From 005a11cf4b0af5bfbbb72f8572681b327675541c Mon Sep 17 00:00:00 2001
From: Matthew Holt <mholt@users.noreply.github.com>
Date: Wed, 11 Sep 2019 18:48:37 -0600
Subject: [PATCH] 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 |  1 +
 modules/caddyhttp/headers/caddyfile.go  | 73 +++++++++++++++++++------
 modules/caddyhttp/headers/headers.go    | 11 ++++
 3 files changed, 69 insertions(+), 16 deletions(-)

diff --git a/caddyconfig/httpcaddyfile/directives.go b/caddyconfig/httpcaddyfile/directives.go
index 573db8d63..14c5f4445 100644
--- a/caddyconfig/httpcaddyfile/directives.go
+++ b/caddyconfig/httpcaddyfile/directives.go
@@ -30,6 +30,7 @@ var defaultDirectiveOrder = []string{
 	"rewrite",
 	"try_files",
 	"headers",
+	"request_header",
 	"encode",
 	"templates",
 	"redir",
diff --git a/modules/caddyhttp/headers/caddyfile.go b/modules/caddyhttp/headers/caddyfile.go
index 12ec8a092..d80600578 100644
--- a/modules/caddyhttp/headers/caddyfile.go
+++ b/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)
 		}
diff --git a/modules/caddyhttp/headers/headers.go b/modules/caddyhttp/headers/headers.go
index e7400041d..ba9d89d1d 100644
--- a/modules/caddyhttp/headers/headers.go
+++ b/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{