+/// An abstract base class for streams implementations that also support a
+/// pwrite operation. This is useful for code that can mostly stream out data,
+/// but needs to patch in a header that needs to know the output size.
+class raw_pwrite_stream : public raw_ostream {
+ virtual void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) = 0;
+
+public:
+ explicit raw_pwrite_stream(bool Unbuffered = false)
+ : raw_ostream(Unbuffered) {}
+ void pwrite(const char *Ptr, size_t Size, uint64_t Offset) {
+#ifndef NDBEBUG
+ uint64_t Pos = tell();
+ // /dev/null always reports a pos of 0, so we cannot perform this check
+ // in that case.
+ if (Pos)
+ assert(Size + Offset <= Pos && "We don't support extending the stream");
+#endif
+ pwrite_impl(Ptr, Size, Offset);
+ }
+};
+