A value that goes into an HTTP header (the User-Agent, a default header). Node's
HTTP layer throws an opaque "Invalid character in header content" at request time
for a CR/LF (or any other C0 control, or DEL) and for any character above U+00FF,
and a custom transport might pass a CR/LF on as a header injection. A blank value
is refused too: it used to be sent as an empty header. Tab (0x09) and Latin-1 are
allowed. Checked by char code so the source stays free of control bytes.
A value that goes into an HTTP header (the User-Agent, a default header). Node's HTTP layer throws an opaque "Invalid character in header content" at request time for a CR/LF (or any other C0 control, or DEL) and for any character above U+00FF, and a custom transport might pass a CR/LF on as a header injection. A blank value is refused too: it used to be sent as an empty header. Tab (0x09) and Latin-1 are allowed. Checked by char code so the source stays free of control bytes.