WIP: create server

Cargo.lock

@@ -470,6 +470,18 @@ version = "0.15.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1aaf95b3e5c8f23aa320147307562d361db0ae0d51242340f558153b4eb2439b"
 
+[[package]]
+name = "educe"
+version = "0.5.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e4bd92664bf78c4d3dba9b7cdafce6fa15b13ed3ed16175218196942e99168a8"
+dependencies = [
+ "enum-ordinalize",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.60",
+]
+
 [[package]]
 name = "either"
 version = "1.11.0"
@@ -491,6 +503,26 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "34aa73646ffb006b8f5147f3dc182bd4bcb190227ce861fc4a4844bf8e3cb2c0"
 
+[[package]]
+name = "enum-ordinalize"
+version = "4.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fea0dcfa4e54eeb516fe454635a95753ddd39acda650ce703031c6973e315dd5"
+dependencies = [
+ "enum-ordinalize-derive",
+]
+
+[[package]]
+name = "enum-ordinalize-derive"
+version = "4.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d28318a75d4aead5c4db25382e8ef717932d0346600cacae6357eb5941bc5ff"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.60",
+]
+
 [[package]]
 name = "env_filter"
 version = "0.1.0"
@@ -964,6 +996,7 @@ dependencies = [
  "dialoguer",
  "env_logger",
  "futures",
+ "futures-util",
  "indoc",
  "itertools",
  "log",
@@ -976,6 +1009,8 @@ dependencies = [
  "sqlx",
  "thiserror",
  "tokio",
+ "tokio-serde",
+ "tokio-stream",
  "tokio-util",
  "toml",
  "uuid",
@@ -1109,6 +1144,26 @@ version = "2.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3148f5046208a5d56bcfc03053e3ca6334e51da8dfb19b6cdc8b306fae3283e"
 
+[[package]]
+name = "pin-project"
+version = "1.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6bf43b791c5b9e34c3d182969b4abb522f9343702850a2e57f460d00d09b4b3"
+dependencies = [
+ "pin-project-internal",
+]
+
+[[package]]
+name = "pin-project-internal"
+version = "1.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2f38a4412a78282e09a2cf38d195ea5420d15ba0602cb375210efbc877243965"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.60",
+]
+
 [[package]]
 name = "pin-project-lite"
 version = "0.2.14"
@@ -1931,6 +1986,21 @@ dependencies = [
  "syn 2.0.60",
 ]
 
+[[package]]
+name = "tokio-serde"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "caf600e7036b17782571dd44fa0a5cea3c82f60db5137f774a325a76a0d6852b"
+dependencies = [
+ "bincode",
+ "bytes",
+ "educe",
+ "futures-core",
+ "futures-sink",
+ "pin-project",
+ "serde",
+]
+
 [[package]]
 name = "tokio-stream"
 version = "0.1.15"

Cargo.toml

@@ -11,6 +11,7 @@ clap = { version = "4.5.4", features = ["derive"] }
 dialoguer = "0.11.0"
 env_logger = "0.11.3"
 futures = "0.3.30"
+futures-util = "0.3.30"
 indoc = "2.0.5"
 itertools = "0.12.1"
 log = "0.4.21"
@@ -23,7 +24,9 @@ serde_json = { version = "1.0.116", features = ["preserve_order"] }
 sqlx = { version = "0.7.4", features = ["runtime-tokio", "mysql", "tls-rustls"] }
 thiserror = "1.0.63"
 tokio = { version = "1.37.0", features = ["rt", "macros"] }
-tokio-util = "0.7.11"
+tokio-serde = { version = "0.9.0", features = ["bincode"] }
+tokio-stream = "0.1.15"
+tokio-util = { version = "0.7.11", features = ["codec"] }
 toml = "0.8.12"
 uuid = { version = "1.10.0", features = ["v4"] }
 

src/server.rs

@@ -0,0 +1,6 @@
+mod common;
+mod database_operations;
+mod entrypoint;
+mod input_sanitization;
+mod protocol;
+mod user_operations;

src/server/common.rs

@@ -0,0 +1,113 @@
+use anyhow::Context;
+use nix::unistd::{Group as LibcGroup, User as LibcUser};
+use sqlx::{Connection, MySqlConnection};
+
+#[cfg(not(target_os = "macos"))]
+use std::ffi::CString;
+
+/// Report the result status of a command.
+/// This is used to display a status message to the user.
+pub enum CommandStatus {
+    /// The command was successful,
+    /// and made modification to the database.
+    SuccessfullyModified,
+
+    /// The command was mostly successful,
+    /// and modifications have been made to the database.
+    /// However, some of the requested modifications failed.
+    PartiallySuccessfullyModified,
+
+    /// The command was successful,
+    /// but no modifications were needed.
+    NoModificationsNeeded,
+
+    /// The command was successful,
+    /// and made no modification to the database.
+    NoModificationsIntended,
+
+    /// The command was cancelled, either through a dialog or a signal.
+    /// No modifications have been made to the database.
+    Cancelled,
+}
+
+// pub fn get_current_unix_user() -> anyhow::Result<User> {
+//     User::from_uid(getuid())
+//         .context("Failed to look up your UNIX username")
+//         .and_then(|u| u.ok_or(anyhow::anyhow!("Failed to look up your UNIX username")))
+// }
+
+pub struct UnixUser {
+    pub username: String,
+    pub uid: u32,
+    pub gid: u32,
+    pub groups: Vec<String>,
+}
+
+#[cfg(target_os = "macos")]
+fn get_unix_groups(_user: &User) -> anyhow::Result<Vec<Group>> {
+    // Return an empty list on macOS since there is no `getgrouplist` function
+    Ok(vec![])
+}
+
+#[cfg(not(target_os = "macos"))]
+fn get_unix_groups(user: &LibcUser) -> anyhow::Result<Vec<LibcGroup>> {
+    let user_cstr =
+        CString::new(user.name.as_bytes()).context("Failed to convert username to CStr")?;
+    let groups = nix::unistd::getgrouplist(&user_cstr, user.gid)?
+        .iter()
+        .filter_map(|gid| match LibcGroup::from_gid(*gid) {
+            Ok(Some(group)) => Some(group),
+            Ok(None) => None,
+            Err(e) => {
+                log::warn!(
+                    "Failed to look up group with GID {}: {}\nIgnoring...",
+                    gid,
+                    e
+                );
+                None
+            }
+        })
+        .collect::<Vec<LibcGroup>>();
+
+    Ok(groups)
+}
+
+impl UnixUser {
+    pub fn from_uid(uid: u32) -> anyhow::Result<Self> {
+        let libc_uid = nix::unistd::Uid::from_raw(uid);
+        let libc_user = LibcUser::from_uid(libc_uid)
+            .context("Failed to look up your UNIX username")?
+            .ok_or(anyhow::anyhow!("Failed to look up your UNIX username"))?;
+
+        let groups = get_unix_groups(&libc_user)?;
+
+        Ok(UnixUser {
+            username: libc_user.name,
+            uid,
+            gid: libc_user.gid.into(),
+            groups: groups.iter().map(|g| g.name.clone()).collect(),
+        })
+    }
+}
+
+/// This function creates a regex that matches items (users, databases)
+/// that belong to the user or any of the user's groups.
+pub fn create_user_group_matching_regex(user: &UnixUser) -> String {
+    if user.groups.is_empty() {
+        format!("{}(_.+)?", user.username)
+    } else {
+        format!("({}|{})(_.+)?", user.username, user.groups.join("|"))
+    }
+}
+
+/// Gracefully close a MySQL connection.
+pub async fn close_database_connection(connection: MySqlConnection) {
+    if let Err(e) = connection
+        .close()
+        .await
+        .context("Failed to close connection properly")
+    {
+        eprintln!("{}", e);
+        eprintln!("Ignoring...");
+    }
+}

