#include "binary_annotator.h"
#include <algorithm>
#include <cstdint>
#include <iostream>
#include <limits>
#include <string>
#include <vector>
#include "flatbuffers/base.h"
#include "flatbuffers/reflection.h"
#include "flatbuffers/util.h"
#include "flatbuffers/verifier.h"
namespace flatbuffers {
namespace {
static bool BinaryRegionSort(const BinaryRegion &a, const BinaryRegion &b) {
return a.offset < b.offset;
}
static void SetError(BinaryRegionComment &comment, BinaryRegionStatus status,
std::string message = "") {
comment.status = status;
comment.status_message = message;
}
static BinaryRegion MakeBinaryRegion(
const uint64_t offset = 0, const uint64_t length = 0,
const BinaryRegionType type = BinaryRegionType::Unknown,
const uint64_t array_length = 0, const uint64_t points_to_offset = 0,
BinaryRegionComment comment = {}) {
BinaryRegion region;
region.offset = offset;
region.length = length;
region.type = type;
region.array_length = array_length;
region.points_to_offset = points_to_offset;
region.comment = std::move(comment);
return region;
}
static BinarySection MakeBinarySection(const std::string &name,
const BinarySectionType type,
std::vector<BinaryRegion> regions) {
BinarySection section;
section.name = name;
section.type = type;
section.regions = std::move(regions);
return section;
}
static BinarySection MakeSingleRegionBinarySection(const std::string &name,
const BinarySectionType type,
const BinaryRegion ®ion) {
std::vector<BinaryRegion> regions;
regions.push_back(region);
return MakeBinarySection(name, type, std::move(regions));
}
static bool IsNonZeroRegion(const uint64_t offset, const uint64_t length,
const uint8_t *const binary) {
for (uint64_t i = offset; i < offset + length; ++i) {
if (binary[i] != 0) { return true; }
}
return false;
}
static bool IsPrintableRegion(const uint64_t offset, const uint64_t length,
const uint8_t *const binary) {
for (uint64_t i = offset; i < offset + length; ++i) {
if (!isprint(binary[i])) { return false; }
}
return true;
}
static BinarySection GenerateMissingSection(const uint64_t offset,
const uint64_t length,
const uint8_t *const binary) {
std::vector<BinaryRegion> regions;
// Check if the region is all zeros or not, as that can tell us if it is
// padding or not.
if (IsNonZeroRegion(offset, length, binary)) {
// Some of the padding bytes are non-zero, so this might be an unknown
// section of the binary.
// TODO(dbaileychess): We could be a bit smarter with different sized
// alignments. For now, the 8 byte check encompasses all the smaller
// alignments.
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::Unknown;
if (length >= 8) {
SetError(comment, BinaryRegionStatus::WARN_NO_REFERENCES);
} else {
SetError(comment, BinaryRegionStatus::WARN_CORRUPTED_PADDING);
}
regions.push_back(MakeBinaryRegion(offset, length * sizeof(uint8_t),
BinaryRegionType::Unknown, length, 0,
comment));
return MakeBinarySection("no known references", BinarySectionType::Unknown,
std::move(regions));
}
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::Padding;
if (length >= 8) {
SetError(comment, BinaryRegionStatus::WARN_PADDING_LENGTH);
}
// This region is most likely padding.
regions.push_back(MakeBinaryRegion(offset, length * sizeof(uint8_t),
BinaryRegionType::Uint8, length, 0,
comment));
return MakeBinarySection("", BinarySectionType::Padding, std::move(regions));
}
} // namespace
std::map<uint64_t, BinarySection> BinaryAnnotator::Annotate() {
flatbuffers::Verifier verifier(bfbs_, static_cast<size_t>(bfbs_length_));
if ((is_size_prefixed_ &&
!reflection::VerifySizePrefixedSchemaBuffer(verifier)) ||
!reflection::VerifySchemaBuffer(verifier)) {
return {};
}
// The binary is too short to read as a flatbuffers.
if (binary_length_ < FLATBUFFERS_MIN_BUFFER_SIZE) { return {}; }
// Make sure we start with a clean slate.
vtables_.clear();
sections_.clear();
// First parse the header region which always start at offset 0.
// The returned offset will point to the root_table location.
const uint64_t root_table_offset = BuildHeader(0);
if (IsValidOffset(root_table_offset)) {
// Build the root table, and all else will be referenced from it.
BuildTable(root_table_offset, BinarySectionType::RootTable,
schema_->root_table());
}
// Now that all the sections are built, make sure the binary sections are
// contiguous.
FixMissingRegions();
// Then scan the area between BinarySections insert padding sections that are
// implied.
FixMissingSections();
return sections_;
}
uint64_t BinaryAnnotator::BuildHeader(const uint64_t header_offset) {
uint64_t offset = header_offset;
std::vector<BinaryRegion> regions;
// If this binary is a size prefixed one, attempt to parse the size.
if (is_size_prefixed_) {
BinaryRegionComment prefix_length_comment;
prefix_length_comment.type = BinaryRegionCommentType::SizePrefix;
bool has_prefix_value = false;
const auto prefix_length = ReadScalar<uoffset64_t>(offset);
if (*prefix_length <= binary_length_) {
regions.push_back(MakeBinaryRegion(offset, sizeof(uoffset64_t),
BinaryRegionType::Uint64, 0, 0,
prefix_length_comment));
offset += sizeof(uoffset64_t);
has_prefix_value = true;
}
if (!has_prefix_value) {
const auto prefix_length = ReadScalar<uoffset_t>(offset);
if (*prefix_length <= binary_length_) {
regions.push_back(MakeBinaryRegion(offset, sizeof(uoffset_t),
BinaryRegionType::Uint32, 0, 0,
prefix_length_comment));
offset += sizeof(uoffset_t);
has_prefix_value = true;
}
}
if (!has_prefix_value) {
SetError(prefix_length_comment, BinaryRegionStatus::ERROR);
}
}
const auto root_table_offset = ReadScalar<uint32_t>(offset);
if (!root_table_offset.has_value()) {
// This shouldn't occur, since we validate the min size of the buffer
// before. But for completion sake, we shouldn't read passed the binary end.
