# Creating a special S3 remote to hold files shareable by URL

(In this example, I'll assume you'll be creating a bucket in S3 named **public-annex** and a special remote in git-annex, which will store its files in the previous bucket, named **public-s3**, but change these names if you are going to do the thing for real)

Set up your special [S3](http://git-annex.branchable.com/special_remotes/S3/) remote with (at least) these options:

    git annex initremote public-s3 type=s3 encryption=none bucket=public-annex chunk=0 public=yes

This way git-annex will upload the files to this repo, (when you call `git
annex copy [FILES...] --to public-s3`) without encrypting them and without
chunking them. And, thanks to the public=yes, they will be
accessible by anyone with the link.

(Note that public=yes was added in git-annex version 5.20150605.
If you have an older version, it will be silently ignored, and you
will instead need to use the AWS dashboard to configure a public get policy
for the bucket.)

Following the example, the files will be accessible at `http://public-annex.s3.amazonaws.com/KEY` where `KEY` is the file key created by git-annex and which you can discover running

    git annex lookupkey FILEPATH

This way you can share a link to each file you have at your S3 remote.

## Sharing all links in a folder

To share all the links in a given folder, for example, you can go to that folder and run (this is an example with the _fish_ shell, but I'm sure you can do the same in _bash_, I just don't know exactly):

    for filename in (ls)
        echo $filename": https://public-annex.s3.amazonaws.com/"(git annex lookupkey $filename)
    end

## Sharing all links matching certain metadata

The same applies to all the filters you can do with git-annex.

For example, let's share links to all the files whose _author_'s name starts with "Mario" and are, in fact, stored at your public-s3 remote.
However, instead of just a list of links we will output a markdown-formatted list of the filenames linked to their S3 urls:

    for filename in (git annex find --metadata "author=Mario*" --and --in public-s3)
       echo "* ["$filename"](https://public-annex.s3.amazonaws.com/"(git annex lookupkey $filename)")"
    end

Very useful.

## Sharing links with time-limited URLs

By using pre-signed URLs it is possible to create limits on how long a URL is valid for retrieving an object. 
To enable use a private S3 bucket for the remotes and then pre-sign actual URL with the script in [AWS-Tools](https://github.com/gdbtek/aws-tools).
Example:

    key=`git annex lookupkey "$fname"`;  sign_s3_url.bash --region 'eu-west-1' --bucket 'mybuck' --file-path $key --aws-access-key-id XX --aws-secret-access-key XX --method 'GET' --minute-expire 10

## Adding the S3 URL as a source

Assuming all files in the current directory are available on S3, this will register the public S3 url for the file in git-annex, making it available for everyone *through git-annex*:

<pre>
git annex find --in public-s3 | while read file ; do
  key=$(git annex lookupkey $file)
  echo $key https://public-annex.s3.amazonaws.com/$key
done | git annex registerurl
</pre>

`registerurl` was introduced in `5.20150317`.

## Manually configuring a public get policy

Here is how to manually configure a public get policy
for a bucket, in the AWS dashboard.

    {
      "Version": "2008-10-17",
      "Statement": [
        {
          "Sid": "AllowPublicRead",
          "Effect": "Allow",
          "Principal": {
            "AWS": "*"
          },
          "Action": "s3:GetObject",
          "Resource": "arn:aws:s3:::public-annex/*"
        }
      ]
    }

This should not be necessary if using a new enough version
of git-annex, which can instead be configured with public=yes.
