fix(http): preserve case-insensitive header precedence

internal/tools/http/http.go

@@ -17,7 +17,6 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"maps"
 	"net/http"
 	"net/url"
 	"slices"
@@ -249,16 +248,26 @@ func getURL(baseURL, path string, pathParams, queryParams parameters.Parameters,
 	return parsedURL.String(), nil
 }
 
+// Merge headers case-insensitively, with later sets overriding earlier sets.
+func mergeHeaders(headerSets ...map[string]string) map[string]string {
+	headers := make(map[string]string)
+	for _, headerSet := range headerSets {
+		for name, value := range headerSet {
+			headers[http.CanonicalHeaderKey(name)] = value
+		}
+	}
+	return headers
+}
+
 // Helper function to generate the HTTP headers upon Tool invocation.
 func getHeaders(headerParams parameters.Parameters, defaultHeaders map[string]string, paramsMap map[string]any) (map[string]string, error) {
 	// Populate header params
-	allHeaders := make(map[string]string)
-	maps.Copy(allHeaders, defaultHeaders)
+	allHeaders := mergeHeaders(defaultHeaders)
 	for _, p := range headerParams {
 		headerValue, ok := paramsMap[p.GetName()]
 		if ok {
 			if strValue, ok := headerValue.(string); ok {
-				allHeaders[p.GetName()] = strValue
+				allHeaders[http.CanonicalHeaderKey(p.GetName())] = strValue
 			} else {
 				return nil, fmt.Errorf("header param %s got value of type %t, not string", p.GetName(), headerValue)
 			}
@@ -274,9 +283,7 @@ func (t Tool) Invoke(ctx context.Context, s sources.Source, params parameters.Pa
 	}
 	// Combine Source and Tool headers.
 	// In case of conflict, Tool header overrides Source header
-	combinedHeaders := make(map[string]string)
-	maps.Copy(combinedHeaders, source.HttpDefaultHeaders())
-	maps.Copy(combinedHeaders, t.Cfg.Headers)
+	combinedHeaders := mergeHeaders(source.HttpDefaultHeaders(), t.Cfg.Headers)
 
 	paramsMap := params.AsMap()
 

internal/tools/http/http_url_test.go

@@ -15,12 +15,48 @@
 package http
 
 import (
+	"maps"
 	"net/url"
 	"testing"
 
 	"github.com/googleapis/mcp-toolbox/internal/util/parameters"
 )
 
+func TestGetHeadersCaseInsensitiveOverride(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		params    map[string]any
+		want      map[string]string
+		wantError bool
+	}{
+		{
+			name:   "provided parameter overrides static header",
+			params: map[string]any{"CONTENT-type": "application/json; charset=UTF-8"},
+			want:   map[string]string{"Content-Type": "application/json; charset=UTF-8"},
+		},
+		{
+			name: "omitted parameter retains static header",
+			want: map[string]string{"Content-Type": "text/plain; charset=UTF-8"},
+		},
+		{
+			name:      "nil parameter retains existing error behavior",
+			params:    map[string]any{"CONTENT-type": nil},
+			wantError: true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			headerParams := parameters.Parameters{parameters.NewStringParameter("CONTENT-type", "content type", parameters.WithStringRequired(false))}
+			got, err := getHeaders(headerParams, map[string]string{"content-type": "text/plain; charset=UTF-8"}, tc.params)
+			if (err != nil) != tc.wantError {
+				t.Fatalf("getHeaders() error = %v, wantError %v", err, tc.wantError)
+			}
+			if !tc.wantError && !maps.Equal(got, tc.want) {
+				t.Fatalf("getHeaders() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
 func TestGetURLHostOverride(t *testing.T) {
 	testCases := []struct {
 		name         string