Re: test ICAP server

[Robin Wood <squid@digi.ninja>]

I've got a bit further with this and I'm starting to understand ICAP talk.

I've got a Go server working which I can talk to through netcat:

$ nc localhost 1344
REQMOD icap://192.168.0.7/ ICAP/1.0
GET / HTTP/1.1
Host: dvwa.test
Accept: text/html, text/plain, image/gif
Accept-Encoding: gzip, compress

ICAP/1.0 200 OK
Encapsulated: req-hdr=0, null-body=141

GET / HTTP/1.1
Host: dvwa.test
Accept: text/html, text/plain, image/gif
Accept-Encoding: gzip, compress
X-Modified-By: Go ICAP Server


On the server side I see:

This is the request

REQMOD icap://192.168.0.7/ ICAP/1.0

Received request: REQMOD icap://192.168.0.7/ ICAP/1.0
Original Request Headers:
GET / HTTP/1.1
Host: dvwa.test
Accept: text/html, text/plain, image/gif
Accept-Encoding: gzip, compress


Modified request sent back

ICAP/1.0 200 OK
Encapsulated: req-hdr=0, null-body=141

GET / HTTP/1.1
Host: dvwa.test
Accept: text/html, text/plain, image/gif
Accept-Encoding: gzip, compress
X-Modified-By: Go ICAP Server


If I try to use curl through Squid pointing at that server:

$ curl "http://dvwa.test/a?xsa" --proxy localhost:3128

dvwa.test is at 192.168.0.42.

I get this in the ICAP server: 

This is the request

REQMOD icap://192.168.0.7:1344/ ICAP/1.0

Received request: REQMOD icap://192.168.0.7:1344/ ICAP/1.0
Original Request Headers:
Host: 192.168.0.7:1344
Date: Fri, 07 Feb 2025 12:26:25 GMT
Encapsulated: req-hdr=0, null-body=93
Allow: 204, trailers


Modified request sent back

ICAP/1.0 200 OK
Encapsulated: req-hdr=0, null-body=155

Host: 192.168.0.7:1344
Date: Fri, 07 Feb 2025 12:26:25 GMT
Encapsulated: req-hdr=0, null-body=93
Allow: 204, trailers
X-Modified-By: Go ICAP Server

Squid then gives the same error as before, ERR_ICAP_FAILURE.

Robin

On Fri, 7 Feb 2025 at 10:15, Robin Wood <squid@digi.ninja> wrote:

Hi

I want to write my own ICAP server, but all the sample code I've found is failing, the majority with this error from squidclient:

squidclient -h 192.168.0.7 -p 1344 icap://192.168.0.7:1344/request_mod
ICAP/1.0 400 Bad Request

And this error when accessed through Squid itself:

ICAP protocol error.

The system returned: [No Error]

This means that some aspect of the ICAP communication failed.

I've got this in my squid.conf:

# Enable ICAP for request and response modification
icap_enable on
icap_service service_req reqmod_precache icap://192.168.0.7:1344/request_mod
icap_service service_resp respmod_precache icap://192.168.0.7:1344/response_mod

# ICAP adaptation rules
adaptation_access service_req allow all
adaptation_access service_resp allow all

And I've tried running both Python and Ruby servers taken from various places. A lot are logging that they've received and replied to requests:

Received request: OPTIONS icap://192.168.0.7:1344/request_mod ICAP/1.0
Responded to OPTIONS request

The servers are all listening, I've checked that:

$ ss -antp | grep 1344
LISTEN     0      4096                       0.0.0.0:1344                  0.0.0.0:*     users:(("ruby",pid=563029,fd=5))

The closest I've got is this one:

https://gist.github.com/digininja/a98b3567e0aeb218d37cdd337bb12f34

It seems to be working as it sees the headers and says it has returned data:

Received request: REQMOD icap://192.168.0.7:1344/request_mod ICAP/1.0
Original Headers:
Host: 192.168.0.7:1344
Date: Fri, 07 Feb 2025 10:10:30 GMT
Encapsulated: req-hdr=0, null-body=91
Preview: 0
Allow: 204, trailers
Modified request sent back

But I still get errors.

What could be wrong?

Does someone have some example server code they know works that I can test to help debug it?

Robin

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