如何将图像二进制文件从 API 调用转换为 Javascript 中的数据 URI？

Question

The Google API I'm using is transmitting images only as binary data.

I have absolutly no idea how to put this into a data URI to display it, thanks for any help!

The call I'm talking about is this API call .

As you can see, it says:

The server returns bytes of the photo.

For the call (it's an extension), I use the chrome_ex_oauth methods. Maybe I need to add something into the header to get real binary data, not string as it comes in right now...

What I need to do is to convert the resulting binary into data URI so I can display it.

---

Ok, I get this out of the XHR request

Now, I dont know binary stuff much. This is somehow encoded binary data i assume? I tried to put this into btoa and other base64 encoders, everything throws an error. I tried to overrideMimeType with different things and the "response" changed in some strange ways, but nothing accepts the data.

So now I have this code:

var nxhr = new XMLHttpRequest();
nxhr.onreadystatechange = function (data) {
    if (nxhr.readyState == 4) {
        console.log(nxhr);
    }
};
nxhr.open(method, url, true);
nxhr.setRequestHeader('GData-Version', '3.0');
nxhr.setRequestHeader('Authorization', oauth.getAuthorizationHeader(url, method, params));
nxhr.send('Data to send');

Anybody else has any idea how to get this for me not understandable response into a data uri???

Thanks for any help

Answer 1

After conducting some tests, here is my answer:

To simply display the image using the <img> tag, you must first encode the result binary with Base64. You can do this in two different ways:

1. Using Javascript: Use a Base64 encoder function, such as this one . After you encode the result binary data, you can display the image using the <img> tag like so: <img src="data:image/*;base64,[BASE64 ENCODED BINARY]" /> . You must replace [BASE64 ENCODED BINARY] with the actual encoded binary of the image. I'm assuming you already know how to change HTML element attributes through Javascript, it's fairly easy to put the encoded binary into the src attribute of the <img> tag.

2. Using PHP (my personal preference) : Once you submit a GET request to the API, it will return you the binary. Simply use the PHP base64_encode() function.

   <img src="data:image/*;base64,<?php echo base64_encode($result); ?>" />

Where, the $result variable is what you get from the API call. You can use the PHP cURL library.

I hope this helps.

Answer 2

Ok I found the solution...

First of all, the request must override the returend Type into x-user-defined

xhr.overrideMimeType('text\/plain; charset=x-user-defined');

After that the data is untouched by the browser.

Use the following Base64 encoder

Base64 = {

            // private property
            _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",

            encodeBinary: function (input) {
                var output = "";
                var bytebuffer;
                var encodedCharIndexes = new Array(4);
                var inx = 0;
                var paddingBytes = 0;

                while (inx < input.length) {
                    // Fill byte buffer array
                    bytebuffer = new Array(3);
                    for (jnx = 0; jnx < bytebuffer.length; jnx++)
                        if (inx < input.length)
                            bytebuffer[jnx] = input.charCodeAt(inx++) & 0xff; // throw away high-order byte, as documented at: https://developer.mozilla.org/En/Using_XMLHttpRequest#Handling_binary_data
                        else
                            bytebuffer[jnx] = 0;

                    // Get each encoded character, 6 bits at a time
                    // index 1: first 6 bits
                    encodedCharIndexes[0] = bytebuffer[0] >> 2;
                    // index 2: second 6 bits (2 least significant bits from input byte 1 + 4 most significant bits from byte 2)
                    encodedCharIndexes[1] = ((bytebuffer[0] & 0x3) << 4) | (bytebuffer[1] >> 4);
                    // index 3: third 6 bits (4 least significant bits from input byte 2 + 2 most significant bits from byte 3)
                    encodedCharIndexes[2] = ((bytebuffer[1] & 0x0f) << 2) | (bytebuffer[2] >> 6);
                    // index 3: forth 6 bits (6 least significant bits from input byte 3)
                    encodedCharIndexes[3] = bytebuffer[2] & 0x3f;

