Develop Reference

JavaScript Blob to FormData with SAPUI5 mobile app

I know there are several threads about this topic, but I was not able to identify the problem in my case.
I have an application, where I upload an image to an endpoint-URL and after processing I'll receive a response. Works fine so far. The file is contained within a formdata object when using FileUploader-Control from SAPUI5.
When switching from file upload to "taking a picture with smartphone-camera", I dont have a file, I have an base64 dataurl (XString) image object.
var oImage = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAABQAA…8ryQAbwUjsV5VUaAX/y+YSPJii2Z9GAAAAABJRU5ErkJggg=="} // some lines are missing > 1 million lines
I thought converting it to blob and appending it to FormData might be the solution, but it does not work at all.
var blob = this.toBlob(oImage)
console.log("Blob", blob); // --> Blob(857809) {size: 857809, type: "image/png"} size: 857809 type: "image/png" __proto__: Blob
var formData = new window.FormData();
formData.append("files", blob, "test.png");
console.log("FormData", formData); // seems empty --> FormData {}__proto__: FormData
Functions (works fine from my perspective)
toBlob: function dataURItoBlob(dataURI) {
var byteString = atob(dataURI.split(',')[1]);
var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0]
var ab = new ArrayBuffer(byteString.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < byteString.length; i++) {
ia[i] = byteString.charCodeAt(i);
}
var bb = new Blob([ab], {
"type": mimeString
});
return bb;
},
This is my problem, FormData is empty and my POST-request throws an undefined error (Loading of data failed: TypeError: Cannot read property 'status' of undefined at constructor.eval (...m/resources/sap/ui/core/library-preload.js?eval:2183:566))
//Create JSON Model with URL
var oModel = new sap.ui.model.json.JSONModel();
var sHeaders = {
"content-type": "multipart/form-data; boundary=---011000010111000001101001",
"APIKey": "<<myKey>>"
};
var oData = {
formData
};
oModel.loadData("/my-destination/service", oData, true, "POST", null, false, sHeaders);
oModel.attachRequestCompleted(function (oEvent) {
var oData = oEvent.getSource().oData;
console.log("Final Response XHR: ", oData);
});
Thanks for any hint

The upload collection is a complex standard control that can be used for attachment management. On desktop it opens a file dialog, on mobile it opens the ios or android photo options, which means picking a photo from the camera roll, or taking a new photo.
Fairly basic example, including the upload URL's and other handlers you'll need. More options are available, adjust to suit your needs. In your XML:
<UploadCollection
uploadUrl="{path:'Key',formatter:'.headerUrl'}/Attachments"
items="{Attachments}"
change="onAttachUploadChange"
fileDeleted="onAttachDelete"
uploadEnabled="true"
uploadComplete="onAttachUploadComplete">
<UploadCollectionItem
documentId="{DocID}"
contributor="{CreatedBy}"
fileName="{ComponentName}"
fileSize="{path:'ComponentSize',formatter:'.formatter.parseFloat'}"
mimeType="{MIMEType}"
thumbnailUrl="{parts:[{path:'MIMEType'},{path:'DocID'}],formatter:'.thumbnailURL'}"
uploadedDate="{path:'CreatedAt', formatter:'.formatter.Date'}" url="{path:'DocID',formatter:'.attachmentURL'}" visibleEdit="false"
visibleDelete="true" />
</UploadCollection>
Here's the handlers. Especially the onAttachUploadChange is important. I should mention there's no explicit post. If the uploadUrl is set correctly a post is triggered anyway.
onAttachUploadChange: function(oEvent) {
var csrf = this.getModel().getSecurityToken();
var oUploader = oEvent.getSource();
var fileName = oEvent.getParameter('files')[0].name;
oUploader.removeAllHeaderParameters();
oUploader.insertHeaderParameter(new UploadCollectionParameter({
name: 'x-csrf-token',
value: csrf
}));
oUploader.insertHeaderParameter(new UploadCollectionParameter({
name: 'Slug',
value: fileName
}));
},
onAttachDelete: function(oEvent) {
var id = oEvent.getParameter('documentId');
var oModel = this.getModel();
//set busy indicator maybe?
oModel.remove(`/Attachments('${encodeURIComponent(id)}')`, {
success: (odata, response) => {
//successful removal
//oModel.refresh();
},
error: err => console.log(err)
});
},
onAttachUploadComplete: function(oEvent) {
var mParams = oEvent.getParameter('mParameters');
//handle errors an success in here. Check `mParams`.
}
as for the formatters to determine URLs, that depends on your setup. In the case below, the stream is set up on the current binding contect, in which case this is one way to do it. You'll need the whole uri so including the /sap/opu/... etc bits.
headerUrl: function() {
return this.getModel().sServiceUrl + this.getView().getBindingContext().getPath()
},
URL for attachments is similar, but generally points to an entity of the attachment service itself.
attachmentURL: function(docid) {
return this.getModel().sServiceUrl + "/Attachments('" + docid + "')/$value";
},
You could fancy it up to check if it's an image, in which case you could include the mime type to show a thumbnail.
There might be better ways of doing this, but I've found this fairly flexible...

