[zbitl] Copy <lib/zbitl/view.h> to <lib/zbitl/internal/container.h>
This is a step towards moving a good chunk of View's logic to another
class, but while preserving history. This is a pure copy. A follow-up CL
will delete complementary lines from the two headers.
Bug: 68585
Change-Id: Ie958004ab6502c5dcb36b1727f03a49609ea7d1c
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/517240
Commit-Queue: Joshua Seaton <joshuaseaton@google.com>
Fuchsia-Auto-Submit: Joshua Seaton <joshuaseaton@google.com>
Reviewed-by: David Greenaway <dgreenaway@google.com>
Reviewed-by: Roland McGrath <mcgrathr@google.com>
diff --git a/zircon/system/ulib/zbitl/include/lib/zbitl/internal/container.h b/zircon/system/ulib/zbitl/include/lib/zbitl/internal/container.h
new file mode 100644
index 0000000..bf119b4
--- /dev/null
+++ b/zircon/system/ulib/zbitl/include/lib/zbitl/internal/container.h
@@ -0,0 +1,1514 @@
+// Copyright 2020 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.
+
+#ifndef LIB_ZBITL_VIEW_H_
+#define LIB_ZBITL_VIEW_H_
+
+#include <inttypes.h>
+#include <lib/cksum.h>
+#include <lib/fitx/result.h>
+#include <zircon/assert.h>
+#include <zircon/boot/image.h>
+
+#include <functional>
+#include <optional>
+#include <type_traits>
+#include <variant>
+
+#include "checking.h"
+#include "decompress.h"
+#include "item.h"
+#include "storage_traits.h"
+
+namespace zbitl {
+
+// Forward-declared; defined below.
+template <typename Storage>
+class View;
+
+// Forward-declared; defined in image.h.
+template <typename Storage>
+class Image;
+
+/// TODO(fxbug.dev/68585): Move this into <lib/zbitl/internal/container.h>
+///
+/// ExampleContainerTraits serves as an definitional examplar for how
+/// "container traits" should be structured. Container traits provide types,
+/// and static constants and methods that abstract how to parse and navigate
+/// a particular container format (e.g., ZBI or BOOTFS).
+///
+/// An "item" is an entry within the container, which is expected to be encoded
+/// by an ("item header", "payload") pair. The payload is the raw binary
+/// content of the item, while the item header provides its metadata, most
+/// important of which is the payload's size and its location in the container.
+/// When parsing, the traits should provide a means of navigating from an item
+/// header to either its payload or to the next item header.
+///
+/// The container is expected to have a special header at offset 0, its
+/// "container header", giving metadata on the container itself, including its
+/// total size. The first item header is expected to immediately follow the
+/// container header.
+struct ExampleContainerTraits {
+ /// The type of a container header, expected to be POD.
+ struct container_header_type {};
+
+ /// The type of an item header, expected to be POD.
+ struct item_header_type {};
+
+ /// The user-facing representation of an item header, which wraps the
+ /// format's raw item_header_type. Being a C-style struct with fields
+ /// possibly only relevant to a parser, the raw item header type may not be a
+ /// relatively useful type to expose to the user.
+ ///
+ /// In practice, the wrapper either stores the `item_header_type` directly
+ /// or it holds a pointer into someplace owned or viewed by an associated
+ /// Storage object. In the latter case, i.e. when Storage represents
+ /// something already in memory, `item_header_wrapper` should be no larger
+ /// than a plain pointer.
+ template <typename StorageTraits>
+ class item_header_wrapper {
+ private:
+ using TraitsHeader = typename StorageTraits::template LocalizedReadResult<item_header_type>;
+
+ public:
+ /// Constructible from an item header, as it would result from a localized
+ /// read.
+ explicit item_header_wrapper(const TraitsHeader& header) {}
+
+ /// Default constructible, copyable, movable, copy-assignable, and move-
+ /// assignable.
+ item_header_wrapper() = default;
+ item_header_wrapper(const item_header_wrapper&) = default;
+ item_header_wrapper(item_header_wrapper&&) noexcept = default;
+ item_header_wrapper& operator=(const item_header_wrapper&) = default;
+ item_header_wrapper& operator=(item_header_wrapper&&) noexcept = default;
+
+ /// The header can be dereferenced as if the type were
+ /// `const item_header_t*` (i.e. `*header` or `header->member`).
+ const item_header_type& operator*() const { return std::declval<const item_header_wrapper&>(); }
+ const item_header_type* operator->() const { return nullptr; }
+ };
+
+ /// Error encapsulates errors encountered in navigating the container, either
+ /// those coming from the storage backend or from structural issues with the
+ /// container itself. ErrorTraits corresponds to the `ErrorTraits` member
+ /// type of a StorageTraits specialization; it serves as a template parameter
+ /// so that Error may be defined in terms of the associated storage error
+ /// type (e.g., as a member).
+ template <typename ErrorTraits>
+ struct Error {};
+
+ /// The name of the associated C++ container type. This is given as a C-style
+ /// string (as opposed to a std::string_view) as the constant is only meant
+ /// to provide context within printf() statements.
+ static constexpr const char* kContainerType = "zbitl::ExampleContainer";
+
+ /// The expected alignment - within the container - of an item header. Must
+ /// be a power of two.
+ static constexpr uint32_t kItemAlignment = 1;
+
+ /// Payloads are expected to be followed by padding up to a multiple of this
+ /// value. This quantity is unrelated to the size of the payload itself.
+ static constexpr uint32_t kPayloadPaddingAlignment = 1;
+
+ /// Whether the payloads lie within the container. A container format may not
+ /// include them properly and instead point to the data elsewhere in the
+ /// storage (as is the case with BOOTFS).
+ static constexpr bool kPayloadsAreContained = false;
+
+ /// Returns the size of a container, as it is encoded in the header. The size
+ /// includes that of the header. It is the responsibility of the caller to
+ /// validate the returned size against the actual storage capacity.
+ static uint32_t ContainerSize(const container_header_type& header) { return sizeof(header); }
+
+ /// Returns the exact size of an item's payload (excluding padding).
+ static uint32_t PayloadSize(const item_header_type& header) { return 0; }
+
+ /// Returns the offset at which a payload is to be found, given the
+ /// associated item header and that header's offset into the container.
+ static uint32_t PayloadOffset(const item_header_type& header, uint32_t item_offset) { return 0; }
+
+ /// Returns the offset of the next item header, given a current item header
+ /// and its offset into the container.
+ ///
+ /// TODO(joshuaseaton): in general, a container header may affect navigation
+ static uint32_t NextItemOffset(const item_header_type& header, uint32_t item_offset) { return 0; }
+
+ /// Validates item and container headers, returning a description of the
+ /// failure in that event. The check is agnostic of storage capacity; for
+ /// example, whether any encoded lengths are sensible are left to the caller
+ /// to validate against the actual storage capacity.
+ static fitx::result<std::string_view> CheckContainerHeader(const container_header_type& header) {
+ return fitx::error{"unimplemented"};
+ }
+
+ static fitx::result<std::string_view> CheckItemHeader(const item_header_type& header) {
+ return fitx::error{"unimplemented"};
+ }
+
+ /// Converts the context of an iteration failure into an Error.
+ template <typename StorageTraits>
+ static Error<typename StorageTraits::ErrorTraits> ToError(
+ typename StorageTraits::storage_type& storage, //
+ std::string_view reason, //
+ /// If the error occurred within the context of a particular item, this
+ /// is its offset; else, for problems with the overall container, this is
+ /// zero.
+ uint32_t item_offset,
+ /// Offset at which the error occurred.
+ uint32_t error_offset,
+ /// If the error occurred within the context of a particular item, this
+ /// is a pointer to its header; else, for problems with the overall
+ /// container, this is nullptr. In particular, we expect `header` to be
+ /// null iff `item_offset` is zero. When `header` is obtained through an
+ /// iterator, the former's lifetime is expected to be tied to the
+ /// latter's.
