text: /*
   *
   * Copyright 2015, Google Inc.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   *     * Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *     * Redistributions in binary form must reproduce the above
   * copyright notice, this list of conditions and the following disclaimer
   * in the documentation and/or other materials provided with the
   * distribution.
   *     * Neither the name of Google Inc. nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   */
  
  #include "src/core/ext/transport/chttp2/transport/timeout_encoding.h"
  
  #include <stdio.h>
  #include <string.h>
  
  #include <grpc/support/port_platform.h>
  #include "src/core/lib/support/string.h"
  
  static int64_t round_up(int64_t x, int64_t divisor) {
    return (x / divisor + (x % divisor != 0)) * divisor;
  }
  
  /* round an integer up to the next value with three significant figures */
  static int64_t round_up_to_three_sig_figs(int64_t x) {
    if (x < 1000) return x;
    if (x < 10000) return round_up(x, 10);
    if (x < 100000) return round_up(x, 100);
    if (x < 1000000) return round_up(x, 1000);
    if (x < 10000000) return round_up(x, 10000);
    if (x < 100000000) return round_up(x, 100000);
    if (x < 1000000000) return round_up(x, 1000000);
    return round_up(x, 10000000);
  }
  
  /* encode our minimum viable timeout value */
  static void enc_tiny(char *buffer) { memcpy(buffer, "1n", 3); }
  
  static void enc_ext(char *buffer, int64_t value, char ext) {
    int n = int64_ttoa(value, buffer);
    buffer[n] = ext;
    buffer[n + 1] = 0;
  }
  
  static void enc_seconds(char *buffer, int64_t sec) {
    if (sec % 3600 == 0) {
      enc_ext(buffer, sec / 3600, 'H');
    } else if (sec % 60 == 0) {
      enc_ext(buffer, sec / 60, 'M');
    } else {
      enc_ext(buffer, sec, 'S');
    }
  }
  
  static void enc_nanos(char *buffer, int64_t x) {
    x = round_up_to_three_sig_figs(x);
    if (x < 100000) {
      if (x % 1000 == 0) {
        enc_ext(buffer, x / 1000, 'u');
      } else {
        enc_ext(buffer, x, 'n');
      }
    } else if (x < 100000000) {
      if (x % 1000000 == 0) {
        enc_ext(buffer, x / 1000000, 'm');
      } else {
        enc_ext(buffer, x / 1000, 'u');
      }
    } else if (x < 1000000000) {
      enc_ext(buffer, x / 1000000, 'm');
    } else {
      /* note that this is only ever called with times of less than one second,
         so if we reach here the time must have been rounded up to a whole second
         (and no more) */
      memcpy(buffer, "1S", 3);
    }
  }
  
  static void enc_micros(char *buffer, int64_t x) {
    x = round_up_to_three_sig_figs(x);
    if (x < 100000) {
      if (x % 1000 == 0) {
        enc_ext(buffer, x / 1000, 'm');
      } else {
        enc_ext(buffer, x, 'u');
      }
    } else if (x < 100000000) {
      if (x % 1000000 == 0) {
        enc_ext(buffer, x / 1000000, 'S');
      } else {
        enc_ext(buffer, x / 1000, 'm');
      }
    } else {
      enc_ext(buffer, x / 1000000, 'S');
    }
  }
  
  void grpc_chttp2_encode_timeout(gpr_timespec timeout, char *buffer) {
    if (timeout.tv_sec < 0) {
      enc_tiny(buffer);
    } else if (timeout.tv_sec == 0) {
      enc_nanos(buffer, timeout.tv_nsec);
    } else if (timeout.tv_sec < 1000 && timeout.tv_nsec != 0) {
      enc_micros(buffer,
                 (int64_t)(timeout.tv_sec * 1000000) +
                     (timeout.tv_nsec / 1000 + (timeout.tv_nsec % 1000 != 0)));
    } else {
      enc_seconds(buffer, timeout.tv_sec + (timeout.tv_nsec != 0));
    }
  }
  
  static int is_all_whitespace(const char *p) {
    while (*p == ' ') p++;
    return *p == 0;
  }
  
  int grpc_chttp2_decode_timeout(const char *buffer, gpr_timespec *timeout) {
    int32_t x = 0;
    const uint8_t *p = (const uint8_t *)buffer;
    int have_digit = 0;
    /* skip whitespace */
    for (; *p == ' '; p++)
      ;
    /* decode numeric part */
    for (; *p >= '0' && *p <= '9'; p++) {
      int32_t digit = (int32_t)(*p - (uint8_t)'0');
      have_digit = 1;
      /* spec allows max. 8 digits, but we allow values up to 1,000,000,000 */
      if (x >= (100 * 1000 * 1000)) {
        if (x != (100 * 1000 * 1000) || digit != 0) {
          *timeout = gpr_inf_future(GPR_TIMESPAN);
          return 1;
        }
      }
      x = x * 10 + digit;
    }
    if (!have_digit) return 0;
    /* skip whitespace */
    for (; *p == ' '; p++)
      ;
    /* decode unit specifier */
    switch (*p) {
      case 'n':
        *timeout = gpr_time_from_nanos(x, GPR_TIMESPAN);
        break;
      case 'u':
        *timeout = gpr_time_from_micros(x, GPR_TIMESPAN);
        break;
      case 'm':
        *timeout = gpr_time_from_millis(x, GPR_TIMESPAN);
        break;
      case 'S':
        *timeout = gpr_time_from_seconds(x, GPR_TIMESPAN);
        break;
      case 'M':
        *timeout = gpr_time_from_minutes(x, GPR_TIMESPAN);
        break;
      case 'H':
        *timeout = gpr_time_from_hours(x, GPR_TIMESPAN);
        break;
      default:
        return 0;
    }
    p++;
    return is_all_whitespace((const char *)p);
  }
  