Get a Image Blob from SQl via PHP and convert Json string

Question

I'm new to posting here so bear with me.

Question : How do I pass an image stored as a blob through php as a json string?

Situation: I have a simple charity database with fields charity_id (int), charity_name (string), picture(blob) and a couple other fields.

I wanna grab the id, charity_name, and picture with php and pass the data as a json string to my android app where it will be parsed with volley library.

I have everything working and getting passed correctly, except my picture field is passing null instead of an string.

<?php 

if($_SERVER['REQUEST_METHOD']=='GET'){

    $id  = $_GET['id'];

    require_once('dbConnect.php');

    $sql = "SELECT charity_id, charity_name,picture FROM charity_table WHERE charity_id = '".$id."'";

    $r = mysqli_query($con,$sql);

    $res = mysqli_fetch_array($r);

    $result = array();


    array_push($result,array(
        "charity_id"=>$res['charity_id'],
        "charity_name"=>$res['charity_name'],
        "picture"=>$res['picture']
        )
    );

    echo json_encode(array("result"=>$result));

    mysqli_close($con);

}

json values passed {"result":[{"charity_id":"1","charity_name":"charity1","picture":null}]}

Because my understanding of the process (and it is probably wrong) is php gets a binary string from sql, this string is then put into a json array, then android reads the array and converts the binary string into a bitmap image.

Answer 1

Rather than store the image as a blob you can store a reference path to the image in your database and then

1. Return a row(s) from your database

2. Using the image reference url, you can download the image as a binary chunk with asynchronous call depending on your requirement.

Answer 2

JSON cannot handle raw binary data, you need to encode it somehow, and the 'how' is almost canonically base64.

Use this on the server side:

array_push($result,array(
    "charity_id"=>$res['charity_id'],
    "charity_name"=>$res['charity_name'],
    "picture"=>base64_encode($res['picture'])
    )
);

and implement the relevant base64 decode on the Android side.

That said, I agree with the other comments on this question that:

1. Files should be stored in the filesystem and only a reference stored in the DB.
2. You should probably serve the images via a separate, simple HTTP request rather than piping it into the JSON.
   • It's worth noting that encoding binary data in a text-safe manner will always inflate the size, and for base64 it's roughly 30% larger.
   • Separate requests can be handled in parallel.

If you're only storing and serving small icons or thumbnails this way it's not too bad, but anything over a few kB in size is going to be a pain in the booty.