+ ///
+ /// std::optional<item_header_type> is not used here to account for any
+ /// flexible array members, which std::optional forbids.
+ const item_header_type* header = nullptr,
+ std::optional<typename StorageTraits::ErrorTraits::error_type> storage_error = std::nullopt) {
+ return {};
+ }
+};
+
+///
+/// ZbiTraits gives a container trait implementation - per
+/// ExampleContainerTraits above - of the ZBI format.
+///
+struct ZbiTraits {
+ using container_header_type = zbi_header_t;
+ using item_header_type = zbi_header_t;
+
+ template <typename StorageTraits>
+ class item_header_wrapper {
+ private:
+ using TraitsHeader = typename StorageTraits::template LocalizedReadResult<item_header_type>;
+
+ public:
+ explicit item_header_wrapper(const TraitsHeader& header)
+ : stored_([&header]() {
+ if constexpr (kCopy) {
+ static_assert(std::is_same_v<item_header_type, TraitsHeader>);
+ return header;
+ } else {
+ static_assert(
+ std::is_same_v<std::reference_wrapper<const item_header_type>, TraitsHeader>);
+ return &(header.get());
+ }
+ }()) {}
+
+ item_header_wrapper() = default;
+ item_header_wrapper(const item_header_wrapper&) = default;
+ item_header_wrapper(item_header_wrapper&&) noexcept = default;
+ item_header_wrapper& operator=(const item_header_wrapper&) = default;
+ item_header_wrapper& operator=(item_header_wrapper&&) noexcept = default;
+
+ const item_header_type& operator*() const {
+ if constexpr (kCopy) {
+ return stored_;
+ } else {
+ return *stored_;
+ }
+ }
+
+ const item_header_type* operator->() const { return &**this; }
+
+ private:
+ // Accesses kCopy.
+ friend View<typename StorageTraits::storage_type>;
+
+ static constexpr bool kCopy = std::is_same_v<TraitsHeader, item_header_type>;
+ static constexpr bool kReference =
+ std::is_same_v<TraitsHeader, std::reference_wrapper<const item_header_type>>;
+ static_assert(kCopy || kReference,
+ "zbitl::StorageTraits specialization's Header function returns wrong type");
+
+ using HeaderStorage = std::conditional_t<kCopy, item_header_type, const item_header_type*>;
+ HeaderStorage stored_;
+ };
+
+ static constexpr const char* kContainerType = "zbitl::View";
+ static constexpr uint32_t kItemAlignment = ZBI_ALIGNMENT;
+ static constexpr uint32_t kPayloadPaddingAlignment = ZBI_ALIGNMENT;
+ static constexpr bool kPayloadsAreContained = true;
+
+ static uint32_t ContainerSize(const container_header_type& header) {
+ return sizeof(header) + header.length;
+ }
+
+ static uint32_t PayloadSize(const item_header_type& header) { return header.length; }
+
+ static uint32_t PayloadOffset(const item_header_type& header, uint32_t item_offset) {
+ return item_offset + sizeof(header);
+ }
+
+ static uint32_t NextItemOffset(const item_header_type& header, uint32_t item_offset) {
+ return item_offset + sizeof(header) + ZBI_ALIGN(header.length);
+ }
+
+ static fitx::result<std::string_view> CheckContainerHeader(const container_header_type& header);
+ static fitx::result<std::string_view> CheckItemHeader(const item_header_type& header);
+
+ template <typename ErrorTraits>
+ struct Error {
+ /// `storage_error_string` gives a redirect to ErrorTraits's static
+ /// `error_string` method for stringifying storage errors; this is used to
+ /// stringify the entirety of Error in contexts where the associated traits
+ /// are not known or accessible.
+ static constexpr auto storage_error_string = &ErrorTraits::error_string;
+
+ /// A string constant describing the error.
+ std::string_view zbi_error{};
+
+ /// This is the offset into the storage object at which an error occurred.
+ /// This is zero for problems with the overall container, which begin()
+ /// detects. In iterator operations, it refers to the offset into the image
+ /// where the item header was (or should have been).
+ uint32_t item_offset = 0;
+
+ /// This reflects the underlying error from accessing the Storage object,
+ /// if any. If storage_error.has_value() is false, then the error is in
+ /// the format of the contents of the ZBI, not in accessing the contents.
+ std::optional<typename ErrorTraits::error_type> storage_error{};
+ };
+
+ template <typename StorageTraits>
+ static Error<typename StorageTraits::ErrorTraits> ToError(
+ typename StorageTraits::storage_type& storage, //
+ std::string_view reason, //
+ uint32_t item_offset, //
+ uint32_t error_offset, //
+ const item_header_type* header = nullptr, //
+ std::optional<typename StorageTraits::ErrorTraits::error_type> storage_error = std::nullopt) {
+ return {reason, error_offset, storage_error};
+ }
+};
+
+/// The zbitl::View class provides functionality for processing ZBI items in various
+/// storage formats.
+///
+/// For example, the entries in a ZBI present in memory can be enumerated as follows:
+///
+/// ```
+/// void ProcessZbiEntries(std::string_view data) {
+/// // Create the view.
+/// zbitl::View<std::string_view> view{data};
+///
+/// // Iterate over entries.
+/// for (const auto& entry : view) {
+/// printf("Found entry of type %x with payload size %ld.\n",
+/// entry.header->type, // entry.header has type similar to "zbi_header_t *".
+/// entry.payload.size()); // entry.payload has type "std::string_view".
+/// }
+///
+/// // Callers are required to check for errors (or call "ignore_error")
+/// // prior to object destruction. See "Error checking" below.
+/// if (auto error = view.take_error(); error.is_error()) {
+/// printf("Error encountered!\n");
+/// // ...
+/// }
+/// }
+// ```
+///
+/// zbitl::View satisfies the C++20 std::forward_range concept; it satisfies the
+/// std::view concept if the Storage and the associated error_type types support
+/// constant-time copy/move/assignment.
+///
+/// ## Error checking
+///
+/// The "error-checking view" pattern means that the container/range/view API
+/// of begin() and end() iterators is supported, but when begin() or
+/// iterator::operator++() encounters an error, it simply returns end() so that
+/// loops terminate normally. Thereafter, take_error() must be called to check
+/// whether the loop terminated because it iterated past the last item or
+/// because it encountered an error. Once begin() has been called,
+/// take_error() must be called before the View is destroyed, so no error goes
+/// undetected. Since all use of iterators updates the error state, use of any
+/// zbitl::View object must be serialized and after begin() or operator++()
+/// yields end(), take_error() must be checked before using begin() again.
+///
+/// ## Iteration
+///
+/// Each time begin() is called the underlying storage is examined afresh, so
+/// it's safe to reuse a zbitl::View object after changing the data. Reducing
+/// the size of the underlying storage invalidates any iterators that pointed
+/// past the new end of the image. It's simplest just to assume that changing
+/// the underlying storage always invalidates all iterators.
+///
+/// ## Storage
+///
+/// The Storage type is some type that can be abstractly considered to have
+/// non-owning "view" semantics: it doesn't hold the storage of the ZBI, it
+/// just refers to it somehow. The zbitl::View:Error type describes errors
+/// encountered while iterating. It uses the associated error_type type to
+/// propagate errors caused by access to the underlying storage.
+///
+/// Usually Storage and error_type types are small and can be copied.
+/// zbitl::View is move-only if Storage is move-only or if error_type is
+/// move-only. Note that copying zbitl::View copies its error-checking state
+/// exactly, so if the original View needed to be checked for errors before
+/// destruction then both the original and the copy need to be checked before
+/// their respective destructions. A moved-from zbitl::View can always be
+/// destroyed without checking.
