1. The problem I’m having:
I’m trying to verify if Caddy’s access logs (specifically the request.headers field when using format json) will show the Transfer-Encoding: chunked header if it’s sent by the client.
Currently, when I send a request with Transfer-Encoding: chunked to Caddy, this header does not appear in Caddy’s JSON access log under request.headers. However, my upstream application (Gunicorn/Flask) does see an HTTP_TRANSFER_ENCODING: chunked header, which I understand maybe that Caddy itself is sending to the upstream???
My specific question is: Should Caddy’s standard JSON access log (at INFO level) include the Transfer-Encoding: chunked header in request.headers if it was part of the original client request to Caddy, or is this header typically processed and consumed by Caddy before the access logging stage due to its hop-by-hop nature? I want to understand if this is expected behavior or if I need to configure Caddy differently to see this specific incoming header in the logs.
The same happens even at DEBUG logging, that is, caddy still doesn’t see the Transfer-Encoding: chunked header
Here’s an example curl command I’m using to send a chunked request:
echo "This is some chunked data." > data.txt
echo "Another line of data." >> data.txt
Then, the curl command:
curl -vL -X POST \
-H "Content-Type: application/x-www-form-urlencoded" \
-H "Transfer-Encoding: chunked" \
--data-binary @data.txt \
http://localhost/
2. Error messages and/or full log output:
The JSON log output for a POST request (note the absence of Transfer-Encoding in request.headers even if the client sent it):
{
"level": "info",
"ts": 1748458248.0549488,
"logger": "http.log.access.log0",
"msg": "handled request",
"request": {
"remote_ip": "::1",
"remote_port": "54566",
"proto": "HTTP/1.1",
"method": "POST",
"host": "localhost",
"uri": "/",
"headers": {
"Accept": [
"*/*"
],
"Content-Type": [
"application/x-www-form-urlencoded"
],
"User-Agent": [
"curl/8.13.0"
]
}
},
"user_id": "",
"duration": 0.009299079,
"size": 4611,
"status": 200,
"resp_headers": {
"Server": [
"Caddy"
],
"Content-Type": [
"text/html; charset=utf-8"
],
"Content-Length": [
"4611"
],
"Date": [
"Wed, 28 May 2025 18:50:48 GMT"
]
}
}
Upstream Gunicorn/Flask log (showing it received Transfer-Encoding from Caddy):
{
'CONTENT_TYPE': 'application/x-www-form-urlencoded',
'HTTP_TRANSFER_ENCODING': 'chunked',
'HTTP_USER_AGENT': 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/136.0.0.0 Safari/537.36',
'HTTP_X_FORWARDED_FOR': '127.0.0.1',
...
}
3. Caddy version:
2.6.2
4. How I installed and ran Caddy:
sudo apt install caddy
a. System environment:
Linux parrot 6.12.12-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.12-1parrot1 (2025-02-27) x86_64 GNU/Linux
b. Command:
caddy run
c. Service/unit/compose file:
N/A
d. My complete Caddy config:
:80 {
reverse_proxy localhost:8000 {
header_down -Server
}
log {
output stdout
format json
level INFO
}
}