Oh, droga, eu percebi isso.
O Squid ignora os cabeçalhos de cache menores que OU IGUAL A UM minuto. Então max-age = 60 é ignorada, mas max-age = 61 funciona como um encanto.
<?php
Header('Cache-Control: max-age=61');
?><html>hi</html>
squid.conf:
http_access allow all
# Squid normally listens to port 3128
http_port 3128 accel defaultsite=localhost no-vhost
cache_peer localhost parent 80 0 no-query originserver name=myAccel
cache_peer_access myAccel allow all
# Uncomment and adjust the following to add a disk cache directory.
cache_dir ufs /usr/local/var/cache/squid 100 16 256
# Leave coredumps in the first cache dir
coredump_dir /usr/local/var/cache/squid
Squid 3.2.9, instalado no OSX via Homebrew
localhost: ~ $ squid -v
Squid Cache: Version 3.2.9
configure options: '--disable-debug' '--disable-dependency-tracking' '--prefix=/usr/local/Cellar/squid/3.2.9' '--localstatedir=/usr/local/var' 'CC=cc' 'CXX=c++' 'PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig'
Começou o squid com squid -f squid.conf -d 2 -N
O envio de dados está retornando cabeçalhos de Cache-Control válidos, que verifiquei como corretos visitando a página no Google Chrome 26 e assistindo no Chrome Dev Tools.
localhost: ~ $ curl -s -o /dev/null --dump-header /dev/stdout http://localhost/test.php
HTTP/1.1 200 OK
Date: Tue, 16 Apr 2013 21:29:33 GMT
Server: Apache/2.2.22 (Unix) DAV/2 PHP/5.3.15 with Suhosin-Patch mod_ssl/2.2.22 OpenSSL/0.9.8r
X-Powered-By: PHP/5.3.15
Cache-Control: max-age=60, public
Content-Length: 16
Content-Type: text/html
X-Pad: avoid browser bug
Mas quando eu consultar a página através do proxy reverso do Squid, eu sempre recebo um erro de cache.
localhost: ~ $ curl -s -o /dev/null --dump-header /dev/stdout http://localhost:3128/test.php
HTTP/1.1 200 OK
Date: Tue, 16 Apr 2013 21:29:34 GMT
Server: Apache/2.2.22 (Unix) DAV/2 PHP/5.3.15 with Suhosin-Patch mod_ssl/2.2.22 OpenSSL/0.9.8r
X-Powered-By: PHP/5.3.15
Cache-Control: max-age=60, public
Content-Length: 16
Content-Type: text/html
X-Cache: MISS from localhost
Via: 1.1 localhost (squid/3.2.9)
Connection: keep-alive
localhost: ~ $ curl -s -o /dev/null --dump-header /dev/stdout http://localhost:3128/test.php
HTTP/1.1 200 OK
Date: Tue, 16 Apr 2013 21:29:38 GMT
Server: Apache/2.2.22 (Unix) DAV/2 PHP/5.3.15 with Suhosin-Patch mod_ssl/2.2.22 OpenSSL/0.9.8r
X-Powered-By: PHP/5.3.15
Cache-Control: max-age=60, public
Content-Length: 16
Content-Type: text/html
X-Cache: MISS from localhost
Via: 1.1 localhost (squid/3.2.9)
Connection: keep-alive
O que há de errado com minha configuração?
Tags proxy cache squid reverse-proxy