+template <typename Storage>
+class View {
+ private:
+ using ContainerTraits = ZbiTraits;
+ using container_header_type = typename ContainerTraits::container_header_type;
+ using item_header_type = typename ContainerTraits::item_header_type;
+
+ public:
+ using storage_type = Storage;
+ using Traits = ExtendedStorageTraits<storage_type>;
+ using storage_error_type = typename Traits::ErrorTraits::error_type;
+ using Error = typename ContainerTraits::template Error<typename Traits::ErrorTraits>;
+ using item_header_wrapper = typename ContainerTraits::template item_header_wrapper<Traits>;
+
+ View() = default;
+ View(const View&) = default;
+ View& operator=(const View&) = default;
+
+ // This is almost the same as the default move behavior. But it also
+ // explicitly resets the moved-from error state to kUnused so that the
+ // moved-from View can be destroyed without checking it.
+ View(View&& other)
+ : storage_(std::move(other.storage_)), error_(std::move(other.error_)), limit_(other.limit_) {
+ other.error_ = Unused{};
+ other.limit_ = 0;
+ }
+ View& operator=(View&& other) {
+ error_ = std::move(other.error_);
+ other.error_ = Unused{};
+ storage_ = std::move(other.storage_);
+ limit_ = other.limit_;
+ other.limit_ = 0;
+ return *this;
+ }
+
+ explicit View(storage_type storage) : storage_(std::move(storage)) {}
+
+ ~View() {
+ ZX_ASSERT_MSG(!std::holds_alternative<Error>(error_), "%s destroyed after error without check",
+ ContainerTraits::kContainerType);
+ ZX_ASSERT_MSG(!std::holds_alternative<NoError>(error_),
+ "%s destroyed after successful iteration without check",
+ ContainerTraits::kContainerType);
+ }
+
+ /// The payload type is provided by the StorageTraits specialization. It's
+ /// opaque to View, but must be default-constructible, copy-constructible,
+ /// and copy-assignable. It's expected to have "view"-style semantics,
+ /// i.e. be small and not own any storage itself but only refer to storage
+ /// owned by the Storage object.
+ using payload_type = typename Traits::payload_type;
+
+ /// The element type is a trivial struct morally equivalent to
+ /// std::pair<item_header_wrapper, payload_type>. Both member types are
+ /// default-constructible, copy-constructible, and copy-assignable, so
+ /// value_type as a whole is as well.
+ struct value_type {
+ item_header_wrapper header;
+ payload_type payload;
+ };
+
+ /// An error type encompassing both read and write failures in accessing the
+ /// source and destination storage objects in the context of a copy
+ /// operation. In the event of a read error, we expect the write_* fields to
+ /// remain unset; in the event of a write error, we expect the read_* fields
+ /// to remain unset.
+ template <typename CopyStorage>
+ struct CopyError {
+ using WriteTraits = StorageTraits<std::decay_t<CopyStorage>>;
+ using WriteError = typename WriteTraits::ErrorTraits::error_type;
+ using ReadError = storage_error_type;
+
+ static auto read_error_string(ReadError error) {
+ return Traits::ErrorTraits::error_string(error);
+ }
+
+ static auto write_error_string(WriteError error) {
+ return WriteTraits::ErrorTraits::error_string(error);
+ }
+
+ /// A string constant describing the error.
+ std::string_view zbi_error{};
+
+ /// This is the offset into the storage object at which a read error
+ /// occured. This field is expected to be unset in the case of a write
+ /// error.
+ uint32_t read_offset = 0;
+
+ /// This reflects the underlying error from accessing the storage object
+ /// that from which the copy was attempted. This field is expected to be
+ /// std::nullopt in the case of a write error.
+ std::optional<storage_error_type> read_error{};
+
+ /// This is the offset into the storage object at which a write error
+ /// occured. This field is expected to be unset in the case of a read
+ /// error.
+ uint32_t write_offset = 0;
+
+ /// This reflects the underlying error from accessing the storage object
+ /// that to which the copy was attempted. This field is expected to be
+ /// std::nullopt in the case of a read error.
+ std::optional<WriteError> write_error{};
+ };
+
+ /// Check the container for errors after using iterators. When begin() or
+ /// iterator::operator++() encounters an error, it simply returns end() so
+ /// that loops terminate normally. Thereafter, take_error() must be called
+ /// to check whether the loop terminated because it iterated past the last
+ /// item or because it encountered an error. Once begin() has been called,
+ /// take_error() must be called before the View is destroyed, so no error
+ /// goes undetected. After take_error() is called the error state is
+ /// consumed and take_error() cannot be called again until another begin() or
+ /// iterator::operator++() call has been made.
+ [[nodiscard]] fitx::result<Error> take_error() {
+ ErrorState result = std::move(error_);
+ error_ = Taken{};
+ if (std::holds_alternative<Error>(result)) {
+ return fitx::error{std::move(std::get<Error>(result))};
+ }
+ ZX_ASSERT_MSG(!std::holds_alternative<Taken>(result), "%s::take_error() was already called",
+ ContainerTraits::kContainerType);
+ return fitx::ok();
+ }
+
+ /// If you explicitly don't care about any error that might have terminated
+ /// the last loop early, then call ignore_error() instead of take_error().
+ void ignore_error() { static_cast<void>(take_error()); }
+
+ /// Trivial accessors for the underlying Storage (view) object.
+ storage_type& storage() { return storage_; }
+ const storage_type& storage() const { return storage_; }
+
+ class iterator {
+ public:
+ /// The default-constructed iterator is invalid for all uses except
+ /// equality comparison.
+ iterator() = default;
+
+ iterator& operator=(const iterator&) = default;
+
+ bool operator==(const iterator& other) const {
+ return other.view_ == view_ && other.offset_ == offset_;
+ }
+
+ bool operator!=(const iterator& other) const { return !(*this == other); }
+
+ iterator& operator++() { // prefix
+ Assert(__func__);
+ view_->StartIteration();
+ const uint32_t next_item_offset = ContainerTraits::NextItemOffset(*value_.header, offset_);
+ Update(next_item_offset);
+ return *this;
+ }
+
+ iterator operator++(int) { // postfix
+ iterator old = *this;
+ ++*this;
+ return old;
+ }
+
+ const View::value_type& operator*() const {
+ Assert(__func__);
+ return value_;
+ }
+
+ const View::value_type* operator->() const {
+ Assert(__func__);
+ return &value_;
+ }
+
+ uint32_t item_offset() const { return offset_; }
+
+ uint32_t payload_offset() const {
+ Assert(__func__);
+ return ContainerTraits::PayloadOffset(*(value_.header), offset_);
+ }
+
+ View& view() const {
+ ZX_ASSERT_MSG(view_, "%s on default-constructed %s::iterator", __func__,
+ ContainerTraits::kContainerType);
+ return *view_;
+ }
+
+ // Iterator traits.
+ using iterator_category = std::input_iterator_tag;
+ using reference = View::value_type&;
+ using value_type = View::value_type;
+ using pointer = View::value_type*;
+ using difference_type = size_t;
+
+ private:
+ // Private fields accessed by Image<Storage>::Append().
+ template <typename ImageStorage>
+ friend class Image;
+
+ // The default-constructed state is almost the same as the end() state:
+ // nothing but operator==() should ever be called if view_ is nullptr.
+ View* view_ = nullptr;
+
+ // The offset into the ZBI of the current item's header. This is 0 in
+ // default-constructed iterators and kEnd_ in end() iterators, where
+ // operator*() can never be called. A valid non-end() iterator holds the
+ // header and payload (references) of the current item for operator*() to
+ // return. If offset_ is at the end of the container, then operator++()
+ // will yield end().
