Note: If the Response has a Response.type of "opaque", the resulting Blob will have a Blob.size of 0 and a Blob.type of empty string "", which renders it useless for methods like URL.createObjectURL().
In our fetch request example (run fetch request live), we create a new request using the Request() constructor, then use it to fetch a JPG. When the fetch is successful, we read a Blob out of the response using blob(), put it into an object URL using URL.createObjectURL(), and then set that URL as the source of an element to display the image.
Fetch Download Blob
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\n Note: If the Response has a\n Response.type of \"opaque\", the resulting Blob\n will have a Blob.size of 0 and a Blob.type of\n empty string \"\", which renders it useless for methods like\n URL.createObjectURL().\n
\n In our fetch request example (run fetch request live), we\n create a new request using the Request() constructor,\n then use it to fetch a JPG. When the fetch is successful, we read a Blob\n out of the response using blob(), put it into an object URL using\n URL.createObjectURL(), and then set that URL as the source of an\n element to display the image.\n
Using javascript fetch and invoking a rest service that returns a blob if successful, otherwise returns an error message as json. How would this be handled in the fetch? The actual service is a asp.net web api implementation that returns a FileStreamResult (or FileContentResult) when successful, otherwise returns an error code with json containing the error message. Below is an example of what I'm trying to do:
Updating from 2 to 3 should be a breeze since there is not many changes to the blob specification.The major cause of a major release is coding standards.- internal WeakMaps was replaced with private fields- internal Buffer.from was replaced with TextEncoder/Decoder- internal buffers was replaced with Uint8Arrays- CommonJS was replaced with ESM- The node stream returned by calling blob.stream() was replaced with whatwg streams- (Read "Differences from other blobs" for more info.)
fetch-blob/from.js comes packed with tools to convert any filepath into either a Blob or a FileIt will not read the content into memory. It will only stat the file for last modified date and file size.
When using both createTemporaryBlob and createTemporaryFilethen you will write data to the temporary folder in their respective OS.The arguments can be anything that fsPromises.writeFile supports. NodeJSv14.17.0+ also supports writing (async)Iterable streams and passing in aAbortSignal, so both NodeJS stream and whatwg streams are supported. When thefile have been written it will return a Blob/File handle with a references tothis temporary location on the disk. When you no longer have a references tothis Blob/File anymore and it have been GC then it will automatically be deleted.
Our Blob & File class are more generic then any other polyfills in the way that it can accept any blob look-a-like itemAn example of this is that our blob implementation can be constructed with parts coming from BlobDataItem (aka a filepath) or from buffer.Blob, It dose not have to implement all the methods - just enough that it can be read/understood by our Blob implementation. The minium requirements is that it has Symbol.toStringTag, size, slice(), stream() methods (the stream methodcan be as simple as being a sync or async iterator that yields Uint8Arrays. If you then wrap it in our Blob or File new Blob([blobDataItem]) then you get all of the other methods that should be implemented in a blob or file (aka: text(), arrayBuffer() and type and a ReadableStream)
IMO rn-fetch-blob would be very valuable library for Expo. Hopefully there will be an easier way to add libraries with native code in the future. I think my best option is to eject at this time in order to unblock the development of my app, and hopefully un-eject in the near future.
As we work our way into the different aspects of development in our journey to become proficient, we'll find that one of the most critical factors in building services is the layer between application and API.
For most developers working on mobile and web, this is a crucial aspect of their work that demands having an intimate understanding of the intricacies of fetching and handling data from APIs and the cloud.
One of the most popular methods for handling files and data fetched from the cloud is the blob, or binar large object. In this post, we'll explore how to fetch and handle blob data in React Native applications properly.
This package library covers all aspects of blob data management and the fetch API necessary for any project. Nevertheless, we'll provide you with a basic fetch alternative implemented in Expo in case your requirements are more basic.
According to Wikipedia: "A binary large object (BLOB or blob) is a collection of binary data stored as a single entity. Blobs are typically images, audio, or other multimedia objects, though sometimes binary executable code is stored as a blob."
What this means is that a blob is essentially a container for data, so it's more easily handled by protocols that fetch and manipulate large media files. So, if you're planning on working in an application with limited resources handling media files like photos or music, you'll be handling blobs.
For this purpose, the fetch API provides a generic definition for the Request and Response objects as well as other aspects of network requests, serving as a mechanism to retrieve resources and interact with a REST API or the cloud.
Using the fetch API to retrieve data in a React Native application is very simple. All you have to do is create an async process that uses the fetch method already available in React Native and follow the asynchronous structure for handling network processes to avoid errors.
Notice that the code is transforming the data into Base64. This is recommended for small resources, like data or small images, because it runs on native code. However, it's not recommended for large files.
If the response is significant, then it's recommended that you stream the file directly into the disk and cache it for processing. Then, you can manipulate it on memory. One example of doing this is with the following code.
There are several ways to provide authentication credentials to our fetch request. In this case, you'll be providing an authentication token that has been previously provided with a separate authentication pipeline.
Finally, if you want to provide feedback to the user so they know how much of the upload or download is completed, you can do so with the uploadProgress and progress methods.
The options are plentiful in terms of features and mechanisms to handle network transactions. Given that much of React Native is built on the rich and robust library of code and packages available in JavaScript, iOS, and Android, the ecosystem of features and alternatives is vast and strong.
This is where the react-native-fs and react-native-blob-util packages come into play. These packages provide native file system access for React Native. In other words, they make file access and data transfer more accessible and efficient for React Native developers, especially for large files like blobs.
In the above code, the array is the blob string value, object values, or a mix of the values we want to convert to a blob. The options include the blob types (mime-type) which can be application/json, text/plain, image/png, and so on.
This will automatically add the react-native-fs package to our project. In a scenario where the automatic linking does not work for some reason, check the official docs to see how to manually link the package to your project.
In the code above, we import DocumentDirectoryPath and writeFile from our react-native-fs package. We use the DocumentDirectoryPath constant to get the directory file path of the location where we want to save our file. Then, we use the writeFile method to save our file with the content of our input.
This method returns a promise that contains an array of objects with properties. These properties include:
ctime: the date that the file was created; this property is only available for iOS
mtime: the date that the file was last modified or changed
name: the name of the file or item
path: contains the absolute path of the file or item
size: shows the size of the file
isFile: a function that returns a boolean that shows if the item is a file or not
isDirectory: a function that returns a boolean that shows if a file is a directory or not
In the code above, we use the try...catch method to read our directory path using the readDir method. Then, we set the response to the directory array in our state. Next, we map through the array using FlatList and render the list of files as shown in the image above.
The readFile method lets us read the contents of a file that we have saved. It also returns a promise containing an array of objects with properties, just like the readDir method. The syntax is as follows:
Next, we click on the file or item that we want to read and set our checkContent state to true. Then, using conditional rendering, we return the ViewFile component only if the checkContent state returns true.
Moving forward, we make use of our readFilemethod to read the contents of our file. First, we check if our item is a file or not using the isFile() function property that we looked at earlier. If it is a file, then we can use readFile to read and display its contents.
Using this information about available or unused storage, we can check if the available storage is smaller or bigger than what we want to download. If it is smaller, the download will be allowed. Otherwise, it will be canceled and an error message will be shown to the user.
This package is a fork of the now-deprecated react-native-fetch-blob package and its first fork, rn-fetch-blob. Since those packages are no longer maintained, the creator continued the project in this fork to go on supporting React Native developers in accessing and transferring data and files easily and efficiently. 152ee80cbc