Add vajson as second serializer backend

score/json/BUILD

@@ -39,6 +39,27 @@ config_setting(
     visibility = ["@score_baselibs//score/json/internal/parser:__subpackages__"],
 )
 
+string_flag(
+    name = "writer_library",
+    build_setting_default = "json_serialize",
+    values = [
+        "json_serialize",
+        "vajson",
+    ],
+)
+
+config_setting(
+    name = "writer_library_json_serialize",
+    flag_values = {":writer_library": "json_serialize"},
+    visibility = ["@score_baselibs//score/json/internal/writer:__subpackages__"],
+)
+
+config_setting(
+    name = "writer_library_vajson",
+    flag_values = {":writer_library": "vajson"},
+    visibility = ["@score_baselibs//score/json/internal/writer:__subpackages__"],
+)
+
 cc_library(
     name = "parser_interface",
     srcs = ["i_json_parser.cpp"],
@@ -116,8 +137,8 @@ cc_library(
     visibility = ["@score_baselibs//score/json:__subpackages__"],
     deps = [
         ":writer_interface",
-        "@score_baselibs//score/json/internal/writer/json_serialize",
-        "@score_baselibs//score/language/safecpp/safe_math",
+        "@score_baselibs//score/json/internal/writer",
+        "@score_baselibs//score/json/internal/writer:writer_backend",
     ],
 )
 
@@ -207,6 +228,10 @@ cc_test(
         "test_warnings",
         "aborts_upon_exception",
     ],
+    local_defines = select({
+        ":writer_library_json_serialize": ["WRITER_JSON_SERIALIZE"],
+        ":writer_library_vajson": ["WRITER_VAJSON"],
+    }),
     tags = ["unit"],
     visibility = [
         "@score_baselibs//score/json:__pkg__",

score/json/README.md

@@ -18,10 +18,12 @@
   - [Requirements](#requirements)
   - [Assumptions of Use](#assumptions-of-use)
   - [Selecting base library](#selecting-base-library)
+  - [Selecting writer library](#selecting-writer-library)
 
 This JSON library is designed as an abstraction layer which can switch to using
 other parsers/serializers under the hood. At the moment it uses vaJson from Vector for parsing,
-which is ASIL D certified. For serialization this library uses a custom implementation.
+which is ASIL D certified. For serialization a custom implementation is used by default, with vaJson
+available as an alternative, [selectable via a feature flag](#selecting-writer-library).
 
 This library requires to be ASIL B certified, so it can be used in other ASIL B
 certified components.
@@ -398,7 +400,7 @@ since they would require high amount of work. Please be aware and note:
 For the most up to date information on Requirements please follow the provided links to CodeBeamer.
 
 Adaptive Platform SW Safety Requirements
-- [The users of the vaJson ibrary SHALL guarantee the integrity of the data used to initialize the `amsr::json::JsonData` buffer.](broken_link_c/issue/6576406)
+- [The users of the vaJson Library SHALL guarantee the integrity of the data used to initialize the `score::json::vajson::JsonData` buffer.](broken_link_c/issue/6576406)
 
 [SW Component Requirements](broken_link_c/tracker/566325?workingSetId=-1&layout_name=document&subtreeRoot=5310849)
 - The JSON-Library shall support at least the functional set of RFC-8259.
@@ -438,3 +440,15 @@ In order to make use of nlohmann json library, feature flag needs to be set. Ple
 bazel test --config=spp_host_clang //score/json/... --//score/json:base_library="nlohmann"
 
 nlohmann json library do not supports hexadecimal. As it is not part of json standard.
+
+## Selecting writer library
+
+Independently of the parser, the serialization backend is selected by the `writer_library` flag. It accepts
+`json_serialize` (the default, a custom implementation) and `vajson` (the vector json library). The parser flag
+`base_library` has no influence on serialization.
+
+bazel test --config=spp_host_clang //score/json/... --//score/json:writer_library="vajson"
+
+Mind that the two backends differ in the representation they emit: `json_serialize` pretty-prints with a four
+space indentation, whereas `vajson` emits compact JSON without any insignificant whitespace between tokens. Both
+produce valid, equivalent JSON, but consumers comparing serialized output byte-wise are affected by the choice.

score/json/internal/writer/BUILD

@@ -0,0 +1,38 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License Version 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+load("@rules_cc//cc:defs.bzl", "cc_library")
+load("@score_baselibs//score/language/safecpp:toolchain_features.bzl", "COMPILER_WARNING_FEATURES")
+
+# Declarations of the serialization backend seam. Exactly one backend provides the definitions; which one is
+# selected by the `//score/json:writer_library` flag below.
+cc_library(
+    name = "writer_backend",
+    hdrs = ["writer_backend.h"],
+    features = COMPILER_WARNING_FEATURES,
+    tags = ["FFI"],
+    visibility = ["@score_baselibs//score/json:__subpackages__"],
+    deps = [
+        "@score_baselibs//score/json/internal/model",
+        "@score_baselibs//score/result",
+    ],
+)
+
+alias(
+    name = "writer",
+    actual = select({
+        "@score_baselibs//score/json:writer_library_json_serialize": "@score_baselibs//score/json/internal/writer/json_serialize:json_serialize_backend",
+        "@score_baselibs//score/json:writer_library_vajson": "@score_baselibs//score/json/internal/writer/vajson:vajson_backend",
+    }),
+    visibility = ["@score_baselibs//score/json:__pkg__"],
+)

score/json/internal/writer/json_serialize/BUILD

@@ -31,6 +31,20 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "json_serialize_backend",
+    srcs = ["json_serialize_backend.cpp"],
+    features = COMPILER_WARNING_FEATURES,
+    tags = ["FFI"],
+    visibility = ["@score_baselibs//score/json/internal/writer:__pkg__"],
+    deps = [
+        ":json_serialize",
+        "@score_baselibs//score/json/internal/writer:writer_backend",
+        "@score_baselibs//score/language/futurecpp",
+        "@score_baselibs//score/language/safecpp/safe_math",
+    ],
+)
+
 cc_test(
     name = "json_serialize_unit_test",
     srcs = [