return std::numeric_limits<uint64_t>::max();
}
const auto root_table_loc = offset + *root_table_offset;
BinaryRegionComment root_offset_comment;
root_offset_comment.type = BinaryRegionCommentType::RootTableOffset;
root_offset_comment.name = schema_->root_table()->name()->str();
if (!IsValidOffset(root_table_loc)) {
SetError(root_offset_comment,
BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
}
regions.push_back(MakeBinaryRegion(offset, sizeof(uint32_t),
BinaryRegionType::UOffset, 0,
root_table_loc, root_offset_comment));
offset += sizeof(uint32_t);
if (IsValidRead(offset, flatbuffers::kFileIdentifierLength) &&
IsPrintableRegion(offset, flatbuffers::kFileIdentifierLength, binary_)) {
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::FileIdentifier;
// Check if the file identifier region has non-zero data, and assume its
// the file identifier. Otherwise, it will get filled in with padding
// later.
regions.push_back(MakeBinaryRegion(
offset, flatbuffers::kFileIdentifierLength * sizeof(uint8_t),
BinaryRegionType::Char, flatbuffers::kFileIdentifierLength, 0,
comment));
}
AddSection(header_offset, MakeBinarySection("", BinarySectionType::Header,
std::move(regions)));
return root_table_loc;
}
BinaryAnnotator::VTable *BinaryAnnotator::GetOrBuildVTable(
const uint64_t vtable_offset, const reflection::Object *const table,
const uint64_t offset_of_referring_table) {
// Get a list of vtables (if any) already defined at this offset.
std::list<VTable> &vtables = vtables_[vtable_offset];
// See if this vtable for the table type has been generated before.
for (VTable &vtable : vtables) {
if (vtable.referring_table == table) { return &vtable; }
}
// If we are trying to make a new vtable and it is already encompassed by
// another binary section, something is corrupted.
if (vtables.empty() && ContainsSection(vtable_offset)) { return nullptr; }
const std::string referring_table_name = table->name()->str();
BinaryRegionComment vtable_size_comment;
vtable_size_comment.type = BinaryRegionCommentType::VTableSize;
const auto vtable_length = ReadScalar<uint16_t>(vtable_offset);
if (!vtable_length.has_value()) {
const uint64_t remaining = RemainingBytes(vtable_offset);
SetError(vtable_size_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
"2");
AddSection(vtable_offset,
MakeSingleRegionBinarySection(
referring_table_name, BinarySectionType::VTable,
MakeBinaryRegion(vtable_offset, remaining,
BinaryRegionType::Unknown, remaining, 0,
vtable_size_comment)));
return nullptr;
}
// Vtables start with the size of the vtable
const uint16_t vtable_size = vtable_length.value();
if (!IsValidOffset(vtable_offset + vtable_size - 1)) {
SetError(vtable_size_comment, BinaryRegionStatus::ERROR_LENGTH_TOO_LONG);
// The vtable_size points to off the end of the binary.
AddSection(vtable_offset,
MakeSingleRegionBinarySection(
referring_table_name, BinarySectionType::VTable,
MakeBinaryRegion(vtable_offset, sizeof(uint16_t),
BinaryRegionType::Uint16, 0, 0,
vtable_size_comment)));
return nullptr;
} else if (vtable_size < 2 * sizeof(uint16_t)) {
SetError(vtable_size_comment, BinaryRegionStatus::ERROR_LENGTH_TOO_SHORT,
"4");
// The size includes itself and the table size which are both uint16_t.
AddSection(vtable_offset,
MakeSingleRegionBinarySection(
referring_table_name, BinarySectionType::VTable,
MakeBinaryRegion(vtable_offset, sizeof(uint16_t),
BinaryRegionType::Uint16, 0, 0,
vtable_size_comment)));
return nullptr;
}
std::vector<BinaryRegion> regions;
regions.push_back(MakeBinaryRegion(vtable_offset, sizeof(uint16_t),
BinaryRegionType::Uint16, 0, 0,
vtable_size_comment));
uint64_t offset = vtable_offset + sizeof(uint16_t);
BinaryRegionComment ref_table_len_comment;
ref_table_len_comment.type =
BinaryRegionCommentType::VTableRefferingTableLength;
// Ensure we can read the next uint16_t field, which is the size of the
// referring table.
const auto table_length = ReadScalar<uint16_t>(offset);
if (!table_length.has_value()) {
const uint64_t remaining = RemainingBytes(offset);
SetError(ref_table_len_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
"2");
AddSection(offset, MakeSingleRegionBinarySection(
referring_table_name, BinarySectionType::VTable,
MakeBinaryRegion(
offset, remaining, BinaryRegionType::Unknown,
remaining, 0, ref_table_len_comment)));
return nullptr;
}
// Then they have the size of the table they reference.
const uint16_t table_size = table_length.value();
if (!IsValidOffset(offset_of_referring_table + table_size - 1)) {
SetError(ref_table_len_comment, BinaryRegionStatus::ERROR_LENGTH_TOO_LONG);
} else if (table_size < 4) {
SetError(ref_table_len_comment, BinaryRegionStatus::ERROR_LENGTH_TOO_SHORT,
"4");
}
regions.push_back(MakeBinaryRegion(offset, sizeof(uint16_t),
BinaryRegionType::Uint16, 0, 0,
ref_table_len_comment));
offset += sizeof(uint16_t);
const uint64_t offset_start = offset;
// A mapping between field (and its id) to the relative offset (uin16_t) from
// the start of the table.
std::map<uint16_t, VTable::Entry> fields;
// Counter for determining if the binary has more vtable entries than the
// schema provided. This can occur if the binary was created at a newer schema
// version and is being processed with an older one.
uint16_t fields_processed = 0;
// Loop over all the fields.
ForAllFields(table, /*reverse=*/false, [&](const reflection::Field *field) {
const uint64_t field_offset = offset_start + field->id() * sizeof(uint16_t);
if (field_offset >= vtable_offset + vtable_size) {
// This field_offset is too large for this vtable, so it must come from a
// newer schema than the binary was create with or the binary writer did
// not write it. For either case, it is safe to ignore.