src/server/database_operations.rs

@@ -0,0 +1,183 @@
+use crate::server::common::UnixUser;
+use crate::server::input_sanitization::quote_identifier;
+use crate::server::input_sanitization::{validate_name, validate_ownership_by_unix_user};
+use crate::server::input_sanitization::{NameValidationError, OwnerValidationError};
+
+use serde::{Deserialize, Serialize};
+use sqlx::prelude::*;
+
+use sqlx::MySqlConnection;
+use std::collections::BTreeMap;
+
+use super::common::create_user_group_matching_regex;
+
+// NOTE: this function is unsafe because it does no input validation.
+async fn unsafe_database_exists(
+    db_name: &str,
+    connection: &mut MySqlConnection,
+) -> Result<bool, sqlx::Error> {
+    let result =
+        sqlx::query("SELECT SCHEMA_NAME FROM information_schema.SCHEMATA WHERE SCHEMA_NAME = ?")
+            .bind(db_name)
+            .fetch_optional(connection)
+            .await?;
+
+    Ok(result.is_some())
+}
+
+pub type CreateDatabasesOutput = BTreeMap<String, Result<(), CreateDatabaseError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum CreateDatabaseError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    DatabaseAlreadyExists,
+    MySqlError(String),
+}
+
+pub async fn create_databases(
+    database_names: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> CreateDatabasesOutput {
+    let mut results = BTreeMap::new();
+
+    for database_name in database_names {
+        if let Err(err) = validate_name(&database_name) {
+            results.insert(
+                database_name.clone(),
+                Err(CreateDatabaseError::SanitizationError(err)),
+            );
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&database_name, unix_user) {
+            results.insert(
+                database_name.clone(),
+                Err(CreateDatabaseError::OwnershipError(err)),
+            );
+            continue;
+        }
+
+        match unsafe_database_exists(&database_name, &mut *connection).await {
+            Ok(true) => {
+                results.insert(
+                    database_name.clone(),
+                    Err(CreateDatabaseError::DatabaseAlreadyExists),
+                );
+                continue;
+            }
+            Err(err) => {
+                results.insert(
+                    database_name.clone(),
+                    Err(CreateDatabaseError::MySqlError(err.to_string())),
+                );
+                continue;
+            }
+            _ => {}
+        }
+
+        let result =
+            sqlx::query(format!("CREATE DATABASE {}", quote_identifier(&database_name)).as_str())
+                .execute(&mut *connection)
+                .await
+                .map(|_| ())
+                .map_err(|err| CreateDatabaseError::MySqlError(err.to_string()));
+
+        results.insert(database_name, result);
+    }
+
+    results
+}
+
+pub type DropDatabasesOutput = BTreeMap<String, Result<(), DropDatabaseError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum DropDatabaseError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    DatabaseDoesNotExist,
+    MySqlError(String),
+}
+
+pub async fn drop_databases(
+    database_names: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> DropDatabasesOutput {
+    let mut results = BTreeMap::new();
+
+    for database_name in database_names {
+        if let Err(err) = validate_name(&database_name) {
+            results.insert(
+                database_name.clone(),
+                Err(DropDatabaseError::SanitizationError(err)),
+            );
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&database_name, unix_user) {
+            results.insert(
+                database_name.clone(),
+                Err(DropDatabaseError::OwnershipError(err)),
+            );
+            continue;
+        }
+
+        match unsafe_database_exists(&database_name, &mut *connection).await {
+            Ok(false) => {
+                results.insert(
+                    database_name.clone(),
+                    Err(DropDatabaseError::DatabaseDoesNotExist),
+                );
+                continue;
+            }
+            Err(err) => {
+                results.insert(
+                    database_name.clone(),
+                    Err(DropDatabaseError::MySqlError(err.to_string())),
+                );
+                continue;
+            }
+            _ => {}
+        }
+
+        let result =
+            sqlx::query(format!("DROP DATABASE {}", quote_identifier(&database_name)).as_str())
+                .execute(&mut *connection)
+                .await
+                .map(|_| ())
+                .map_err(|err| DropDatabaseError::MySqlError(err.to_string()));
+
+        results.insert(database_name, result);
+    }
+
+    results
+}
+
+pub type ListDatabasesOutput = Result<Vec<String>, ListDatabasesError>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum ListDatabasesError {
+    MySqlError(String),
+}
+
+pub async fn list_databases_for_user(
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> Result<Vec<String>, ListDatabasesError> {
+    sqlx::query(
+        r#"
+          SELECT `SCHEMA_NAME` AS `database`
+          FROM `information_schema`.`SCHEMATA`
+          WHERE `SCHEMA_NAME` NOT IN ('information_schema', 'performance_schema', 'mysql', 'sys')
+            AND `SCHEMA_NAME` REGEXP ?
+        "#,
+    )
+    .bind(create_user_group_matching_regex(unix_user))
+    .fetch_all(connection)
+    .await
+    .and_then(|rows| {
+        rows.into_iter()
+            .map(|row| row.try_get::<String, _>("database"))
+            .collect::<Result<Vec<String>, sqlx::Error>>()
+    })
+    .map_err(|err| ListDatabasesError::MySqlError(err.to_string()))
+}

