Re-add upb/bindings/stdc++/string.h, which is still used in tests.

upb/bindings/stdc++/string.h

@@ -0,0 +1,64 @@
+
+#ifndef UPB_STDCPP_H_
+#define UPB_STDCPP_H_
+
+#include "upb/sink.h"
+
+namespace upb {
+
+template <class T>
+class FillStringHandler {
+ public:
+  static void SetHandler(BytesHandler* handler) {
+    upb_byteshandler_setstartstr(handler, &FillStringHandler::StartString,
+                                 NULL);
+    upb_byteshandler_setstring(handler, &FillStringHandler::StringBuf, NULL);
+  }
+
+ private:
+  // TODO(haberman): add UpbBind/UpbMakeHandler support to BytesHandler so these
+  // can be prettier callbacks.
+  static void* StartString(void *c, const void *hd, size_t size) {
+    UPB_UNUSED(hd);
+    UPB_UNUSED(size);
+
+    T* str = static_cast<T*>(c);
+    str->clear();
+    return c;
+  }
+
+  static size_t StringBuf(void* c, const void* hd, const char* buf, size_t n,
+                          const BufferHandle* h) {
+    UPB_UNUSED(hd);
+    UPB_UNUSED(h);
+
+    T* str = static_cast<T*>(c);
+    try {
+      str->append(buf, n);
+      return n;
+    } catch (const std::exception&) {
+      return 0;
+    }
+  }
+};
+
+class StringSink {
+ public:
+  template <class T>
+  explicit StringSink(T* target) {
+    // TODO(haberman): we need to avoid rebuilding a new handler every time,
+    // but with class globals disallowed for google3 C++ this is tricky.
+    FillStringHandler<T>::SetHandler(&handler_);
+    input_.Reset(&handler_, target);
+  }
+
+  BytesSink* input() { return &input_; }
+
+ private:
+  BytesHandler handler_;
+  BytesSink input_;
+};
+
+}  // namespace upb
+
+#endif  // UPB_STDCPP_H_