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213 lines (200 loc) · 10.5 KB
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/* Copyright (C) 2026 Sebastiano Merlino; SPDX-License-Identifier: LGPL-2.1-or-later */
#include <algorithm>
#include <string>
#include <vector>
#include <httpserver/detail/qpack_decoder.hpp>
namespace httpserver::detail {
auto qpack_decoder::inspect_prefix(std::span<const std::uint8_t> input, const qpack_dynamic_table& table) noexcept -> section_prefix {
const auto encoded = qpack_decode_integer(input, 8, {});
if (!encoded.status.ok()) return {encoded.status};
std::uint64_t required = 0;
if (encoded.value != 0) {
const auto max_entries = table.maximum_capacity() / 32;
const auto full_range = 2 * max_entries;
if (max_entries == 0 || encoded.value > full_range || table.insert_count() > qpack_integer_maximum - max_entries) {
return {{qpack_state::malformed}};
}
const auto max_value = table.insert_count() + max_entries;
const auto max_wrapped = (max_value / full_range) * full_range;
if (encoded.value - 1 > qpack_integer_maximum - max_wrapped) return {{qpack_state::malformed}};
required = max_wrapped + encoded.value - 1;
if (required > max_value) {
if (required <= full_range) return {{qpack_state::malformed}};
required -= full_range;
}
if (required == 0) return {{qpack_state::malformed}};
}
const auto base_wire = input.subspan(encoded.consumed);
const auto delta = qpack_decode_integer(base_wire, 7, {});
if (!delta.status.ok()) return {delta.status, required};
std::uint64_t base;
if ((base_wire[0] & 0x80) != 0) {
if (delta.value >= required) return {{qpack_state::malformed}, required};
base = required - delta.value - 1;
} else {
if (delta.value > qpack_integer_maximum - required) return {{qpack_state::malformed}, required};
base = required + delta.value;
}
return {{}, required, base, encoded.consumed + delta.consumed};
}
auto qpack_decoder::decode(std::span<const std::uint8_t> input, qpack_section_limits limits) const -> qpack_section_result {
try {
return decode_allocated(input, limits);
} catch (const std::bad_alloc&) {
return {{qpack_state::limit_exceeded}, {}};
} catch (const std::length_error&) {
return {{qpack_state::limit_exceeded}, {}};
}
}
auto qpack_decoder::decode_allocated(std::span<const std::uint8_t> input, qpack_section_limits limits) const -> qpack_section_result {
if (input.size() > limits.max_compressed_bytes) return {{qpack_state::limit_exceeded}, {}};
std::size_t count = 0;
auto status = process(input, limits, nullptr, count);
if (!status.ok()) return {complete(status), {}};
qpack_section_result result;
result.fields.reserve(count);
status = process(input, limits, &result.fields, count);
if (!status.ok()) return {complete(status), {}};
return result;
}
auto qpack_decoder::decode_dynamic(std::span<const std::uint8_t> input, const qpack_dynamic_table& table, qpack_section_limits limits) const -> qpack_section_result {
if (!table.initialized() || table.role() != qpack_table_role::decoder) return {{qpack_state::invalid_argument}, {}};
if (input.size() > limits.max_compressed_bytes) return {{qpack_state::limit_exceeded}, {}};
try {
return decode_dynamic_allocated(input, table, limits, inspect_prefix(input, table));
} catch (const std::bad_alloc&) {
return {{qpack_state::limit_exceeded}, {}};
} catch (const std::length_error&) {
return {{qpack_state::limit_exceeded}, {}};
}
}
auto qpack_decoder::decode_dynamic_allocated(std::span<const std::uint8_t> input, const qpack_dynamic_table& table, qpack_section_limits limits, section_prefix section) const -> qpack_section_result {
if (!section.status.ok()) return {complete(section.status), {}, section.required};
if (section.required > table.insert_count()) return {{qpack_state::inserts_unavailable}, {}, section.required};
std::size_t count = 0;
auto status = process(input, limits, nullptr, count, &table, §ion);
if (!status.ok()) return {complete(status), {}, section.required};
qpack_section_result result;
result.required_insert_count = section.required;
result.fields.reserve(count);
status = process(input, limits, &result.fields, count, &table, §ion);
if (!status.ok()) return {complete(status), {}, section.required};
return result;
}
auto qpack_decoder::prefix(std::span<const std::uint8_t> input) noexcept -> qpack_integer_result {
const auto required = qpack_decode_integer(input, 8, {});
if (!required.status.ok()) return required;
if (required.value != 0) return {{qpack_state::malformed}};
const auto base_wire = input.subspan(required.consumed);
const auto base = qpack_decode_integer(base_wire, 7, {});
if (!base.status.ok()) return base;
// With Required Insert Count zero, the sign would make Base negative.
