everything works.

Output

Fragments (after running make) with some comments:

request from curl comes:

[core:trace5] Request received from client: GET /proxied/ HTTP/1.1 
[http:trace4] Headers received from client: 
[http:trace4]   Host: localhost:8080 
[http:trace4]   User-Agent: curl/7.81.0 
[http:trace4]   Accept: */*

proxy directive matches, and makes the request to itself, without /proxy:

[proxy:trace2] AH03461: attempting to match URI path '/proxied/' against prefix '/proxied/' for proxying 
[proxy:trace1] AH03464: URI path '/proxied/' matches proxy handler 'proxy:http://localhost:8080/'

The proxied response is being filtered, we see all the filters in order

inflate:

[filter:trace4] Content-Type 'text/html' ... 
[filter:trace4] ... matched 'text/html' 
[filter:trace2] Content-Type condition for 'inflate' matched

proxy-html (but NO ACTION HAPPENS):

[xml2enc:debug] AH01430: Content-Type is text/html 
[xml2enc:debug] AH01434: Charset ISO-8859-1 not supported by libxml2; trying apr_xlate 
[xml2enc:debug] AH01439: xml2enc: consuming 156 bytes from bucket 
[xml2enc:debug] AH01441: xml2enc: converted 156/156 bytes 
[filter:trace4] Content-Type 'text/html;charset=utf-8' ... 
[filter:trace4] ... matched 'text/html' 
[filter:trace2] Content-Type condition for 'proxy-html' matched

substitute (replaces title via regex)

[filter:trace4] Content-Type 'text/html;charset=utf-8' ... 
[filter:trace4] ... matched 'text/html' 
[filter:trace2] Content-Type condition for 'substitute' matched 
[substitute:trace8] Line read (140 bytes): <html><head><meta charset="utf-8"><link rel="stylesheet" href="/style.css"><title>Main page</title></head><body><h1>Title</h1></body></html> 
[substitute:trace8] Replacing regex:'Title' by 'REPLACED TITLE' 
[substitute:trace8] Matching found 
[substitute:trace8] Result: 'REPLACED TITLE'

deflate:

[filter:trace4] Content-Type 'text/html;charset=utf-8' ... 
[filter:trace4] ... matched 'text/html' 
[filter:trace2] Content-Type condition for 'deflate' matched

Sent back to curl:

[http:trace3] Response sent with status 200, headers: 
[http:trace5]   Date: Tue, 04 Jun 2024 10:19:36 GMT 
[http:trace5]   Server: Apache/2.4.52 (Ubuntu) 
[http:trace4]   Last-Modified: Tue, 04 Jun 2024 09:58:25 GMT 
[http:trace4]   Accept-Ranges: bytes 
[http:trace4]   Content-Type: text/html;charset=utf-8 
[http:trace4]   Vary: Accept-Encoding 
[http:trace4]   Content-Length: 149 
[proxy_http:trace2] end body send

so curl receives index.html with substituted title, but with the href being untouched:

<html><head><meta charset="utf-8"><link rel="stylesheet" href="/style.css"><title>Main page</title></head><body><h1>REPLACED TITLE</h1></body></html>

eudoxos/rproxy

Debugging Proxy HTML

Solved

Output