If the consumer is unable to consume data as fast as the producer can produce it, then the producer will be paused until the consumer catches up. Error handling can be a little tricky with streams.
By default, errors are not forwarded upstream with pipe because it would be difficult to determine where the error occurred. Errors can be forwarded manually or the pipeline method of the stream module can be used to automate error forwarding and cleanup.
As mentioned in the post on buffering , the request object passed to the request listener is a readable stream. To validate the file size, I create a FileValidator class based on the Transform class and then pipe the request stream into a new instance of the FileValidator class. Once the controller logic has passed along the readable stream and related metadata, the database logic can begin to stream in the file contents.
To start, an empty blob is inserted into the database and a pointer to it is returned as an out bind. The pointer is an instance of the Lob class of node-oracledb.
The Lob class is implemented as a Duplex stream, so it supports both reading and writing depending on the context. The readable stream is piped into the Lob instance, and when the file finishes streaming in the transaction is committed.
When downloading a file from the database, the controller logic will be passed an instance of the Lob class from the database API. In this case, the Lob instance is a readable stream, so its output can be piped into the response object which will stream the data to the client.
The trick is to wait until the streaming is done before closing the connection to the database. Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information. Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies.
It is mandatory to procure user consent prior to running these cookies on your website. Leave a Reply Cancel reply Your email address will not be published. It also takes a callback function which is called if there is an error within the pipeline or once the pipeline is finished.
Downloading a file is just one use of Node streams, you can find streams popping up all over the place. In this post we used a readable stream to download the file and a writable stream to write it to disk. You can also create readable streams of files and, if you are making POST requests with Got, you can stream the upload of data too. Objects like process. For more on streams, check the Node. If you liked this post please share it or follow philnash on Twitter. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 10 months ago. Active 7 months ago. Removing the logic for the flag fixed it. Just wanted to point that out if someone had the issues with the approach.
Is there a memory leak in this answer: stackoverflow. You can add timeout like I did in http. The memory leak is only if the file take too long to be downloaded. Based on the other answers above and some subtle issues, here is my attempt. Check the file does not exist before hitting the network by using fs. Only create the fs. This reduces the amount of fs. Even on a OK we can still possibly reject due to an EEXIST file already exists imagine another process created the file whilst we were doing network calls.
Recursively call download if you get a Moved Permanently or Found Moved Temporarily redirect following the link location provided in the header. The issue with some of the other answers recursively calling download was that they called resolve download instead of download This way the nested chain of promises resolve in the correct order.
It might seem cool to clean up the temp file asynchronously, but I chose to reject only after that completed too so I know that everything start to finish is done when this promise resolves or rejects.
Josh Peak Josh Peak 4, 4 4 gold badges 33 33 silver badges 48 48 bronze badges. You shouldn't waste resources doing the download if the destination file already exists. Do the check first if possible. Phil Really good point. I have updated the example with an earlier guard check before falling into the recursive networking calls but left the success file handling code the same.
This short circuit guard statement should save some time in this case now. JoshPeak what if the file is updated on server. This solution is only checking the name of the resource. If the file is different on the server then comparing modifed timestamps and hashes of content would be required conditions to invalidate the local cache.
Correct cache invalidation is beyond the scope of this question and warrants it's own question and depends how servers implement HTTP ETag protocols.
Vince Yuan's code is great but it seems to be something wrong. But we don't check the result if callback callback err. Feel Physics Feel Physics 2, 4 4 gold badges 23 23 silver badges 36 36 bronze badges. I prefer request because you can use both http and https with it.
Looks like Request has been deprecated github. No new changes are expected to land. In fact, none have landed for some time. Wai Ha Lee 8, 62 62 gold badges 57 57 silver badges 86 86 bronze badges.
Idan Dagan Idan Dagan 7, 3 3 gold badges 29 29 silver badges 38 38 bronze badges. Roman Podlinov Roman Podlinov
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