Pretty print JSON

pretty_print_json.php

<?php

// https://github.com/GerHobbelt/nicejson-php/blob/master/nicejson.php

// original code: http://www.daveperrett.com/articles/2008/03/11/format-json-with-php/
// adapted to allow native functionality in php version >= 5.4.0

/**
* Format a flat JSON string to make it more human-readable
*
* @param string $json The original JSON string to process
*        When the input is not a string it is assumed the input is RAW
*        and should be converted to JSON first of all.
* @return string Indented version of the original JSON string
*/
function json_format($json) {
  if (!is_string($json))
  {
    if (phpversion() && phpversion() >= 5.4)
    {
      return json_encode($json, JSON_PRETTY_PRINT);
    }
    $json = json_encode($json);
  }
  
  $result = '';
  $pos = 0;               // indentation level
  $strLen = strlen($json);
  $indentStr = "  ";
  $newLine = "\n";
  $prevChar = '';
  $outOfQuotes = true;

  for ($i = 0; $i < $strLen; $i++)
  {
    // Grab the next character in the string
    $char = substr($json, $i, 1);

    // Are we inside a quoted string?
    if ($char == '"' && $prevChar != '\\')
    {
      $outOfQuotes = !$outOfQuotes;
    }
    // If this character is the end of an element,
    // output a new line and indent the next line
    else if (($char == '}' || $char == ']') && $outOfQuotes)
    {
      $result .= $newLine;
      $pos--;
      for ($j = 0; $j < $pos; $j++)
      {
        $result .= $indentStr;
      }
    }
    // eat all non-essential whitespace in the input as we do our own here and it would only mess up our process
    else if ($outOfQuotes && false !== strpos(" \t\r\n", $char))
    {
      continue;
    }

    // Add the character to the result string
    $result .= $char;
    // always add a space after a field colon:
    if ($char == ':' && $outOfQuotes)
    {
      $result .= ' ';
    }

    // If the last character was the beginning of an element,
    // output a new line and indent the next line
    if (($char == ',' || $char == '{' || $char == '[') && $outOfQuotes)
    {
      $result .= $newLine;
      if ($char == '{' || $char == '[')
      {
        $pos++;
      }
      for ($j = 0; $j < $pos; $j++)
      {
        $result .= $indentStr;
      }
    }
    $prevChar = $char;
  }

  return $result;
}