simple CSV r/w utility

csv_rw.php

<?php
// First pass at a small CSV r/w utility. Before hacking at this, consider https://packagist.org/search/?q=csv

/**
 *  extracts the list of fields of a given associative array,
 *  @param    array[][] $data
 *  @return   array[]
 *  @throws Exception
 *    if provided associative array is inconsistent
 */
function fields($data){
  // extract field names from first item
  if(empty($data)){
    return array();
  }
  $sample=$data[0];
  $fields=array();
  foreach($sample as $key=>$value){
    $fields[] = $key;
  }
  // check consistency
  foreach($data as $datum){
    // ensure datum does not have extra fields
    foreach($datum as $key=>$value){
      if (!in_array($key,$fields)){
        $message = "the following item has an extra field '$key':\n" . print_r($datum,1);
        throw new Exception($message);
      }
    }
    // ensure datum is not missing fields
    // array_key_exists returns TRUE if value is NULL, isset does not
    foreach($fields as $field){
      if (!array_key_exists($field, $datum)){
        $message = "the following item does not have a field '$field':\n" . print_r($datum,1);
        throw new Exception($message);
      }
    }
  }
  return $fields;
}
/**
 *  assembles CSV equivalent for given associative array
 *  @param    array[][] $data
 *  @return   string
 *  @throws Exception
 *    if provided associative array is inconsistent
 */
function write_csv($data){
  $fields = fields($data);
  // write data to string stream
  $handle = fopen('data://text/plain;base64,','w');
  fputcsv($handle,$fields,',', '"');
  foreach($data as $datum){
    fputcsv($handle, $datum, ',', '"');
  }
  // dump and close string stream
  $output = stream_get_contents($handle,-1, 0);
  fclose($handle);
  return $output;
}

/**
 *  reads multiple lines of CSV data into associative arrays
 *  does not respect header/non-header
 *
 *  @param  string $string
 *  @return array[]|array[][]
 */
function read_csv_rows($string){
  $data = array();
  $handle = fopen('data://text/plain;base64,','w');
  fwrite($handle, $string);
  fseek($handle, 0);
  while ( $item = fgetcsv($handle, 0, ',', '"', '\\') ){
    $data[] = $item;
  }
  fclose($handle);
  return $data;
}

/**
 *  reads CSV string including a header into an associative array
 *  @param  string $string
 *  @return array[][]
 *  @throws Exception
 *    if provided CSV string is inconsistent
 */
function read_csv($string){
  list($header,$data) = explode("\n", $string, 2);
  // extract field names from header
  $header_export = read_csv_rows($header);
  $fields = $header_export[0];

  // extract data from the rest
  $data_export = read_csv_rows($data);
  // assign labels to retrieved data:
  $data = array();
  foreach($data_export as $item){
    $datum = array();
    foreach($item as $key => $value){
      if (!isset($fields[$key])){
        $message = "The following item has extra fields:\n" . print_r($item,1);
        throw new Exception($message);
      }
      $datum[$fields[$key]]= $value;
    }
    $data[] = $datum;
  }
  // check whether assembled data is consitent
  fields($data);
  return $data;
}

/**
 *  dummy testing utility to be killed in favor of PHPUnit ASAP.
 */
function test_case($json_data){
  try {
    $data = json_decode($json_data,true);
    $csv  = write_csv($data);
    print $csv;
    $ext  = read_csv($csv);
    if (print_r($data,1) === print_r($ext,1)){
      print "success\n";
    } else {
      print "failure, mismatch\n";
    }
  } catch (Exception $e){
    print "failure, caught Exception:\n";
    print $e->getMessage();
  }
}

$test= 'good.json';
print "running test $test, should succeed:\n";
test_case(file_get_contents($test));
print "---------\n";

$test= 'missing_field.json';
print "running test $test, should fail; missing field comment:\n";
test_case(file_get_contents($test));
print "---------\n";

$test= 'extra_field.json';
print "running test $test, should fail; extra field age:\n";
test_case(file_get_contents($test));
print "---------\n";

extra_field.json

[
    {
        "id": 12,
        "name": "Mary-Anne",
        "comment": "Multiline\nis\nOK"
    },
    {
        "id": "13",
        "name": "John O'connor",
        "comment": "Double Quotes like '\"' OK",
        "age" : 42
    },
    {
        "id": 14,
        "name": "",
        "comment": null
    }
]

good.json

[
    {
        "id": 12,
        "name": "Mary-Anne",
        "comment": "Multiline\nis\nOK"
    },
    {
        "id": "13",
        "name": "John O'connor",
        "comment": "Double Quotes like '\"' OK"
    },
    {
        "id": 14,
        "name": "",
        "comment": null
    }
]

missing_field.json

[
    {
        "id": 12,
        "name": "Mary-Anne",
        "comment": "Multiline\nis\nOK"
    },
    {
        "id": "13",
        "name": "John O'connor",
        "comment": "Double Quotes like '\"' OK"
    },
    {
        "id": 14,
        "name": ""
    }
]