// TODO(dbaileychess): We could show which fields are not set an their
// default values if we want. We just need a way to make it obvious that
// it isn't part of the buffer.
return;
}
BinaryRegionComment field_comment;
field_comment.type = BinaryRegionCommentType::VTableFieldOffset;
field_comment.name = std::string(field->name()->c_str()) +
"` (id: " + std::to_string(field->id()) + ")";
const auto offset_from_table = ReadScalar<uint16_t>(field_offset);
if (!offset_from_table.has_value()) {
const uint64_t remaining = RemainingBytes(field_offset);
SetError(field_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "2");
regions.push_back(MakeBinaryRegion(field_offset, remaining,
BinaryRegionType::Unknown, remaining,
0, field_comment));
return;
}
if (!IsValidOffset(offset_of_referring_table + offset_from_table.value() -
1)) {
SetError(field_comment, BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
regions.push_back(MakeBinaryRegion(field_offset, sizeof(uint16_t),
BinaryRegionType::VOffset, 0, 0,
field_comment));
return;
}
VTable::Entry entry;
entry.field = field;
entry.offset_from_table = offset_from_table.value();
fields.insert(std::make_pair(field->id(), entry));
std::string default_label;
if (offset_from_table.value() == 0) {
// Not present, so could be default or be optional.
if (field->required()) {
SetError(field_comment,
BinaryRegionStatus::ERROR_REQUIRED_FIELD_NOT_PRESENT);
// If this is a required field, make it known this is an error.
regions.push_back(MakeBinaryRegion(field_offset, sizeof(uint16_t),
BinaryRegionType::VOffset, 0, 0,
field_comment));
return;
} else {
// Its an optional field, so get the default value and interpret and
// provided an annotation for it.
if (IsScalar(field->type()->base_type())) {
default_label += "<defaults to ";
default_label += IsFloat(field->type()->base_type())
? std::to_string(field->default_real())
: std::to_string(field->default_integer());
default_label += "> (";
} else {
default_label += "<null> (";
}
default_label +=
reflection::EnumNameBaseType(field->type()->base_type());
default_label += ")";
}
}
field_comment.default_value = default_label;
regions.push_back(MakeBinaryRegion(field_offset, sizeof(uint16_t),
BinaryRegionType::VOffset, 0, 0,
field_comment));
fields_processed++;
});
// Check if we covered all the expectant fields. If not, we need to add them
// as unknown fields.
uint16_t expectant_vtable_fields =
(vtable_size - sizeof(uint16_t) - sizeof(uint16_t)) / sizeof(uint16_t);
// Prevent a bad binary from declaring a really large vtable_size, that we can
// not independently verify.
expectant_vtable_fields = std::min(
static_cast<uint16_t>(fields_processed * 3), expectant_vtable_fields);
for (uint16_t id = fields_processed; id < expectant_vtable_fields; ++id) {
const uint64_t field_offset = offset_start + id * sizeof(uint16_t);
const auto offset_from_table = ReadScalar<uint16_t>(field_offset);
BinaryRegionComment field_comment;
field_comment.type = BinaryRegionCommentType::VTableUnknownFieldOffset;
field_comment.index = id;
if (!offset_from_table.has_value()) {
const uint64_t remaining = RemainingBytes(field_offset);
SetError(field_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "2");
regions.push_back(MakeBinaryRegion(field_offset, remaining,
BinaryRegionType::Unknown, remaining,
0, field_comment));
continue;
}
VTable::Entry entry;
entry.field = nullptr; // No field to reference.
entry.offset_from_table = offset_from_table.value();
fields.insert(std::make_pair(id, entry));
regions.push_back(MakeBinaryRegion(field_offset, sizeof(uint16_t),
BinaryRegionType::VOffset, 0, 0,
field_comment));
}
// If we have never added this vtable before record the Binary section.
if (vtables.empty()) {
sections_[vtable_offset] = MakeBinarySection(
referring_table_name, BinarySectionType::VTable, std::move(regions));
} else {
// Add the current table name to the name of the section.
sections_[vtable_offset].name += ", " + referring_table_name;
}
VTable vtable;
vtable.referring_table = table;
vtable.fields = std::move(fields);
vtable.table_size = table_size;
vtable.vtable_size = vtable_size;
// Add this vtable to the collection of vtables at this offset.
vtables.push_back(std::move(vtable));
// Return the vtable we just added.
return &vtables.back();
}
void BinaryAnnotator::BuildTable(const uint64_t table_offset,
const BinarySectionType type,
const reflection::Object *const table) {
if (ContainsSection(table_offset)) { return; }
BinaryRegionComment vtable_offset_comment;
vtable_offset_comment.type = BinaryRegionCommentType::TableVTableOffset;
const auto vtable_soffset = ReadScalar<int32_t>(table_offset);
if (!vtable_soffset.has_value()) {
const uint64_t remaining = RemainingBytes(table_offset);
SetError(vtable_offset_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
"4");
AddSection(
table_offset,
MakeSingleRegionBinarySection(
table->name()->str(), type,
MakeBinaryRegion(table_offset, remaining, BinaryRegionType::Unknown,
remaining, 0, vtable_offset_comment)));
// If there aren't enough bytes left to read the vtable offset, there is
// nothing we can do.
return;
}
// Tables start with the vtable
const uint64_t vtable_offset = table_offset - vtable_soffset.value();
if (!IsValidOffset(vtable_offset)) {
SetError(vtable_offset_comment,
BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
AddSection(table_offset,
MakeSingleRegionBinarySection(
table->name()->str(), type,
MakeBinaryRegion(table_offset, sizeof(int32_t),
BinaryRegionType::SOffset, 0, vtable_offset,
vtable_offset_comment)));
// There isn't much to do with an invalid vtable offset, as we won't be able
// to intepret the rest of the table fields.
return;
}
std::vector<BinaryRegion> regions;
regions.push_back(MakeBinaryRegion(table_offset, sizeof(int32_t),
BinaryRegionType::SOffset, 0,
vtable_offset, vtable_offset_comment));
// Parse the vtable first so we know what the rest of the fields in the table
// are.
const VTable *const vtable =
GetOrBuildVTable(vtable_offset, table, table_offset);
if (vtable == nullptr) {
// There is no valid vtable for this table, so we cannot process the rest of
// the table entries.
