Build a Rust App with CockroachDB and the Rust-Postgres Driver

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This tutorial shows you how build a simple Rust application with CockroachDB and the Rust-Postgres driver.

Before you begin

You must have Rust and Cargo installed. For instructions on installing Rust and Cargo, see the Cargo documentation.

Step 1. Start CockroachDB

Choose your installation method

You can install a CockroachDB serverless cluster using either the CockroachDB Cloud Console, a web-based graphical user interface (GUI) tool, or ccloud, a command-line interface (CLI) tool.

Create a free cluster

  1. If you haven't already, sign up for a CockroachDB Cloud account.
  2. Log in to your CockroachDB Cloud account.
  3. On the Clusters page, click Create Cluster.
  4. On the Create your cluster page, select Serverless.

    Unless you change your monthly budget, this cluster will be free forever.

  5. Click Create cluster.

    Your cluster will be created in a few seconds and the Create SQL user dialog will display.

Create a SQL user

The Create SQL user dialog allows you to create a new SQL user and password.

  1. Enter a username in the SQL user field or use the one provided by default.
  2. Click Generate & save password.
  3. Copy the generated password and save it in a secure location.
  4. Click Next.

    Currently, all new users are created with full privileges. For more information and to change the default settings, see Granting privileges and Using roles.

Get the connection string

The Connect to cluster dialog shows information about how to connect to your cluster.

  1. Select General connection string from the Select option dropdown.
  2. Open the General connection string section, then copy the connection string provided and save it in a secure location.

    The sample application used in this tutorial uses system CA certificates for server certificate verification, so you can skip the Download CA Cert instructions.

    Note:

    The connection string is pre-populated with your username, password, cluster name, and other details. Your password, in particular, will be provided only once. Save it in a secure place (Cockroach Labs recommends a password manager) to connect to your cluster in the future. If you forget your password, you can reset it by going to the SQL Users page.

Follow these steps to create a CockroachDB serverless cluster using the ccloud CLI tool.

Note:

The ccloud CLI tool is in Preview.

Install ccloud

Choose your OS:

You can install ccloud using either Homebrew or by downloading the binary.

Use Homebrew

  1. Install Homebrew.
  2. Install using the ccloud tap:

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    brew install cockroachdb/tap/ccloud
    

Download the binary

In a terminal, enter the following command to download and extract the ccloud binary and add it to your PATH:

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curl https://binaries.cockroachdb.com/ccloud/ccloud_darwin-amd64_0.2.5.tar.gz | tar -xJ && cp -i ccloud /usr/local/bin/

Use the ARM 64 binary if you have an M1 Mac:

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curl https://binaries.cockroachdb.com/ccloud/ccloud_darwin-arm64_0.2.5.tar.gz | tar -xJ && cp -i ccloud /usr/local/bin/

In a terminal, enter the following command to download and extract the ccloud binary and add it to your PATH:

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curl https://binaries.cockroachdb.com/ccloud/ccloud_linux-amd64_0.2.5.tar.gz | tar -xz && cp -i ccloud /usr/local/bin/

In a PowerShell window, enter the following command to download and extract the ccloud binary and add it to your PATH:

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$ErrorActionPreference = "Stop"; [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; $ProgressPreference = 'SilentlyContinue'; $null = New-Item -Type Directory -Force $env:appdata/ccloud; Invoke-WebRequest -Uri https://binaries.cockroachdb.com/ccloud/ccloud_windows-amd64_0.2.5.zip -OutFile ccloud.zip; Expand-Archive -Force -Path ccloud.zip; Copy-Item -Force ccloud/ccloud.exe -Destination $env:appdata/ccloud; $Env:PATH += ";$env:appdata/ccloud"; # We recommend adding ";$env:appdata/ccloud" to the Path variable for your system environment. See https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_environment_variables#saving-changes-to-environment-variables for more information.

Run ccloud quickstart to create a new cluster, create a SQL user, and retrieve the connection string.

The easiest way of getting started with CockroachDB Cloud is to use ccloud quickstart. The ccloud quickstart command guides you through logging in to CockroachDB Cloud, creating a new CockroachDB serverless with a $0 spend limit, and connecting to the new cluster. Run ccloud quickstart and follow the instructions:

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ccloud quickstart

The ccloud quickstart command will open a browser window to log you in to CockroachDB Cloud. If you are new to CockroachDB Cloud, you can register using one of the single sign-on (SSO) options, or create a new account using an email address.

The ccloud quickstart command will prompt you for the cluster name, cloud provider, and cloud provider region, then ask if you want to connect to the cluster. Each prompt has default values that you can select, or change if you want a different option.

Select General connection string, then copy the connection string displayed and save it in a secure location. The connection string is the line starting postgresql://.

? How would you like to connect? General connection string
Retrieving cluster info: succeeded
 Downloading cluster cert to /Users/maxroach/.postgresql/root.crt: succeeded
postgresql://maxroach:ThisIsNotAGoodPassword@free-tier4.aws-us-west-2.cockroachlabs.cloud:26257/defaultdb?options=--cluster%3Ddim-dog-147&sslmode=verify-full&sslrootcert=%2FUsers%2Fmaxroach%2F.postgresql%2Froot.crt

  1. If you haven't already, download the CockroachDB binary.
  2. Run the cockroach start-single-node command:

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    $ cockroach start-single-node --advertise-addr 'localhost' --insecure
    

    This starts an insecure, single-node cluster.