+ uint32_t offset_ = 0;
+
+ // end() uses a different offset_ value to distinguish a true end iterator
+ // from a particular view from a default-constructed iterator from nowhere.
+ static constexpr uint32_t kEnd_ = std::numeric_limits<uint32_t>::max();
+
+ // This is left uninitialized until a successful increment sets it.
+ // It is only examined by a dereference, which is invalid without
+ // a successful increment.
+ value_type value_{};
+
+ // This is called only by begin() and end().
+ friend class View;
+ iterator(View* view, bool is_end) : view_(view) {
+ ZX_DEBUG_ASSERT(view_);
+ if (is_end) {
+ offset_ = kEnd_;
+ } else {
+ Update(sizeof(container_header_type));
+ }
+ }
+
+ // Updates the state of the iterator to reflect a new offset.
+ void Update(uint32_t next_item_offset) {
+ ZX_DEBUG_ASSERT(next_item_offset >= sizeof(container_header_type));
+ ZX_DEBUG_ASSERT_MSG(next_item_offset <= view_->limit_,
+ "%s::iterator next_item_offset %#" PRIx32 " > limit_ %#" PRIx32,
+ ContainerTraits::kContainerType, next_item_offset, view_->limit_);
+ ZX_DEBUG_ASSERT(next_item_offset % ContainerTraits::kItemAlignment == 0);
+
+ if (next_item_offset == view_->limit_) {
+ // Reached the end.
+ *this = view_->end();
+ return;
+ }
+ if (view_->limit_ < next_item_offset ||
+ view_->limit_ - next_item_offset < sizeof(item_header_type)) {
+ Fail("container too short for next item header");
+ return;
+ }
+
+ if (auto header = view_->ItemHeader(next_item_offset); header.is_error()) {
+ // Failed to read the next header.
+ Fail("cannot read item header", std::move(header.error_value()));
+ return;
+ } else if (auto header_error = ContainerTraits::CheckItemHeader(header.value());
+ header_error.is_error()) {
+ Fail(header_error.error_value());
+ return;
+ } else {
+ value_.header = item_header_wrapper(header.value());
+ }
+
+ // If payloads lie within the container, we validate that this particular
+ // payload does indeed fit within; else, we can only check that it fits
+ // within the storage itself.
+ //
+ // TODO(fxbug.dev/68585): while this level of generality is neither
+ // useful nor sensible to View, it soon will be for a BOOTFS-related
+ // refactoring of this logic.
+ uint32_t payload_limit = view_->limit_;
+ if constexpr (!ContainerTraits::kPayloadsAreContained) {
+ auto result = Traits::Capacity(view_->storage());
+ if (result.is_error()) {
+ Fail("cannot determine storage capacity", std::move(result).error_value(), 0);
+ return;
+ }
+ payload_limit = std::move(result).value();
+ }
+
+ const uint32_t payload_offset =
+ ContainerTraits::PayloadOffset(*value_.header, next_item_offset);
+ const uint32_t payload_size = ContainerTraits::PayloadSize(*value_.header);
+ const uint32_t padded_payload_size =
+ (payload_size + ContainerTraits::kPayloadPaddingAlignment - 1) &
+ -ContainerTraits::kPayloadPaddingAlignment;
+ if (payload_offset > payload_limit ||
+ padded_payload_size < payload_size || // ensure aligned size didn't overflow
+ padded_payload_size > payload_limit - payload_offset) {
+ if constexpr (ContainerTraits::kPayloadsAreContained) {
+ Fail("container too short for next item payload");
+ } else {
+ Fail("storage too small for next item payload");
+ }
+ return;
+ }
+
+ if (auto payload = Traits::Payload(view_->storage(), payload_offset, payload_size);
+ payload.is_error()) {
+ Fail("cannot extract payload view", std::move(payload.error_value()), payload_offset);
+ return;
+ } else {
+ value_.payload = std::move(payload.value());
+ }
+ offset_ = next_item_offset;
+ }
+
+ void Fail(std::string_view sv, std::optional<storage_error_type> storage_error = std::nullopt,
+ std::optional<uint32_t> error_offset = std::nullopt) {
+ view_->Fail(ContainerTraits::template ToError<Traits>(
+ view_->storage(), sv, offset_, error_offset.value_or(offset_), &(*value_.header),
+ std::move(storage_error)));
+ *this = view_->end();
+ }
+
+ void Assert(const char* func) const {
+ ZX_ASSERT_MSG(view_, "%s on default-constructed %s::iterator", func,
+ ContainerTraits::kContainerType);
+ ZX_ASSERT_MSG(offset_ != kEnd_, "%s on %s::end() iterator", func,
+ ContainerTraits::kContainerType);
+ }
+ };
+
+ // This returns its own error state and does not affect the `take_error()`
+ // state of the View.
+ fitx::result<Error, container_header_type> container_header() {
+ auto to_error = [this](
+ std::string_view reason, uint32_t error_offset = 0,
+ std::optional<storage_error_type> storage_error = std::nullopt) -> Error {
+ return ContainerTraits::template ToError<Traits>(storage(), reason, 0, error_offset, nullptr,
+ std::move(storage_error));
+ };
+ auto capacity_error = Traits::Capacity(storage());
+ if (capacity_error.is_error()) {
+ return fitx::error{to_error("cannot determine storage capacity", 0,
+ std::move(capacity_error).error_value())};
+ }
+ uint32_t capacity = capacity_error.value();
+
+ // Minimal bounds check before trying to read.
+ if (capacity < sizeof(container_header_type)) {
+ return fitx::error(to_error("container header doesn't fit. Truncated?", capacity));
+ }
+
+ // Read and validate the container header.
+ auto header_error = ContainerHeader();
+ if (header_error.is_error()) {
+ // Failed to read the container header.
+ return fitx::error{
+ to_error("cannot read container header", 0, std::move(header_error).error_value())};
+ }
+
+ container_header_type header = std::move(header_error).value();
+
+ auto check_error = ContainerTraits::CheckContainerHeader(header);
+ if (check_error.is_error()) {
+ return fitx::error{to_error(check_error.error_value())};
+ }
+ const uint32_t size = ContainerTraits::ContainerSize(header);
+ if (size < sizeof(header) || size > capacity) {
+ return fitx::error{to_error("container doesn't fit. Truncated?")};
+ }
+
+ return fitx::ok(header);
+ }
+
+ /// After calling begin(), it's mandatory to call take_error() before
+ /// destroying the View object. An iteration that encounters an error will
+ /// simply end early, i.e. begin() or operator++() will yield an iterator
+ /// that equals end(). At the end of a loop, call take_error() to check for
+ /// errors. It's also acceptable to call take_error() during an iteration
+ /// that hasn't reached end() yet, but it cannot be called again before the
+ /// next begin() or operator++() call.
+ iterator begin() {
+ StartIteration();
+ auto header = container_header();
+ if (header.is_error()) {
+ Fail(header.error_value());
+ limit_ = 0; // Reset from past uses.
+ return end();
+ }
+ // The container's "payload" is all the items. Don't scan past it.
+ limit_ = ContainerTraits::ContainerSize(header.value());
+ return {this, false};
+ }
+
+ iterator end() { return {this, true}; }
+
+ size_t size_bytes() {
+ if (std::holds_alternative<Unused>(error_)) {
+ ZX_ASSERT(limit_ == 0);
+
+ // Taking the size before doing begin() takes extra work.
+ auto capacity_error = Traits::Capacity(storage());
+ if (capacity_error.is_ok()) {
+ uint32_t capacity = capacity_error.value();
+ if (capacity >= sizeof(container_header_type)) {
+ auto header_error = ContainerHeader();
+ if (header_error.is_ok()) {
+ container_header_type header = std::move(header_error).value();
+ const uint32_t size = ContainerTraits::ContainerSize(header);
+ if (sizeof(header) <= size && size <= capacity) {
+ return size;
+ }
+ }
+ }
+ }
+ }
+ return limit_;
+ }
+
+ // Replace an item's header with a new one, using an iterator into this
+ // view. This never changes the existing item's length (nor its payload).