Use the base64 preview of the binary data response (zip file) in angularjs

I always get this error in the downloaded zip file C:\Users\me\Downloads\test.zip: Unexpected end of archive
My current code is:
var blob = new Blob([data], { // data here is the binary content
type: 'octet/stream',
});
var zipUrl = window.URL.createObjectURL(blob);
var fileName = orderNo;
fileName += '.zip';
downloadFile(null, fileName, null, zipUrl, null); // just creates a hidden anchor tag and triggers the download
The response of the call is a binary (I think). Binary Content Here
But the preview is a base64. Base64 Content. And it is the correct one. The way I verify it is by using this fiddle.
You can refer to the screenshot of the network here
I put the base64 content in this line var sampleBytes = base64ToArrayBuffer(''); And the zip downloaded just opens fine.
Things I have tried so far.
Adding this headers to the GET call
var headers = {
Accept: 'application/octet-stream',
responseType: 'blob',
};
But I get Request header field responseType is not allowed by Access-Control-Allow-Headers in preflight response.
We're using an already ajax.service.js in our AngularJS project.
From this answer
var blob = new Blob([yourBinaryDataAsAnArrayOrAsAString], {type: "application/octet-stream"});
var fileName = "myFileName.myExtension";
saveAs(blob, fileName);
There are other things that I have tried that I have not listed. I will edit the questions once I find them again
But where I'm current at right now. The preview is correct base64 of the binary file. Is it possible to use that instead of the binary? (If it is I will not find the other methods that I've tested) I tried some binary to base64 converters but they don't work.

So I just went and ditched using the ajax.service.js, that we have, for this specific call.
I used the xhr snippet from this answer. I just added the headers necessary for our call: tokens and auth stuff.
And I used this code snippet for the conversion thing.
And the code looks like this:
fetchBlob(url, function (blob) {
// Array buffer to Base64:
var base64 = btoa(String.fromCharCode.apply(null, new Uint8Array(blob)));
var blob = new Blob([base64ToArrayBuffer(base64)], {
type: 'octet/stream',
});
var zipUrl = window.URL.createObjectURL(blob);
var fileName = orderNo;
fileName += ' Attachments ';
fileName += moment().format('DD-MMM-YYYY');
fileName += '.zip';
downloadFile(null, fileName, null, zipUrl, null); // create a hidden anchor tag and trigger download
});
function fetchBlob(uri, callback) {
var xhr = new XMLHttpRequest();
xhr.open('GET', uri, true);
xhr.responseType = 'arraybuffer';
var x = AjaxService.getAuthHeaders();
xhr.setRequestHeader('auth_stuff', x['auth_stuff']);
xhr.setRequestHeader('token_stuff', x['token_stuff']);
xhr.setRequestHeader('Accept', 'application/octet-stream');
xhr.onload = function (e) {
if (this.status == 200) {
var blob = this.response;
if (callback) {
callback(blob);
}
}
};
return xhr.send();
};
function base64ToArrayBuffer(base64) {
var binaryString = window.atob(base64);
var binaryLen = binaryString.length;
var bytes = new Uint8Array(binaryLen);
for (var i = 0; i < binaryLen; i++) {
var ascii = binaryString.charCodeAt(i);
bytes[i] = ascii;
};
return bytes;
}

create and automatically force download file using js

I have used HTML file reader API to read the file,
and i got the below result
data:application/pdf;base64,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...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
How to write a file and force download the same file using the above string?