return;
}
// This is the size and length of this table.
const uint16_t table_size = vtable->table_size;
uint64_t table_end_offset = table_offset + table_size;
if (!IsValidOffset(table_end_offset - 1)) {
// We already validated the table size in BuildVTable, but we have to make
// sure we don't use a bad value here.
table_end_offset = binary_length_;
}
// We need to iterate over the vtable fields by their offset in the binary,
// not by their IDs. So copy them over to another vector that we can sort on
// the offset_from_table property.
std::vector<VTable::Entry> fields;
for (const auto &vtable_field : vtable->fields) {
fields.push_back(vtable_field.second);
}
std::stable_sort(fields.begin(), fields.end(),
[](const VTable::Entry &a, const VTable::Entry &b) {
return a.offset_from_table < b.offset_from_table;
});
// Iterate over all the fields by order of their offset.
for (size_t i = 0; i < fields.size(); ++i) {
const reflection::Field *field = fields[i].field;
const uint16_t offset_from_table = fields[i].offset_from_table;
if (offset_from_table == 0) {
// Skip non-present fields.
continue;
}
// The field offsets are relative to the start of the table.
const uint64_t field_offset = table_offset + offset_from_table;
if (!IsValidOffset(field_offset)) {
// The field offset is larger than the binary, nothing we can do.
continue;
}
// We have a vtable entry for a non-existant field, that means its a binary
// generated by a newer schema than we are currently processing.
if (field == nullptr) {
// Calculate the length of this unknown field.
const uint64_t unknown_field_length =
// Check if there is another unknown field after this one.
((i + 1 < fields.size())
? table_offset + fields[i + 1].offset_from_table
// Otherwise use the known end of the table.
: table_end_offset) -
field_offset;
if (unknown_field_length == 0) { continue; }
std::string hint;
if (unknown_field_length == 4) {
const auto relative_offset = ReadScalar<uint32_t>(field_offset);
if (relative_offset.has_value()) {
// The field is 4 in length, so it could be an offset? Provide a hint.
hint += "<possibly an offset? Check Loc: +0x";
hint += ToHex(field_offset + relative_offset.value());
hint += ">";
}
}
BinaryRegionComment unknown_field_comment;
unknown_field_comment.type = BinaryRegionCommentType::TableUnknownField;
if (!IsValidRead(field_offset, unknown_field_length)) {
const uint64_t remaining = RemainingBytes(field_offset);
SetError(unknown_field_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
std::to_string(unknown_field_length));
regions.push_back(MakeBinaryRegion(field_offset, remaining,
BinaryRegionType::Unknown, remaining,
0, unknown_field_comment));
continue;
}
unknown_field_comment.default_value = hint;
regions.push_back(MakeBinaryRegion(
field_offset, unknown_field_length, BinaryRegionType::Unknown,
unknown_field_length, 0, unknown_field_comment));
continue;
}
if (IsScalar(field->type()->base_type())) {
// These are the raw values store in the table.
const uint64_t type_size = GetTypeSize(field->type()->base_type());
const BinaryRegionType region_type =
GetRegionType(field->type()->base_type());
BinaryRegionComment scalar_field_comment;
scalar_field_comment.type = BinaryRegionCommentType::TableField;
scalar_field_comment.name =
std::string(field->name()->c_str()) + "` (" +
reflection::EnumNameBaseType(field->type()->base_type()) + ")";
if (!IsValidRead(field_offset, type_size)) {
const uint64_t remaining = RemainingBytes(field_offset);
SetError(scalar_field_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
std::to_string(type_size));
regions.push_back(MakeBinaryRegion(field_offset, remaining,
BinaryRegionType::Unknown, remaining,
0, scalar_field_comment));
continue;
}
if (IsUnionType(field)) {
// This is a type for a union. Validate the value
const auto enum_value = ReadScalar<uint8_t>(field_offset);
// This should always have a value, due to the IsValidRead check above.
if (!IsValidUnionValue(field, enum_value.value())) {
SetError(scalar_field_comment,
BinaryRegionStatus::ERROR_INVALID_UNION_TYPE);
regions.push_back(MakeBinaryRegion(field_offset, type_size,
region_type, 0, 0,
scalar_field_comment));
continue;
}
}
regions.push_back(MakeBinaryRegion(field_offset, type_size, region_type,
0, 0, scalar_field_comment));
continue;
}
// Read the offset
uint64_t offset = 0;
uint64_t length = sizeof(uint32_t);
BinaryRegionType region_type = BinaryRegionType::UOffset;
if (field->offset64()) {
length = sizeof(uint64_t);
region_type = BinaryRegionType::UOffset64;
offset = ReadScalar<uint64_t>(field_offset).value_or(0);
} else {
offset = ReadScalar<uint32_t>(field_offset).value_or(0);
}
// const auto offset_from_field = ReadScalar<uint32_t>(field_offset);
uint64_t offset_of_next_item = 0;
BinaryRegionComment offset_field_comment;
offset_field_comment.type = BinaryRegionCommentType::TableOffsetField;
offset_field_comment.name = field->name()->c_str();
const std::string offset_prefix =
"offset to field `" + std::string(field->name()->c_str()) + "`";
// Validate any field that isn't inline (i.e., non-structs).
if (!IsInlineField(field)) {
if (offset == 0) {
const uint64_t remaining = RemainingBytes(field_offset);
SetError(offset_field_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "4");
regions.push_back(MakeBinaryRegion(field_offset, remaining,
BinaryRegionType::Unknown, remaining,
0, offset_field_comment));
continue;
}
offset_of_next_item = field_offset + offset;
if (!IsValidOffset(offset_of_next_item)) {
SetError(offset_field_comment,
BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
regions.push_back(MakeBinaryRegion(field_offset, length, region_type, 0,
offset_of_next_item,
offset_field_comment));
continue;
}
}
switch (field->type()->base_type()) {
case reflection::BaseType::Obj: {
const reflection::Object *next_object =
schema_->objects()->Get(field->type()->index());
if (next_object->is_struct()) {
// Structs are stored inline.
