How does S3 generate the URL with putObject method?

Recently, I noticed a question on a forum about the AWS SDK S3Client class.

The person was using the putObject method of S3Client to upload a file to an Amazon S3 bucket.

After that, he needed to figure out the URL which could be used to access that file. He had figured out that uploading a file called cat.gif could be accessed with the URL “https://s3.eu-west-3.amazonaws.com/aws.mybucket.es/mysite/httpdocs/cat.gif”.

The problem was that when he uploaded a file whose name included special characters, such as an accented o – “รณ” – he couldn’t figure out a consistent way to construct the URL. A character with an accent got URL encoded, but the parenthesis character in a file name did not!

He was trying to figure out the implementation details for the putObject method, and couldn’t find any documentation about it.

The answer to his question was that he was asking the wrong question! There’s a software principle that you should “write code to the interface, not to the implementation“.

As consumers of the S3Client API, we should not be trying to figure out the URL to an uploaded file. Rather, we should be asking the interface for the URL. If AWS revealed the details of their URL construction scheme, it would be very painful if they ever decided to change it, both for them and for users of S3. Further, programmers everywhere would be forced to implement the algorithm that AWS declared for URL construction in all the different languages that are supported by the AWS SDK. That’s a lot of duplicated effort.

Fortunately, AWS gives us an interface that can be used to obtain the URL after a file is uploaded. The result of S3Client->putObject contains an ObjectURL property. We can use that to get the URL, which we can record however we want for later use. Here’s an example:

...
$result = $s3->putObject(...);
$url = $result['ObjectURL'];
...

The full source code for this example of using the S3Client putObject method is at github.

So you see that there’s no need to figure out how AWS implements the URL for our file. AWS gives us the URL immediately when our file is uploaded.

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