Warning: I don't have IE available to test with, but this was based off code that DOES work under IE.
My DataURL is an image so I had to change out the header. You might not have to with your header -- but I left the code in place so you could see how it was done.
Thanks to IE, you need two different processes.
On IE, you convert your DataURI to a blob then download the blob.
On everything else, you would just download the URI itself.
document.getElementById("d_button").addEventListener("click", download);
var filename="testfile";
// FROM http://stackoverflow.com/questions/12168909/blob-from-dataurl
function dataURItoBlob(dataURI) {
// convert base64 to raw binary data held in a string
// doesn't handle URLEncoded DataURIs - see SO answer #6850276 for code that does this
var byteString = atob(dataURI.split(',')[1]);
// separate out the mime component
var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0]
// write the bytes of the string to an ArrayBuffer
var ab = new ArrayBuffer(byteString.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < byteString.length; i++) {
ia[i] = byteString.charCodeAt(i);
}
// write the ArrayBuffer to a blob, and you're done
var blob = new Blob([ab], {
type: mimeString
});
return blob;
// Old code
// var bb = new BlobBuilder();
// bb.append(ab);
// return bb.getBlob(mimeString);
}
const dataURI = "data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==";
function download() {
if (window.navigator.msSaveBlob) { // for IE
const blob = dataURItoBlob(dataURI);
window.navigator.msSaveBlob(blob, `${filename}.png`);
return;
}
let dt = dataURI;
/* Change MIME type to trick the browser to downlaod the file instead of displaying it */
dt = dt.replace(/^data:image\/[^;]*/, "data:application/octet-stream");
/* In addition to <a>'s "download" attribute, you can define HTTP-style headers */
dt = dt.replace(/^data:application\/octet-stream/, `data:application/octet-stream;headers=Content-Disposition%3A%20attachment%3B%20filename=${filename}.png`);
this.href = dt;
}
Download this

I got answer using <a> tag force the download the file.
var element = document.createElement('a');
element.setAttribute('href',text );
element.setAttribute('download', filename);
element.setAttribute('target', '_blank');
element.style.display = 'none';
document.body.appendChild(element);
$("#page_header").removeClass('loader');
element.click();

I got another answer using force the download the file.
using this link install file saver (https://www.npmjs.com/package/file-saver)
result : 'data:application/pdf;base64,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...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'
file_name : 'sample.jpg'
fileType : 'image/jpeg'
**Function Call**
this.urltoFile(result, file_name, fileType)
.then(function(file){
var blob = new Blob ([file], {type: fileType});
FileSaver.saveAs(blob, file_name);
this.loading = false;
});
**function definition**
urltoFile(url, filename, mimeType){
return (fetch(url)
.then(function(res){return res.arrayBuffer();})
.then(function(buf){return new File([buf], filename, {type:mimeType});})
)},

JS - How to compute MD5 on binary data

EDIT: changed title from "JS File API - write and read UTF-8 data is inconsistent" to reflect the actual question.
I have some binary content i need to calculate the MD5 of. The content is a WARC file, that means that it holds text as well as encoded images. To avoid errors in the file saving, I convert and store all the data in arrayBuffers. All the data is put in UInt8Arrays to convert it to UTF-8.
My first attempt, for testing, is to use the saveAs library to save files from Chrome extensions. This means I was using a blob object to be passed on to the method and create the file.
var b = new Blob(arrayBuffers, {type: "text/plain;charset=utf-8"});
saveAs(b,'name.warc');
I haven't found a tool to compute the MD5 from a Blob object so what I was doing was using a FileReader to read the blob file as binary data and then use an MD5 tool (I used cryptoJS as well as a tool from faultylabs) to compute the result.
f = new FileReader();
f.readAsBinaryString(b);
f.onloadend = function(a){
console.log( 'Original file checksum: ', faultylabs.MD5(this.result) );
}
The resources (images) are downloaded directly in arraybuffer format so I have no need to convert them.
The result was wrong, meaning that checking the MD5 from the code and checking it from the file I saved on my local machine gave 2 different results. Reading as text, obviously shoots out an error.
The workaround I found, consists in writing the blob object on the disk using the filesystem API and then read it back as binary data, compute the MD5 and then save that retrieved file as WARC file (not directly the blob object but this "refreshed" version of the file).
In this case the computed MD5 is fine ( I calculate it on the "refreshed" version of the warc file) but when I launch the WARC replay instance with the "refreshed" warc archive, it throws me errors - while with the original file I don't have any problem (but the MD5 is not correct).
var fd = new FormData();
// To compute the md5 hash and to have it correct on the server side, we need to write the file to the system, read it back and then calculate the md5 value.
// We need to send this version of the warc file to the server as well.
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
function computeWARC_MD5(callback,formData) {
window.requestFileSystem(window.TEMPORARY, b.size, onInitFs);
function onInitFs(fs) {
fs.root.getFile('warc.warc', {create: true}, function(fileEntry) {
fileEntry.createWriter(function(fileWriter) {
fileWriter.onwriteend = function(e) {
readAndMD5();
};
fileWriter.onerror = function(e) {
console.error('Write failed: ' + e.toString());
};
fileWriter.write(b);
});
});
function readAndMD5() {
fs.root.getFile('warc.warc', {}, function(fileEntry) {
fileEntry.file( function(file) {
var reader = new FileReader();
reader.onloadend = function(e) {
var warcMD5 = faultylabs.MD5( this.result );
console.log(warcMD5);
var g = new Blob([this.result],{type: "text/plain;charset=utf-8"});
saveAs(g, o_request.file);
formData.append('warc_file', g)
formData.append('warc_checksum_md5', warcMD5.toLowerCase());
callback(formData);
};
reader.readAsBinaryString(file);
});
});
}
}
}
function uploadData(formData) {
// upload
$.ajax({
type: 'POST',
url: server_URL_upload,
data: fd,
processData: false,
contentType: false,
// [SPECS] fire a progress event named progress at the XMLHttpRequestUpload object about every 50ms or for every byte transmitted, whichever is least frequent
xhrFields: {
onprogress: function (e) {
if (e.lengthComputable) {
console.log(e.loaded / e.total * 100 + '%');
}
}
}
}).done(function(data) {
console.log('done uploading!');
//displayMessage(port_to_page, 'Upload finished!', 'normal')
//port_to_page.postMessage( { method:"doneUpload" } );
});
}
computeWARC_MD5(uploadData, fd);
saveAs(b, 'warc.warc');
Could anybody explain me why there is this discrepancy? What am I missing in treating all the objects I am dealing with as binary data (store, read)?

