Code Quality in JS

Talk with your neighbor: Try to list at least 5 Code Quality standards we expect to achieve for your JS in this course (e.g. as specific as "line lengths < 100 characters" or "good variable descriptive identifier names")

CSE 154

Lecture 19 - PHP III: Web Services with File I/O and JSON

Agenda

Important Course Details

• No exploration session this week. Next week on React
• Reminder: CP4 out.
• HW4 is out, due May 24th, 11:00pm

Web Services with JSON

PHP File I/O

Web Services with File I/O

Web Services with File I/O and JSON

Reminder: Associative Arrays

Associative arrays are arrays that have keys with assigned values (similar to Maps in Java, dictionaries in Python, or JSON objects in JS)

$tas = array("AA" => "Daniel Hsu", "AB" => "Chao Hsu Lin",
             "AC" => "Jack Venberg", "AD" => "Sandy Yang",
             "AE" => "Ann Shan", "AF" => "Manchen Jin",
             "AG" => "Hudson Gilmore", "AH" => "Manny Munoz",
             "AI" => "Will Bigelow", "AJ" => "Zach Wu");
$tas["ZZ"] = "Jeremy Zhang";

PHP

$ages = array(); # empty array (length 0)
$ages["Whitney"] = 18; # stores 17 at the location where "Whitney" is stored

PHP

foreach and associative arrays

foreach ($array_name as $key => $value)  {
  ...
}

PHP (template)

$tas = array("AA" => "Daniel Hsu", ...);
foreach ($tas as $section => $ta)  {
  echo "{$ta} leads section {$section}.\n";
}

PHP (example)

Daniel Hsu leads section AA.
Chao Hsu Lin leads section AB.
Jack Venberg leads section AC.
Sandy Yang Chen leads section AD.
...

Output

in_array vs array_key_exists

in_array tests whether a value is in an array

array_key_exists tests whether a key is in an array

$tas = array("AA" => "Daniel Hsu", ...);
in_array("AA", $tas);           # false
in_array("Jeremy Zhang", $tas); # true
array_key_exists("AA", $tas);   # true

PHP (example)

Web services with JSON

Building a simple service that returns JSON

Try using the following steps in jsontest.php

1. Create an array and assign it to a variable ($output = array() for example )
2. Gather your data in the associative array ($output) with the key/value pairs you want to return in your JSON object
3. Use json_encode($output) to "stringify" your associative array into a JSON formatted string.
4. Ensure you have set your header correctly before you print anything!
   (e.g. header("Content-Type: application/json");)
5. Print the JSON formatted string!

NOTE: we can also use json_decode to convert JSON strings into PHP arrays.

Example: JSONtest server code

<?php
  header("Content-Type: application/json");

  $output = array();
  $output["name"] = "Miranda";
  $output["hobbies"] = array("pottery", "softball",
                             "cycling", "watching youtube");

  print(json_encode($output));
?>

Produces:

{
  "name":"Miranda",
  "hobbies":["pottery","softball", "cycling", "watching youtube"]
}

PHP

Now let's build a web service

New case study: Points Of Interest

<backstory>
It's week 7 and I'm ready for a vacation, but I can't decide where to go. So I want a tool that will randomly pick from a list of "Points of Interests" (vacation spots) and give me some guidance. I know I have already built the randomizer and JSONTest - so I want something similar...
</backstory>

To start we will use a modified version of JSONtest as a prototype

Sample code

Step 1: Define the API

Let's first determine how the users will interact with the API. Questions we can ask might be:

• What data might a user need?
• What might be the easiest format for the user to use this data in?

For Points of Interest we're looking for:

• A city that one might want to travel to
• A list of Points of Interest (sites) for that city, including for each:
  • The name of the site
  • An image of the site
  • A review of the site

Example: Points of Interest sample output

{
  "cities" : [
    {
      "name": "Seattle",
      "sites": [
        {
          "name": "Space Needle",
          "image": "....",
          "review": ".... "
        }
      ]
    },
    {
      "name": "New York",
      "sites": [
        {
          "name": "Ellis Island",
          "image": "....",
          "review": ".... "
        },
        {
          "name": "Statue of Liberty",
          "image": "....",
          "review": ".... "
        }
      ]
    }
    ...
  ]
}

Step 2: Determine how to view the data

Given the information we may store in the server, how might we want to view it?

• Is the data simple enough to return as plain text (so the end user doesn't have to split to view different parts)?
• Where might I need more structured information that requires responding with JSON encoded data?
• What "filters" might I want on that data? Do I want all of it? Some of it? Just one at a time?

Example: Points of Interest requests

For our Points of Interest API we want three types of data:

• All of the cities we have with at least one point of interest each. (city=all)
• A random city with the point of interest(s) for that city (city=random)
• The Point(s) of Interest for a city that is specified by the user (city={cityname})

For each Point of Interest we want:

• The name (e.g. Space Needle)
• An image
• A review

Step 3: Write your server code to handle the requests

• Think of the conditionals you need to handle your request
• Remember to check if the $_GET and $_POST indices for those requests are set (using isset), and handle the error correctly if not.
• You can use conditional statements to figure out which query parameter to handle.
• Remember to be careful about using $_GET vs $_POST where needed (for now we're using $_GET).
• Oh and don't forget to handle other error cases as well.
• Put the correct headers in each part of the conditional... then look to see if there is any refactoring you can do!

