#ffi #tarantool

tarantool-module

Tarantool C API bindings

3 unstable releases

0.2.1 Nov 10, 2020
0.2.0 Nov 5, 2020
0.1.0 Aug 28, 2020

#175 in #ffi

BSD-2-Clause

120KB
2K SLoC

Tarantool C API bindings

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Tarantool API bindings for Rust. This library contains the following Tarantool API's:

  • Box: spaces, indexes, sequences
  • Fibers: fiber attributes, conditional variables
  • CoIO
  • Transactions
  • Latches
  • Tuple utils
  • Logging (see https://docs.rs/log/0.4.11/log/)
  • Error handling

Links:

See also:

Caution! The library is currently under development. API may be unstable until version 1.0 will be released.

Getting Started

These instructions will get a copy of the project up and running on your local machine. For deployment, check out the deployment notes at the end of the tutorial.

Prerequisites

  • rustc 1.45.0 or newer (other versions were not tested)
  • tarantool 2.2

Usage

Add the following lines to your project Cargo.toml:

[dependencies]
tarantool-module = "0.2"

[lib]
crate-type = ["cdylib"]

See https://github.com/picodata/brod for example usage.

Stored procedures

Tarantool can call Rust code via a plugin, from Lua using FFI, or as a stored procedure. This tutorial only is about the third option, Rust stored procedures. In fact Rust routines are always "C functions" to Tarantool but the phrase "stored procedure" is commonly used for historical reasons.

This tutorial contains the following simple steps:

  1. examples/easy - prints "hello world";
  2. examples/harder - decodes a passed parameter value;
  3. examples/hardest - uses this library to do a DBMS insert;
  4. examples/read - uses this library to do a DBMS select;
  5. examples/write - uses this library to do a DBMS replace.

By following the instructions and seeing that the results users should become confident in writing their own stored procedures.

Preparation

Check that these items exist on the computer:

  • Tarantool 2.2
  • A rustc compiler + cargo builder. Any modern version should work

Create cargo project:

$ cargo init --lib

Add the following lines to Cargo.toml:

[package]
name = "easy"
version = "0.1.0"
edition = "2018"
# author, license, etc

[dependencies]
tarantool-module = "0.2.0" # (1)
serde = "1.0" # (2)

[lib]
crate-type = ["cdylib"] # (3)
  1. add to dependencies tarantool-module library;
  2. add to dependencies Serde, this is optional and required if you want to use rust structures as a tuple values (see this example);
  3. you need to compile dynamic library.

Requests will be done using Tarantool as a client. Start Tarantool, and enter these requests:

box.cfg{listen=3306}
box.schema.space.create('capi_test')
box.space.capi_test:create_index('primary')
net_box = require('net.box')
capi_connection = net_box:new(3306)

In plain language: create a space named capi_test, and make a connection to self named capi_connection.

Leave the client running. It will be used to enter more requests later.

Easy

Edit lib.rs file and add the following lines:

use std::os::raw::c_int;
use tarantool_module::tuple::{FunctionArgs, FunctionCtx};

#[no_mangle]
pub extern "C" fn easy(_: FunctionCtx, _: FunctionArgs) -> c_int {
    println!("hello world");
    0
}

#[no_mangle]
pub extern "C" fn easy2(_: FunctionCtx, _: FunctionArgs) -> c_int {
    println!("hello world -- easy2");
    0
}

Compile the program:

$ cargo build

Start another shell. Change directory (cd) so that it is the same as the directory that the client is running in. Copy the compiled library (it is located in subfolder target/debug at you project sources folder) to the current folder and rename it to easy.so

Now go back to the client and execute these requests:

box.schema.func.create('easy', {language = 'C'})
box.schema.user.grant('guest', 'execute', 'function', 'easy')
capi_connection:call('easy')

If these requests appear unfamiliar, read the descriptions of box.schema.func.create(), box.schema.user.grant() and conn:call().

The function that matters is capi_connection:call('easy').

