First version of new API for Launch Manager

score/launch_manager/src/lm_control/src/fixed_string.hpp

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+/********************************************************************************
+ * 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
+ ********************************************************************************/
+
+#ifndef SCORE_MW_LIFECYCLE_FIXED_STRING_HPP
+#define SCORE_MW_LIFECYCLE_FIXED_STRING_HPP
+
+#include <array>
+#include <cstddef>
+#include <cstring>
+#include <string_view>
+
+namespace score::mw::lifecycle
+{
+
+/// @brief Allocation-free, fixed-capacity string with a null-termination invariant.
+///
+/// Stores a null-terminated string in a plain `std::array` of size `MaxLength + 1`.
+/// Designed for use across API boundaries where heap allocation is undesirable and
+/// a bounded string length is acceptable.
+///
+/// @tparam MaxLength Maximum number of usable characters, excluding the null terminator.
+///                   The internal storage is `MaxLength + 1` bytes so the terminator
+///                   always fits.
+///
+/// @par Invariant
+/// The stored string is always null-terminated. Every constructor and assignment path
+/// enforces this. Characters beyond the null terminator are indeterminate and must
+/// not be read directly — use `as_string_view()` or `data()` instead.
+///
+/// @par Copying and moving
+/// Copy and move are compiler-generated (rule of zero). The `std::array` storage
+/// carries no heap resource, so the generated forms are correct and efficient.
+///
+/// @par Ordering
+/// No `operator<` is provided. `FixedString` values have no meaningful ordering.
+///
+/// @par Cross-capacity comparison
+/// `FixedString<N>` and `FixedString<M>` are distinct types, but free-function
+/// `operator==` / `operator!=` overloads allow comparing them by string content.
+template <std::size_t MaxLength>
+struct FixedString
+{
+    /// @brief Construct an empty string (equivalent to "").
+    ///
+    /// Only `storage_[0]` is set to `'\0'`; the rest of the array is indeterminate.
+    /// This is intentional — zeroing `MaxLength + 1` bytes on every default
+    /// construction would be wasteful when the value is immediately overwritten.
+    constexpr FixedString() noexcept
+    {
+        storage_[0] = '\0';
+    }
+
+    /// @brief Construct from a string_view, truncating if necessary.
+    ///
+    /// If `s.size() > MaxLength`, only the first `MaxLength` characters are stored.
+    /// No error is raised at this level — detection and logging of over-length
+    /// strings must happen at the user side where the source and context are
+    /// available.
+    ///
+    /// @param s Source string. Does not require to be null-terminated.
+    constexpr explicit FixedString(std::string_view s) noexcept
+    {
+        const auto len = std::min(s.size(), MaxLength);
+        for (std::size_t i = 0; i < len; ++i) {
+            storage_[i] = s[i];
+        }
+        storage_[len] = '\0';
+    }
+
+    /// @brief Assign from a string_view, truncating if necessary.
+    ///
+    /// Behaves identically to the string_view constructor: copies up to
+    /// `MaxLength` characters and always null-terminates. If `s.size() >
+    /// MaxLength`, only the first `MaxLength` characters are stored - no
+    /// error is raised at this level.
+    ///
+    /// Allows direct assignment from string literals and std::string_view
+    /// without constructing a temporary FixedString:
+    /// @code
+    ///   FixedString name;
+    ///   name = "Running";
+    /// @endcode
+    ///
+    /// @param s Source string. Does not require to be null-terminated.
+    ///
+    /// @returns Reference to this instance.
+    constexpr FixedString& operator=(std::string_view s) noexcept
+    {
+        const auto len = std::min(s.size(), MaxLength);
+        for (std::size_t i = 0; i < len; ++i) {
+            storage_[i] = s[i];
+        }
+        storage_[len] = '\0';
+        return *this;
+    }
+
+    /// @brief Returns the fixed character capacity of the FixedString.
+    ///
+    /// The returned value is equal to the template parameter `MaxLength` and
+    /// represents the maximum number of characters that can be stored, excluding
+    /// the terminating null character.
+    ///
+    /// @return Maximum number of usable characters.
+    static constexpr std::size_t max_size() noexcept
+    {
+        return MaxLength;
+    }
+
+    /// @brief Returns the current length of the FixedString.
+    ///
+    /// The returned value represents the number of characters currently stored,
+    /// excluding the terminating null character. Returns 0 for a
+    /// default-constructed or cleared instance.
+    ///
+    /// Equivalent to `as_string_view().size()`.
+    ///
+    /// @return Number of stored characters.
+    std::size_t size() const noexcept
+    {
+        return as_string_view().size();
+    }
+
+    /// @brief Checks whether the FixedString is empty.
+    ///
+    /// A FixedString is considered empty when it contains no characters.
+    /// Returns true for a default-constructed or cleared instance.
+    ///
+    /// Equivalent to `size() == 0`.
+    ///
+    /// @return true if the FixedString is empty; otherwise, false.
+    bool empty() const noexcept
+    {
+        return storage_[0] == '\0';
+    }
+
+    /// @brief Clears the contents of the FixedString.
+    ///
+    /// After this call, the FixedString is empty, `size()` returns 0,
+    /// and `as_string_view()` returns an empty string.
+    ///
+    /// Only the terminating null character at the beginning of the internal
+    /// storage is written; the remaining storage is left unchanged.
+    void clear() noexcept
+    {
+        storage_[0] = '\0';
+    }
+
+    /// @brief Returns the contents of the FixedString as a std::string_view.
+    ///
+    /// The returned view refers directly to the internal storage of this
+    /// FixedString and does not own the underlying character data.