src/server/database_privilege_operations.rs

@@ -0,0 +1,885 @@
+//! Database privilege operations
+//!
+//! This module contains functions for querying, modifying,
+//! displaying and comparing database privileges.
+//!
+//! A lot of the complexity comes from two core components:
+//!
+//! - The privilege editor that needs to be able to print
+//!   an editable table of privileges and reparse the content
+//!   after the user has made manual changes.
+//!
+//! - The comparison functionality that tells the user what
+//!   changes will be made when applying a set of changes
+//!   to the list of database privileges.
+
+use std::collections::{BTreeSet, HashMap};
+
+use anyhow::{anyhow, Context};
+use indoc::indoc;
+use itertools::Itertools;
+use prettytable::Table;
+use serde::{Deserialize, Serialize};
+use sqlx::{mysql::MySqlRow, prelude::*, MySqlConnection};
+
+use crate::core::{
+    common::{
+        create_user_group_matching_regex, get_current_unix_user, quote_identifier, rev_yn, yn,
+    },
+    database_operations::validate_database_name,
+};
+
+/// This is the list of fields that are used to fetch the db + user + privileges
+/// from the `db` table in the database. If you need to add or remove privilege
+/// fields, this is a good place to start.
+pub const DATABASE_PRIVILEGE_FIELDS: [&str; 13] = [
+    "db",
+    "user",
+    "select_priv",
+    "insert_priv",
+    "update_priv",
+    "delete_priv",
+    "create_priv",
+    "drop_priv",
+    "alter_priv",
+    "index_priv",
+    "create_tmp_table_priv",
+    "lock_tables_priv",
+    "references_priv",
+];
+
+pub fn db_priv_field_human_readable_name(name: &str) -> String {
+    match name {
+        "db" => "Database".to_owned(),
+        "user" => "User".to_owned(),
+        "select_priv" => "Select".to_owned(),
+        "insert_priv" => "Insert".to_owned(),
+        "update_priv" => "Update".to_owned(),
+        "delete_priv" => "Delete".to_owned(),
+        "create_priv" => "Create".to_owned(),
+        "drop_priv" => "Drop".to_owned(),
+        "alter_priv" => "Alter".to_owned(),
+        "index_priv" => "Index".to_owned(),
+        "create_tmp_table_priv" => "Temp".to_owned(),
+        "lock_tables_priv" => "Lock".to_owned(),
+        "references_priv" => "References".to_owned(),
+        _ => format!("Unknown({})", name),
+    }
+}
+
+/// This struct represents the set of privileges for a single user on a single database.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, PartialOrd, Ord)]
+pub struct DatabasePrivilegeRow {
+    pub db: String,
+    pub user: String,
+    pub select_priv: bool,
+    pub insert_priv: bool,
+    pub update_priv: bool,
+    pub delete_priv: bool,
+    pub create_priv: bool,
+    pub drop_priv: bool,
+    pub alter_priv: bool,
+    pub index_priv: bool,
+    pub create_tmp_table_priv: bool,
+    pub lock_tables_priv: bool,
+    pub references_priv: bool,
+}
+
+impl DatabasePrivilegeRow {
+    pub fn empty(db: &str, user: &str) -> Self {
+        Self {
+            db: db.to_owned(),
+            user: user.to_owned(),
+            select_priv: false,
+            insert_priv: false,
+            update_priv: false,
+            delete_priv: false,
+            create_priv: false,
+            drop_priv: false,
+            alter_priv: false,
+            index_priv: false,
+            create_tmp_table_priv: false,
+            lock_tables_priv: false,
+            references_priv: false,
+        }
+    }
+
+    pub fn get_privilege_by_name(&self, name: &str) -> bool {
+        match name {
+            "select_priv" => self.select_priv,
+            "insert_priv" => self.insert_priv,
+            "update_priv" => self.update_priv,
+            "delete_priv" => self.delete_priv,
+            "create_priv" => self.create_priv,
+            "drop_priv" => self.drop_priv,
+            "alter_priv" => self.alter_priv,
+            "index_priv" => self.index_priv,
+            "create_tmp_table_priv" => self.create_tmp_table_priv,
+            "lock_tables_priv" => self.lock_tables_priv,
+            "references_priv" => self.references_priv,
+            _ => false,
+        }
+    }
+
+    pub fn diff(&self, other: &DatabasePrivilegeRow) -> DatabasePrivilegeRowDiff {
+        debug_assert!(self.db == other.db && self.user == other.user);
+
+        DatabasePrivilegeRowDiff {
+            db: self.db.clone(),
+            user: self.user.clone(),
+            diff: DATABASE_PRIVILEGE_FIELDS
+                .into_iter()
+                .skip(2)
+                .filter_map(|field| {
+                    DatabasePrivilegeChange::new(
+                        self.get_privilege_by_name(field),
+                        other.get_privilege_by_name(field),
+                        field,
+                    )
+                })
+                .collect(),
+        }
+    }
+}
+
+#[inline]
+fn get_mysql_row_priv_field(row: &MySqlRow, position: usize) -> Result<bool, sqlx::Error> {
+    let field = DATABASE_PRIVILEGE_FIELDS[position];
+    let value = row.try_get(position)?;
+    match rev_yn(value) {
+        Some(val) => Ok(val),
+        _ => {
+            log::warn!(r#"Invalid value for privilege "{}": '{}'"#, field, value);
+            Ok(false)
+        }
+    }
+}
+
+impl FromRow<'_, MySqlRow> for DatabasePrivilegeRow {
+    fn from_row(row: &MySqlRow) -> Result<Self, sqlx::Error> {
+        Ok(Self {
+            db: row.try_get("db")?,
+            user: row.try_get("user")?,
+            select_priv: get_mysql_row_priv_field(row, 2)?,
+            insert_priv: get_mysql_row_priv_field(row, 3)?,
+            update_priv: get_mysql_row_priv_field(row, 4)?,
+            delete_priv: get_mysql_row_priv_field(row, 5)?,
+            create_priv: get_mysql_row_priv_field(row, 6)?,
+            drop_priv: get_mysql_row_priv_field(row, 7)?,
+            alter_priv: get_mysql_row_priv_field(row, 8)?,
+            index_priv: get_mysql_row_priv_field(row, 9)?,
+            create_tmp_table_priv: get_mysql_row_priv_field(row, 10)?,
+            lock_tables_priv: get_mysql_row_priv_field(row, 11)?,
+            references_priv: get_mysql_row_priv_field(row, 12)?,
+        })
+    }
+}
+
+/// Get all users + privileges for a single database.
+pub async fn get_database_privileges(
+    database_name: &str,
+    connection: &mut MySqlConnection,
+) -> anyhow::Result<Vec<DatabasePrivilegeRow>> {
+    let unix_user = get_current_unix_user()?;
+    validate_database_name(database_name, &unix_user)?;
+
+    let result = sqlx::query_as::<_, DatabasePrivilegeRow>(&format!(
+        "SELECT {} FROM `db` WHERE `db` = ?",
+        DATABASE_PRIVILEGE_FIELDS
+            .iter()
+            .map(|field| quote_identifier(field))
+            .join(","),
+    ))
+    .bind(database_name)
+    .fetch_all(connection)
+    .await
+    .context("Failed to show database")?;
+
+    Ok(result)
+}
+
+/// Get all database + user + privileges pairs that are owned by the current user.
+pub async fn get_all_database_privileges(
+    connection: &mut MySqlConnection,
+) -> anyhow::Result<Vec<DatabasePrivilegeRow>> {
+    let unix_user = get_current_unix_user()?;
+
+    let result = sqlx::query_as::<_, DatabasePrivilegeRow>(&format!(
+        indoc! {r#"
+          SELECT {} FROM `db` WHERE `db` IN
+          (SELECT DISTINCT `SCHEMA_NAME` AS `database`
+            FROM `information_schema`.`SCHEMATA`
+            WHERE `SCHEMA_NAME` NOT IN ('information_schema', 'performance_schema', 'mysql', 'sys')
+              AND `SCHEMA_NAME` REGEXP ?)
+        "#},
+        DATABASE_PRIVILEGE_FIELDS
