Add byte_stream for zero-copy serialization, and add support in ZMQ-JSON.

contrib/epee/include/byte_slice.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2019, The Monero Project
+// Copyright (c) 2019-2020, The Monero Project
 //
 // All rights reserved.
 //
@@ -39,6 +39,7 @@
 namespace epee
 {
   struct byte_slice_data;
+  class byte_stream;
 
   struct release_byte_slice
   {
@@ -50,6 +51,12 @@ namespace epee
     }
   };
 
+  //! Frees ref count + buffer allocated internally by `byte_buffer`.
+  struct release_byte_buffer
+  {
+    void operator()(std::uint8_t* buf) const noexcept;
+  };
+
   /*! Inspired by slices in golang. Storage is thread-safe reference counted,
       allowing for cheap copies or range selection on the bytes. The bytes
       owned by this class are always immutable.
@@ -104,6 +111,9 @@ namespace epee
     //! Convert `buffer` into a slice using one allocation for shared count.
     explicit byte_slice(std::string&& buffer);
 
+    //! Convert `stream` into a slice with zero allocations.
+    explicit byte_slice(byte_stream&& stream) noexcept;
+
     byte_slice(byte_slice&& source) noexcept;
     ~byte_slice() noexcept = default;
 
@@ -149,5 +159,19 @@ namespace epee
     //! \post `empty()` \return Ownership of ref-counted buffer.
     std::unique_ptr<byte_slice_data, release_byte_slice> take_buffer() noexcept;
   };
+
+  //! Alias for a buffer that has space for a `byte_slice` ref count.
+  using byte_buffer = std::unique_ptr<std::uint8_t, release_byte_buffer>;
+
+  /*! \return `buf` with a new size of exactly `length`. New bytes not
+        initialized. A `nullptr` is returned on allocation failure. */
+  byte_buffer byte_buffer_resize(byte_buffer buf, std::size_t length) noexcept;
+
+  /*! Increase `buf` of size `current` by `more` bytes.
+
+    \throw std::range_error if `current + more` exceeds `size_t` bounds.
+    \return Buffer of `current + more` bytes. A `nullptr` is returned on
+      allocation failure. */
+  byte_buffer byte_buffer_increase(byte_buffer buf, std::size_t current, std::size_t more);
 } // epee