tls_reader.h

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/*
* TLS Data Reader
* (C) 2010-2011,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_TLS_READER_H_
#define BOTAN_TLS_READER_H_
 
#include <botan/assert.h>
#include <botan/secmem.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/mem_utils.h>
#include <span>
#include <string>
#include <vector>
 
namespace Botan::TLS {
 
/**
* Helper class for decoding TLS protocol messages
*/
class BOTAN_TEST_API TLS_Data_Reader final {
   public:
      TLS_Data_Reader(const char* type, std::span<const uint8_t> buf_in) :
            m_typename(type), m_buf(buf_in), m_offset(0) {}
 
      void assert_done() const {
         if(has_remaining()) {
            throw_decode_error("Extra bytes at end of message");
         }
      }
 
      size_t read_so_far() const { return m_offset; }
 
      size_t remaining_bytes() const { return m_buf.size() - m_offset; }
 
      bool has_remaining() const { return (remaining_bytes() > 0); }
 
      std::vector<uint8_t> get_remaining() {
         const std::span rest = m_buf.subspan(m_offset);
         return std::vector<uint8_t>(rest.begin(), rest.end());
      }
 
      std::vector<uint8_t> get_data_read_so_far() {
         const std::span first = m_buf.first(m_offset);
         return std::vector<uint8_t>(first.begin(), first.end());
      }
 
      void discard_next(size_t bytes) {
         assert_at_least(bytes);
         m_offset += bytes;
      }
 
      uint32_t get_uint32_t() {
         assert_at_least(4);
         const uint32_t result =
            make_uint32(m_buf[m_offset], m_buf[m_offset + 1], m_buf[m_offset + 2], m_buf[m_offset + 3]);
         m_offset += 4;
         return result;
      }
 
      uint32_t get_uint24_t() {
         assert_at_least(3);
         const uint32_t result = make_uint32(0, m_buf[m_offset], m_buf[m_offset + 1], m_buf[m_offset + 2]);
         m_offset += 3;
         return result;
      }
 
      uint16_t get_uint16_t() {
         assert_at_least(2);
         const uint16_t result = make_uint16(m_buf[m_offset], m_buf[m_offset + 1]);
         m_offset += 2;
         return result;
      }
 
      uint16_t peek_uint16_t() const {
         assert_at_least(2);
         return make_uint16(m_buf[m_offset], m_buf[m_offset + 1]);
      }
 
      uint8_t get_byte() {
         assert_at_least(1);
         const uint8_t result = m_buf[m_offset];
         m_offset += 1;
         return result;
      }
 
      template <typename T, typename Container>
      Container get_elem(size_t num_elems) {
         assert_at_least(num_elems * sizeof(T));
 
         Container result(num_elems);
 
         for(size_t i = 0; i != num_elems; ++i) {
            result[i] = load_be<T>(&m_buf[m_offset], i);
         }
 
         m_offset += num_elems * sizeof(T);
 
         return result;
      }
 
      std::vector<uint8_t> get_tls_length_value(size_t len_bytes) {
         return get_fixed<uint8_t>(get_length_field(len_bytes));
      }
 
      template <typename T>
      std::vector<T> get_range(size_t len_bytes, size_t min_elems, size_t max_elems) {
         const size_t num_elems = get_num_elems(len_bytes, sizeof(T), min_elems, max_elems);
 
         return get_elem<T, std::vector<T>>(num_elems);
      }
 
      template <typename T>
      std::vector<T> get_range_vector(size_t len_bytes, size_t min_elems, size_t max_elems) {
         const size_t num_elems = get_num_elems(len_bytes, sizeof(T), min_elems, max_elems);
 
         return get_elem<T, std::vector<T>>(num_elems);
      }
 
      std::string get_string(size_t len_bytes, size_t min_bytes, size_t max_bytes) {
         std::vector<uint8_t> v = get_range_vector<uint8_t>(len_bytes, min_bytes, max_bytes);
         return bytes_to_string(v);
      }
 
      template <typename T>
      std::vector<T> get_fixed(size_t size) {
         return get_elem<T, std::vector<T>>(size);
      }
 
   private:
      size_t get_length_field(size_t len_bytes) {
         assert_at_least(len_bytes);
 
         if(len_bytes == 1) {
            return get_byte();
         } else if(len_bytes == 2) {
            return get_uint16_t();
         } else if(len_bytes == 3) {
            return get_uint24_t();
         }
 
         throw_decode_error("Bad length size");
      }
 
      size_t get_num_elems(size_t len_bytes, size_t T_size, size_t min_elems, size_t max_elems) {
         const size_t byte_length = get_length_field(len_bytes);
 
         if(byte_length % T_size != 0) {
            throw_decode_error("Size isn't multiple of T");
         }
 
         const size_t num_elems = byte_length / T_size;
 
         if(num_elems < min_elems || num_elems > max_elems) {
            throw_decode_error("Length field outside parameters");
         }
 
         return num_elems;
      }
 
      void assert_at_least(size_t n) const;
 
      [[noreturn]] void throw_decode_error(std::string_view why) const;
 
      const char* m_typename;
      std::span<const uint8_t> m_buf;
      size_t m_offset;
};
 
/**
* Helper function for encoding length-tagged vectors
*/
template <typename T, typename Alloc>
inline void append_tls_length_value(std::vector<uint8_t, Alloc>& buf,
                                    const T* vals,
                                    size_t vals_size,
                                    size_t tag_size) {
   const size_t T_size = sizeof(T);
   const size_t val_bytes = T_size * vals_size;
 
   BOTAN_ARG_CHECK(tag_size == 1 || tag_size == 2 || tag_size == 3, "Invalid TLS tag size");
 
   const size_t max_possible_size = (1 << (8 * tag_size)) - 1;
 
   BOTAN_ARG_CHECK(val_bytes <= max_possible_size, "Value too large to encode");
 
   for(size_t i = 0; i != tag_size; ++i) {
      buf.push_back(get_byte_var(sizeof(val_bytes) - tag_size + i, val_bytes));
   }
 
   for(size_t i = 0; i != vals_size; ++i) {
      for(size_t j = 0; j != T_size; ++j) {
         buf.push_back(get_byte_var(j, vals[i]));
      }
   }
}
 
template <typename T, typename Alloc>
inline void append_tls_length_value(std::vector<uint8_t, Alloc>& buf, std::span<const T> vals, size_t tag_size) {
   append_tls_length_value(buf, vals.data(), vals.size(), tag_size);
}
 
template <typename T, typename Alloc, typename Alloc2>
inline void append_tls_length_value(std::vector<uint8_t, Alloc>& buf,
                                    const std::vector<T, Alloc2>& vals,
                                    size_t tag_size) {
   append_tls_length_value(buf, std::span{vals}, tag_size);
}
 
template <typename Alloc>
inline void append_tls_length_value(std::vector<uint8_t, Alloc>& buf, std::string_view str, size_t tag_size) {
   append_tls_length_value(buf, as_span_of_bytes(str), tag_size);
}
 
}  // namespace Botan::TLS
 
#endif