+            .iter()
+            .map(|field| format!("`{field}`"))
+            .join(","),
+    ))
+    .bind(create_user_group_matching_regex(&unix_user))
+    .fetch_all(connection)
+    .await
+    .context("Failed to show databases")?;
+
+    Ok(result)
+}
+
+/*************************/
+/* CLI INTERFACE PARSING */
+/*************************/
+
+/// See documentation for [`DatabaseCommand::EditDbPrivs`].
+pub fn parse_privilege_table_cli_arg(arg: &str) -> anyhow::Result<DatabasePrivilegeRow> {
+    let parts: Vec<&str> = arg.split(':').collect();
+    if parts.len() != 3 {
+        anyhow::bail!("Invalid argument format. See `edit-db-privs --help` for more information.");
+    }
+
+    let db = parts[0].to_string();
+    let user = parts[1].to_string();
+    let privs = parts[2].to_string();
+
+    let mut result = DatabasePrivilegeRow {
+        db,
+        user,
+        select_priv: false,
+        insert_priv: false,
+        update_priv: false,
+        delete_priv: false,
+        create_priv: false,
+        drop_priv: false,
+        alter_priv: false,
+        index_priv: false,
+        create_tmp_table_priv: false,
+        lock_tables_priv: false,
+        references_priv: false,
+    };
+
+    for char in privs.chars() {
+        match char {
+            's' => result.select_priv = true,
+            'i' => result.insert_priv = true,
+            'u' => result.update_priv = true,
+            'd' => result.delete_priv = true,
+            'c' => result.create_priv = true,
+            'D' => result.drop_priv = true,
+            'a' => result.alter_priv = true,
+            'I' => result.index_priv = true,
+            't' => result.create_tmp_table_priv = true,
+            'l' => result.lock_tables_priv = true,
+            'r' => result.references_priv = true,
+            'A' => {
+                result.select_priv = true;
+                result.insert_priv = true;
+                result.update_priv = true;
+                result.delete_priv = true;
+                result.create_priv = true;
+                result.drop_priv = true;
+                result.alter_priv = true;
+                result.index_priv = true;
+                result.create_tmp_table_priv = true;
+                result.lock_tables_priv = true;
+                result.references_priv = true;
+            }
+            _ => anyhow::bail!("Invalid privilege character: {}", char),
+        }
+    }
+
+    Ok(result)
+}
+
+/**********************************/
+/* EDITOR CONTENT DISPLAY/DISPLAY */
+/**********************************/
+
+/// Generates a single row of the privileges table for the editor.
+pub fn format_privileges_line_for_editor(
+    privs: &DatabasePrivilegeRow,
+    username_len: usize,
+    database_name_len: usize,
+) -> String {
+    DATABASE_PRIVILEGE_FIELDS
+        .into_iter()
+        .map(|field| match field {
+            "db" => format!("{:width$}", privs.db, width = database_name_len),
+            "user" => format!("{:width$}", privs.user, width = username_len),
+            privilege => format!(
+                "{:width$}",
+                yn(privs.get_privilege_by_name(privilege)),
+                width = db_priv_field_human_readable_name(privilege).len()
+            ),
+        })
+        .join(" ")
+        .trim()
+        .to_string()
+}
+
+const EDITOR_COMMENT: &str = r#"
+# Welcome to the privilege editor.
+# Each line defines what privileges a single user has on a single database.
+# The first two columns respectively represent the database name and the user, and the remaining columns are the privileges.
+# If the user should have a certain privilege, write 'Y', otherwise write 'N'.
+#
+# Lines starting with '#' are comments and will be ignored.
+"#;
+
+/// Generates the content for the privilege editor.
+///
+/// The unix user is used in case there are no privileges to edit,
+/// so that the user can see an example line based on their username.
+pub fn generate_editor_content_from_privilege_data(
+    privilege_data: &[DatabasePrivilegeRow],
+    unix_user: &str,
+) -> String {
+    let example_user = format!("{}_user", unix_user);
+    let example_db = format!("{}_db", unix_user);
+
+    // NOTE: `.max()`` fails when the iterator is empty.
+    //       In this case, we know that the only fields in the
+    //       editor will be the example user and example db name.
+    //       Hence, it's put as the fallback value, despite not really
+    //       being a "fallback" in the normal sense.
+    let longest_username = privilege_data
+        .iter()
+        .map(|p| p.user.len())
+        .max()
+        .unwrap_or(example_user.len());
+
+    let longest_database_name = privilege_data
+        .iter()
+        .map(|p| p.db.len())
+        .max()
+        .unwrap_or(example_db.len());
+
+    let mut header: Vec<_> = DATABASE_PRIVILEGE_FIELDS
+        .into_iter()
+        .map(db_priv_field_human_readable_name)
+        .collect();
+
+    // Pad the first two columns with spaces to align the privileges.
+    header[0] = format!("{:width$}", header[0], width = longest_database_name);
+    header[1] = format!("{:width$}", header[1], width = longest_username);
+
+    let example_line = format_privileges_line_for_editor(
+        &DatabasePrivilegeRow {
+            db: example_db,
+            user: example_user,
+            select_priv: true,
+            insert_priv: true,
+            update_priv: true,
+            delete_priv: true,
+            create_priv: false,
+            drop_priv: false,
+            alter_priv: false,
+            index_priv: false,
+            create_tmp_table_priv: false,
+            lock_tables_priv: false,
+            references_priv: false,
+        },
+        longest_username,
+        longest_database_name,
+    );
+
+    format!(
+        "{}\n{}\n{}",
+        EDITOR_COMMENT,
+        header.join(" "),
+        if privilege_data.is_empty() {
+            format!("# {}", example_line)
+        } else {
+            privilege_data
+                .iter()
+                .map(|privs| {
+                    format_privileges_line_for_editor(
+                        privs,
+                        longest_username,
+                        longest_database_name,
+                    )
+                })
+                .join("\n")
+        }
+    )
+}
+
+#[derive(Debug)]
+enum PrivilegeRowParseResult {
+    PrivilegeRow(DatabasePrivilegeRow),
+    ParserError(anyhow::Error),
+    TooFewFields(usize),
+    TooManyFields(usize),
+    Header,
+    Comment,
+    Empty,
+}
+
+#[inline]
+fn parse_privilege_cell_from_editor(yn: &str, name: &str) -> anyhow::Result<bool> {
+    rev_yn(yn)
+        .ok_or_else(|| anyhow!("Expected Y or N, found {}", yn))
+        .context(format!("Could not parse {} privilege", name))
+}
+
+#[inline]
+fn editor_row_is_header(row: &str) -> bool {
+    row.split_ascii_whitespace()
+        .zip(DATABASE_PRIVILEGE_FIELDS.iter())
+        .map(|(field, priv_name)| (field, db_priv_field_human_readable_name(priv_name)))
+        .all(|(field, header_field)| field == header_field)
+}
+
+/// Parse a single row of the privileges table from the editor.
+fn parse_privilege_row_from_editor(row: &str) -> PrivilegeRowParseResult {
+    if row.starts_with('#') || row.starts_with("//") {
+        return PrivilegeRowParseResult::Comment;
+    }
+
+    if row.trim().is_empty() {
+        return PrivilegeRowParseResult::Empty;
+    }
+
+    let parts: Vec<&str> = row.trim().split_ascii_whitespace().collect();
+
+    match parts.len() {