                    // Determine whether padding happened, and adjust accordingly
                    paddingBytes = inx - (input.length - 1);
                    switch (paddingBytes) {
                        case 2:
                            // Set last 2 characters to padding char
                            encodedCharIndexes[3] = 64;
                            encodedCharIndexes[2] = 64;
                            break;
                        case 1:
                            // Set last character to padding char
                            encodedCharIndexes[3] = 64;
                            break;
                        default:
                            break; // No padding - proceed
                    }
                    // Now we will grab each appropriate character out of our keystring
                    // based on our index array and append it to the output string
                    for (jnx = 0; jnx < encodedCharIndexes.length; jnx++)
                        output += this._keyStr.charAt(encodedCharIndexes[jnx]);
                }
                return output;
            }
        };

There is the magic stuff posted by mozilla which didnt let me encode the stuff correctly

bytebuffer[jnx] = input.charCodeAt(inx++) & 0xff

The final code would look then like this...

oauth.authorize(function () {
    var method = "GET", params = {}, url = photo.href;

    var nxhr = new XMLHttpRequest();
    nxhr.onreadystatechange = function (data) {
        if (nxhr.readyState == 4) {
            console.log("<img src='data:image/*;base64," + Base64.encodeBinary(nxhr.response) + "' />");
        }
    };
    nxhr.open(method, url, true);
    nxhr.setRequestHeader('GData-Version', '3.0');
    nxhr.setRequestHeader('Authorization', oauth.getAuthorizationHeader(url, method, params));
    nxhr.overrideMimeType('text\/plain; charset=x-user-defined'); 
});

PS If you put the "data:image/*" into the browser window directly, it will download the file and would not be able to open it. But if you put it directly into an img src it works fine!

Answer 3

All the other solutions are obsolete. No Base64 is needed. Check out my answer on Getting BLOB data from XHR request .

Answer 4

I know this is a very old question, but since this is in reference to images and binary data over XHR, the secret sauce for me is in two important steps:

Step 1: Ensure you use a custom user-defined character set to prevent the browser from altering the content. eg

xhr.overrideMimeType('text\/plain; charset=x-user-defined');

Step 2: Use String.fromCharCode(response.charCodeAt(...) & 0xff) to get past the issue with btoa() not being able to handle binary strings. This was inspired by the gist @ https://gist.github.com/graylikeme/867848 (and it is currently black magic to me right now).

End Eesult: Here's a simplified version of what that comes out to. Note that typically you'd also be doing this because you need to send Authorization headers or something too, but that's not included in this example.

<div id="output-el"></div>
<script>
    var xhr = new XMLHttpRequest();
    xhr.addEventListener('readystatechange', function() {
        var outputEl = document.getElementById('xhr-output');

        // Done?
        if (this.readyState === 4) {

            // Make sure this is an image.
            var contentType = this.getResponseHeader('content-type');
            if (contentType !== null && contentType.indexOf('image/') === 0) {
                // Prepare binary response so we can base64 encode it (and btoa() function doesn't freak out).
                // Thanks to: https://gist.github.com/graylikeme/867848
                var response = this.responseText;
                var binary = '';
                for(i=0; i < response.length; i++) {
                    binary += String.fromCharCode(response.charCodeAt(i) & 0xff);
                }

                // Drop into data URI.
                var encoded = btoa(binary);
                outputEl.innerHTML = `<img alt="image preview" src="data:${contentType};base64,${encoded}">`;

            } else {
                console.log('Got a non-image response:', this.responseText);
            }
        }
    });

    // Make sure browser doesn't alter the response before we handle it.
    xhr.overrideMimeType('text\/plain; charset=x-user-defined');
    xhr.open('GET', 'https://example.com/path/to/some/image.jpg');
    xhr.send();
</script>

Answer 5

If you're using a data: URI, I take it you don't care about older browsers. In that case, use btoa() as suggested in How can you encode a string to Base64 in JavaScript? , and fall back on the alternative mentioned in the second answer . Then, the data: URI is simple:

data:image/*;base64,<the btoa output>