Change API of raw_istream to be more similar to raw_ostream.

wpiutil/include/support/raw_istream.h

@@ -16,21 +16,37 @@ class raw_istream {
  public:
   raw_istream() = default;
   virtual ~raw_istream() = default;
-  virtual bool read(void* data, std::size_t len) = 0;
+
+  raw_istream& read(void* data, std::size_t len) {
+    read_impl(data, len);
+    return *this;
+  }
+
   virtual void close() = 0;
 
+  bool has_error() const { return m_error; }
+  void clear_error() { m_error = false; }
+
   raw_istream(const raw_istream&) = delete;
   raw_istream& operator=(const raw_istream&) = delete;
+
+ protected:
+  void error_detected() { m_error = true; }
+
+ private:
+  virtual void read_impl(void* data, std::size_t len) = 0;
+
+  bool m_error = false;
 };
 
 class raw_mem_istream : public raw_istream {
  public:
   raw_mem_istream(const char* mem, std::size_t len) : m_cur(mem), m_left(len) {}
-  virtual ~raw_mem_istream() = default;
-  virtual bool read(void* data, std::size_t len);
-  virtual void close() {}
+  void close() override;
 
  private:
+  void read_impl(void* data, std::size_t len) override;
+
   const char* m_cur;
   std::size_t m_left;
 };