+        n if (n < DATABASE_PRIVILEGE_FIELDS.len()) => {
+            return PrivilegeRowParseResult::TooFewFields(n)
+        }
+        n if (n > DATABASE_PRIVILEGE_FIELDS.len()) => {
+            return PrivilegeRowParseResult::TooManyFields(n)
+        }
+        _ => {}
+    }
+
+    if editor_row_is_header(row) {
+        return PrivilegeRowParseResult::Header;
+    }
+
+    let row = DatabasePrivilegeRow {
+        db: (*parts.first().unwrap()).to_owned(),
+        user: (*parts.get(1).unwrap()).to_owned(),
+        select_priv: match parse_privilege_cell_from_editor(
+            parts.get(2).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[2],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        insert_priv: match parse_privilege_cell_from_editor(
+            parts.get(3).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[3],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        update_priv: match parse_privilege_cell_from_editor(
+            parts.get(4).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[4],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        delete_priv: match parse_privilege_cell_from_editor(
+            parts.get(5).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[5],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        create_priv: match parse_privilege_cell_from_editor(
+            parts.get(6).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[6],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        drop_priv: match parse_privilege_cell_from_editor(
+            parts.get(7).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[7],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        alter_priv: match parse_privilege_cell_from_editor(
+            parts.get(8).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[8],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        index_priv: match parse_privilege_cell_from_editor(
+            parts.get(9).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[9],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        create_tmp_table_priv: match parse_privilege_cell_from_editor(
+            parts.get(10).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[10],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        lock_tables_priv: match parse_privilege_cell_from_editor(
+            parts.get(11).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[11],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+        references_priv: match parse_privilege_cell_from_editor(
+            parts.get(12).unwrap(),
+            DATABASE_PRIVILEGE_FIELDS[12],
+        ) {
+            Ok(p) => p,
+            Err(e) => return PrivilegeRowParseResult::ParserError(e),
+        },
+    };
+
+    PrivilegeRowParseResult::PrivilegeRow(row)
+}
+
+// TODO: return better errors
+
+pub fn parse_privilege_data_from_editor_content(
+    content: String,
+) -> anyhow::Result<Vec<DatabasePrivilegeRow>> {
+    content
+        .trim()
+        .split('\n')
+        .map(|line| line.trim())
+        .map(parse_privilege_row_from_editor)
+        .map(|result| match result {
+            PrivilegeRowParseResult::PrivilegeRow(row) => Ok(Some(row)),
+            PrivilegeRowParseResult::ParserError(e) => Err(e),
+            PrivilegeRowParseResult::TooFewFields(n) => Err(anyhow!(
+                "Too few fields in line. Expected to find {} fields, found {}",
+                DATABASE_PRIVILEGE_FIELDS.len(),
+                n
+            )),
+            PrivilegeRowParseResult::TooManyFields(n) => Err(anyhow!(
+                "Too many fields in line. Expected to find {} fields, found {}",
+                DATABASE_PRIVILEGE_FIELDS.len(),
+                n
+            )),
+            PrivilegeRowParseResult::Header => Ok(None),
+            PrivilegeRowParseResult::Comment => Ok(None),
+            PrivilegeRowParseResult::Empty => Ok(None),
+        })
+        .filter_map(|result| result.transpose())
+        .collect::<anyhow::Result<Vec<DatabasePrivilegeRow>>>()
+}
+
+/*****************************/
+/* CALCULATE PRIVILEGE DIFFS */
+/*****************************/
+
+/// This struct represents encapsulates the differences between two
+/// instances of privilege sets for a single user on a single database.
+///
+/// The `User` and `Database` are the same for both instances.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, PartialOrd, Ord)]
+pub struct DatabasePrivilegeRowDiff {
+    pub db: String,
+    pub user: String,
+    pub diff: BTreeSet<DatabasePrivilegeChange>,
+}
+
+/// This enum represents a change for a single privilege.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, PartialOrd, Ord)]
+pub enum DatabasePrivilegeChange {
+    YesToNo(String),
+    NoToYes(String),
+}
+
+impl DatabasePrivilegeChange {
+    pub fn new(p1: bool, p2: bool, name: &str) -> Option<DatabasePrivilegeChange> {
+        match (p1, p2) {
+            (true, false) => Some(DatabasePrivilegeChange::YesToNo(name.to_owned())),
+            (false, true) => Some(DatabasePrivilegeChange::NoToYes(name.to_owned())),
+            _ => None,
+        }
+    }
+}
+
+/// This enum encapsulates whether a [`DatabasePrivilegeRow`] was intrduced, modified or deleted.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, PartialOrd, Ord)]
+pub enum DatabasePrivilegesDiff {
+    New(DatabasePrivilegeRow),
+    Modified(DatabasePrivilegeRowDiff),
+    Deleted(DatabasePrivilegeRow),
+}
+
+/// This function calculates the differences between two sets of database privileges.
+/// It returns a set of [`DatabasePrivilegesDiff`] that can be used to display or
+/// apply a set of privilege modifications to the database.
+pub fn diff_privileges(
+    from: &[DatabasePrivilegeRow],
+    to: &[DatabasePrivilegeRow],
+) -> BTreeSet<DatabasePrivilegesDiff> {
+    let from_lookup_table: HashMap<(String, String), DatabasePrivilegeRow> = HashMap::from_iter(
+        from.iter()
+            .cloned()
+            .map(|p| ((p.db.clone(), p.user.clone()), p)),
+    );
+
+    let to_lookup_table: HashMap<(String, String), DatabasePrivilegeRow> = HashMap::from_iter(
+        to.iter()
+            .cloned()
+            .map(|p| ((p.db.clone(), p.user.clone()), p)),
+    );
+
+    let mut result = BTreeSet::new();
+
+    for p in to {
+        if let Some(old_p) = from_lookup_table.get(&(p.db.clone(), p.user.clone())) {
+            let diff = old_p.diff(p);
+            if !diff.diff.is_empty() {
+                result.insert(DatabasePrivilegesDiff::Modified(diff));
+            }
+        } else {
+            result.insert(DatabasePrivilegesDiff::New(p.clone()));
+        }
+    }
+
+    for p in from {
+        if !to_lookup_table.contains_key(&(p.db.clone(), p.user.clone())) {
+            result.insert(DatabasePrivilegesDiff::Deleted(p.clone()));
+        }
+    }
+
+    result
+}
+
+/// Uses the result of [`diff_privileges`] to modify privileges in the database.
+pub async fn apply_privilege_diffs(
+    diffs: BTreeSet<DatabasePrivilegesDiff>,
+    connection: &mut MySqlConnection,
+) -> anyhow::Result<()> {
+    for diff in diffs {
+        match diff {
+            DatabasePrivilegesDiff::New(p) => {
+                let tables = DATABASE_PRIVILEGE_FIELDS
+                    .iter()
+                    .map(|field| format!("`{field}`"))
+                    .join(",");
+
+                let question_marks = std::iter::repeat("?")
+                    .take(DATABASE_PRIVILEGE_FIELDS.len())
+                    .join(",");
+
+                sqlx::query(