BuildStruct(field_offset, regions, field->name()->c_str(),
next_object);
} else {
offset_field_comment.default_value = "(table)";
regions.push_back(MakeBinaryRegion(field_offset, length, region_type,
0, offset_of_next_item,
offset_field_comment));
BuildTable(offset_of_next_item, BinarySectionType::Table,
next_object);
}
} break;
case reflection::BaseType::String: {
offset_field_comment.default_value = "(string)";
regions.push_back(MakeBinaryRegion(field_offset, length, region_type, 0,
offset_of_next_item,
offset_field_comment));
BuildString(offset_of_next_item, table, field);
} break;
case reflection::BaseType::Vector: {
offset_field_comment.default_value = "(vector)";
regions.push_back(MakeBinaryRegion(field_offset, length, region_type, 0,
offset_of_next_item,
offset_field_comment));
BuildVector(offset_of_next_item, table, field, table_offset,
vtable->fields);
} break;
case reflection::BaseType::Vector64: {
offset_field_comment.default_value = "(vector64)";
regions.push_back(MakeBinaryRegion(field_offset, length, region_type, 0,
offset_of_next_item,
offset_field_comment));
BuildVector(offset_of_next_item, table, field, table_offset,
vtable->fields);
} break;
case reflection::BaseType::Union: {
const uint64_t union_offset = offset_of_next_item;
// The union type field is always one less than the union itself.
const uint16_t union_type_id = field->id() - 1;
auto vtable_field = vtable->fields.find(union_type_id);
if (vtable_field == vtable->fields.end()) {
// TODO(dbaileychess): need to capture this error condition.
break;
}
offset_field_comment.default_value = "(union)";
const uint64_t type_offset =
table_offset + vtable_field->second.offset_from_table;
const auto realized_type = ReadScalar<uint8_t>(type_offset);
if (!realized_type.has_value()) {
const uint64_t remaining = RemainingBytes(type_offset);
SetError(offset_field_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "1");
regions.push_back(MakeBinaryRegion(
type_offset, remaining, BinaryRegionType::Unknown, remaining, 0,
offset_field_comment));
continue;
}
if (!IsValidUnionValue(field, realized_type.value())) {
// We already export an error in the union type field, so just skip
// building the union itself and it will default to an unreference
// Binary section.
continue;
}
const std::string enum_type =
BuildUnion(union_offset, realized_type.value(), field);
offset_field_comment.default_value =
"(union of type `" + enum_type + "`)";
regions.push_back(MakeBinaryRegion(field_offset, length, region_type, 0,
union_offset, offset_field_comment));
} break;
default: break;
}
}
// Handle the case where there is padding after the last known binary
// region. Calculate where we left off towards the expected end of the
// table.
const uint64_t i = regions.back().offset + regions.back().length + 1;
if (i < table_end_offset) {
const uint64_t pad_bytes = table_end_offset - i + 1;
BinaryRegionComment padding_comment;
padding_comment.type = BinaryRegionCommentType::Padding;
regions.push_back(MakeBinaryRegion(i - 1, pad_bytes * sizeof(uint8_t),
BinaryRegionType::Uint8, pad_bytes, 0,
padding_comment));
}
AddSection(table_offset,
MakeBinarySection(table->name()->str(), type, std::move(regions)));
}
uint64_t BinaryAnnotator::BuildStruct(const uint64_t struct_offset,
std::vector<BinaryRegion> ®ions,
const std::string referring_field_name,
const reflection::Object *const object) {
if (!object->is_struct()) { return struct_offset; }
uint64_t offset = struct_offset;
// Loop over all the fields in increasing order
ForAllFields(object, /*reverse=*/false, [&](const reflection::Field *field) {
if (IsScalar(field->type()->base_type())) {
// Structure Field value
const uint64_t type_size = GetTypeSize(field->type()->base_type());
const BinaryRegionType region_type =
GetRegionType(field->type()->base_type());
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::StructField;
comment.name = referring_field_name + "." + field->name()->str();
comment.default_value = "of '" + object->name()->str() + "' (" +
std::string(reflection::EnumNameBaseType(
field->type()->base_type())) +
")";
if (!IsValidRead(offset, type_size)) {
const uint64_t remaining = RemainingBytes(offset);
SetError(comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
std::to_string(type_size));
regions.push_back(MakeBinaryRegion(offset, remaining,
BinaryRegionType::Unknown, remaining,
0, comment));
// TODO(dbaileychess): Should I bail out here? This sets offset to the
// end of the binary. So all other reads in the loop should fail.
offset += remaining;
return;
}
regions.push_back(
MakeBinaryRegion(offset, type_size, region_type, 0, 0, comment));
offset += type_size;
} else if (field->type()->base_type() == reflection::BaseType::Obj) {
// Structs are stored inline, even when nested.
offset = BuildStruct(offset, regions,
referring_field_name + "." + field->name()->str(),
schema_->objects()->Get(field->type()->index()));
} else if (field->type()->base_type() == reflection::BaseType::Array) {
const bool is_scalar = IsScalar(field->type()->element());
const uint64_t type_size = GetTypeSize(field->type()->element());
const BinaryRegionType region_type =
GetRegionType(field->type()->element());
// Arrays are just repeated structures.
for (uint16_t i = 0; i < field->type()->fixed_length(); ++i) {
if (is_scalar) {
BinaryRegionComment array_comment;
array_comment.type = BinaryRegionCommentType::ArrayField;
array_comment.name =
referring_field_name + "." + field->name()->str();
array_comment.index = i;
array_comment.default_value =
"of '" + object->name()->str() + "' (" +
std::string(
reflection::EnumNameBaseType(field->type()->element())) +
")";
if (!IsValidRead(offset, type_size)) {
const uint64_t remaining = RemainingBytes(offset);
SetError(array_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
std::to_string(type_size));
regions.push_back(MakeBinaryRegion(offset, remaining,
BinaryRegionType::Unknown,
remaining, 0, array_comment));
// TODO(dbaileychess): Should I bail out here? This sets offset to
// the end of the binary. So all other reads in the loop should
// fail.
offset += remaining;
break;
}
regions.push_back(MakeBinaryRegion(offset, type_size, region_type, 0,
0, array_comment));
offset += type_size;
} else {
// Array of Structs.
