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fuchsia / fuchsia / 03e7f8cd6bb69df241a51274957fcf612bab7c55 / . / zircon / system / ulib / zbitl / include / lib / zbitl / view.h
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// 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_