+                    format!("INSERT INTO `db` ({}) VALUES ({})", tables, question_marks).as_str(),
+                )
+                .bind(p.db)
+                .bind(p.user)
+                .bind(yn(p.select_priv))
+                .bind(yn(p.insert_priv))
+                .bind(yn(p.update_priv))
+                .bind(yn(p.delete_priv))
+                .bind(yn(p.create_priv))
+                .bind(yn(p.drop_priv))
+                .bind(yn(p.alter_priv))
+                .bind(yn(p.index_priv))
+                .bind(yn(p.create_tmp_table_priv))
+                .bind(yn(p.lock_tables_priv))
+                .bind(yn(p.references_priv))
+                .execute(&mut *connection)
+                .await?;
+            }
+            DatabasePrivilegesDiff::Modified(p) => {
+                let tables = p
+                    .diff
+                    .iter()
+                    .map(|diff| match diff {
+                        DatabasePrivilegeChange::YesToNo(name) => format!("`{}` = 'N'", name),
+                        DatabasePrivilegeChange::NoToYes(name) => format!("`{}` = 'Y'", name),
+                    })
+                    .join(",");
+
+                sqlx::query(
+                    format!("UPDATE `db` SET {} WHERE `db` = ? AND `user` = ?", tables).as_str(),
+                )
+                .bind(p.db)
+                .bind(p.user)
+                .execute(&mut *connection)
+                .await?;
+            }
+            DatabasePrivilegesDiff::Deleted(p) => {
+                sqlx::query("DELETE FROM `db` WHERE `db` = ? AND `user` = ?")
+                    .bind(p.db)
+                    .bind(p.user)
+                    .execute(&mut *connection)
+                    .await?;
+            }
+        }
+    }
+    Ok(())
+}
+
+fn display_privilege_cell(diff: &DatabasePrivilegeRowDiff) -> String {
+    diff.diff
+        .iter()
+        .map(|change| match change {
+            DatabasePrivilegeChange::YesToNo(name) => {
+                format!("{}: Y -> N", db_priv_field_human_readable_name(name))
+            }
+            DatabasePrivilegeChange::NoToYes(name) => {
+                format!("{}: N -> Y", db_priv_field_human_readable_name(name))
+            }
+        })
+        .join("\n")
+}
+
+/// Displays the difference between two sets of database privileges.
+pub fn display_privilege_diffs(diffs: &BTreeSet<DatabasePrivilegesDiff>) -> String {
+    let mut table = Table::new();
+    table.set_titles(row!["Database", "User", "Privilege diff",]);
+    for row in diffs {
+        match row {
+            DatabasePrivilegesDiff::New(p) => {
+                table.add_row(row![
+                    p.db,
+                    p.user,
+                    "(New user)\n".to_string()
+                        + &display_privilege_cell(
+                            &DatabasePrivilegeRow::empty(&p.db, &p.user).diff(p)
+                        )
+                ]);
+            }
+            DatabasePrivilegesDiff::Modified(p) => {
+                table.add_row(row![p.db, p.user, display_privilege_cell(p),]);
+            }
+            DatabasePrivilegesDiff::Deleted(p) => {
+                table.add_row(row![
+                    p.db,
+                    p.user,
+                    "(All privileges removed)\n".to_string()
+                        + &display_privilege_cell(
+                            &p.diff(&DatabasePrivilegeRow::empty(&p.db, &p.user))
+                        )
+                ]);
+            }
+        }
+    }
+
+    table.to_string()
+}
+
+/*********/
+/* TESTS */
+/*********/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_database_privilege_change_creation() {
+        assert_eq!(
+            DatabasePrivilegeChange::new(true, false, "test"),
+            Some(DatabasePrivilegeChange::YesToNo("test".to_owned()))
+        );
+        assert_eq!(
+            DatabasePrivilegeChange::new(false, true, "test"),
+            Some(DatabasePrivilegeChange::NoToYes("test".to_owned()))
+        );
+        assert_eq!(DatabasePrivilegeChange::new(true, true, "test"), None);
+        assert_eq!(DatabasePrivilegeChange::new(false, false, "test"), None);
+    }
+
+    #[test]
+    fn test_diff_privileges() {
+        let row_to_be_modified = DatabasePrivilegeRow {
+            db: "db".to_owned(),
+            user: "user".to_owned(),
+            select_priv: true,
+            insert_priv: true,
+            update_priv: true,
+            delete_priv: true,
+            create_priv: true,
+            drop_priv: true,
+            alter_priv: true,
+            index_priv: false,
+            create_tmp_table_priv: true,
+            lock_tables_priv: true,
+            references_priv: false,
+        };
+
+        let mut row_to_be_deleted = row_to_be_modified.clone();
+        "user2".clone_into(&mut row_to_be_deleted.user);
+
+        let from = vec![row_to_be_modified.clone(), row_to_be_deleted.clone()];
+
+        let mut modified_row = row_to_be_modified.clone();
+        modified_row.select_priv = false;
+        modified_row.insert_priv = false;
+        modified_row.index_priv = true;
+
+        let mut new_row = row_to_be_modified.clone();
+        "user3".clone_into(&mut new_row.user);
+
+        let to = vec![modified_row.clone(), new_row.clone()];
+
+        let diffs = diff_privileges(&from, &to);
+
+        assert_eq!(
+            diffs,
+            BTreeSet::from_iter(vec![
+                DatabasePrivilegesDiff::Deleted(row_to_be_deleted),
+                DatabasePrivilegesDiff::Modified(DatabasePrivilegeRowDiff {
+                    db: "db".to_owned(),
+                    user: "user".to_owned(),
+                    diff: BTreeSet::from_iter(vec![
+                        DatabasePrivilegeChange::YesToNo("select_priv".to_owned()),
+                        DatabasePrivilegeChange::YesToNo("insert_priv".to_owned()),
+                        DatabasePrivilegeChange::NoToYes("index_priv".to_owned()),
+                    ]),
+                }),
+                DatabasePrivilegesDiff::New(new_row),
+            ])
+        );
+    }
+
+    #[test]
+    fn ensure_generated_and_parsed_editor_content_is_equal() {
+        let permissions = vec![
+            DatabasePrivilegeRow {
+                db: "db".to_owned(),
+                user: "user".to_owned(),
+                select_priv: true,
+                insert_priv: true,
+                update_priv: true,
+                delete_priv: true,
+                create_priv: true,
+                drop_priv: true,
+                alter_priv: true,
+                index_priv: true,
+                create_tmp_table_priv: true,
+                lock_tables_priv: true,
+                references_priv: true,
+            },
+            DatabasePrivilegeRow {
+                db: "db2".to_owned(),
+                user: "user2".to_owned(),
+                select_priv: false,
+                insert_priv: false,
+                update_priv: false,
+                delete_priv: false,
+                create_priv: false,
+                drop_priv: false,
+                alter_priv: false,
+                index_priv: false,
+                create_tmp_table_priv: false,
+                lock_tables_priv: false,
+                references_priv: false,
+            },
+        ];
+
+        let content = generate_editor_content_from_privilege_data(&permissions, "user");
+
+        let parsed_permissions = parse_privilege_data_from_editor_content(content).unwrap();
+
+        assert_eq!(permissions, parsed_permissions);
+    }
+}

