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Programming language: Erlang
Latest version: v0.2.3

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Build Status Another Badge

Erlang client for crate.

This client is in an alpha state and, though tested very intensively, not yet verified to be rock-solid in a production environment.


Tested with OTP releases R16B, 17 and 18.


Rebar 3

Craterl is built using rebar3, using it in your project is highly recommended.

Here is how you'd add it to your dependencies.

If you want to load a craterl release from hex.pm, configure it like so:


Or load it directly from github:

    {craterl, {git, "git://github.com/crate/craterl.git", {tag, "0.2.3"}}}

Rebar 2

You can also use craterl in your project using rebar2, though rebar3 is recommended.

With rebar2 you need to load craterl from github. Use a git tag or a commit ref in order to get reproducable builds:

    {craterl, "0.2.3", {git, "git://github.com/crate.craterl.git", {tag, "0.2.3}}}


Craterl releases are hosted on hex.pm.

Declare it as a dependency in your mix.exs file:

def deps do
    [{:craterl, "~> 0.2.3"}]

Or load it directly from github:

def deps do
    [{:craterl, git: "git://github.com/crate/craterl.git", tag: "0.2.3"}]


Normally you'd start craterl as part of your application's startup, so the Erlang/OTP application framework will take care of actually starting craterl.

However, if you want to play around with craterl on the erlang or elixir shell you can start it up with the following convenience method:

ok = craterl:start().

Having a running craterl application, the next step is starting a client instance using a variant of the craterl:new() function:

ClientSpec = {local, my_client}.
Servers = [{<<"localhost">>, 4200}, "localhost:4201"].
Options = [{poolsize, 1000}, {timeout, 5000}].
ClientRef = craterl:new(ClientSpec, Servers, Options).

It is possible to create many clients on one erlang node. craterl client instances are created using a client spec which is a tuple you would use when registering a process, like {local, your_name}. The process name, your_name in this example, must be unique on a node.


The following options can be used to change the behaviour of a newly created craterl client:

  • poolname - string() or binary(), the name of the connection pool, handled by hackney (erlang http client)
  • poolsize - integer(), the size of the connection pool, also handled by hackney
  • timeout - integer(), the receive and connect timeout for connections to crate servers, in milliseconds
  • ssl_options - term(), the same options the erlang ssl module accepts as ssloptions()
  • ssl_insecure - boolean(), whether ssl certificates should be validated or not


Options = [
    {poolname, "my_pool"}, 
    {poolsize, 200}, {timeout, 6000}, 
    {ssl_insecure, false}, 
    {ssl_options, [
        {cipers, [{rsa, aes_256_cbc, sha}]}, 
        {cacerts, MyDerEncodedCaCerts}
ClientRef = craterl:new({local, craterl}, [{<<"localhost">>, 4200}], Options).

See the documentation of the craterl module for more detailed api documentation.


Issuing SQL statements using craterl is possible with one of the variants of craterl:sql():

{ok Response} = craterl:sql("select id, name from sys.cluster").
[[<<"89b8f6bf-4082-415b-937e-7de66b67f6fe">>, <<"crate">>]] = craterl_resp:rows(Response).
[<<"id">>,<<"name">>] = craterl_resp:column_names(Response).

Stmt = <<"select * from user where id in (?, ?, ?)">>.
Args = [1, 2, 3].
{ok, Response2} = craterl:sql(ClientRef, Stmt, Args).

For issuing multiple INSERT / DELETE or UPDATE requests with one roundtrip, the craterl:sql_bulk() functions can be used:

Stmt = <<"insert into t (id, name) values (?, ?)">>.
BulkArgs = [[1, <<"Ford">>], [2, <<"Trillian">>], [3, <<"Zaphod">>]].
{ok, BulkResponse} = craterl:sql_bulk(ClientRef, Stmt, BulkArgs).
BulkResults = craterl_resp:bulk_results(BulkResponse).
[1,1,1] = lists:map(fun craterl_resp:row_count/1, BulkResults).

Stmt2 = <<"update t set new_column=? where id=?">>.
BulkArgs2 = [[<<"funky">>, 1], [<<"shizzle">>, 2], [<<"indeed">>, 3]].
{ok, BulkResponse2} = craterl:sql_bulk(Stmt2, BulkArgs2).
BulkResults2 = craterl_resp:bulk_results(BulkResponse2).
[1,1,1] = lists:map(fun craterl_resp:row_count/1, BulkResults2).

{ok, SelectResponse} = craterl:sql("select * from t").
 [3,<<"Zaphod">>,<<"indeed">>]] = craterl_resp:rows(SelectResponse).

Every sql api function has a variant that accepts a ClientRef as first argument that is an atom referencing a craterl client that has been started using a variant craterl:new() in order to issue your request against a specific server / cluster.


Crate is able to store blobs, files, binary somethings. They can be replicated to make sure you won't lose data.

Craterl fully supports storing, retrieving and manipulating blobs.

At first a blob table is needed to store blobs into:

{ok, SqlResponse} = craterl:sql("create blob table myblobs with (number_of_replicas=1)").

It is possible to upload blobs from stuff you have available in ram or from a file:

Content = <<"awesome!">>.
{ok, {created, HashDigest}} = craterl:blob_put(<<"myblobs">>, Content).
HashDigest = <<"040f06fd774092478d450774f5ba30c5da78acc8">>.

File = <<"/usr/share/dict/words">>
{ok,{created, WordsHash}} = craterl:blob_put_file(ClientRef, <<"myblobs">>, <<"/usr/share/dict/words">>).
WordsHash = <<"a62edf8685920f7d5a95113020631cdebd18a185">>.

You can get blobs to memory or to file. Both methods will make use of chunked HTTP encoding so you will receive the blob piece by piece and won't load big blobs into memory at once.

{ok, GetDataFun} = craterl:blob_get(<<"myblobs">>, WordsHash).
{ok, done}

NewWordsFile = <<"/tmp/blobwords">>
{ok, NewWordsFile} = craterl:blob_get_to_file(<<"myblobs">>, WordsHash, NewWordsFile).

Check for existence of blobs:

ok = craterl:blob_exists(ClientRef, <<"myblobs">>, WordsHash).
{error, 404} = craterl:blob_exists(craterl, <<"myblobs">>, <<"doesnotexist">>).

Delete blobs:

ok = craterl:blob_delete(<<"myblobs">>, WordsHash).
{error, 404} = craterl:blob_delete(<<"myblobs">>, WordsHash).

Every blob api function, like the sql functions, has a variant that accepts a ClientRef as first argument that is an atom referencing a craterl client that has been started using a variant of craterl:new().


Simply call make test to run the unit and integration tests for craterl.


Are very welcome, be it code, constructive feedback, money, or some motivating words!