if ((base_wire[0] & 0x80) != 0) return {{qpack_state::malformed}};
return {{}, 0, required.consumed + base.consumed};
}
auto qpack_decoder::read_name(std::span<const std::uint8_t> input, std::size_t remaining, std::size_t encoded_limit, wire_field& field, const qpack_dynamic_table* table, std::uint64_t base,
std::uint64_t required) noexcept -> qpack_status {
const auto bits = input[0];
if ((bits & 0x80) != 0 || (bits & 0x40) != 0) {
field.indexed = (bits & 0x80) != 0;
const auto static_bit = field.indexed ? 0x40 : 0x10;
if ((bits & static_bit) == 0 && !table) return {qpack_state::malformed};
const auto index = qpack_decode_integer(input, field.indexed ? 6 : 4, {});
if (!index.status.ok()) return index.status;
if (bits & static_bit) {
field.entry = qpack_static_lookup(index.value);
if (!field.entry) return {qpack_state::malformed};
field.name_size = field.entry->name.size();
field.value_size = field.indexed ? field.entry->value.size() : 0;
} else {
field.dynamic = table->section_relative(base, index.value);
if (!field.dynamic || field.dynamic->absolute >= required) return {qpack_state::malformed};
field.name_size = field.dynamic->name.size();
field.value_size = field.indexed ? field.dynamic->value.size() : 0;
}
field.consumed = index.consumed;
field.never_indexed = !field.indexed && (bits & 0x20) != 0;
} else if ((bits & 0x20) != 0) {
const auto name = qpack_inspect_string(input, {encoded_limit, remaining - 32}, 3, 8);
if (!name.status.ok()) return name.status;
field.name_wire = input.first(name.consumed);
field.name_size = static_cast<std::size_t>(name.value);
field.consumed = name.consumed;
field.never_indexed = (bits & 0x10) != 0;
} else {
if (!table) return {qpack_state::malformed};
field.indexed = (bits & 0x10) != 0;
const auto index = qpack_decode_integer(input, field.indexed ? 4 : 3, {});
if (!index.status.ok()) return index.status;
field.dynamic = table->post_base(base, index.value);
if (!field.dynamic || field.dynamic->absolute >= required) return {qpack_state::malformed};
field.name_size = field.dynamic->name.size();
field.value_size = field.indexed ? field.dynamic->value.size() : 0;
field.consumed = index.consumed;
field.never_indexed = !field.indexed && (bits & 8) != 0;
}
return {};
}
auto qpack_decoder::read_field(std::span<const std::uint8_t> input, std::size_t& remaining, std::size_t encoded_limit, wire_field& field, const qpack_dynamic_table* table, std::uint64_t base,
std::uint64_t required) noexcept -> qpack_status {
if (remaining < 32) return {qpack_state::limit_exceeded};
auto status = read_name(input, remaining, encoded_limit, field, table, base, required);
if (!status.ok()) return status;
if (field.name_size > remaining - 32) return {qpack_state::limit_exceeded};
if (!field.indexed) {
const auto value_wire = input.subspan(field.consumed);
const auto value = qpack_inspect_string(value_wire, {encoded_limit, remaining - 32 - field.name_size});
if (!value.status.ok()) return value.status;
field.value_wire = value_wire.first(value.consumed);
field.value_size = static_cast<std::size_t>(value.value);
field.consumed += value.consumed;
}
return qpack_admit_field(field.name_size, field.value_size, remaining) ? qpack_status{} : qpack_status{qpack_state::limit_exceeded};
}
auto qpack_decoder::materialize(const wire_field& field) -> qpack_field {
qpack_field out;
out.never_indexed = field.never_indexed;
if (field.dynamic) {
out.name = field.dynamic->name;
} else if (field.entry) {
out.name = field.entry->name;
} else {
out.name = qpack_decode_string(field.name_wire, {field.name_wire.size(), field.name_size}, 3, 8).value;
}
if (field.indexed) {
out.value = field.dynamic ? field.dynamic->value : std::string(field.entry->value);
} else {
out.value = qpack_decode_string(field.value_wire, {field.value_wire.size(), field.value_size}).value;
}
return out;
}
auto qpack_decoder::process(std::span<const std::uint8_t> input, qpack_section_limits limits, std::vector<qpack_field>* output, std::size_t& count, const qpack_dynamic_table* table,
const section_prefix* frozen) -> qpack_status {
section_prefix section;
if (frozen) {
section = *frozen;
} else if (table) {
section = inspect_prefix(input, *table);
} else {
const auto legacy = prefix(input);
section = {legacy.status, 0, 0, legacy.consumed};
}
if (!section.status.ok()) return section.status;
input = input.subspan(section.consumed);
auto remaining = limits.max_expanded_bytes;
count = 0;
std::uint64_t largest_required = 0;
while (!input.empty()) {
if (count == limits.max_fields) return {qpack_state::limit_exceeded};
wire_field field;
const auto status = read_field(input, remaining, limits.max_compressed_bytes, field, table, section.base, section.required);
if (!status.ok()) return status;
if (field.dynamic) largest_required = std::max(largest_required, field.dynamic->absolute + 1);
if (output != nullptr) output->push_back(materialize(field));
input = input.subspan(field.consumed);
++count;
}
if (table && largest_required != section.required) return {qpack_state::malformed};
return {};
}
} // namespace httpserver::detail