src/server/entrypoint.rs

@@ -0,0 +1,89 @@
+use futures_util::{SinkExt, StreamExt};
+use sqlx::MySqlConnection;
+use tokio::net::UnixStream;
+use tokio_serde::{formats::Bincode, Framed as SerdeFramed};
+use tokio_util::codec::{Framed, LengthDelimitedCodec};
+
+// use crate::server::
+
+use crate::server::protocol::{Request, Response};
+
+use super::{
+    common::UnixUser, database_operations::{create_databases, drop_databases}, user_operations::{create_database_users, drop_database_users, set_password_for_database_user}
+};
+
+pub type ClientToServerMessageStream<'a> = SerdeFramed<
+    Framed<&'a mut UnixStream, LengthDelimitedCodec>,
+    Request,
+    Response,
+    Bincode<Request, Response>,
+>;
+
+pub async fn run_server(
+    socket: &mut UnixStream,
+    unix_user: &UnixUser,
+    db_connection: &mut MySqlConnection,
+) -> anyhow::Result<()> {
+    let length_delimited = Framed::new(socket, LengthDelimitedCodec::new());
+    let mut stream: ClientToServerMessageStream =
+        tokio_serde::Framed::new(length_delimited, Bincode::default());
+
+    // TODO: better error handling
+    let request = match stream.next().await {
+        Some(Ok(request)) => request,
+        Some(Err(e)) => return Err(e.into()),
+        None => return Err(anyhow::anyhow!("No request received")),
+    };
+
+    match request {
+        Request::CreateDatabases(databases) => {
+            let result = create_databases(databases, unix_user, db_connection).await;
+            stream.send(Response::CreateDatabases(result)).await?;
+            stream.flush().await?;
+        }
+        Request::DropDatabases(databases) => {
+            let result = drop_databases(databases, unix_user, db_connection).await;
+            stream.send(Response::DropDatabases(result)).await?;
+            stream.flush().await?;
+        }
+        Request::ListDatabases => {
+            println!("Listing databases");
+            // let result = list_databases(unix_user, db_connection).await;
+            // stream.send(Response::ListDatabases(result)).await?;
+            // stream.flush().await?;
+        }
+        Request::ListPrivileges(users) => {
+            println!("Listing privileges for users: {:?}", users);
+        }
+        Request::ModifyPrivileges(()) => {
+            println!("Modifying privileges");
+        }
+        Request::CreateUsers(db_users) => {
+            let result = create_database_users(db_users, unix_user, db_connection).await;
+            stream.send(Response::CreateUsers(result)).await?;
+            stream.flush().await?;
+        }
+        Request::DropUsers(db_users) => {
+            let result = drop_database_users(db_users, unix_user, db_connection).await;
+            stream.send(Response::DropUsers(result)).await?;
+            stream.flush().await?;
+        }
+        Request::PasswdUser(db_user, password) => {
+            let result =
+                set_password_for_database_user(&db_user, &password, unix_user, db_connection).await;
+            stream.send(Response::PasswdUser(result)).await?;
+            stream.flush().await?;
+        }
+        Request::ListUsers(db_users) => {
+            println!("Listing users: {:?}", db_users);
+        }
+        Request::LockUsers(db_users) => {
+            println!("Locking users: {:?}", db_users);
+        }
+        Request::UnlockUsers(db_users) => {
+            println!("Unlocking users: {:?}", db_users);
+        }
+    }
+
+    Ok(())
+}