+ // So the header can be `{.type = XYZ}` alone or whatever fields and flags
+ // matter. Note this returns only the storage error type, not an Error since
+ // no ZBI format errors are possible here, only a storage failure to update.
+ //
+ // This method is not available if zbitl::StorageTraits<storage_type>
+ // doesn't support mutation.
+ template <typename T = Traits, typename = std::enable_if_t<T::CanWrite()>>
+ fitx::result<storage_error_type> EditHeader(const iterator& item, const zbi_header_t& header) {
+ item.Assert(__func__);
+ if (auto result = WriteHeader(header, item.item_offset(), item.value_.header->length);
+ result.error_value()) {
+ return result.take_error();
+ }
+ return fitx::ok();
+ }
+
+ // When the iterator is mutable and not a temporary, make the next
+ // operator*() consistent with the new header if it worked. For kReference
+ // storage types, the change is reflected intrinsically.
+ template <typename T = Traits, typename = std::enable_if_t<T::CanWrite()>>
+ fitx::result<storage_error_type> EditHeader(iterator& item, const zbi_header_t& header) {
+ item.Assert(__func__);
+ auto result = WriteHeader(header, item.item_offset(), item.value_.header->length);
+ if constexpr (item_header_wrapper::kCopy) {
+ if (result.is_ok()) {
+ item.value_.header.stored_ = result.value();
+ }
+ }
+ if (result.is_error()) {
+ return result.take_error();
+ }
+ return fitx::ok();
+ }
+
+ // Verifies that a given View iterator points to an item with a valid CRC32.
+ fitx::result<Error, bool> CheckCrc32(iterator it) {
+ auto [header, payload] = *it;
+ if (!(header->flags & ZBI_FLAG_CRC32)) {
+ return fitx::ok(true);
+ }
+
+ uint32_t item_crc32 = 0;
+ auto compute_crc32 = [&item_crc32](ByteView chunk) -> fitx::result<fitx::failed> {
+ // The cumulative value in principle will not be updated by the
+ // CRC32 of empty data, so do not bother with computation in
+ // this case; doing so, we also sidestep any issues around how
+ // `crc32()` handles the corner case of a nullptr.
+ if (!chunk.empty()) {
+ item_crc32 =
+ crc32(item_crc32, reinterpret_cast<const uint8_t*>(chunk.data()), chunk.size());
+ }
+ return fitx::ok();
+ };
+
+ // An item's CRC32 is computed as the hash of its header with its
+ // crc32 field set to 0, combined with the hash of its payload.
+ zbi_header_t header_without_crc32 = *header;
+ header_without_crc32.crc32 = 0;
+ static_cast<void>(compute_crc32(
+ {reinterpret_cast<std::byte*>(&header_without_crc32), sizeof(header_without_crc32)}));
+
+ auto result = Read(payload, header->length, compute_crc32);
+ if (result.is_error()) {
+ return fitx::error{Error{
+ .zbi_error = "cannot compute item CRC32",
+ .item_offset = it.item_offset(),
+ .storage_error = std::move(result).error_value(),
+ }};
+ }
+ ZX_DEBUG_ASSERT(result.value().is_ok());
+ return fitx::ok(item_crc32 == header->crc32);
+ }
+
+ // Copy a range of the underlying storage into an existing piece of storage,
+ // which can be any mutable type with sufficient capacity. The Error return
+ // value is for a read error. The "success" return value indicates there was
+ // no read error. It's another fitx::result<storage_error_type> for the
+ // writing side (which may be different than the type used in
+ // Error::storage_error). The optional `to_offset` argument says where in
+ // `to` the data is written, as a byte offset that is zero by default.
+ template <typename CopyStorage>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> Copy(CopyStorage&& to, uint32_t offset,
+ uint32_t length, uint32_t to_offset = 0) {
+ using CopyTraits = typename View<std::decay_t<CopyStorage>>::Traits;
+ using ErrorType = CopyError<std::decay_t<CopyStorage>>;
+
+ if (size_t size = size_bytes(); length > size || offset > size - length) {
+ return fitx::error{ErrorType{.zbi_error = "offset + length exceeds ZBI size"}};
+ } else if (to_offset + length < std::max(to_offset, length)) {
+ return fitx::error{ErrorType{.zbi_error = "to_offset + length overflows"}};
+ }
+
+ if (auto result = CopyTraits::EnsureCapacity(to, to_offset + length); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot increase capacity",
+ .write_offset = to_offset + length,
+ .write_error = std::move(result).error_value(),
+ }};
+ }
+
+ auto payload = Traits::Payload(storage(), offset, length);
+ if (payload.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot translate ZBI offset to storage",
+ .read_offset = offset,
+ .read_error = std::move(std::move(payload).error_value()),
+ }};
+ }
+ if constexpr (Traits::CanUnbufferedRead() && CopyTraits::CanUnbufferedWrite()) {
+ // Combine buffered reading with mapped writing to do it all at once.
+ auto mapped = CopyTraits::Write(to, to_offset, length);
+ if (mapped.is_error()) {
+ // No read error detected because a "write" error was detected first.
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write to destination storage",
+ .write_offset = to_offset,
+ .write_error = std::move(mapped).error_value(),
+ }};
+ }
+ auto result = Traits::Read(storage(), payload.value(), mapped.value(), length);
+ if (result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot read from source storage",
+ .read_offset = offset,
+ .read_error = std::move(result).error_value(),
+ }};
+ }
+ // No read error, no write error.
+ return fitx::ok();
+ } else {
+ auto write = [&to, to_offset](ByteView chunk) mutable //
+ -> fitx::result<typename CopyTraits::ErrorTraits::error_type> {
+ if (auto result = CopyTraits::Write(to, to_offset, chunk); result.is_error()) {
+ return std::move(result).take_error();
+ }
+ to_offset += static_cast<uint32_t>(chunk.size());
+ return fitx::ok();
+ };
+ auto result = Read(payload.value(), length, write);
+ if (result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot read from source storage",
+ .read_offset = offset,
+ .read_error = std::move(std::move(result).error_value()),
+ }};
+ }
+ if (auto write_result = std::move(result).value(); write_result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write to destination storage",
+ .write_offset = to_offset,
+ .write_error = std::move(write_result).error_value(),
+ }};
+ }
+ return fitx::ok();
+ }
+ }
+
+ // Copy a range of the underlying storage into a freshly-created new piece of
+ // storage (whatever that means for this storage type). The Error return
+ // value is for a read error. The "success" return value indicates there was
+ // no read error. It's another fitx::result<read_error_type, T> for some
+ // T akin to storage_type, possibly storage_type itself. For example, all
+ // the unowned VMO storage types yield zx::vmo as the owning equivalent
+ // storage type. If the optional `to_offset` argument is nonzero, the new
+ // storage starts with that many zero bytes before the copied data.
+ template <typename T = Traits, // SFINAE check for Traits::Create method.
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, CreateStorage> Copy(uint32_t offset, uint32_t length,
+ uint32_t to_offset = 0) {
+ auto copy = CopyWithSlop(offset, length, to_offset,
+ [to_offset](uint32_t slop) { return slop == to_offset; });
+ if (copy.is_error()) {
+ return std::move(copy).take_error();
+ }
+ auto [new_storage, slop] = std::move(copy).value();
+ ZX_DEBUG_ASSERT(slop == to_offset);
+ return fitx::ok(std::move(new_storage));
+ }
+
+ // Copy a single item's payload into supplied storage.
