service: define request X-headers interface

service/meta.go

@@ -1,5 +1,13 @@
 package service
 
+import (
+	"io"
+)
+
+type extHdrSrcWrapper struct {
+	extHdrSrc ExtendedHeadersSource
+}
+
 // CutMeta returns current value and sets RequestMetaHeader to empty value.
 func (m *RequestMetaHeader) CutMeta() RequestMetaHeader {
 	cp := *m
@@ -11,3 +19,53 @@ func (m *RequestMetaHeader) CutMeta() RequestMetaHeader {
 func (m *RequestMetaHeader) RestoreMeta(v RequestMetaHeader) {
 	*m = v
 }
+
+// ExtendedHeadersSignedData wraps passed ExtendedHeadersSource and returns SignedDataSource.
+func ExtendedHeadersSignedData(headers ExtendedHeadersSource) SignedDataSource {
+	return &extHdrSrcWrapper{
+		extHdrSrc: headers,
+	}
+}
+
+// SignedData returns extended headers in a binary representation.
+func (s extHdrSrcWrapper) SignedData() ([]byte, error) {
+	return SignedDataFromReader(s)
+}
+
+// SignedDataSize returns the length of extended headers slice.
+func (s extHdrSrcWrapper) SignedDataSize() (res int) {
+	if s.extHdrSrc != nil {
+		for _, h := range s.extHdrSrc.ExtendedHeaders() {
+			if h != nil {
+				res += len(h.Key()) + len(h.Value())
+			}
+		}
+	}
+
+	return
+}
+
+// ReadSignedData copies a binary representation of the extended headers to passed buffer.
+//
+// If buffer length is less than required, io.ErrUnexpectedEOF returns.
+func (s extHdrSrcWrapper) ReadSignedData(p []byte) (int, error) {
+	sz := s.SignedDataSize()
+	if len(p) < sz {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	if s.extHdrSrc != nil {
+		off := 0
+		for _, h := range s.extHdrSrc.ExtendedHeaders() {
+			if h == nil {
+				continue
+			}
+
+			off += copy(p[off:], []byte(h.Key()))
+
+			off += copy(p[off:], []byte(h.Value()))
+		}
+	}
+
+	return sz, nil
+}

service/types.go

@@ -301,3 +301,14 @@ type BearerToken interface {
 type BearerTokenSource interface {
 	GetBearerToken() BearerToken
 }
+
+// ExtendedHeader is an interface of string key-value pair with read access.
+type ExtendedHeader interface {
+	Key() string
+	Value() string
+}
+
+// ExtendedHeadersSource is an interface of ExtendedHeader list with read access.
+type ExtendedHeadersSource interface {
+	ExtendedHeaders() []ExtendedHeader
+}