#include "source/common/json/json_sanitizer.h"

#include "source/common/common/assert.h"

#include "source/common/common/thread.h"

#include "source/common/json/json_internal.h"

#include "absl/strings/str_format.h"

#include "utf8_validity.h"

namespace Envoy {

namespace Json {

// clang-format off

// SPELLCHECKER(off)

//

// Performance benchmarks show this is slightly faster as an array of uint32_t

// rather than an array of bool.

static constexpr uint32_t needs_slow_sanitizer[256] = {

  // Control-characters 0-31 all require escapes.

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  // Pass through printable characters starting with space. Double-quote and

  // backslash require an escape.

  0, 0, 1 /* " */, 0, 0, 0, 0, 0,         //  !"#$%&'

  0, 0, 0, 0, 0, 0, 0, 0,                 // ()*+,-.7

  0, 0, 0, 0, 0, 0, 0, 0,                 // 01234567

  0, 0, 0, 0, 0, 0, 0, 0,                 // 89:;<=>?

  0, 0, 0, 0, 0, 0, 0, 0,                 // @ABCDEFG

  0, 0, 0, 0, 0, 0, 0, 0,                 // HIJKLMNO

  0, 0, 0, 0, 0, 0, 0, 0,                 // PQRSTUVW

  0, 0, 0, 0, 1 /* backslash */, 0, 0, 0, // XYZ[\]^_

  0, 0, 0, 0, 0, 0, 0, 0,                 // `abcdefg

  0, 0, 0, 0, 0, 0, 0, 0,                 // hijklmno

  0, 0, 0, 0, 0, 0, 0, 0,                 // pqrstuvw

  0, 0, 0, 0, 0, 0, 0, 1,                 // xyz{|}~\177

  // 0x80-0xff, all of which require calling the slow sanitizer.

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

};

// SPELLCHECKER(on)

// clang-format on

absl::string_view sanitize(std::string& buffer, absl::string_view str) {

  // Fast-path to see whether any escapes or utf-encoding are needed. If str has

  // only unescaped ascii characters, we can simply return it.

  //

  // Benchmarks show it's faster to just rip through the string with no

  // conditionals, so we only check the arithmetically ORed condition after the

  // loop. This avoids branches and allows simpler loop unrolling by the

  // compiler.

  static_assert(ARRAY_SIZE(needs_slow_sanitizer) == 256);

  uint32_t need_slow = 0;

  for (char c : str) {

    // We need to escape control characters, characters >= 127, and double-quote

    // and backslash.

    need_slow |= needs_slow_sanitizer[static_cast<uint8_t>(c)];

  }

  if (need_slow == 0) {

    return str; // Fast path, should be executed most of the time.

  }

  if (utf8_range::IsStructurallyValid(str)) {

    // The Nlohmann JSON library supports serialization and is not too slow. A

    // hand-rolled sanitizer can be a little over 2x faster at the cost of added

    // production complexity. The main drawback is that this code cannot be used

    // in the data plane as it throws exceptions. Should this become an issue,

    // #20428 can be revived which is faster and doesn't throw exceptions, but

    // adds complexity to the production code base.

    buffer = Nlohmann::Factory::serialize(str);

    return stripDoubleQuotes(buffer);

  } else {

    // If Nlohmann throws an error, emit a hex escape for any character

    // requiring it. This can occur for invalid utf-8 sequences, and we don't

    // want to crash the server if such a sequence makes its way into a string

    // we need to serialize. For example, if admin endpoint /stats?format=json

    // is called, and a stat name was synthesized from dynamic content such as a

    // gRPC method.

    //

    // Note that JSON string escapes are always 4 digit hex. 3 digit octal would

    // be more compact, and is legal JavaScript, but not legal JSON. See

    // https://www.json.org/json-en.html for details.

    //

    // TODO(jmarantz): It would better to use the compact JSON escapes for

    // quotes, slashes, backspace, form-feed, linefeed, CR, and tab, in which

    // case we'd also need to modify jsonEquivalentStrings in

    // test/common/json/json_sanitizer_test_util.h. We don't expect to hit this

    // often, so it isn't a priority to use these more compact encodings.

    buffer.clear();

    for (char c : str) {

      if (needs_slow_sanitizer[static_cast<uint8_t>(c)]) {

        buffer.append(absl::StrFormat("\\u%04x", c));

      } else {

        buffer.append(1, c);

      }

    }

  }

  return buffer;

}

absl::string_view stripDoubleQuotes(absl::string_view str) {

  if (str.size() >= 2 && str[0] == '"' && str[str.size() - 1] == '"') {

    str = str.substr(1, str.size() - 2);

  } else {

    ASSERT(false,

           absl::StrCat("stripDoubleQuotes called on a str that lacks double-quotes: ", str));

  }

  return str;

}

} // namespace Json

} // namespace Envoy