+ template <typename CopyStorage>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> CopyRawItem(CopyStorage&& to,
+ const iterator& it) {
+ return Copy(std::forward<CopyStorage>(to), it.payload_offset(), (*it).header->length);
+ }
+
+ // Copy a single item's payload into newly-created storage.
+ template < // SFINAE check for Traits::Create method.
+ typename T = Traits,
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, CreateStorage> CopyRawItem(const iterator& it) {
+ return Copy(it.payload_offset(), (*it).header->length);
+ }
+
+ // Copy a single item's header and payload into supplied storage.
+ template <typename CopyStorage>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> CopyRawItemWithHeader(CopyStorage&& to,
+ const iterator& it) {
+ return Copy(std::forward<CopyStorage>(to), it.item_offset(),
+ sizeof(zbi_header_t) + (*it).header->length);
+ }
+
+ // Copy a single item's header and payload into newly-created storage.
+ template < // SFINAE check for Traits::Create method.
+ typename T = Traits,
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, CreateStorage> CopyRawItemWithHeader(const iterator& it) {
+ return Copy(it.item_offset(), sizeof(zbi_header_t) + (*it).header->length);
+ }
+
+ // Copy a single item's payload into supplied storage, including
+ // decompressing a ZBI_TYPE_STORAGE_* item if necessary. This statically
+ // determines based on the input and output storage types whether it has to
+ // use streaming decompression or can use the one-shot mode (which is more
+ // efficient and requires less scratch memory). So the unused part of the
+ // decompression library can be elided at link time.
+ //
+ // If decompression is necessary, then this calls `scratch(size_t{bytes})` to
+ // allocate scratch memory for the decompression engine. This returns
+ // `fitx::result<std::string_view, T>` where T is any movable object that has
+ // a `get()` method returning a pointer (of any type implicitly converted to
+ // `void*`) to the scratch memory. The returned object is destroyed after
+ // decompression is finished and the scratch memory is no longer needed.
+ //
+ // zbitl::decompress:DefaultAllocator is a default-constructible class that
+ // can serve as `scratch`. The overloads below with fewer arguments use it.
+ template <typename CopyStorage, typename ScratchAllocator>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> CopyStorageItem(CopyStorage&& to,
+ const iterator& it,
+ ScratchAllocator&& scratch) {
+ if (auto compressed = IsCompressedStorage(*(*it).header)) {
+ return DecompressStorage(std::forward<CopyStorage>(to), it,
+ std::forward<ScratchAllocator>(scratch));
+ }
+ return CopyRawItem(std::forward<CopyStorage>(to), it);
+ }
+
+ template <typename ScratchAllocator, typename T = Traits,
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, CreateStorage> CopyStorageItem(
+ const iterator& it, ScratchAllocator&& scratch) {
+ using ErrorType = CopyError<CreateStorage>;
+
+ if (auto compressed = IsCompressedStorage(*(*it).header)) {
+ // Create new storage to decompress the payload into.
+ auto to = Traits::Create(storage(), *compressed, 0);
+ if (to.is_error()) {
+ // No read error because a "write" error happened first.
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot create storage",
+ .write_offset = 0,
+ .write_error = std::move(to).error_value(),
+ }};
+ }
+ auto to_storage = std::move(to).value();
+ if (auto result = DecompressStorage(to_storage, it, std::forward<ScratchAllocator>(scratch));
+ result.is_error()) {
+ return result.take_error();
+ }
+ return fitx::ok(std::move(to_storage));
+ }
+ return CopyRawItem(it);
+ }
+
+ // These overloads have the effect of default arguments for the allocator
+ // arguments to the general versions above, but template argument deduction
+ // doesn't work with default arguments.
+
+ template <typename CopyStorage>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> CopyStorageItem(CopyStorage&& to,
+ const iterator& it) {
+ return CopyStorageItem(std::forward<CopyStorage>(to), it, decompress::DefaultAllocator);
+ }
+
+ template <typename T = Traits, typename = std::enable_if_t<T::CanCreate()>>
+ auto CopyStorageItem(const iterator& it) {
+ return CopyStorageItem(it, decompress::DefaultAllocator);
+ }
+
+ // Copy the subrange `[first,last)` of the ZBI into supplied storage.
+ // The storage will contain a new ZBI container with only those items.
+ template <typename CopyStorage>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> Copy(CopyStorage&& to, const iterator& first,
+ const iterator& last) {
+ using CopyTraits = StorageTraits<std::decay_t<CopyStorage>>;
+ using ErrorType = CopyError<std::decay_t<CopyStorage>>;
+
+ auto [offset, length] = RangeBounds(first, last);
+ if (auto result = Copy(to, offset, length, sizeof(zbi_header_t)); result.is_error()) {
+ return std::move(result).take_error();
+ }
+ const zbi_header_t header = ZBI_CONTAINER_HEADER(length);
+ ByteView out{reinterpret_cast<const std::byte*>(&header), sizeof(header)};
+ if (auto result = CopyTraits::Write(to, 0, out); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write container header",
+ .write_offset = 0,
+ .write_error = std::move(result).error_value(),
+ }};
+ }
+ return fitx::ok();
+ }
+
+ // Copy the subrange `[first,last)` of the ZBI into newly-created storage.
+ // The storage will contain a new ZBI container with only those items.
+ template <typename T = Traits,
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, CreateStorage> Copy(const iterator& first,
+ const iterator& last) {
+ using CopyTraits = StorageTraits<CreateStorage>;
+ using ErrorType = CopyError<CreateStorage>;
+
+ auto [offset, length] = RangeBounds(first, last);
+
+ // We allow the copy to leave padding ("slop") prior to the copied objects
+ // if desired. This lets some storage backends to be more efficient (e.g.,
+ // VMOs can clone pages instead of copying them).
+ //
+ // The amount of slop must be large enough for us to insert a container
+ // header and possibly an additional discard item.
+ constexpr auto slopcheck = [](uint32_t slop) {
+ return slop == sizeof(zbi_header_t) ||
+ (slop >= 2 * sizeof(zbi_header_t) && slop % ZBI_ALIGNMENT == 0);
+ };
+ auto copy = CopyWithSlop(offset, length, sizeof(zbi_header_t), slopcheck);
+ if (copy.is_error()) {
+ return std::move(copy).take_error();
+ }
+ auto [new_storage, slop] = std::move(copy).value();
+
+ if (slop > sizeof(zbi_header_t)) {
+ // Write out a discarded item header to take up all the slop left over
+ // after the container header.
+ ZX_DEBUG_ASSERT(slop >= 2 * sizeof(zbi_header_t));
+
+ zbi_header_t hdr{};
+ hdr.type = ZBI_TYPE_DISCARD;
+ hdr.length = slop - (2 * sizeof(zbi_header_t));
+ hdr = SanitizeHeader(hdr);
+ ByteView out{reinterpret_cast<const std::byte*>(&hdr), sizeof(hdr)};
+ uint32_t to_offset = sizeof(zbi_header_t);
+ if (auto result = CopyTraits::Write(new_storage, to_offset, out); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write discard item",
+ .write_offset = to_offset,
+ .write_error = std::move(result).error_value(),
+ }};
+ }
+ length += sizeof(zbi_header_t) + hdr.length;
+ }
+
+ // Write the new container header.
+ const zbi_header_t hdr = ZBI_CONTAINER_HEADER(length);
+ ByteView out{reinterpret_cast<const std::byte*>(&hdr), sizeof(hdr)};
+ if (auto result = CopyTraits::Write(new_storage, 0, out); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write container header",
+ .write_offset = 0,
+ .write_error = std::move(result).error_value(),
+ }};
+ }
+
+ return fitx::ok(std::move(new_storage));
+ }
+
+ // This is public mostly just for tests to assert on it.
+ template <typename CopyStorage = Storage>
+ static constexpr bool CanZeroCopy() {
+ // Reading directly into buffer has no extra copies for a receiver that can
+ // do unbuffered writes.
