docs/_storage/write-to-read.md

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Storage write and read

Once a user authenticates and a DApp obtains authentication, the application interacts with Gaia through the blockstack.js library. There are two simple methods for working with data in Gaia hub: the putFile() and getFile() methods. This section goes into greater detail about the methods, how they interact with a hub, and how to use them.

Write-to and Read-from URL Guarantees

Gaia is built on a driver model that supports many storage services. So, with very few lines of code, you can interact with providers on Amazon S3, Dropbox, and so forth. The simple getFile() and putFile() interfaces are kept simple because Blockstack assumes and wants to encourage a community of open-source-data-management libraries.

The performance and simplicity-oriented guarantee of the Gaia specification is that when an application submits a write-to https://myhub.service.org/store/foo/bar URL, the application is guaranteed to be able to read from the https://myreads.com/foo/bar URL. Note that, while the prefix in the write-to url (for example,myhub.service.org/store) and the read-from URL (https://myreads.com) are different, the foo/bar suffixes are the same.

By default, putFile() encrypts information while getFile() decrypts it by default. Data stored in an encrypted format means only the user that stored it can view it. For applications that want other users to view data, the application should set the encrypt option to false. And, corresponding, the decrypt option on getFile() should also be false.

Consistent, identical suffixes allow an application to know exactly where a written file can be read from, given the read prefix. The Gaia service defines a hub_info endpoint to obtain that read prefix:

GET /hub_info/

The endpoint returns a JSON object with a read_url_prefix, for example, if my service returns:

{ ...,
  "read_url_prefix": "https://myservice.org/read/"
}

The data be read with this getFile() and this address:

https://myservice.org/read/1DHvWDj834zPAkwMhpXdYbCYh4PomwQfzz/0/profile.json

The application is guaranteed that the profile is written with putFile() this request address:

https://myservice.org/store/1DHvWDj834zPAkwMhpXdYbCYh4PomwQfzz/0/profile.json

When you use the putFile() method it takes the user data and POSTs it to the user's Gaia storage hub. The data POSTs directly to the hub, the blockchain is not used and no data is stored there. The limit on file upload is currently 25mb.

Address-based access-control

Access control in a Gaia storage hub is performed on a per-address basis. Writes to URLs /store/<address>/<file> are allowed only if the writer can demonstrate that they control that address. This is achieved via the authentication token which is a message signed by the private key associated with that address. The message itself is a challenge text, returned via the /hub_info/ endpoint.

Reads can be done by everybody. The URLs to a user's app data are in a canonical location in their profile. For example, here's how you would get data from the  Banter app, stored under the Blockstack ID gavin.id.   1. Get the bucket URL  bash  $ BUCKET_URL="$(curl -sL https://core.blockstack.org/v1/users/gavin.id | jq -r '."gavin.id"["profile"]["apps"]["https://banter.pub"]')"  $ echo "$BUCKET_URL"  https://gaia.blockstack.org/hub/16E485MVpR3QpmjVkRgej7ya2Vnzu3jyTR/    2. Get the data  bash  $ curl -sL "${BUCKET_URL%%/}/Message/3e866af471d0-4072-beba-06ad1e7ad4bd"  {"content":"Anyone here?","votes":[],"createdBy":"gavin.id",...} 

This data is public and unencrypted. The same works for encrypted data. Only the holder of the private key used for encryption would be able to decrypt the data.