Basically I tried another route and converted the blob file back to arraybuffer and computed the MD5 on that. At that point, the file's MD5 and the arraybuffer's are the same.
var b = new Blob(arrayBuffers, {type: "text/plain;charset=utf-8"});
var blobHtml = new Blob( [str2ab(o_request.main_page_html)], {type: "text/plain;charset=utf-8"} );
f = new FileReader();
f.readAsArrayBuffer(b);
f.onloadend = function(a){
var warcMD5 = faultylabs.MD5(this.result);
var fd = new FormData();
fd.append('warc_file', b)
fd.append('warc_checksum_md5', warcMD5.toLowerCase());
uploadData(fd);
}
I guess the result from a binary string and from a buffer array is different, that's why also the MD5 is inconsistent.

Create a download link from a Blob URL

In a Google chrome extension I am working on, a file is downloaded from a server with an XMLHttpRequest. This file contains some binary data which are stored in an ArrayBuffer object. In order to provide the possibility to download this file I am using the createObjectURL API.
function publish(data) {
if (!window.BlobBuilder && window.WebKitBlobBuilder) {
window.BlobBuilder = window.WebKitBlobBuilder;
}
var builder = new BlobBuilder();
builder.append(data);
var blob = builder.getBlob();
var url = window.webkitURL.createObjectURL(blob);
$("#output").append($("<a/>").attr({href: url}).append("Download"));
}
It is working fine; except that the filename is an opaque UUID like 9a8f6a0f-dd0c-4715-85dc-7379db9ce142. Is there any way to force this filename to something more user-friendly?

you can force an arbitrary filename by setting the "download" attribute of your anchor
see: http://updates.html5rocks.com/2011/08/Downloading-resources-in-HTML5-a-download

I have never tried it before, but it should be possible to create a new File object (which allows you to specify a file name) and write your blob to it. Something along the lines of:
function publish(data, filename) {
if (!window.BlobBuilder && window.WebKitBlobBuilder) {
window.BlobBuilder = window.WebKitBlobBuilder;
}
fs.root.getFile(filename, {
create: true
}, function (fileEntry) {
// Create a FileWriter object for our FileEntry (log.txt).
fileEntry.createWriter(function (fileWriter) {
fileWriter.onwriteend = function (e) {
console.log('Write completed.');
};
fileWriter.onerror = function (e) {
console.log('Write failed: ' + e.toString());
};
var builder = new BlobBuilder();
builder.append(data);
var blob = builder.getBlob();
fileWriter.write(blob);
}, errorHandler);
}, errorHandler);
}
I think this could work for you.