Step 4: Write code to handle each request type

How will your data be stored on the server?

How will you convert the data into the right format for sending back to the caller?

That's all great, but I don't want to have my PHP file get bloated with the associative array. There has to be a better way to store this information.

Besides, I'm still missing the images, and multiple Points of Interest per city!

Let's explore storing the data in a different way

PHP File I/O

From Wikipedia

PHP I/O Functions

Reading Files - IMPORTANT SLIDE!

Hello
  how r u?

  I'm fine

                

array("Hello\n", #0
  "how r u?\n",    #1
  "\n",            #2
  "I'm fine\n"     #3
  )
                

"Hello\n
  how r u\n    # a single
  \n           # string
  I'm fine\n"
                

The file function returns lines of a file as an array (\n at end of each).

file_get_contents returns entire contents of a file as a single string.

file_put_contents writes a string into a file.

Sidebar: Default Parameter Values

A quick note because you will see this in some of the PHP documentation

function name(parameterName=value, ..., parameterName=value) {
  statements;
}

PHP (template)

function print_separated($str, $separator=", ") {
  if (strlen($str) < 0) {
    echo $str[0];
    for ($i = 1; $i < strlen($str); $i++) {
      echo $separator . $str[$i];
    }
  }
}
print_separated("hello");      # h, e, l, l, o
print_separated("hello", "-"); # h-e-l-l-o

PHP (example)

If no value is passed, the default will be used (defaults must come last)

The file Function

filereturns the lines of a file as an array of strings.

But each ends with \n; to strip it, use an optional second parameter:

$cities = file("cities.txt");
foreach ($cities as $city) { # for ($i = 0; $i < count($cities); $i++)
  echo $city;                # no newline needed here!
}

PHP

$lines = file("cities.txt", FILE_IGNORE_NEW_LINES);
foreach ($cities as $city) {
  echo "{$city}\n";              # a newline is now needed!
}

PHP

Common idiom: foreach or for loop over lines of file

Reading/Writing an Entire File

# reverse a file
$text = file_get_contents("poem.txt");
$text = strrev($text);
file_put_contents("poem.txt", $text);

PHP

file_get_contents returns entire contents of a file as a string

• if the file doesn't exist, you will get a warning and an empty return string

file_put_contents writes a string into a file, replacing its old contents

• if the file doesn't exist, it will be created

Appending to a File

# add a new line to a file
$new_text = "P.S. ILY, GTG TTYL!~";
file_put_contents("poem.txt", $new_text, FILE_APPEND);

PHP

file_put_contents can be called with an optional third parameter to append (add to end) rather than overwrite.

Splitting/Joining Strings

$arr = explode(delimiter, string);
$str = implode(delimiter, array);

PHP (template)

$s = "CSE 154 A";
$a = explode(" ", $s);     # ("CSE", "154", "A")
$s2 = implode("...", $a);  # "CSE...154...A"  

PHP (example)

explode and implode convert between strings and arrays.

For more complex strings, you can use regular expressions.

Example with explode

Seattle, Space Needle
New York, Ellis Island
Boston, Boston Harbor
Philadelphia, Valley Forge

contents of cities.txt

foreach (file("cities.txt", FILE_IGNORE_NEW_LINES) as $city) {
  $tokens = explode(",", $city);
  echo "The best place to visit in " . $tokens[0] .
         " is " . $tokens[1] . ".\n";
}

PHP

output

Unpacking an array: list

The list function "unpacks" an array into a set of variables.

When you now a file or line's exact length/format, use file and list to unpack it

list($var1, ..., $varN) = array;

PHP (template)

Kyle Thayer
(206) 154 2017
17-154-0123

contents of personal.txt

list($name, $phone, $ssn) = file("personal.txt");
...
list($area_code, $prefix, $suffix) = explode(" ", $phone);  

PHP

Reading Directories - IMPORTANT SLIDE!

Can accept a general path with the * wildcard (more powerful).

Example: Points of Interests in Files

Suppose we store information about each Point of Interest in a file in a city subdirectory.

The name of the file is the name of the Point of Interest

Each file contains 2 lines

• The URL of an image of the Point of Interest
• The review of the Point of Interest

glob Example

# Get all of the information from the cities
$cities = glob("cities/*/*");
foreach ($cities as $city) {
  $text = file_get_contents($city);
  echo (basename($city) . " : " . $text . "\n");
}

PHP

glob can match a wildcard path with the * character

• glob("foo/bar/*.doc") returns all .doc files in the foo/bar subdirectory
• glob("food*") returns all files whose names begin with "food"

The basename function strips any leading directory from a file path

• basename("foo/bar/baz.txt") returns "baz.txt"

scandir Example

foreach (scandir("cities/") as $city) {
  echo "I found a city: {$city}\n";
}

PHP

scandir includes current directory (".") and parent ("..") in the array.

Don't need basename with scandir; returns file names only without directory

Putting it all together: File Based Points of Interest

The pointsofinterest.zip example has been put together for you to look explore (note that it is not yet finished, and also could use some refactoring to meet the Code Quality Guide!)

Code Quality in a Web Service

Where did you see adherence to the similar code quality guidlines as for JS?

What was similar?

What was different?