Its first job is to find the 'easy' function, which should be easy because by default Tarantool looks on the current directory for a file named easy.so.

Its second job is to call the 'easy' function. Since the easy() function in lib.rs begins with println!("hello world"), the words "hello world" will appear on the screen.

Its third job is to check that the call was successful. Since the easy() function in lib.rs ends with return 0, there is no error message to display and the request is over.

The result should look like this:

tarantool> capi_connection:call('easy')
hello world
---
- []
...

Now let's call the other function in lib.rs - easy2(). This is almost the same as the easy() function, but there's a detail: when the file name is not the same as the function name, then we have to specify {file-name}.{function-name}

box.schema.func.create('easy.easy2', {language = 'C'})
box.schema.user.grant('guest', 'execute', 'function', 'easy.easy2')
capi_connection:call('easy.easy2')

... and this time the result will be hello world -- easy2.

Conclusion: calling a Rust function is easy.

Harder

Create a new crate "harder". Put these lines to lib.rs:

use serde::{Deserialize, Serialize};
use std::os::raw::c_int;
use tarantool_module::tuple::{AsTuple, FunctionArgs, FunctionCtx, Tuple};

#[derive(Serialize, Deserialize)]
struct Args {
    pub fields: Vec<i32>,
}

impl AsTuple for Args {}

#[no_mangle]
pub extern "C" fn harder(_: FunctionCtx, args: FunctionArgs) -> c_int {
    let args: Tuple = args.into(); // (1)
    let args = args.into_struct::<Args>().unwrap(); // (2)
    println!("field_count = {}", args.fields.len());

    for val in args.fields {
        println!("val={}", val);
    }

    0
}
  1. extract tuple from special structure FunctionArgs
  2. deserialize tuple into rust structure

Compile the program, producing a library file named harder.so.

Now go back to the client and execute these requests:

box.schema.func.create('harder', {language = 'C'})
box.schema.user.grant('guest', 'execute', 'function', 'harder')
passable_table = {}
table.insert(passable_table, 1)
table.insert(passable_table, 2)
table.insert(passable_table, 3)
capi_connection:call('harder', passable_table)

This time the call is passing a Lua table (passable_table) to the harder() function. The harder() function will see it, it's in the char args parameter.

And now the screen looks like this:

tarantool> capi_connection:call('harder', passable_table)
field_count = 3
val=1
val=2
val=3
---
- []
...

Conclusion: decoding parameter values passed to a rust function is not easy at first, but there are routines to do the job.

Hardest

Create a new crate "hardest". Put these lines to lib.rs:

use std::os::raw::c_int;

use serde::{Deserialize, Serialize};

use tarantool_module::space::Space;
use tarantool_module::tuple::{AsTuple, FunctionArgs, FunctionCtx};

#[derive(Serialize, Deserialize)]
struct Row {
    pub int_field: i32,
    pub str_field: String,
}

impl AsTuple for Row {}

#[no_mangle]
pub extern "C" fn hardest(ctx: FunctionCtx, _: FunctionArgs) -> c_int {
    let mut space = Space::find("capi_test").unwrap(); // (1)
    let result = space.insert( // (3)
        &Row { // (2)
            int_field: 10000,
            str_field: "String 2".to_string(),
        }
    );
    ctx.return_tuple(result.unwrap().unwrap()).unwrap()
}

This time the rust function is doing three things:

  1. finding the capi_test space by calling Space::find_by_name() method;
  2. row structure can be passed as is, it will be serialized to tuple automaticaly;
  3. inserting a tuple using .insert().

Compile the program, producing a library file named hardest.so.

Now go back to the client and execute these requests:

box.schema.func.create('hardest', {language = "C"})
box.schema.user.grant('guest', 'execute', 'function', 'hardest')
box.schema.user.grant('guest', 'read,write', 'space', 'capi_test')
capi_connection:call('hardest')

Now, still on the client, execute this request:

box.space.capi_test:select()

The result should look like this:

tarantool> box.space.capi_test:select()
---
- - [10000, 'String 2']
...

This proves that the hardest() function succeeded.

