json: Introduce chunked_buffer

Signed-off-by: Ben Pope <ben@redpanda.com>

src/v/json/chunked_buffer.h

@@ -0,0 +1,59 @@
+// Copyright 2024 Redpanda Data, Inc.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.md
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0
+
+#pragma once
+
+#include "bytes/iobuf.h"
+#include "json/encodings.h"
+
+namespace json {
+
+namespace impl {
+
+/**
+ * \brief An in-memory output stream with non-contiguous memory allocation.
+ */
+template<typename Encoding>
+struct generic_chunked_buffer {
+    using Ch = Encoding::Ch;
+
+    /**
+     * \defgroup Implement rapidjson::Stream
+     */
+    /**@{*/
+
+    void Put(Ch c) { _impl.append(&c, sizeof(Ch)); }
+    void Flush() {}
+
+    //! Get the size of string in bytes in the string buffer.
+    size_t GetSize() const { return _impl.size_bytes(); }
+
+    //! Get the length of string in Ch in the string buffer.
+    size_t GetLength() const { return _impl.size_bytes() / sizeof(Ch); }
+
+    void Reserve(size_t s) { _impl.reserve(s); }
+
+    void Clear() { _impl.clear(); }
+
+    /**@}*/
+
+    iobuf as_iobuf() && { return std::move(_impl); }
+
+private:
+    iobuf _impl;
+};
+
+} // namespace impl
+
+template<typename Encoding>
+using generic_chunked_buffer = impl::generic_chunked_buffer<Encoding>;
+
+using chunked_buffer = generic_chunked_buffer<UTF8<>>;
+
+} // namespace json

src/v/json/json.cc

@@ -9,6 +9,7 @@
 
 #include "json/json.h"
 
+#include "json/chunked_buffer.h"
 #include "json/stringbuffer.h"
 
 namespace json {
@@ -175,4 +176,43 @@ template void rjson_serialize<json::StringBuffer>(
 template void rjson_serialize<json::StringBuffer>(
   json::Writer<json::StringBuffer>& w, const std::filesystem::path& path);
 
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, short v);
+
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, bool v);
+
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, long long v);
+
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, int v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, unsigned int v);
+
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, long v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, unsigned long v);
+
+template void
+rjson_serialize<chunked_buffer>(json::Writer<chunked_buffer>& w, double v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, std::string_view s);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, const net::unresolved_address& v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, const std::chrono::milliseconds& v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, const std::chrono::seconds& v);
+
+template void rjson_serialize<chunked_buffer>(
+  json::Writer<chunked_buffer>& w, const std::filesystem::path& path);
+
 } // namespace json