Redbot reports that my webpage has invalid header:
The ETag header's syntax isn't valid.
My headers are set to:
ETag: 4ae413bd
Why is it invalid?
What is the syntax for an ETag?
Try ETag: "4ae413bd"
.
The value of an ETag must follow the ABNF form:
entity-tag = [ weak ] opaque-tag
weak = "W/"
opaque-tag = quoted-string
quoted-string = ( <"> *(qdtext | quoted-pair ) <"> )
qdtext = <any TEXT except <">>
quoted-pair = "\" CHAR
CHAR = <any US-ASCII character (octets 0 - 127)>
TEXT = <any OCTET except CTLs, but including LWS>
OCTET = <any 8-bit sequence of data>
LWS = [CRLF] 1*( SP | HT )
CTL = <any US-ASCII control character (octets 0 - 31) and DEL (127)>
CRLF = CR LF
CR = <US-ASCII CR, carriage return (13)>
LF = <US-ASCII LF, linefeed (10)>
SP = <US-ASCII SP, space (32)>
HT = <US-ASCII HT, horizontal-tab (9)>
, which is basically ([wW]/)?"([^"]|\\")*"
in regular regex.
Note that both "\"
and "/"
are valid values for etags.
References: section-14.19, section-3.11, section-2.2.