Case-sensitive issue in header_down of reverse proxy

[nnnlog]

Three or four parameters of header_down use Regex, and one does simply overwriting.
Caddy did not simply make a case-sensitive distinction of the header key value when it overwrites it, but I experienced a case-sensitive distinction of the header key value when I used Regex.
I think it is not intended.

Reproduction of issue.

example.com {
        reverse_proxy {
                to http://127.0.0.1:8000
                header_down Location (http://)(.*) https://$2
        }
}

The above setting replaces the Location header's value with https if the value starts with http. It worked only when it was a Location, not location.

example.com {
        reverse_proxy {
                to http://127.0.0.1:8000
                header_down Location https://example.com
        }
}

In comparison, the task of simply changing to https://example.com worked when the header was named location.

Version

v2.4.5

[francislavoie]

Ah, yeah I see the problem. We're using a map[string][]Replacement for the replacements, where string is the header field name in the case that was configured. I think we need to call http.CanonicalHeaderKey() on fieldName in the code here, and/or probably use hdr.Get() and hdr.Set() instead or directly accessing the header map:

caddy/modules/caddyhttp/headers/headers.go

Lines 214 to 248 in 46ab93b

	// replace
	for fieldName, replacements := range ops.Replace {
	fieldName = repl.ReplaceAll(fieldName, "")
	// all fields...
	if fieldName == "*" {
	for _, r := range replacements {
	search := repl.ReplaceAll(r.Search, "")
	replace := repl.ReplaceAll(r.Replace, "")
	for fieldName, vals := range hdr {
	for i := range vals {
	if r.re != nil {
	hdr[fieldName][i] = r.re.ReplaceAllString(hdr[fieldName][i], replace)
	} else {
	hdr[fieldName][i] = strings.ReplaceAll(hdr[fieldName][i], search, replace)
	}
	}
	}
	}
	continue
	}
	// ...or only with the named field
	for _, r := range replacements {
	search := repl.ReplaceAll(r.Search, "")
	replace := repl.ReplaceAll(r.Replace, "")
	for i := range hdr[fieldName] {
	if r.re != nil {
	hdr[fieldName][i] = r.re.ReplaceAllString(hdr[fieldName][i], replace)
	} else {
	hdr[fieldName][i] = strings.ReplaceAll(hdr[fieldName][i], search, replace)
	}
	}
	}
	}

[mholt]

Thanks for the report! And thanks Francis for investigating.