add functional options for adding/removing headers

runnables/httpserver/middleware/headers/headers.go

@@ -56,18 +56,18 @@ func JSON() httpserver.HandlerFunc {
 //	// Development setup with all methods
 //	CORS("http://localhost:3000", "GET,POST,PUT,PATCH,DELETE,OPTIONS", "*")
 func CORS(allowOrigin, allowMethods, allowHeaders string) httpserver.HandlerFunc {
-	headers := HeaderMap{
+	corsHeaders := HeaderMap{
 		"Access-Control-Allow-Origin":  allowOrigin,
 		"Access-Control-Allow-Methods": allowMethods,
 		"Access-Control-Allow-Headers": allowHeaders,
 	}
 
 	// Add credentials header if origin is not wildcard
 	if allowOrigin != "*" {
-		headers["Access-Control-Allow-Credentials"] = "true"
+		corsHeaders["Access-Control-Allow-Credentials"] = "true"
 	}
 
-	return New(headers)
+	return NewWithOperations(WithSet(corsHeaders))
 }
 
 // Security creates a middleware that sets common security headers.

runnables/httpserver/middleware/headers/options.go

@@ -0,0 +1,101 @@
+package headers
+
+import (
+	"net/http"
+
+	"github.com/robbyt/go-supervisor/runnables/httpserver"
+)
+
+// HeaderOperation represents a single header manipulation operation
+type HeaderOperation func(*headerOperations)
+
+type headerOperations struct {
+	setHeaders    http.Header
+	addHeaders    http.Header
+	removeHeaders []string
+}
+
+// WithSet creates an operation to set (replace) headers
+func WithSet(headers HeaderMap) HeaderOperation {
+	return func(ops *headerOperations) {
+		if ops.setHeaders == nil {
+			ops.setHeaders = make(http.Header)
+		}
+		for key, value := range headers {
+			ops.setHeaders.Set(key, value)
+		}
+	}
+}
+
+// WithSetHeader creates an operation to set a single header
+func WithSetHeader(key, value string) HeaderOperation {
+	return func(ops *headerOperations) {
+		if ops.setHeaders == nil {
+			ops.setHeaders = make(http.Header)
+		}
+		ops.setHeaders.Set(key, value)
+	}
+}
+
+// WithAdd creates an operation to add (append) headers
+func WithAdd(headers HeaderMap) HeaderOperation {
+	return func(ops *headerOperations) {
+		if ops.addHeaders == nil {
+			ops.addHeaders = make(http.Header)
+		}
+		for key, value := range headers {
+			ops.addHeaders.Add(key, value)
+		}
+	}
+}
+
+// WithAddHeader creates an operation to add a single header
+func WithAddHeader(key, value string) HeaderOperation {
+	return func(ops *headerOperations) {
+		if ops.addHeaders == nil {
+			ops.addHeaders = make(http.Header)
+		}
+		ops.addHeaders.Add(key, value)
+	}
+}
+
+// WithRemove creates an operation to remove headers
+func WithRemove(headerNames ...string) HeaderOperation {
+	return func(ops *headerOperations) {
+		ops.removeHeaders = append(ops.removeHeaders, headerNames...)
+	}
+}
+
+// NewWithOperations creates a middleware with full header control using functional options.
+// Operations are executed in order: remove → set → add
+func NewWithOperations(operations ...HeaderOperation) httpserver.HandlerFunc {
+	ops := &headerOperations{}
+	for _, operation := range operations {
+		operation(ops)
+	}
+
+	return func(rp *httpserver.RequestProcessor) {
+		writer := rp.Writer()
+
+		// 1. Remove headers first
+		for _, key := range ops.removeHeaders {
+			writer.Header().Del(key)
+		}
+
+		// 2. Set headers (replace)
+		for key, values := range ops.setHeaders {
+			if len(values) > 0 {
+				writer.Header().Set(key, values[0])
+			}
+		}
+
+		// 3. Add headers (append)
+		for key, values := range ops.addHeaders {
+			for _, value := range values {
+				writer.Header().Add(key, value)
+			}
+		}
+
+		rp.Next()
+	}
+}