Empty PHP output from MySQL database for a longblob

问题

I have an Android application that takes a photo, converts the bitmap to Base64 and submits the Base64 string to a MySQL database (via PHP) to be stored as a longblob. This part works great! In fact, I can download the longblob from phpMyAdmin as a perfect Base64 string and easily convert to a JPEG photo.

The problem is my PHP code for getting the blob returns an empty string:

{
    "owner":"Unknown",
    "pet_name":"Unknown",
    "last_seen":"2019-04-09 11:17:19",
    "contact":"999-888-7654",
    "description":"rubber ducky, lotsa fun",
    ***"photo":""***,
    "location":"Some location"
}

The PHP getter:

function getReports() {
    $stmt = $this->con->prepare("SELECT owner, pet_name, last_seen, contact, description, photo, location FROM Pets");
    $stmt->execute();
    $stmt->bind_result($owner, $pet_name, $last_seen, $contact, $description, $photo, $location);

    $reports = array();

    while($stmt->fetch()) {
        $report  = array();
        $report['owner'] = $owner;
        $report['pet_name'] = $pet_name;
        $report['last_seen'] = $last_seen;
        $report['contact'] = $contact;
        $report['description'] = $description;
        $report['photo'] = $photo;
        $report['location'] = $location;

        array_push($reports, $report);
    }

    return $reports;
}

An interesting side note, if instead of the above code I use the below code I DO get the complete Base64 string, but with added escape () and newline (\n) characters all throughout:

//Select everything from table
$sql= "SELECT * FROM Pets";

//Confirm results
if($result = mysqli_query($con, $sql)) {
    //Results? Create array for results and array for data
    $resultArray = array();
    $tempArray = array();

    //Loop through results
    while($row=$result->fetch_object()) {
        // Add each result in results array
        $tempArray=$row;
        array_push($resultArray,$tempArray);
    }

    //Encode array to JSON and output results
    echo json_encode($resultArray);
}

I would like to find a way to fix the above PHP code. I'm thinking perhaps my string is too long for the $photo value? Any advice would be extremely appreciated.

Update: from Selecting Blob from MYSQL, getting null I did manage to the Base64 to output now instead of an empty string. however, I still have the problem of the escape and newline characters.

Any help here?

回答1:

I managed to get the original function to output the Base64 line by casting as such:

    $stmt = $this->con->prepare("SELECT owner, pet_name, last_seen, contact, description, CAST(photo as CHAR(1000000) CHARACTER SET utf8) as photo, location FROM Pets");

While this allowed for the Base64 string to be received it still included the unwanted characters. The unwanted characters were caused by JSON_ENCODE. Below is what I used to fix it.

Basically, 1. remove the added chars and 2. tell JSON_ENCODE to not print the escape chars with JSON_UNESCAPED_SLASHES.

For the function getReports()

function getReports() {
    $stmt = $this->con->prepare("SELECT owner, pet_name, last_seen, contact, description, CAST(photo as CHAR(1000000) CHARACTER SET utf8) as photo, location FROM Pets");
    $stmt->execute();
    $stmt->bind_result($owner, $pet_name, $last_seen, $contact, $description, $photo, $location);

    $reports = array();

    while($stmt->fetch()) {
        $report  = array();
        $report['owner'] = $owner;
        $report['pet_name'] = $pet_name;
        $report['last_seen'] = $last_seen;
        $report['contact'] = $contact;
        $report['description'] = $description;
        $photo = str_replace("\n","",$photo);
        $photo = str_replace("\\/","/", $photo);
        $photo = stripcslashes($photo);
        $report['photo'] = $photo;
        $report['location'] = $location;

        array_push($reports, $report);
    }

    return $reports;
}

And in the Api script, changed the return from

echo json_encode($resultArray);

to

echo json_encode($resultArray, JSON_UNESCAPED_SLASHES);

Now everything works fantastic. Is this best practice? I am not sure. I'm certain storing base64 is probably not...

来源：https://stackoverflow.com/questions/55623350/empty-php-output-from-mysql-database-for-a-longblob