Read

Create a new crate "read". Put these lines to lib.rs:

use std::os::raw::c_int;

use serde::{Deserialize, Serialize};

use tarantool_module::space::Space;
use tarantool_module::tuple::{AsTuple, FunctionArgs, FunctionCtx};

#[derive(Serialize, Deserialize, Debug)]
struct Row {
    pub int_field: i32,
    pub str_field: String,
}

impl AsTuple for Row {}

#[no_mangle]
pub extern "C" fn read(_: FunctionCtx, _: FunctionArgs) -> c_int {
    let space = Space::find("capi_test").unwrap(); // (1)

    let key = 10000;
    let result = space.get(&(key,)).unwrap(); // (2, 3)
    assert!(result.is_some());

    let result = result.unwrap().into_struct::<Row>().unwrap(); // (4)
    println!("value={:?}", result);

    0
}
  1. once again, finding the capi_test space by calling Space::find();
  2. formatting a search key = 10000 using rust tuple literal (an alternative to serializing structures);
  3. getting a tuple using .get();
  4. deserializing result.

Compile the program, producing a library file named read.so.

Now go back to the client and execute these requests:

box.schema.func.create('read', {language = "C"})
box.schema.user.grant('guest', 'execute', 'function', 'read')
box.schema.user.grant('guest', 'read,write', 'space', 'capi_test')
capi_connection:call('read')

The result of capi_connection:call('read') should look like this:

tarantool> capi_connection:call('read')
uint value=10000.
string value=String 2.
---
- []
...

This proves that the read() function succeeded.

Write

Create a new crate "write". Put these lines to lib.rs:

use std::os::raw::c_int;

use tarantool_module::error::{set_error, Error, TarantoolErrorCode};
use tarantool_module::fiber::sleep;
use tarantool_module::space::Space;
use tarantool_module::transaction::start_transaction;
use tarantool_module::tuple::{FunctionArgs, FunctionCtx};

#[no_mangle]
pub extern "C" fn hardest(ctx: FunctionCtx, _: FunctionArgs) -> c_int {
    let mut space = match Space::find("capi_test").unwrap() { // (1)
        None => {
            return set_error(
                file!(),
                line!(),
                &TarantoolErrorCode::ProcC,
                "Can't find space capi_test",
            )
        }
        Some(space) => space,
    };

    let row = (1, 22); // (2)

    start_transaction(|| -> Result<(), Error> { // (3)
        space.replace(&row, false)?; // (4)
        Ok(()) // (5)
    })
    .unwrap();

    sleep(0.001);
    ctx.return_mp(&row).unwrap() // (6)
}
  1. once again, finding the capi_test space by calling Space::find_by_name();
  2. preparing row value;
  3. starting a transaction;
  4. replacing a tuple in box.space.capi_test
  5. ending a transaction:
    • commit if closure returns Ok()
    • rollback on Error();
  6. use the .return_mp() method to return the entire tuple to the caller and let the caller display it.

Compile the program, producing a library file named write.so.

Now go back to the client and execute these requests:

box.schema.func.create('write', {language = "C"})
box.schema.user.grant('guest', 'execute', 'function', 'write')
box.schema.user.grant('guest', 'read,write', 'space', 'capi_test')
capi_connection:call('write')

The result of capi_connection:call('write') should look like this:

tarantool> capi_connection:call('write')
---
- [[1, 22]]
...

This proves that the write() function succeeded.

Conclusion: Rust "stored procedures" have full access to the database.

Cleaning up

  • Get rid of each of the function tuples with box.schema.func.drop.
  • Get rid of the capi_test space with box.schema.capi_test:drop().
  • Remove the *.so files that were created for this tutorial.

Running the tests

To invoke the automated tests run:

make
make test

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

Authors

  • Anton Melnikov
  • Dmitriy Koltsov

© 2020 Picodata.io https://github.com/picodata

License

This project is licensed under the BSD License - see the LICENSE file for details

Dependencies

~1.2–2MB
~44K SLoC