lib/wlan/common/element_splitter.cpp

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <wlan/common/element.h>
#include <wlan/common/from_bytes.h>
#include <wlan/common/element_splitter.h>

namespace wlan {
namespace common {

static void SkipIfTooShort(Span<const uint8_t>* span) {
    const ElementHeader* header = FromBytes<ElementHeader>(*span);
    if (header == nullptr || header->len + sizeof(ElementHeader) > span->size()) {
        // If there is not enough remaining bytes to hold the full element,
        // move the iterator to the end
        *span = Span { span->data() + span->size(), static_cast<size_t>(0u) };
    }
}

ElementIterator::ElementIterator(Span<const uint8_t> buffer) : remaining_(buffer) {
    SkipIfTooShort(&remaining_);
}

std::tuple<element_id::ElementId, Span<const uint8_t>>
ElementIterator::operator* () const {
    const ElementHeader* header = FromBytes<ElementHeader>(remaining_);
    ZX_ASSERT(header != nullptr);
    return {
        static_cast<element_id::ElementId>(header->id),
        remaining_.subspan(sizeof(ElementHeader), header->len),
    };
}

ElementIterator& ElementIterator::operator++() {
    const ElementHeader* header = FromBytes<ElementHeader>(remaining_);
    ZX_ASSERT(header != nullptr);
    remaining_ = remaining_.subspan(sizeof(ElementHeader) + header->len);
    SkipIfTooShort(&remaining_);
    return *this;
}

static bool SpansHaveSameEnd(wlan::Span<const uint8_t> a, wlan::Span<const uint8_t> b) {
    return a.data() + a.size() == b.data() + b.size();
}

bool operator== (const ElementIterator& a, const ElementIterator& b) {
    // Comparing iterators from different containers is not legal
    ZX_DEBUG_ASSERT(SpansHaveSameEnd(a.remaining_, b.remaining_));
    return a.remaining_.data() == b.remaining_.data();
}

bool operator!= (const ElementIterator& a, const ElementIterator& b) {
    return !(a == b);
}

} // common
} // wlan