feat(mcp): add opt-in request metadata bridge for tool handlers (#5550)

mcp/request_metadata.go

@@ -0,0 +1,150 @@
+package mcp
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/zeromicro/go-zero/rest/pathvar"
+)
+
+// RequestMetadata carries selected request-scoped values into MCP handlers.
+type RequestMetadata struct {
+	Headers map[string][]string
+	Query   map[string][]string
+	Path    map[string]string
+}
+
+type requestMetadataCtxKey struct{}
+
+// RequestMetadataFromContext returns metadata extracted at the transport boundary.
+func RequestMetadataFromContext(ctx context.Context) (RequestMetadata, bool) {
+	metadata, ok := requestMetadataFromContext(ctx)
+	if !ok {
+		return RequestMetadata{}, false
+	}
+
+	return normalizeRequestMetadata(metadata), true
+}
+
+// HeaderFromContext returns the first header value for key.
+func HeaderFromContext(ctx context.Context, key string) (string, bool) {
+	metadata, ok := requestMetadataFromContext(ctx)
+	if !ok {
+		return "", false
+	}
+
+	vals := metadata.Headers[http.CanonicalHeaderKey(key)]
+	if len(vals) == 0 {
+		return "", false
+	}
+
+	return vals[0], true
+}
+
+// QueryFromContext returns the first query value for key.
+func QueryFromContext(ctx context.Context, key string) (string, bool) {
+	metadata, ok := requestMetadataFromContext(ctx)
+	if !ok {
+		return "", false
+	}
+
+	vals := metadata.Query[key]
+	if len(vals) == 0 {
+		return "", false
+	}
+
+	return vals[0], true
+}
+
+// PathFromContext returns the path variable value for key.
+func PathFromContext(ctx context.Context, key string) (string, bool) {
+	metadata, ok := requestMetadataFromContext(ctx)
+	if !ok {
+		return "", false
+	}
+
+	val, ok := metadata.Path[key]
+	if !ok {
+		return "", false
+	}
+
+	return val, true
+}
+
+func requestMetadataFromContext(ctx context.Context) (RequestMetadata, bool) {
+	metadata, ok := ctx.Value(requestMetadataCtxKey{}).(RequestMetadata)
+	if !ok {
+		return RequestMetadata{}, false
+	}
+
+	return metadata, true
+}
+
+// DefaultRequestMetadataExtractor extracts headers, query values, and path variables.
+func DefaultRequestMetadataExtractor(r *http.Request) RequestMetadata {
+	metadata := RequestMetadata{
+		Headers: make(map[string][]string, len(r.Header)),
+		Query:   make(map[string][]string),
+		Path:    clonePathVars(pathvar.Vars(r)),
+	}
+
+	for key, vals := range r.Header {
+		metadata.Headers[http.CanonicalHeaderKey(key)] = append([]string(nil), vals...)
+	}
+
+	if r.URL != nil {
+		for key, vals := range r.URL.Query() {
+			metadata.Query[key] = append([]string(nil), vals...)
+		}
+	}
+
+	return metadata
+}
+
+func normalizeRequestMetadata(metadata RequestMetadata) RequestMetadata {
+	return RequestMetadata{
+		Headers: cloneCanonicalHeaderValues(metadata.Headers),
+		Query:   cloneHeaderValues(metadata.Query),
+		Path:    clonePathVars(metadata.Path),
+	}
+}
+
+func cloneHeaderValues(values map[string][]string) map[string][]string {
+	if len(values) == 0 {
+		return nil
+	}
+
+	cloned := make(map[string][]string, len(values))
+	for key, vals := range values {
+		cloned[key] = append([]string(nil), vals...)
+	}
+
+	return cloned
+}
+
+func cloneCanonicalHeaderValues(values map[string][]string) map[string][]string {
+	if len(values) == 0 {
+		return nil
+	}
+
+	cloned := make(map[string][]string, len(values))
+	for key, vals := range values {
+		canonical := http.CanonicalHeaderKey(key)
+		cloned[canonical] = append(cloned[canonical], vals...)
+	}
+
+	return cloned
+}
+
+func clonePathVars(values map[string]string) map[string]string {
+	if len(values) == 0 {
+		return nil
+	}
+
+	cloned := make(map[string]string, len(values))
+	for key, val := range values {
+		cloned[key] = val
+	}
+
+	return cloned
+}