+ using CopyTraits = typename View<std::decay_t<CopyStorage>>::Traits;
+ return Traits::template CanOneShotRead<std::byte, /*LowLocality=*/false>() ||
+ (Traits::CanUnbufferedRead() && CopyTraits::CanUnbufferedWrite());
+ }
+
+ protected:
+ // Fetches the container header.
+ fitx::result<storage_error_type,
+ typename Traits::template LocalizedReadResult<container_header_type>>
+ ContainerHeader() {
+ return Traits::template LocalizedRead<container_header_type>(storage(), 0);
+ }
+
+ // Fetches an item header at a given offset.
+ fitx::result<storage_error_type, typename Traits::template LocalizedReadResult<item_header_type>>
+ ItemHeader(uint32_t offset) {
+ return Traits::template LocalizedRead<item_header_type>(storage(), offset);
+ }
+
+ // WriteHeader sanitizes and optionally updates the length of a provided
+ // header, writes it to the provided offset, and returns the modified header
+ // on success.
+ fitx::result<storage_error_type, zbi_header_t> WriteHeader(
+ zbi_header_t header, uint32_t offset, std::optional<uint32_t> new_length = std::nullopt) {
+ header = SanitizeHeader(header);
+ if (new_length.has_value()) {
+ header.length = new_length.value();
+ }
+ if (auto result = Traits::Write(storage(), offset, AsBytes(header)); result.is_error()) {
+ return fitx::error{std::move(result.error_value())};
+ }
+ return fitx::ok(header);
+ }
+
+ private:
+ struct Unused {};
+ struct NoError {};
+ struct Taken {};
+ using ErrorState = std::variant<Unused, NoError, Error, Taken>;
+
+ void StartIteration() {
+ ZX_ASSERT_MSG(!std::holds_alternative<Error>(error_),
+ "%s iterators used without taking prior error", ContainerTraits::kContainerType);
+ error_ = NoError{};
+ }
+
+ void Fail(Error error) {
+ ZX_DEBUG_ASSERT_MSG(!std::holds_alternative<Error>(error_),
+ "Fail in error state: missing %s::StartIteration() call?",
+ ContainerTraits::kContainerType);
+ ZX_DEBUG_ASSERT_MSG(!std::holds_alternative<Unused>(error_),
+ "Fail in Unused: missing %s::StartIteration() call?",
+ ContainerTraits::kContainerType);
+ error_ = std::move(error);
+ }
+
+ template <typename Callback>
+ auto Read(payload_type payload, uint32_t length, Callback&& callback)
+ -> fitx::result<storage_error_type, decltype(callback(ByteView{}))> {
+ if constexpr (Traits::template CanOneShotRead<std::byte, /*LowLocality=*/false>()) {
+ if (auto result = Traits::template Read<std::byte, false>(storage(), payload, length);
+ result.is_error()) {
+ return result.take_error();
+ } else {
+ return fitx::ok(callback(result.value()));
+ }
+ } else {
+ return Traits::Read(storage(), payload, length, std::forward<Callback>(callback));
+ }
+ }
+
+ template <typename SlopCheck,
+ // SFINAE check for Traits::Create method.
+ typename T = Traits,
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<CopyError<CreateStorage>, std::pair<CreateStorage, uint32_t>> CopyWithSlop(
+ uint32_t offset, uint32_t length, uint32_t to_offset, SlopCheck&& slopcheck) {
+ using ErrorType = CopyError<CreateStorage>;
+
+ if (size_t size = size_bytes(); length > size || offset > size - length) {
+ return fitx::error{ErrorType{.zbi_error = "offset + length exceeds ZBI size"}};
+ } else if (to_offset + length < std::max(to_offset, length)) {
+ return fitx::error{ErrorType{.zbi_error = "to_offset + length overflows"}};
+ }
+
+ if (auto result = Clone(offset, length, to_offset, std::forward<SlopCheck>(slopcheck));
+ result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot read from storage",
+ .read_offset = offset,
+ .read_error = std::move(result).error_value(),
+ }};
+ } else if (result.value()) {
+ // Clone did the job!
+ return fitx::ok(std::move(*std::move(result).value()));
+ }
+
+ // Fall back to Create and copy via Read and Write.
+ if (auto result = Traits::Create(storage(), to_offset + length, to_offset); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot create storage",
+ .read_offset = offset,
+ .read_error = std::move(result).error_value(),
+ }};
+ } else {
+ auto copy = std::move(result).value();
+ static_assert(
+ std::is_convertible_v<typename StorageTraits<decltype(copy)>::ErrorTraits::error_type,
+ storage_error_type>,
+ "StorageTraits::Create yields type with incompatible error_type");
+ auto copy_result = Copy(copy, offset, length, to_offset);
+ if (copy_result.is_error()) {
+ return std::move(copy_result).take_error();
+ }
+ return fitx::ok(std::make_pair(std::move(copy), uint32_t{to_offset}));
+ }
+ }
+
+ template <typename SlopCheck, typename T = Traits>
+ fitx::result<storage_error_type, typename T::template CloneResult<>> Clone(
+ uint32_t offset, uint32_t length, uint32_t to_offset, SlopCheck&& slopcheck) {
+ return Traits::Clone(storage(), offset, length, to_offset, std::forward<SlopCheck>(slopcheck));
+ }
+
+ // This overload is only used if SFINAE detected no Traits::Clone method.
+ template <typename T = Traits, // SFINAE check for Traits::Create method.
+ typename CreateStorage = std::decay_t<typename T::template CreateResult<>>>
+ fitx::result<storage_error_type, std::optional<std::pair<CreateStorage, uint32_t>>> Clone(...) {
+ return fitx::ok(std::nullopt); // Can't do it.
+ }
+
+ // Returns [offset, length] in the storage to cover the given item range.
+ auto RangeBounds(const iterator& first, const iterator& last) {
+ uint32_t offset = first.item_offset();
+ uint32_t limit = limit_;
+ if (last != end()) {
+ limit = last.item_offset();
+ }
+ return std::make_pair(offset, limit - offset);
+ }
+
+ static constexpr std::optional<uint32_t> IsCompressedStorage(const zbi_header_t& header) {
+ const bool compressible = TypeIsStorage(header.type);
+ const bool compressed = header.flags & ZBI_FLAG_STORAGE_COMPRESSED;
+ if (compressible && compressed) {
+ return header.extra;
+ }
+ return std::nullopt;
+ }
+
+ template <typename CopyStorage, typename ScratchAllocator>
+ fitx::result<CopyError<std::decay_t<CopyStorage>>> DecompressStorage(CopyStorage&& to,
+ const iterator& it,
+ ScratchAllocator&& scratch) {
+ using ErrorType = CopyError<std::decay_t<CopyStorage>>;
+ using ToTraits = typename View<std::decay_t<CopyStorage>>::Traits;
+ constexpr bool bufferless_output = ToTraits::CanUnbufferedWrite();
+
+ const auto [header, payload] = *it;
+ const uint32_t compressed_size = header->length;
+ const uint32_t uncompressed_size = header->extra;
+
+ if (auto result = ToTraits::EnsureCapacity(to, uncompressed_size); result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot increase capacity",
+ .write_offset = uncompressed_size,
+ .write_error = std::move(result).error_value(),
+ }};
+ }
+
+ auto decompress_error = [&](auto&& result) {
+ return fitx::error{ErrorType{
+ .zbi_error = result.error_value(),
+ .read_offset = it.item_offset(),
+ }};
+ };
+
+ constexpr std::string_view kZbiErrorCorruptedOrBadData =
+ "bad or corrupted data: uncompressed length not as expected";
+
+ if constexpr (Traits::template CanOneShotRead<std::byte, /*LowLocality=*/false>()) {
+ // All the data is on hand in one shot. Fetch it first.
