headers: New 'request_header' directive; handle Host header specially

Before this change, only response headers could be manipulated with the
Caddyfile's 'header' directive.

Also handle the request Host header specially, since the Go standard
library treats it separately from the other header fields...

caddyconfig/httpcaddyfile/directives.go

@@ -30,6 +30,7 @@ var defaultDirectiveOrder = []string{
 	"rewrite",
 	"try_files",
 	"headers",
+	"request_header",
 	"encode",
 	"templates",
 	"redir",

modules/caddyhttp/headers/caddyfile.go

@@ -24,9 +24,11 @@ import (
 
 func init() {
 	httpcaddyfile.RegisterHandlerDirective("headers", parseCaddyfile)
+	httpcaddyfile.RegisterHandlerDirective("request_header", parseReqHdrCaddyfile)
 }
 
-// parseCaddyfile sets up the handler from Caddyfile tokens. Syntax:
+// parseCaddyfile sets up the handler for response headers from
+// Caddyfile tokens. Syntax:
 //
 //     headers [<matcher>] [[+|-]<field> <value>] {
 //         [+][<field>] [<value>]
@@ -43,9 +45,11 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 		if h.NextArg() {
 			hasArgs = true
 			field := h.Val()
-			h.NextArg()
-			value := h.Val()
-			processCaddyfileLine(hdr, field, value)
+			var value string
+			if h.NextArg() {
+				value = h.Val()
+			}
+			processCaddyfileLineRespHdr(hdr, field, value)
 		}
 
 		// if not, they should be in a block
@@ -58,31 +62,68 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 			if h.NextArg() {
 				value = h.Val()
 			}
-			processCaddyfileLine(hdr, field, value)
+			processCaddyfileLineRespHdr(hdr, field, value)
 		}
 	}
 	return hdr, nil
 }
 
-func processCaddyfileLine(hdr *Headers, field, value string) {
-	if strings.HasPrefix(field, "+") {
-		if hdr.Response == nil {
-			hdr.Response = &RespHeaderOps{HeaderOps: new(HeaderOps)}
+// parseReqHdrCaddyfile sets up the handler for request headers
+// from Caddyfile tokens. Syntax:
+//
+//     request_header [<matcher>] [[+|-]<field> <value>]
+//
+func parseReqHdrCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	hdr := new(Headers)
+	for h.Next() {
+		if !h.NextArg() {
+			return nil, h.ArgErr()
 		}
+		field := h.Val()
+		var value string
+		if h.NextArg() {
+			value = h.Val()
+		}
+
+		if hdr.Request == nil {
+			hdr.Request = new(HeaderOps)
+		}
+		if strings.HasPrefix(field, "+") {
+			if hdr.Request.Add == nil {
+				hdr.Request.Add = make(http.Header)
+			}
+			hdr.Request.Add.Set(field[1:], value)
+		} else if strings.HasPrefix(field, "-") {
+			hdr.Request.Delete = append(hdr.Request.Delete, field[1:])
+		} else {
+			if hdr.Request.Set == nil {
+				hdr.Request.Set = make(http.Header)
+			}
+			hdr.Request.Set.Set(field, value)
+		}
+
+		if h.NextArg() {
+			return nil, h.ArgErr()
+		}
+	}
+	return hdr, nil
+}
+
+func processCaddyfileLineRespHdr(hdr *Headers, field, value string) {
+	if hdr.Response == nil {
+		hdr.Response = &RespHeaderOps{
+			HeaderOps: new(HeaderOps),
+			Deferred:  true,
+		}
+	}
+	if strings.HasPrefix(field, "+") {
 		if hdr.Response.Add == nil {
 			hdr.Response.Add = make(http.Header)
 		}
 		hdr.Response.Add.Set(field[1:], value)
 	} else if strings.HasPrefix(field, "-") {
-		if hdr.Response == nil {
-			hdr.Response = &RespHeaderOps{HeaderOps: new(HeaderOps)}
-		}
 		hdr.Response.Delete = append(hdr.Response.Delete, field[1:])
-		hdr.Response.Deferred = true
 	} else {
-		if hdr.Response == nil {
-			hdr.Response = &RespHeaderOps{HeaderOps: new(HeaderOps)}
-		}
 		if hdr.Response.Set == nil {
 			hdr.Response.Set = make(http.Header)
 		}

modules/caddyhttp/headers/headers.go

@@ -58,7 +58,18 @@ type RespHeaderOps struct {
 
 func (h Headers) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
 	repl := r.Context().Value(caddy.ReplacerCtxKey).(caddy.Replacer)
+
 	apply(h.Request, r.Header, repl)
+
+	// request header's Host is handled specially by the
+	// Go standard library, so if that header was changed,
+	// change it in the Host field since the Header won't
+	// be used
+	if intendedHost := r.Header.Get("Host"); intendedHost != "" {
+		r.Host = intendedHost
+		r.Header.Del("Host")
+	}
+
 	if h.Response != nil {
 		if h.Response.Deferred || h.Response.Require != nil {
 			w = &responseWriterWrapper{