reverseproxy: Caddyfile health check headers, host header support (#3948)

* reverse_proxy: 1.health check headers can be set through Caddyfile using health_headers directive; 2.health check header host can be set properly

* reverse_proxy:
replace example with syntax definition
inline health_headers directive parse function

* bugfix: change caddyfile_adapt testcase file from space to tab

* reverseproxy: modify health_header value document as optional and add more test cases

3 files changed, 86 insertions, 1 deletions

diff --git a/caddytest/integration/caddyfile_adapt/reverse_proxy_health_headers.txt b/caddytest/integration/caddyfile_adapt/reverse_proxy_health_headers.txt
new file mode 100644
index 0000000..a3d842a
--- /dev/null
+++ b/caddytest/integration/caddyfile_adapt/reverse_proxy_health_headers.txt
@@ -0,0 +1,57 @@
+:8884
+
+reverse_proxy 127.0.0.1:65535 {
+	health_headers {
+		Host example.com
+		X-Header-Key 95ca39e3cbe7
+		X-Header-Keys VbG4NZwWnipo 335Q9/MhqcNU3s2TO
+		X-Empty-Value
+	}
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":8884"
+					],
+					"routes": [
+						{
+							"handle": [
+								{
+									"handler": "reverse_proxy",
+									"health_checks": {
+										"active": {
+											"headers": {
+												"Host": [
+													"example.com"
+												],
+												"X-Empty-Value": [
+													""
+												],
+												"X-Header-Key": [
+													"95ca39e3cbe7"
+												],
+												"X-Header-Keys": [
+													"VbG4NZwWnipo",
+													"335Q9/MhqcNU3s2TO"
+												]
+											}
+										}
+									},
+									"upstreams": [
+										{
+											"dial": "127.0.0.1:65535"
+										}
+									]
+								}
+							]
+						}
+					]
+				}
+			}
+		}
+	}
+}
diff --git a/modules/caddyhttp/reverseproxy/caddyfile.go b/modules/caddyhttp/reverseproxy/caddyfile.go
index 4a69287..57f425a 100644
--- a/modules/caddyhttp/reverseproxy/caddyfile.go
+++ b/modules/caddyhttp/reverseproxy/caddyfile.go
@@ -63,6 +63,9 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 //         health_timeout <duration>
 //         health_status <status>
 //         health_body <regexp>
+//         health_headers {
+//             <field> [<values...>]
+//         }
 //
 //         # passive health checking
 //         max_fails <num>
@@ -313,6 +316,26 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				}
 				h.HealthChecks.Active.Port = portNum
 
+			case "health_headers":
+				healthHeaders := make(http.Header)
+				for d.Next() {
+					for d.NextBlock(0) {
+						key := d.Val()
+						values := d.RemainingArgs()
+						if len(values) == 0 {
+							values = append(values, "")
+						}
+						healthHeaders[key] = values
+					}
+				}
+				if h.HealthChecks == nil {
+					h.HealthChecks = new(HealthChecks)
+				}
+				if h.HealthChecks.Active == nil {
+					h.HealthChecks.Active = new(ActiveHealthChecks)
+				}
+				h.HealthChecks.Active.Headers = healthHeaders
+
 			case "health_interval":
 				if !d.NextArg() {
 					return d.ArgErr()
diff --git a/modules/caddyhttp/reverseproxy/healthchecks.go b/modules/caddyhttp/reverseproxy/healthchecks.go
index 285834b..42003b6 100644
--- a/modules/caddyhttp/reverseproxy/healthchecks.go
+++ b/modules/caddyhttp/reverseproxy/healthchecks.go
@@ -26,6 +26,7 @@ import (
 	"regexp"
 	"runtime/debug"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/caddyserver/caddy/v2"
@@ -241,7 +242,11 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, host H
 		return fmt.Errorf("making request: %v", err)
 	}
 	for key, hdrs := range h.HealthChecks.Active.Headers {
-		req.Header[key] = hdrs
+		if strings.ToLower(key) == "host" {
+			req.Host = h.HealthChecks.Active.Headers.Get(key)
+		} else {
+			req.Header[key] = hdrs
+		}
 	}
 
 	// do the request, being careful to tame the response body