add streaming websocket server and client (#62)

sherpa-onnx/csrc/tee-stream.h

@@ -0,0 +1,61 @@
+// Code in this file is copied and modified from
+// https://wordaligned.org/articles/cpp-streambufs
+
+#ifndef SHERPA_ONNX_CSRC_TEE_STREAM_H_
+#define SHERPA_ONNX_CSRC_TEE_STREAM_H_
+#include <ostream>
+#include <streambuf>
+#include <string>
+
+namespace sherpa_onnx {
+
+template <typename char_type, typename traits = std::char_traits<char_type>>
+class basic_teebuf : public std::basic_streambuf<char_type, traits> {
+ public:
+  using int_type = typename traits::int_type;
+
+  basic_teebuf(std::basic_streambuf<char_type, traits> *sb1,
+               std::basic_streambuf<char_type, traits> *sb2)
+      : sb1(sb1), sb2(sb2) {}
+
+ private:
+  int sync() override {
+    int const r1 = sb1->pubsync();
+    int const r2 = sb2->pubsync();
+    return r1 == 0 && r2 == 0 ? 0 : -1;
+  }
+
+  int_type overflow(int_type c) override {
+    int_type const eof = traits::eof();
+
+    if (traits::eq_int_type(c, eof)) {
+      return traits::not_eof(c);
+    } else {
+      char_type const ch = traits::to_char_type(c);
+      int_type const r1 = sb1->sputc(ch);
+      int_type const r2 = sb2->sputc(ch);
+
+      return traits::eq_int_type(r1, eof) || traits::eq_int_type(r2, eof) ? eof
+                                                                          : c;
+    }
+  }
+
+ private:
+  std::basic_streambuf<char_type, traits> *sb1;
+  std::basic_streambuf<char_type, traits> *sb2;
+};
+
+using teebuf = basic_teebuf<char>;
+
+class TeeStream : public std::ostream {
+ public:
+  TeeStream(std::ostream &o1, std::ostream &o2)
+      : std::ostream(&tbuf), tbuf(o1.rdbuf(), o2.rdbuf()) {}
+
+ private:
+  teebuf tbuf;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_TEE_STREAM_H_