From 3ff6ca1efc8cc825d08f6b86d6897d85cde973a1 Mon Sep 17 00:00:00 2001
From: Roland Reichwein <Roland.Reichwein@bmw.de>
Date: Sun, 16 Aug 2026 17:31:19 +0200
Subject: [PATCH] Fix ambiguous byte_stream_reader construction from
 etl::span<uint8_t> (#1537)

Add unsigned char/const unsigned char span overloads to byte_stream_reader
to match byte_stream_writer, resolving overload ambiguity (#1533). Add
tests covering span construction for both classes.

Co-authored-by: John Wellbelove <jwellbelove@users.noreply.github.com>
---
 include/etl/byte_stream.h | 22 ++++++++++++++++
 test/test_byte_stream.cpp | 53 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/include/etl/byte_stream.h b/include/etl/byte_stream.h
index 51dc9e92..76a4bf04 100644
--- a/include/etl/byte_stream.h
+++ b/include/etl/byte_stream.h
@@ -508,6 +508,28 @@ namespace etl
     {
     }
 
+    //***************************************************************************
+    /// Construct from span.
+    //***************************************************************************
+    byte_stream_reader(etl::span<unsigned char> span_, etl::endian stream_endianness_)
+      : pdata(reinterpret_cast<const char*>(span_.begin()))
+      , pcurrent(reinterpret_cast<const char*>(span_.begin()))
+      , stream_length(span_.size_bytes())
+      , stream_endianness(stream_endianness_)
+    {
+    }
+
+    //***************************************************************************
+    /// Construct from span.
+    //***************************************************************************
+    byte_stream_reader(etl::span<const unsigned char> span_, etl::endian stream_endianness_)
+      : pdata(reinterpret_cast<const char*>(span_.begin()))
+      , pcurrent(reinterpret_cast<const char*>(span_.begin()))
+      , stream_length(span_.size_bytes())
+      , stream_endianness(stream_endianness_)
+    {
+    }
+
     //***************************************************************************
     /// Construct from range.
     //***************************************************************************
diff --git a/test/test_byte_stream.cpp b/test/test_byte_stream.cpp
index 06b2a453..514dbd81 100644
--- a/test/test_byte_stream.cpp
+++ b/test/test_byte_stream.cpp
@@ -188,6 +188,59 @@ namespace
       CHECK(reader_little.get_endianness() == etl::endian::little);
     }
 
+    //*************************************************************************
+    TEST(byte_stream_writer_construct_from_span)
+    {
+      char storage[8];
+
+      etl::span<char>         char_span(storage, storage + ETL_OR_STD17::size(storage));
+      etl::byte_stream_writer writer_char(char_span, etl::endian::little);
+      CHECK_EQUAL(char_span.size(), writer_char.capacity());
+
+      etl::span<unsigned char> uchar_span(reinterpret_cast<unsigned char*>(storage), ETL_OR_STD17::size(storage));
+      etl::byte_stream_writer  writer_uchar(uchar_span, etl::endian::little);
+      CHECK_EQUAL(uchar_span.size(), writer_uchar.capacity());
+    }
+
+    //*************************************************************************
+    TEST(byte_stream_reader_construct_from_span)
+    {
+      char storage[8] = {0};
+
+      etl::span<char>         char_span(storage, storage + ETL_OR_STD17::size(storage));
+      etl::byte_stream_reader reader_char(char_span, etl::endian::little);
+      CHECK_EQUAL(char_span.size(), reader_char.size_bytes());
+
+      etl::span<const char>   const_char_span(storage, storage + ETL_OR_STD17::size(storage));
+      etl::byte_stream_reader reader_const_char(const_char_span, etl::endian::little);
+      CHECK_EQUAL(const_char_span.size(), reader_const_char.size_bytes());
+
+      etl::span<unsigned char> uchar_span(reinterpret_cast<unsigned char*>(storage), ETL_OR_STD17::size(storage));
+      etl::byte_stream_reader  reader_uchar(uchar_span, etl::endian::little);
+      CHECK_EQUAL(uchar_span.size(), reader_uchar.size_bytes());
+
+      etl::span<const unsigned char> const_uchar_span(reinterpret_cast<const unsigned char*>(storage), ETL_OR_STD17::size(storage));
+      etl::byte_stream_reader        reader_const_uchar(const_uchar_span, etl::endian::little);
+      CHECK_EQUAL(const_uchar_span.size(), reader_const_uchar.size_bytes());
+    }
+
+    //*************************************************************************
+    // https://github.com/ETLCPP/etl/issues/1533
+    // Passing an etl::span<uint8_t> to byte_stream_writer/byte_stream_reader
+    // must not be ambiguous.
+    TEST(byte_stream_reader_writer_construct_from_span_uint8_t_no_ambiguity)
+    {
+      uint8_t storage[8] = {0};
+
+      etl::span<uint8_t> data(storage, ETL_OR_STD17::size(storage));
+
+      etl::byte_stream_writer writer(etl::span<uint8_t>(data), etl::endian::little);
+      etl::byte_stream_reader reader(etl::span<uint8_t>(data), etl::endian::little);
+
+      CHECK_EQUAL(data.size(), writer.capacity());
+      CHECK_EQUAL(data.size(), reader.size_bytes());
+    }
+
     //*************************************************************************
     TEST(write_bool)
     {