//
// TODO(dbaileychess): This works, but the comments on the fields lose
// some context. Need to figure a way how to plumb the nested arrays
// comments together that isn't too confusing.
offset =
BuildStruct(offset, regions,
referring_field_name + "." + field->name()->str(),
schema_->objects()->Get(field->type()->index()));
}
}
}
// Insert any padding after this field.
const uint16_t padding = field->padding();
if (padding > 0 && IsValidOffset(offset + padding)) {
BinaryRegionComment padding_comment;
padding_comment.type = BinaryRegionCommentType::Padding;
regions.push_back(MakeBinaryRegion(offset, padding,
BinaryRegionType::Uint8, padding, 0,
padding_comment));
offset += padding;
}
});
return offset;
}
void BinaryAnnotator::BuildString(const uint64_t string_offset,
const reflection::Object *const table,
const reflection::Field *const field) {
// Check if we have already generated this string section, and this is a
// shared string instance.
if (ContainsSection(string_offset)) { return; }
std::vector<BinaryRegion> regions;
const auto string_length = ReadScalar<uint32_t>(string_offset);
BinaryRegionComment string_length_comment;
string_length_comment.type = BinaryRegionCommentType::StringLength;
if (!string_length.has_value()) {
const uint64_t remaining = RemainingBytes(string_offset);
SetError(string_length_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
"4");
regions.push_back(MakeBinaryRegion(string_offset, remaining,
BinaryRegionType::Unknown, remaining, 0,
string_length_comment));
} else {
const uint32_t string_size = string_length.value();
const uint64_t string_end =
string_offset + sizeof(uint32_t) + string_size + sizeof(char);
if (!IsValidOffset(string_end - 1)) {
SetError(string_length_comment,
BinaryRegionStatus::ERROR_LENGTH_TOO_LONG);
regions.push_back(MakeBinaryRegion(string_offset, sizeof(uint32_t),
BinaryRegionType::Uint32, 0, 0,
string_length_comment));
} else {
regions.push_back(MakeBinaryRegion(string_offset, sizeof(uint32_t),
BinaryRegionType::Uint32, 0, 0,
string_length_comment));
BinaryRegionComment string_comment;
string_comment.type = BinaryRegionCommentType::StringValue;
regions.push_back(MakeBinaryRegion(string_offset + sizeof(uint32_t),
string_size, BinaryRegionType::Char,
string_size, 0, string_comment));
BinaryRegionComment string_terminator_comment;
string_terminator_comment.type =
BinaryRegionCommentType::StringTerminator;
regions.push_back(MakeBinaryRegion(
string_offset + sizeof(uint32_t) + string_size, sizeof(char),
BinaryRegionType::Char, 0, 0, string_terminator_comment));
}
}
AddSection(string_offset,
MakeBinarySection(std::string(table->name()->c_str()) + "." +
field->name()->c_str(),
BinarySectionType::String, std::move(regions)));
}
void BinaryAnnotator::BuildVector(
const uint64_t vector_offset, const reflection::Object *const table,
const reflection::Field *const field, const uint64_t parent_table_offset,
const std::map<uint16_t, VTable::Entry> vtable_fields) {
if (ContainsSection(vector_offset)) { return; }
BinaryRegionComment vector_length_comment;
vector_length_comment.type = BinaryRegionCommentType::VectorLength;
const bool is_64_bit_vector =
field->type()->base_type() == reflection::BaseType::Vector64;
flatbuffers::Optional<uint64_t> vector_length;
uint32_t vector_length_size_type = 0;
BinaryRegionType region_type = BinaryRegionType::Uint32;
BinarySectionType section_type = BinarySectionType::Vector;
if (is_64_bit_vector) {
auto v = ReadScalar<uint64_t>(vector_offset);
if (v.has_value()) { vector_length = v.value(); }
vector_length_size_type = sizeof(uint64_t);
region_type = BinaryRegionType::Uint64;
section_type = BinarySectionType::Vector64;
} else {
auto v = ReadScalar<uint32_t>(vector_offset);
if (v.has_value()) { vector_length = v.value(); }
vector_length_size_type = sizeof(uint32_t);
region_type = BinaryRegionType::Uint32;
section_type = BinarySectionType::Vector;
}
if (!vector_length.has_value()) {
const uint64_t remaining = RemainingBytes(vector_offset);
SetError(vector_length_comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
"4");
AddSection(
vector_offset,
MakeSingleRegionBinarySection(
std::string(table->name()->c_str()) + "." + field->name()->c_str(),
BinarySectionType::Vector,
MakeBinaryRegion(vector_offset, remaining,
BinaryRegionType::Unknown, remaining, 0,
vector_length_comment)));
return;
}
// Validate there are enough bytes left in the binary to process all the
// items.
const uint64_t last_item_offset =
vector_offset + vector_length_size_type +
vector_length.value() * GetElementSize(field);
if (!IsValidOffset(last_item_offset - 1)) {
SetError(vector_length_comment, BinaryRegionStatus::ERROR_LENGTH_TOO_LONG);
AddSection(
vector_offset,
MakeSingleRegionBinarySection(
std::string(table->name()->c_str()) + "." + field->name()->c_str(),
BinarySectionType::Vector,
MakeBinaryRegion(vector_offset, vector_length_size_type,
region_type, 0, 0, vector_length_comment)));
return;
}
std::vector<BinaryRegion> regions;
regions.push_back(MakeBinaryRegion(vector_offset, vector_length_size_type,
region_type, 0, 0, vector_length_comment));
// Consume the vector length offset.
uint64_t offset = vector_offset + vector_length_size_type;
switch (field->type()->element()) {
case reflection::BaseType::Obj: {
const reflection::Object *object =
schema_->objects()->Get(field->type()->index());
if (object->is_struct()) {
// Vector of structs
for (size_t i = 0; i < vector_length.value(); ++i) {
// Structs are inline to the vector.