+ ByteView compressed_data;
+ if (auto result =
+ Traits::template Read<std::byte, false>(storage(), payload, compressed_size);
+ result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot read compressed payload",
+ .read_offset = it.item_offset(),
+ .read_error = std::move(result).error_value(),
+ }};
+ } else {
+ compressed_data = result.value();
+ }
+
+ if constexpr (bufferless_output) {
+ // Decompression can write directly into the output storage in memory.
+ // So this can use one-shot decompression.
+
+ auto mapped = ToTraits::Write(to, 0, uncompressed_size);
+ if (mapped.is_error()) {
+ // Read succeeded, but write failed.
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write to storage in-place",
+ .write_offset = 0,
+ .write_error = std::move(mapped).error_value(),
+ }};
+ }
+ const auto uncompressed_data = static_cast<std::byte*>(mapped.value());
+
+ auto result =
+ decompress::OneShot::Decompress({uncompressed_data, uncompressed_size}, compressed_data,
+ std::forward<ScratchAllocator>(scratch));
+ if (result.is_error()) {
+ return decompress_error(result);
+ }
+ } else {
+ // Writing to the output storage requires a temporary buffer.
+ auto create_result = decompress::Streaming::Create<true>(
+ compressed_data, std::forward<ScratchAllocator>(scratch));
+ if (create_result.is_error()) {
+ return decompress_error(create_result);
+ }
+ auto& decompress = create_result.value();
+ uint32_t outoffset = 0;
+ while (!compressed_data.empty()) {
+ // Decompress as much data as the decompressor wants to.
+ // It updates compressed_data to remove what it's consumed.
+ ByteView out;
+ if (auto result = decompress(compressed_data); result.is_error()) {
+ return decompress_error(result);
+ } else {
+ out = {result.value().data(), result.value().size()};
+ }
+ if (!out.empty()) {
+ // Flush the output buffer to the storage.
+ if (auto write = ToTraits::Write(to, outoffset, out); write.is_error()) {
+ // Read succeeded, but write failed.
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write to storage",
+ .write_offset = outoffset,
+ .write_error = std::move(write).error_value(),
+ }};
+ }
+ outoffset += static_cast<uint32_t>(out.size());
+ }
+ }
+
+ if (outoffset != uncompressed_size) {
+ return fitx::error{ErrorType{.zbi_error = kZbiErrorCorruptedOrBadData}};
+ }
+ }
+ } else {
+ std::byte* outptr = nullptr;
+ size_t outlen = 0;
+ uint32_t outoffset = 0;
+ if constexpr (bufferless_output) {
+ // Decompression can write directly into the output storage in memory.
+ auto mapped = ToTraits::Write(to, 0, uncompressed_size);
+ if (mapped.is_error()) {
+ // Read succeeded, but write failed.
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot write to storage in-place",
+ .write_offset = 0,
+ .write_error = std::move(mapped).error_value(),
+ }};
+ }
+
+ outptr = static_cast<std::byte*>(mapped.value());
+ outlen = uncompressed_size;
+ }
+
+ auto create = [&](ByteView probe) {
+ return decompress::Streaming::Create<!bufferless_output>(
+ probe, std::forward<ScratchAllocator>(scratch));
+ };
+ std::optional<std::decay_t<decltype(create({}).value())>> decompressor;
+
+ // We have to read the first chunk just to decode its compression header.
+ auto read_chunk = [&](ByteView chunk) -> fitx::result<ErrorType> {
+ using ChunkError = fitx::error<ErrorType>;
+
+ if (!decompressor) {
+ // First chunk. Set up the decompressor.
+ if (auto result = create(chunk); result.is_error()) {
+ return decompress_error(result);
+ } else {
+ decompressor.emplace(std::move(result).value());
+ }
+ }
+
+ // Decompress the chunk.
+ while (!chunk.empty()) {
+ if constexpr (bufferless_output) {
+ auto result = (*decompressor)({outptr, outlen}, chunk);
+ if (result.is_error()) {
+ return ChunkError(decompress_error(result));
+ }
+ outptr = result.value().data();
+ outlen = result.value().size();
+ outoffset += uncompressed_size - static_cast<uint32_t>(outlen);
+ } else {
+ ByteView out;
+ if (auto result = (*decompressor)(chunk); result.is_error()) {
+ return ChunkError(decompress_error(result));
+ } else {
+ out = {result.value().data(), result.value().size()};
+ }
+ if (!out.empty()) {
+ // Flush the output buffer to the storage.
+ auto write = ToTraits::Write(to, outoffset, out);
+ if (write.is_error()) {
+ // Read succeeded, but write failed.
+ return ChunkError(ErrorType{
+ .zbi_error = "cannot write to storage",
+ .write_offset = outoffset,
+ .write_error = std::move(write).error_value(),
+ });
+ }
+ outoffset += static_cast<uint32_t>(out.size());
+ }
+ }
+ }
+
+ if (outoffset != uncompressed_size) {
+ return ChunkError(ErrorType{.zbi_error = kZbiErrorCorruptedOrBadData});
+ }
+ return fitx::ok();
+ };
+
+ auto result = Traits::Read(storage(), payload, compressed_size, read_chunk);
+ if (result.is_error()) {
+ return fitx::error{ErrorType{
+ .zbi_error = "cannot read compressed payload",
+ .read_offset = it.item_offset(),
+ .read_error = std::move(result).error_value(),
+ }};
+ }
+
+ auto read_chunk_result = std::move(result).value();
+ if (read_chunk_result.is_error()) {
+ return read_chunk_result.take_error();
+ }
+ }
+
+ return fitx::ok();
+ }
+
+ storage_type storage_;
+ ErrorState error_;
+ uint32_t limit_ = 0;
+};
+
+// Deduction guide: View v(T{}) instantiates View<T>.
+template <typename Storage>
+explicit View(Storage) -> View<Storage>;
+
+// Convert a pointer to an in-memory ZBI into a Storage type.
+//
+// We require that `zbi` is a pointer to a valid ZBI container header followed
+// by its payload. Basic magic checks on the header are performed; if they
+// fail, we return a Storage spanning just the header but no payload under the
+// assumption that the "length" field of the header is invalid.
+//
+// The template parameter `Storage` may be any storage type that can be
+// constructed with arguments the arguments (const std::byte*, size_t),
+// representing the start and length of the in-memory ZBI.
+template <typename Storage = ByteView>
+Storage StorageFromRawHeader(const zbi_header_t* zbi) {
+ if (zbi->magic != ZBI_ITEM_MAGIC || zbi->type != ZBI_TYPE_CONTAINER ||
+ zbi->extra != ZBI_CONTAINER_MAGIC) {
+ // Invalid header. Don't trust the `length` field.
+ return Storage(reinterpret_cast<const std::byte*>(zbi), sizeof(zbi_header_t));
+ }
+
+ // Return Storage covering the entire header and payload.
+ return Storage(reinterpret_cast<const std::byte*>(zbi), sizeof(zbi_header_t) + zbi->length);
+}
+
+} // namespace zbitl
+
+#endif // LIB_ZBITL_VIEW_H_
diff --git a/zircon/system/ulib/zbitl/include/lib/zbitl/view.h b/zircon/system/ulib/zbitl/include/lib/zbitl/view.h
index f507910..bf119b4 100644
--- a/zircon/system/ulib/zbitl/include/lib/zbitl/view.h
+++ b/zircon/system/ulib/zbitl/include/lib/zbitl/view.h
@@ -31,6 +31,7 @@
template <typename Storage>
class Image;
+/// TODO(fxbug.dev/68585): Move this into <lib/zbitl/internal/container.h>
///
/// ExampleContainerTraits serves as an definitional examplar for how
/// "container traits" should be structured. Container traits provide types,