  3. Take note of the following connection information in the SQL shell welcome text:

    CockroachDB node starting at 2021-08-30 17:25:30.06524 +0000 UTC (took 4.3s)
    build:               CCL v21.1.6 @ 2021/07/20 15:33:43 (go1.15.11)
    webui:               http://localhost:8080
    sql:                 postgresql://root@localhost:26257?sslmode=disable
    

    You'll use the sql connection string to connect to the cluster later in this tutorial.

Warning:

The --insecure flag used in this tutorial is intended for non-production testing only. To run CockroachDB in production, use a secure cluster instead.

Step 2. Get the code

Clone the code's GitHub repo:

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$ git clone https://github.com/cockroachdb/example-app-rust-postgres

The project has the following structure:

├── Cargo.toml
├── LICENSE
├── README.md
└── src
    └── main.rs

The Cargo.toml file is the configuration file for the example, and sets the dependencies for the project.

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[package]
name = "bank"
version = "0.1.0"
edition = "2021"

[dependencies]
openssl = "0.10.41"
postgres-openssl = "0.5.0"
chrono = "0.4.22"

[dependencies.postgres]
version = "0.19.3"
features = [
    "with-uuid-1"
]

[dependencies.uuid]
version = "1.1.2"

The main function is the entry point for the application, with the code for connecting to the cluster, creating the accounts table, creating accounts in that table, and transferring money between two accounts.

The execute_txn function wraps database operations in the context of an explicit transaction. If a retry error is thrown, the function will retry committing the transaction, with exponential backoff, until the maximum number of retries is reached (by default, 15).

Note:

CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.

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/// Runs op inside a transaction and retries it as needed.
/// On non-retryable failures, the transaction is aborted and
/// rolled back; on success, the transaction is committed.
fn execute_txn<T, F>(client: &mut Client, op: F) -> Result<T, Error>
where
    F: Fn(&mut Transaction) -> Result<T, Error>,
{
    let mut txn = client.transaction()?;
    loop {
        // Set a retry savepoint 
        // See https://www.cockroachlabs.com/docs/stable/advanced-client-side-transaction-retries
        let mut sp = txn.savepoint("cockroach_restart")?;
        match op(&mut sp).and_then(|t| sp.commit().map(|_| t)) {
            Err(ref err)
                if err
                    .code()
                    .map(|e| *e == SqlState::T_R_SERIALIZATION_FAILURE)
                    .unwrap_or(false) => {}
            r => break r,
        }
    }
    .and_then(|t| txn.commit().map(|_| t))
}
// 

The transfer_funds function calls execute_txn to perform the actual transfer of funds from one account to the other.

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fn transfer_funds(txn: &mut Transaction, from: Uuid, to: Uuid, amount: i64) -> Result<(), Error> {
    // Read the balance.
    let from_balance: i64 = txn
        .query_one("SELECT balance FROM accounts WHERE id = $1", &[&from])?
        .get(0);

    assert!(from_balance >= amount);

    // Perform the transfer.
    txn.execute(
        "UPDATE accounts SET balance = balance - $1 WHERE id = $2",
        &[&amount, &from],
    )?;
    txn.execute(
        "UPDATE accounts SET balance = balance + $1 WHERE id = $2",
        &[&amount, &to],
    )?;
    Ok(())
}
// 

Step 3. Run the code

  1. In a terminal go to the example-app-rust-postgres directory.

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    cd example-app-rust-postgres
    
  2. Set the DATABASE_URL environment variable to the connection string to your CockroachDB Cloud cluster:

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    $ export DATABASE_URL="postgresql://root@localhost:26257?sslmode=disable"
    

    1. Edit the connection string you copied earlier and replace sslmode=verify-full with sslmode=require.

      Warning:

      You must change the sslmode in your connection string to sslmode=require, as the Rust postgres driver does not recognize sslmode=verify-full. This example uses postgres-openssl, which will perform host verification when the sslmode=require option is set, so require is functionally equivalent to verify-full.

      For example:

      postgresql://maxroach:ThisIsNotAGoodPassword@free-tier4.aws-us-west-2.cockroachlabs.cloud:26257/bank?options=--cluster%3Ddim-dog-147&sslmode=require
      
    2. Set the DATABASE_URL environment variable to the modified connection string.

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      $ export DATABASE_URL="{connection-string}"
      

      Where {connection-string} is the modified connection string.

    The app uses the connection string saved to the DATABASE_URL environment variable to connect to your cluster and execute the code.

  3. Run the code to create a table and insert some rows:

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    cargo run
    

    The output should look similar to the following:

      Compiling bank v0.1.0 (/Users/maxroach/go/src/github.com/cockroachdb/example-app-rust-postgres)
        Finished dev [unoptimized + debuginfo] target(s) in 8.00s
         Running `target/debug/bank`
    Creating accounts table if it doesn't already exist.
    Deleted existing accounts.
    Balances before transfer:
    account id: 8e88f765-b532-4071-a23d-1b33729d01cb  balance: $250
    account id: c6de70e2-78e0-484b-ae5b-6ac2aa43d9ec  balance: $1000
    Final balances:
    account id: 8e88f765-b532-4071-a23d-1b33729d01cb  balance: $350
    account id: c6de70e2-78e0-484b-ae5b-6ac2aa43d9ec  balance: $900
    

What's next?

Read more about using the Rust-Postgres driver.

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