MB-69242: Create Sink interface

Add a base-class/interface Sink

Change-Id: I63ee1ed23e66f1d4175ec0175736bcff97d9c806
Reviewed-on: https://review.couchbase.org/c/platform/+/237050
Reviewed-by: Trond Norbye <trond.norbye@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>

Author: jimwwalker

include/platform/file_sink.h

@@ -10,6 +10,8 @@
 
 #pragma once
 
+#include <platform/sink.h>
+
 #include <cstdio>
 #include <filesystem>
 #include <limits>
@@ -20,7 +22,7 @@ namespace cb::io {
  * A sink which writes to a file and throws std::system_error on failures to
  * write the data to the file.
  */
-class FileSink {
+class FileSink : public Sink {
 public:
     enum class Mode {
         /// Append to the file if it exists, otherwise create a new file
@@ -51,7 +53,7 @@ class FileSink {
      * Write a blob of data to the end of the file
      * @param data The data to write to the file
      */
-    void sink(std::string_view data);
+    void sink(std::string_view data) override;
 
     /**
      * (Explicit) Flush any uncommited data to the file system
@@ -61,7 +63,7 @@ class FileSink {
      * @throws std::system_error if there is an error writing the data to the
      *                           file
      */
-    std::size_t fsync();
+    std::size_t fsync() override;
 
     /**
      * Close the file (flushing any pending data). Trying to write to the file
@@ -71,10 +73,10 @@ class FileSink {
      * @throws std::system_error if there is an error writing the data to the
      *                           file
      */
-    std::size_t close();
+    std::size_t close() override;
 
     /// Get the number of bytes written to the file so far
-    std::size_t getBytesWritten() const {
+    std::size_t getBytesWritten() const override {
         return bytes_written;
     }
 

include/platform/sink.h

@@ -0,0 +1,27 @@
+/*
+ *     Copyright 2025-Present Couchbase, Inc.
+ *
+ *   Use of this software is governed by the Business Source License included
+ *   in the file licenses/BSL-Couchbase.txt.  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, included in
+ *   the file licenses/APL2.txt.
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <string_view>
+namespace cb::io {
+
+// Abstract Sink for moving data from network to a destination
+class Sink {
+public:
+    virtual ~Sink() = default;
+    virtual void sink(std::string_view data) = 0;
+    virtual std::size_t fsync() = 0;
+    virtual std::size_t close() = 0;
+    virtual std::size_t getBytesWritten() const = 0;
+};
+
+} // namespace cb::io