push: Implement HTTP/2 server push (#3573)

* push: Implement HTTP/2 server push (close #3551)

* push: Abstract header ops by embedding into new struct type

This will allow us to add more fields to customize headers in
push-specific ways in the future.

* push: Ensure Link resources are pushed before response is written

* Change header name from X-Caddy-Push to Caddy-Push

1 files changed, 99 insertions, 0 deletions

diff --git a/modules/caddyhttp/push/caddyfile.go b/modules/caddyhttp/push/caddyfile.go
new file mode 100644
index 0000000..a70d5d5
--- /dev/null
+++ b/modules/caddyhttp/push/caddyfile.go
@@ -0,0 +1,99 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package push
+
+import (
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp/headers"
+)
+
+func init() {
+	httpcaddyfile.RegisterHandlerDirective("push", parseCaddyfile)
+}
+
+// parseCaddyfile sets up the push handler. Syntax:
+//
+//     push [<matcher>] [<resource>] {
+//         [GET|HEAD] <resource>
+//         headers {
+//             [+]<field> [<value|regexp> [<replacement>]]
+//             -<field>
+//         }
+//     }
+//
+// A single resource can be specified inline without opening a
+// block for the most common/simple case. Or, a block can be
+// opened and multiple resources can be specified, one per
+// line, optionally preceded by the method. The headers
+// subdirective can be used to customize the headers that
+// are set on each (synthetic) push request, using the same
+// syntax as the 'header' directive for request headers.
+// Placeholders are accepted in resource and header field
+// name and value and replacement tokens.
+func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	handler := new(Handler)
+
+	for h.Next() {
+		if h.NextArg() {
+			handler.Resources = append(handler.Resources, Resource{Target: h.Val()})
+		}
+
+		// optional block
+		for outerNesting := h.Nesting(); h.NextBlock(outerNesting); {
+			switch h.Val() {
+			case "headers":
+				if h.NextArg() {
+					return nil, h.ArgErr()
+				}
+				for innerNesting := h.Nesting(); h.NextBlock(innerNesting); {
+					// include current token, which we treat as an argument here
+					args := []string{h.Val()}
+					args = append(args, h.RemainingArgs()...)
+
+					if handler.Headers == nil {
+						handler.Headers = new(HeaderConfig)
+					}
+					switch len(args) {
+					case 1:
+						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], "", "")
+					case 2:
+						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], "")
+					case 3:
+						headers.CaddyfileHeaderOp(&handler.Headers.HeaderOps, args[0], args[1], args[2])
+					default:
+						return nil, h.ArgErr()
+					}
+				}
+
+			case "GET", "HEAD":
+				method := h.Val()
+				if !h.NextArg() {
+					return nil, h.ArgErr()
+				}
+				target := h.Val()
+				handler.Resources = append(handler.Resources, Resource{
+					Method: method,
+					Target: target,
+				})
+
+			default:
+				handler.Resources = append(handler.Resources, Resource{Target: h.Val()})
+			}
+		}
+	}
+
+	return handler, nil
+}