const uint64_t next_offset =
BuildStruct(offset, regions, "[" + NumToString(i) + "]", object);
if (next_offset == offset) { break; }
offset = next_offset;
}
} else {
// Vector of objects
for (size_t i = 0; i < vector_length.value(); ++i) {
BinaryRegionComment vector_object_comment;
vector_object_comment.type =
BinaryRegionCommentType::VectorTableValue;
vector_object_comment.index = i;
const auto table_relative_offset = ReadScalar<uint32_t>(offset);
if (!table_relative_offset.has_value()) {
const uint64_t remaining = RemainingBytes(offset);
SetError(vector_object_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "4");
regions.push_back(
MakeBinaryRegion(offset, remaining, BinaryRegionType::Unknown,
remaining, 0, vector_object_comment));
break;
}
// The table offset is relative from the offset location itself.
const uint64_t table_offset = offset + table_relative_offset.value();
if (!IsValidOffset(table_offset)) {
SetError(vector_object_comment,
BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
regions.push_back(MakeBinaryRegion(
offset, sizeof(uint32_t), BinaryRegionType::UOffset, 0,
table_offset, vector_object_comment));
offset += sizeof(uint32_t);
continue;
}
if (table_offset == parent_table_offset) {
SetError(vector_object_comment,
BinaryRegionStatus::ERROR_CYCLE_DETECTED);
// A cycle detected where a table vector field is pointing to
// itself. This should only happen in corrupted files.
regions.push_back(MakeBinaryRegion(
offset, sizeof(uint32_t), BinaryRegionType::UOffset, 0,
table_offset, vector_object_comment));
offset += sizeof(uint32_t);
continue;
}
regions.push_back(MakeBinaryRegion(
offset, sizeof(uint32_t), BinaryRegionType::UOffset, 0,
table_offset, vector_object_comment));
// Consume the offset to the table.
offset += sizeof(uint32_t);
BuildTable(table_offset, BinarySectionType::Table, object);
}
}
} break;
case reflection::BaseType::String: {
// Vector of strings
for (size_t i = 0; i < vector_length.value(); ++i) {
BinaryRegionComment vector_object_comment;
vector_object_comment.type = BinaryRegionCommentType::VectorStringValue;
vector_object_comment.index = i;
const auto string_relative_offset = ReadScalar<uint32_t>(offset);
if (!string_relative_offset.has_value()) {
const uint64_t remaining = RemainingBytes(offset);
SetError(vector_object_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "4");
regions.push_back(
MakeBinaryRegion(offset, remaining, BinaryRegionType::Unknown,
remaining, 0, vector_object_comment));
break;
}
// The string offset is relative from the offset location itself.
const uint64_t string_offset = offset + string_relative_offset.value();
if (!IsValidOffset(string_offset)) {
SetError(vector_object_comment,
BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
regions.push_back(MakeBinaryRegion(
offset, sizeof(uint32_t), BinaryRegionType::UOffset, 0,
string_offset, vector_object_comment));
offset += sizeof(uint32_t);
continue;
}
regions.push_back(MakeBinaryRegion(
offset, sizeof(uint32_t), BinaryRegionType::UOffset, 0,
string_offset, vector_object_comment));
BuildString(string_offset, table, field);
offset += sizeof(uint32_t);
}
} break;
case reflection::BaseType::Union: {
// Vector of unions
// Unions have both their realized type (uint8_t for now) that are
// stored separately. These are stored in the field->index() - 1
// location.
const uint16_t union_type_vector_id = field->id() - 1;
auto vtable_entry = vtable_fields.find(union_type_vector_id);
if (vtable_entry == vtable_fields.end()) {
// TODO(dbaileychess): need to capture this error condition.
break;
}
const uint64_t union_type_vector_field_offset =
parent_table_offset + vtable_entry->second.offset_from_table;
const auto union_type_vector_field_relative_offset =
ReadScalar<uint16_t>(union_type_vector_field_offset);
if (!union_type_vector_field_relative_offset.has_value()) {
const uint64_t remaining = RemainingBytes(offset);
BinaryRegionComment vector_union_comment;
vector_union_comment.type = BinaryRegionCommentType::VectorUnionValue;
SetError(vector_union_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "2");
regions.push_back(MakeBinaryRegion(offset, remaining,
BinaryRegionType::Unknown, remaining,
0, vector_union_comment));
break;
}
// Get the offset to the first type (the + sizeof(uint32_t) is to skip
// over the vector length which we already know). Validation happens
// within the loop below.
const uint64_t union_type_vector_data_offset =
union_type_vector_field_offset +
union_type_vector_field_relative_offset.value() + sizeof(uint32_t);
for (size_t i = 0; i < vector_length.value(); ++i) {
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::VectorUnionValue;
comment.index = i;
const auto union_relative_offset = ReadScalar<uint32_t>(offset);
if (!union_relative_offset.has_value()) {
const uint64_t remaining = RemainingBytes(offset);
SetError(comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "4");
regions.push_back(MakeBinaryRegion(offset, remaining,
BinaryRegionType::Unknown,
remaining, 0, comment));
break;
}
// The union offset is relative from the offset location itself.
const uint64_t union_offset = offset + union_relative_offset.value();
if (!IsValidOffset(union_offset)) {
SetError(comment, BinaryRegionStatus::ERROR_OFFSET_OUT_OF_BINARY);
regions.push_back(MakeBinaryRegion(offset, sizeof(uint32_t),
BinaryRegionType::UOffset, 0,
union_offset, comment));
continue;
}
const auto realized_type =
ReadScalar<uint8_t>(union_type_vector_data_offset + i);
if (!realized_type.has_value()) {
SetError(comment, BinaryRegionStatus::ERROR_INCOMPLETE_BINARY, "1");
regions.push_back(MakeBinaryRegion(
offset, 0, BinaryRegionType::Unknown, 0, 0, comment));
continue;
}
if (!IsValidUnionValue(vtable_entry->second.field->type()->index(),
realized_type.value())) {
// We already export an error in the union type field, so just skip
// building the union itself and it will default to an unreference
// Binary section.
offset += sizeof(uint32_t);
continue;
}
const std::string enum_type =
BuildUnion(union_offset, realized_type.value(), field);
comment.default_value = "(`" + enum_type + "`)";
regions.push_back(MakeBinaryRegion(offset, sizeof(uint32_t),
BinaryRegionType::UOffset, 0,
union_offset, comment));
offset += sizeof(uint32_t);
}
} break;
default: {
if (IsScalar(field->type()->element())) {
const BinaryRegionType binary_region_type =
GetRegionType(field->type()->element());
const uint64_t type_size = GetTypeSize(field->type()->element());
// TODO(dbaileychess): It might be nicer to user the
// BinaryRegion.array_length field to indicate this.
