This document describes the high-level design and implementation of the Gaia storage system. It includes specifications for backend storage drivers and interactions between developer APIs and the Gaia service.
Developers who wish to use the Gaia storage system should see the
blockstack.js APIs
documented here and here.
Gaia works by hosting data in one or more existing storage systems of the user's choice. These storage systems are typically cloud storage systems. We currently have driver support for S3 and Azure Blob Storage, but the driver model allows for other backend support as well. The point is, the user gets to choose where their data lives, and Gaia enables applications to access it via a uniform API.
Blockstack applications use the Gaia storage system to store data on behalf of a user. When the user logs in to an application, the authentication process gives the application the URL of a Gaia hub, which performs writes on behalf of that user. The Gaia hub authenticates writes to a location by requiring a valid authentication token, generated by a private key authorized to write at that location.
A performance and simplicity oriented guarantee of the Gaia
specification is that when an application submits a write to a URL
https://myhub.service.org/store/foo/bar, the application is guaranteed to
be able to read from a URL https://myreads.com/foo/bar. While the
prefix of the read-from URL may change between the two, the suffix
must be the same as the write-to URL.
This allows an application to know exactly where a written file can be read from, given the read prefix. To obtain that read prefix, the Gaia service defines an endpoint:
GET /hub_info/
which returns a JSON object with a read_url_prefix.
For example, if my service returns:
{ ...,
"read_url_prefix": "https://myservice.org/read/"
}I know that if I submit a write request to:
https://myservice.org/store/1DHvWDj834zPAkwMhpXdYbCYh4PomwQfzz/0/profile.json
That I will be able to read that file from:
https://myservice.org/read/1DHvWDj834zPAkwMhpXdYbCYh4PomwQfzz/0/profile.json
Access control in a gaia storage hub is performed on a per-address
basis. Writes to URLs /store/<address>/<file> are only allowed if
the writer can demonstrate that they control that address. This is
achieved via an 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.
In more detail, this signed message is:
BASE64({ "signature" : ECDSA_SIGN(SHA256(challenge-text)),
"publickey" : PUBLICKEY_HEX })
Currently, challenge-text must match the known challenge-text on the gaia storage hub. However, as future work enables more extensible forms of authentication, we could extend this to allow the auth token to include the challenge-text as well, which the gaia storage hub would then need to also validate.
A gaia storage hub will store the written data exactly as
given. This means that the storage hub does not provide many
different kinds of guarantees about the data. It does not ensure that
data is validly formatted, contains valid signatures, or is
encrypted. Rather, the design philosophy is that these concerns are
client-side concerns. Client libraries (such as blockstack.js) are
capable of providing these guarantees, and we use a liberal definition of
the end-to-end principle to guide this design decision.
A configuration JSON file should be stored either in the top-level directory
of the hub server, or a file location may be specified in the environment
variable CONFIG_PATH.
An example configuration file is provided in (./hub/config.sample.json) You can specify the logging level, the number of social proofs required for addresses to write to the system, the backend driver, the credentials for that backend driver, and the readURL for the storage provider.
A private hub services requests for a single user. This is controlled via whitelisting the addresses allowed to write files. In order to support application storage, because each application uses a different app- and user-specific address, each application you wish to use must be added to the whitelist separately. An extensible authentication approach would obviate the need for this manual whitelisting, but that remains as future work.
An open-membership hub will allow writes for any address top-level directory, each request will still be validated such that write requests must provide valid authentication tokens for that address. Operating in this mode is recommended for service and identity providers who wish to support many different users.
In order to limit the users that may interact with such a hub to users who provide social proofs of identity, we support an execution mode where the hub checks that a user's profile.json object contains social proofs in order to be able to write to other locations. This can be configured via the config.json.
Gaia hub drivers are fairly simple. The biggest requirement is the ability to fulfill the write-to/read-from URL guarantee. As currently implemented a gaia hub driver must implement the following two functions:
/**
* Performs the actual write of a file to `path`
* the file must be readable at `${getReadURLPrefix()}/${storageToplevel}/${path}`
*
* @param { String } options.path - path of the file.
* @param { String } options.storageToplevel - the top level directory to store the file in
* @param { String } options.contentType - the HTTP content-type of the file
* @param { stream.Readable } options.stream - the data to be stored at `path`
* @param { Integer } options.contentLength - the bytes of content in the stream
* @returns { Promise } that resolves to the public-readable URL of the stored content.
*/
performWrite (options: { path, contentType,
stream, contentLength: Number })
/**
* Return the prefix for reading files from.
* a write to the path `foo` should be readable from
* `${getReadURLPrefix()}foo`
* @returns {String} the read url prefix.
*/
getReadURLPrefix ()The Gaia storage API defines only three endpoints.
GET ${read-url-prefix}/${address}/${path}
This returns the data stored by the gaia hub at ${path}. In order
for this to be usable from web applications, this read path must
set the appropriate CORS headers. The HTTP Content-Type of the file
should match the Content-Type of the corresponding write.
POST ${hubUrl}/store/${address}/${path}
This performs a write to the gaia hub at ${path}.
On success, it returns a 202 status, and a JSON object:
{
"publicUrl": "${read-url-prefix}/${address}/${path}"
}The POST must contain an authentication header with a bearer token.
The bearer token's content and generation is described in
the access control section of this
document.
GET ${hubUrl}/hub_info/
Returns a JSON object:
{
"challenge_text": "text-which-must-be-signed-to-validate-requests",
"read_url_prefix": "${read-url-prefix}"
}Some service providers may wish to provide hub services to a limited set of different users, with a provider-specific method of authenticating that a user or address is within that set. In order to provide that functionality, our hub implementation would need to be extensible enough to allow plugging in different authentication models.
Gaia nodes can request data from other Gaia nodes, and can store data to other Gaia nodes. In effect, Gaia nodes can be "chained together" in arbitrarily complex ways. This creates an opportunity to create a decentralized storage marketplace.
For example, Alice can make her Gaia node public and program it to store data to her Amazon S3 bucket and her Dropbox account. Bob can then POST data to Alice's node, causing her node to replicate data to both providers. Later, Charlie can read Bob's data from Alice's node, causing Alice's node to fetch and serve back the data from her cloud storage. Neither Bob nor Charlie have to set up accounts on Amazon S3 and Dropbox this way, since Alice's node serves as an intermediary between them and the storage providers.
Since Alice is on the read/write path between Bob and Charlie and cloud storage, she has the opportunity to make optimizations. First, she can program her Gaia node to synchronously write data to local disk and asynchronously back it up to S3 and Dropbox. This would speed up Bob's writes, but at the cost of durability (i.e. Alice's node could crash before replicating to the cloud).
In addition, Alice can program her Gaia node to service all reads from disk. This would speed up Charlie's reads, since he'll get the latest data without having to hit back-end cloud storage providers.
Since Alice is providing a service to Bob and Charlie, she will want compensation. This can be achieved by having both of them send her money via the underlying blockchain.
To do so, she would register her node's IP address in a
.storage namespace in Blockstack, and post her rates per gigabyte in her node's
profile and her payment address. Once Bob and Charlie sent her payment, her
node would begin accepting reads and writes from them up to the capacity
purchased. They would continue sending payments as long as Alice provides them
with service.
Other experienced Gaia node operators would register their nodes in .storage, and
compete for users by offerring better durability, availability, performance,
extra storage features, and so on.
Our deployed service places some modest limitations on file uploads and rate limits. Currently, the service will only allow up to 20 write requests per second and a maximum file size of 5MB. However, these limitations are only for our service, if you deploy your own Gaia hub, these limitations are not necessary.