headers: Support default header values in Caddyfile with '?' (#3807)

* implement default values for header directive

closes #3804

* remove `set_default` header op and rely on "require" handler instead

This has the following advantages over the previous attempt:

- It does not introduce a new operation for headers, but rather nicely
  extends over an existing feature in the header handler.
- It removes the need to specify the header as "deferred" because it is
  already implicitely deferred by the use of the require handler. This
  should be less confusing to the user.

* add integration test for header directive in caddyfile

* bubble up errors when parsing caddyfile header directive

* don't export unnecessarily and don't canonicalize headers unnecessarily

* fix response headers not passed in blocks

* caddyfile: fix clash when using default header in block

Each header is now set in a separate handler so that it doesn't clash
with other headers set/added/deleted in the same block.

* caddyhttp: New idle_timeout default of 5m

* reverseproxy: fix random hangs on http/2 requests with server push (#3875)

see https://github.com/golang/go/issues/42534

* Refactor and cleanup with improvements

* More specific link

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>
Co-authored-by: Денис Телюх <telyukh.denis@gmail.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/modules/caddyhttp/push/caddyfile.go b/modules/caddyhttp/push/caddyfile.go
index a70d5d5..61b868c 100644
--- a/modules/caddyhttp/push/caddyfile.go
+++ b/modules/caddyhttp/push/caddyfile.go
@@ -59,6 +59,8 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 					return nil, h.ArgErr()
 				}
 				for innerNesting := h.Nesting(); h.NextBlock(innerNesting); {
+					var err error
+
 					// include current token, which we treat as an argument here
 					args := []string{h.Val()}
 					args = append(args, h.RemainingArgs()...)
@@ -66,16 +68,21 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 					if handler.Headers == nil {
 						handler.Headers = new(HeaderConfig)
 					}
+
 					switch len(args) {
 					case 1:
-						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], "", "")
+						err = headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], "", "")
 					case 2:
-						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], "")
+						err = headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], "")
 					case 3:
-						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], args[2])
+						err = headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], args[2])
 					default:
 						return nil, h.ArgErr()
 					}
+
+					if err != nil {
+						return nil, h.Err(err.Error())
+					}
 				}
 
 			case "GET", "HEAD":