for (size_t i = 0; i < vector_length.value(); ++i) {
BinaryRegionComment vector_scalar_comment;
vector_scalar_comment.type = BinaryRegionCommentType::VectorValue;
vector_scalar_comment.index = i;
if (!IsValidRead(offset, type_size)) {
const uint64_t remaining = RemainingBytes(offset);
SetError(vector_scalar_comment,
BinaryRegionStatus::ERROR_INCOMPLETE_BINARY,
std::to_string(type_size));
regions.push_back(
MakeBinaryRegion(offset, remaining, BinaryRegionType::Unknown,
remaining, 0, vector_scalar_comment));
break;
}
if (IsUnionType(field->type()->element())) {
// This is a type for a union. Validate the value
const auto enum_value = ReadScalar<uint8_t>(offset);
// This should always have a value, due to the IsValidRead check
// above.
if (!IsValidUnionValue(field->type()->index(),
enum_value.value())) {
SetError(vector_scalar_comment,
BinaryRegionStatus::ERROR_INVALID_UNION_TYPE);
regions.push_back(MakeBinaryRegion(offset, type_size,
binary_region_type, 0, 0,
vector_scalar_comment));
offset += type_size;
continue;
}
}
regions.push_back(MakeBinaryRegion(offset, type_size,
binary_region_type, 0, 0,
vector_scalar_comment));
offset += type_size;
}
}
} break;
}
AddSection(vector_offset,
MakeBinarySection(std::string(table->name()->c_str()) + "." +
field->name()->c_str(),
section_type, std::move(regions)));
}
std::string BinaryAnnotator::BuildUnion(const uint64_t union_offset,
const uint8_t realized_type,
const reflection::Field *const field) {
const reflection::Enum *next_enum =
schema_->enums()->Get(field->type()->index());
const reflection::EnumVal *enum_val = next_enum->values()->Get(realized_type);
if (ContainsSection(union_offset)) { return enum_val->name()->c_str(); }
const reflection::Type *union_type = enum_val->union_type();
if (union_type->base_type() == reflection::BaseType::Obj) {
const reflection::Object *object =
schema_->objects()->Get(union_type->index());
if (object->is_struct()) {
// Union of vectors point to a new Binary section
std::vector<BinaryRegion> regions;
BuildStruct(union_offset, regions, field->name()->c_str(), object);
AddSection(
union_offset,
MakeBinarySection(std::string(object->name()->c_str()) + "." +
field->name()->c_str(),
BinarySectionType::Union, std::move(regions)));
} else {
BuildTable(union_offset, BinarySectionType::Table, object);
}
}
// TODO(dbaileychess): handle the other union types.
return enum_val->name()->c_str();
}
void BinaryAnnotator::FixMissingRegions() {
std::vector<BinaryRegion> regions_to_insert;
for (auto ¤t_section : sections_) {
BinarySection §ion = current_section.second;
if (section.regions.empty()) {
// TODO(dbaileychess): is this possible?
continue;
}
uint64_t offset = section.regions[0].offset + section.regions[0].length;
for (size_t i = 1; i < section.regions.size(); ++i) {
BinaryRegion ®ion = section.regions[i];
const uint64_t next_offset = region.offset;
if (!IsValidOffset(next_offset)) {
// TODO(dbaileychess): figure out how we get into this situation.
continue;
}
if (offset < next_offset) {
const uint64_t padding_bytes = next_offset - offset;
BinaryRegionComment comment;
comment.type = BinaryRegionCommentType::Padding;
if (IsNonZeroRegion(offset, padding_bytes, binary_)) {
SetError(comment, BinaryRegionStatus::WARN_NO_REFERENCES);
regions_to_insert.push_back(
MakeBinaryRegion(offset, padding_bytes, BinaryRegionType::Unknown,
padding_bytes, 0, comment));
} else {
regions_to_insert.push_back(
MakeBinaryRegion(offset, padding_bytes, BinaryRegionType::Uint8,
padding_bytes, 0, comment));
}
}
offset = next_offset + region.length;
}
if (!regions_to_insert.empty()) {
section.regions.insert(section.regions.end(), regions_to_insert.begin(),
regions_to_insert.end());
std::stable_sort(section.regions.begin(), section.regions.end(),
BinaryRegionSort);
regions_to_insert.clear();
}
}
}
void BinaryAnnotator::FixMissingSections() {
uint64_t offset = 0;
std::vector<BinarySection> sections_to_insert;
for (auto ¤t_section : sections_) {
BinarySection §ion = current_section.second;
const uint64_t section_start_offset = current_section.first;
const uint64_t section_end_offset =
section.regions.back().offset + section.regions.back().length;
if (offset < section_start_offset) {
// We are at an offset that is less then the current section.
const uint64_t pad_bytes = section_start_offset - offset + 1;
sections_to_insert.push_back(
GenerateMissingSection(offset - 1, pad_bytes, binary_));
}
offset = section_end_offset + 1;
}
// Handle the case where there are still bytes left in the binary that are
// unaccounted for.
if (offset < binary_length_) {
const uint64_t pad_bytes = binary_length_ - offset + 1;
sections_to_insert.push_back(
GenerateMissingSection(offset - 1, pad_bytes, binary_));
}
for (const BinarySection §ion_to_insert : sections_to_insert) {
AddSection(section_to_insert.regions[0].offset, section_to_insert);
}
}
bool BinaryAnnotator::ContainsSection(const uint64_t offset) {
auto it = sections_.lower_bound(offset);
// If the section is found, check that it is exactly equal its offset.
if (it != sections_.end() && it->first == offset) { return true; }
// If this was the first section, there are no other previous sections to
// check.
if (it == sections_.begin()) { return false; }
// Go back one section.
--it;
// And check that if the offset is covered by the section.
return offset >= it->first && offset < it->second.regions.back().offset +
it->second.regions.back().length;
}
} // namespace flatbuffers