+    ///
+    /// The view remains valid only while this FixedString instance exists and
+    /// its contents are not modified.
+    ///
+    /// @return A std::string_view representing the stored character sequence.
+    std::string_view as_string_view() const noexcept
+    {
+        return std::string_view{storage_.data()};
+    }
+
+    /// @brief Returns a pointer to the stored null-terminated character sequence.
+    ///
+    /// The returned pointer refers directly to the internal storage of this
+    /// FixedString and is suitable for use with APIs expecting a C-style string.
+    ///
+    /// The pointer remains valid only while this FixedString instance exists and
+    /// its contents are not modified.
+    ///
+    /// @return Pointer to the stored null-terminated character sequence.
+    const char* data() const noexcept
+    {
+        return storage_.data();
+    }
+
+    /// @brief Equality comparison with another FixedString of the same capacity.
+    ///
+    /// Equality is determined by comparing the string representations of
+    /// both instances.
+    ///
+    /// @param other The FixedString instance to compare against.
+    ///
+    /// @return true if both FixedString objects represent the same string;
+    ///         otherwise, false.
+    bool operator==(const FixedString& other) const noexcept
+    {
+        // strcmp does a single optimised pass — avoids the two strlen calls
+        // that constructing string_views would require.
+        return std::strcmp(storage_.data(), other.storage_.data()) == 0;
+    }
+
+    /// @brief Equality comparison with a string_view.
+    ///
+    /// Allows comparisons such as `fs == "Running"` without constructing
+    /// a temporary FixedString.
+    ///
+    /// @param other The string value to compare against.
+    ///
+    /// @return true if this FixedString represents the same string as
+    ///         @p other; otherwise, false.
+    bool operator==(std::string_view other) const noexcept
+    {
+        // other.size() is already known — use it as a length guard and for
+        // memcmp, avoiding strlen on our storage.
+        if (other.size() > MaxLength) {
+            return false;
+        }
+        return std::strncmp(storage_.data(), other.data(), other.size()) == 0
+               && storage_[other.size()] == '\0';
+    }
+
+    /// @brief Inequality comparison with another FixedString of the same capacity.
+    ///
+    /// Inequality is determined by comparing the string representations of
+    /// both instances.
+    ///
+    /// @param other The FixedString instance to compare against.
+    ///
+    /// @return true if the FixedString objects represent different strings;
+    ///         otherwise, false.
+    bool operator!=(const FixedString& other) const noexcept
+    {
+        return !(*this == other);
+    }
+
+    /// @brief Inequality comparison with a string_view.
+    ///
+    /// Allows comparisons such as `fs != "Running"` without constructing
+    /// a temporary FixedString.
+    ///
+    /// @param other The string value to compare against.
+    ///
+    /// @return true if this FixedString represents a different string
+    ///         than @p other; otherwise, false.
+    bool operator!=(std::string_view other) const noexcept
+    {
+        return !(*this == other);
+    }
+
+  private:
+    std::array<char, MaxLength + 1U> storage_;
+};
+
+/// @brief Equality comparison between FixedString instances of different capacities.
+///
+/// Equality is determined by comparing the string representations of both
+/// instances, regardless of their storage capacities.
+///
+/// For example, a `FixedString<128>` and a `FixedString<64>` containing the
+/// same character sequence compare equal.
+///
+/// @tparam N Capacity of the left-hand FixedString.
+/// @tparam M Capacity of the right-hand FixedString.
+/// @param lhs The left-hand FixedString instance.
+/// @param rhs The right-hand FixedString instance.
+/// @return true if both FixedString objects represent the same string;
+///         otherwise, false.
+template <std::size_t N, std::size_t M>
+bool operator==(const FixedString<N>& lhs, const FixedString<M>& rhs) noexcept
+{
+    return std::strcmp(lhs.data(), rhs.data()) == 0;
+}
+
+/// @brief Inequality comparison between FixedString instances of different capacities.
+///
+/// Inequality is determined by comparing the string representations of both
+/// instances, regardless of their storage capacities.
+///
+/// For example, a `FixedString<128>` and a `FixedString<64>` containing
+/// different character sequences compare not equal.
+///
+/// @tparam N Capacity of the left-hand FixedString.
+/// @tparam M Capacity of the right-hand FixedString.
+/// @param lhs The left-hand FixedString instance.
+/// @param rhs The right-hand FixedString instance.
+/// @return true if the FixedString objects represent different strings;
+///         otherwise, false.
+template <std::size_t N, std::size_t M>
+bool operator!=(const FixedString<N>& lhs, const FixedString<M>& rhs) noexcept
+{
+    return !(lhs == rhs);
+}
+
+/// @brief Stream insertion operator for FixedString.
+///
+/// Writes the string representation of the FixedString to the specified
+/// output stream.
+///
+/// The operator is templated on the stream type so it can be used with any
+/// ostream-compatible stream (for example, `std::ostream` or mw::log streams)
+/// without introducing additional dependencies in this header.
+///
+/// @tparam Stream Type of the output stream.
+/// @tparam MaxLength Maximum capacity of the FixedString.
+/// @param os The output stream.
+/// @param fs The FixedString instance to write.
+/// @return A reference to the output stream.
+template <typename Stream, std::size_t MaxLength>
+Stream& operator<<(Stream& os, const FixedString<MaxLength>& fs)
+{
+    return os << fs.data();
+}
+
+}  // namespace score::mw::lifecycle
+
+#endif  // SCORE_MW_LIFECYCLE_FIXED_STRING_HPP