Add upstream header replacements (TODO: tests, docs)

caddyhttp/proxy/proxy.go

@@ -94,6 +94,8 @@ type UpstreamHost struct {
 	// is healthy and any non-zero value indicates unhealthy.
 	Unhealthy                    int32
 	HealthCheckResult            atomic.Value
+	UpstreamHeaderReplacements   headerReplacements
+	DownstreamHeaderReplacements headerReplacements
 }
 
 // Down checks whether the upstream host is down or not.
@@ -220,7 +222,7 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 		// set headers for request going upstream
 		if host.UpstreamHeaders != nil {
 			// modify headers for request that will be sent to the upstream host
-			mutateHeadersByRules(outreq.Header, host.UpstreamHeaders, replacer)
+			mutateHeadersByRules(outreq.Header, host.UpstreamHeaders, replacer, host.UpstreamHeaderReplacements)
 			if hostHeaders, ok := outreq.Header["Host"]; ok && len(hostHeaders) > 0 {
 				outreq.Host = hostHeaders[len(hostHeaders)-1]
 			}
@@ -230,7 +232,7 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 		// headers coming back downstream
 		var downHeaderUpdateFn respUpdateFn
 		if host.DownstreamHeaders != nil {
-			downHeaderUpdateFn = createRespHeaderUpdateFn(host.DownstreamHeaders, replacer)
+			downHeaderUpdateFn = createRespHeaderUpdateFn(host.DownstreamHeaders, replacer, host.UpstreamHeaderReplacements)
 		}
 
 		// Before we retry the request we have to make sure
@@ -376,13 +378,13 @@ func createUpstreamRequest(rw http.ResponseWriter, r *http.Request) (*http.Reque
 	return outreq, cancel
 }
 
-func createRespHeaderUpdateFn(rules http.Header, replacer httpserver.Replacer) respUpdateFn {
+func createRespHeaderUpdateFn(rules http.Header, replacer httpserver.Replacer, replacements headerReplacements) respUpdateFn {
 	return func(resp *http.Response) {
-		mutateHeadersByRules(resp.Header, rules, replacer)
+		mutateHeadersByRules(resp.Header, rules, replacer, replacements)
 	}
 }
 
-func mutateHeadersByRules(headers, rules http.Header, repl httpserver.Replacer) {
+func mutateHeadersByRules(headers, rules http.Header, repl httpserver.Replacer, replacements headerReplacements) {
 	for ruleField, ruleValues := range rules {
 		if strings.HasPrefix(ruleField, "+") {
 			for _, ruleValue := range ruleValues {
@@ -400,6 +402,17 @@ func mutateHeadersByRules(headers, rules http.Header, repl httpserver.Replacer)
 			}
 		}
 	}
+
+	for ruleField, ruleValues := range replacements {
+		for _, ruleValue := range ruleValues {
+			replacement := repl.Replace(ruleValue.to)
+			original := headers.Get(ruleField)
+			if len(replacement) > 0 && len(original) > 0 {
+				replaced := ruleValue.regexp.ReplaceAllString(original, replacement)
+				headers.Set(ruleField, replaced)
+			}
+		}
+	}
 }
 
 const CustomStatusContextCancelled = 499

caddyhttp/proxy/upstream.go

@@ -23,8 +23,10 @@ import (
 	"io/ioutil"
 	"net"
 	"net/http"
+	"net/textproto"
 	"net/url"
 	"path"
+	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -71,12 +73,30 @@ type staticUpstream struct {
 	MaxFails           int32
 	resolver           srvResolver
 	CaCertPool         *x509.CertPool
+	upstreamHeaderReplacements   headerReplacements
+	downstreamHeaderReplacements headerReplacements
 }
 
 type srvResolver interface {
 	LookupSRV(context.Context, string, string, string) (string, []*net.SRV, error)
 }
 
+type headerReplacement struct {
+	regexp *regexp.Regexp
+	to     string
+}
+
+type headerReplacements map[string][]headerReplacement
+
+func (h headerReplacements) Add(key string, value headerReplacement) {
+	key = textproto.CanonicalMIMEHeaderKey(key)
+	h[key] = append(h[key], value)
+}
+
+func (h headerReplacements) Del(key string) {
+	delete(h, textproto.CanonicalMIMEHeaderKey(key))
+}
+
 // NewStaticUpstreams parses the configuration input and sets up
 // static upstreams for the proxy middleware. The host string parameter,
 // if not empty, is used for setting the upstream Host header for the
@@ -98,6 +118,8 @@ func NewStaticUpstreams(c caddyfile.Dispenser, host string) ([]Upstream, error)
 			KeepAlive:                    http.DefaultMaxIdleConnsPerHost,
 			Timeout:                      30 * time.Second,
 			resolver:                     net.DefaultResolver,
+			upstreamHeaderReplacements:   make(headerReplacements),
+			downstreamHeaderReplacements: make(headerReplacements),
 		}
 
 		if !c.Args(&upstream.from) {
@@ -223,6 +245,8 @@ func (u *staticUpstream) NewHost(host string) (*UpstreamHost, error) {
 		WithoutPathPrefix:            u.WithoutPathPrefix,
 		MaxConns:                     u.MaxConns,
 		HealthCheckResult:            atomic.Value{},
+		UpstreamHeaderReplacements:   u.upstreamHeaderReplacements,
+		DownstreamHeaderReplacements: u.downstreamHeaderReplacements,
 	}
 
 	baseURL, err := url.Parse(uh.Name)
@@ -431,7 +455,18 @@ func parseBlock(c *caddyfile.Dispenser, u *staticUpstream, hasSrv bool) error {
 		}
 		u.HealthCheck.ContentString = c.Val()
 	case "header_upstream":
-		var header, value string
+		var header, value, replaced string
+		if c.Args(&header, &value, &replaced) {
+			// Don't allow - or + in replacements
+			if strings.HasPrefix(header, "-") || strings.HasPrefix(header, "+") {
+				return c.ArgErr()
+			}
+			r, err := regexp.Compile(value)
+			if err != nil {
+				return c.ArgErr()
+			}
+			u.upstreamHeaderReplacements.Add(header, headerReplacement{r, replaced})
+		} else {
 			if !c.Args(&header, &value) {
 				// When removing a header, the value can be optional.
 				if !strings.HasPrefix(header, "-") {
@@ -439,8 +474,20 @@ func parseBlock(c *caddyfile.Dispenser, u *staticUpstream, hasSrv bool) error {
 				}
 			}
 			u.upstreamHeaders.Add(header, value)
+		}
 	case "header_downstream":
-		var header, value string
+		var header, value, replaced string
+		if c.Args(&header, &value, &replaced) {
+			// Don't allow - or + in replacements
+			if strings.HasPrefix(header, "-") || strings.HasPrefix(header, "+") {
+				return c.ArgErr()
+			}
+			r, err := regexp.Compile(value)
+			if err != nil {
+				return c.ArgErr()
+			}
+			u.upstreamHeaderReplacements.Add(header, headerReplacement{r, replaced})
+		} else {
 			if !c.Args(&header, &value) {
 				// When removing a header, the value can be optional.
 				if !strings.HasPrefix(header, "-") {
@@ -448,6 +495,7 @@ func parseBlock(c *caddyfile.Dispenser, u *staticUpstream, hasSrv bool) error {
 				}
 			}
 			u.downstreamHeaders.Add(header, value)
+		}
 	case "transparent":
 		// Note: X-Forwarded-For header is always being appended for proxy connections
 		// See implementation of createUpstreamRequest in proxy.go