src/server/input_sanitization.rs

@@ -0,0 +1,251 @@
+use super::common::UnixUser;
+
+use serde::{Deserialize, Serialize};
+
+const MAX_NAME_LENGTH: usize = 64;
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Serialize, Deserialize)]
+pub enum NameValidationError {
+    EmptyString,
+    InvalidCharacters,
+    TooLong,
+}
+
+pub fn validate_name(name: &str) -> Result<(), NameValidationError> {
+    if name.is_empty() {
+        Err(NameValidationError::EmptyString)
+    } else if name.len() > MAX_NAME_LENGTH {
+        Err(NameValidationError::TooLong)
+    } else if !name
+        .chars()
+        .all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '-')
+    {
+        Err(NameValidationError::InvalidCharacters)
+    } else {
+        Ok(())
+    }
+}
+
+// TODO: move to cli
+
+// pub fn validate_name_or_error(name: &str, db_or_user: DbOrUser) -> anyhow::Result<()> {
+//     match validate_name(name) {
+//         NameValidationError::Valid => Ok(()),
+//         NameValidationError::EmptyString => {
+//             anyhow::bail!("{} name cannot be empty.", db_or_user.capitalized())
+//         }
+//         NameValidationError::TooLong => anyhow::bail!(
+//             "{} is too long. Maximum length is 64 characters.",
+//             db_or_user.capitalized()
+//         ),
+//         NameValidationError::InvalidCharacters => anyhow::bail!(
+//             indoc! {r#"
+//               Invalid characters in {} name: '{}'
+
+//               Only A-Z, a-z, 0-9, _ (underscore) and - (dash) are permitted.
+//             "#},
+//             db_or_user.lowercased(),
+//             name
+//         ),
+//     }
+// }
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Serialize, Deserialize)]
+pub enum OwnerValidationError {
+    // The name is valid, but none of the given prefixes matched the name
+    NoMatch,
+
+    // The name is empty, which is invalid
+    StringEmpty,
+
+    // The name is in the format "_<postfix>", which is invalid
+    MissingPrefix,
+
+    // The name is in the format "<prefix>_", which is invalid
+    MissingPostfix,
+}
+
+pub fn validate_ownership_by_unix_user(
+    name: &str,
+    user: &UnixUser,
+) -> Result<(), OwnerValidationError> {
+    let prefixes = std::iter::once(user.username.clone())
+        .chain(user.groups.iter().cloned())
+        .collect::<Vec<String>>();
+
+    validate_ownership_by_prefixes(name, &prefixes)
+}
+
+/// Core logic for validating the ownership of a database name.
+/// This function checks if the given name matches any of the given prefixes.
+/// These prefixes will in most cases be the user's unix username and any
+/// unix groups the user is a member of.
+pub fn validate_ownership_by_prefixes(
+    name: &str,
+    prefixes: &[String],
+) -> Result<(), OwnerValidationError> {
+    if name.is_empty() {
+        return Err(OwnerValidationError::StringEmpty);
+    }
+
+    if name.starts_with('_') {
+        return Err(OwnerValidationError::MissingPrefix);
+    }
+
+    let (prefix, _) = match name.split_once('_') {
+        Some(pair) => pair,
+        None => return Err(OwnerValidationError::MissingPostfix),
+    };
+
+    if !prefixes.iter().any(|g| g == prefix) {
+        return Err(OwnerValidationError::NoMatch);
+    }
+
+    Ok(())
+}
+
+// TODO: move to cli
+
+/// Validate the ownership of a database name or database user name.
+/// This function takes the name of a database or user and a unix user,
+/// for which it fetches the user's groups. It then checks if the name
+/// is prefixed with the user's username or any of the user's groups.
+// pub fn validate_ownership_or_error<'a>(
+//     name: &'a str,
+//     user: &User,
+//     db_or_user: DbOrUser,
+// ) -> anyhow::Result<&'a str> {
+//     let user_groups = get_unix_groups(user)?;
+//     let prefixes = std::iter::once(user.name.clone())
+//         .chain(user_groups.iter().map(|g| g.name.clone()))
+//         .collect::<Vec<String>>();
+
+//     match validate_ownership_by_prefixes(name, &prefixes) {
+//         OwnerValidationResult::Match => Ok(name),
+//         OwnerValidationResult::NoMatch => {
+//             anyhow::bail!(
+//                 indoc! {r#"
+//                   Invalid {} name prefix: '{}' does not match your username or any of your groups.
+//                   Are you sure you are allowed to create {} names with this prefix?
+
+//                   Allowed prefixes:
+//                     - {}
+//                   {}
+//                 "#},
+//                 db_or_user.lowercased(),
+//                 name,
+//                 db_or_user.lowercased(),
+//                 user.name,
+//                 user_groups
+//                     .iter()
+//                     .filter(|g| g.name != user.name)
+//                     .map(|g| format!("  - {}", g.name))
+//                     .sorted()
+//                     .join("\n"),
+//             );
+//         }
+//         _ => anyhow::bail!(
+//             "'{}' is not a valid {} name.",
+//             name,
+//             db_or_user.lowercased()
+//         ),
+//     }
+// }
+
+#[inline]
+pub fn quote_literal(s: &str) -> String {
+    format!("'{}'", s.replace('\'', r"\'"))
+}
+
+#[inline]
+pub fn quote_identifier(s: &str) -> String {
+    format!("`{}`", s.replace('`', r"\`"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_quote_literal() {
+        let payload = "' OR 1=1 --";
+        assert_eq!(quote_literal(payload), r#"'\' OR 1=1 --'"#);
+    }
+
+    #[test]
+    fn test_quote_identifier() {
+        let payload = "` OR 1=1 --";
+        assert_eq!(quote_identifier(payload), r#"`\` OR 1=1 --`"#);
+    }
+
+    #[test]
+    fn test_validate_name() {
+        assert_eq!(validate_name(""), Err(NameValidationError::EmptyString));
+        assert_eq!(validate_name("abcdefghijklmnopqrstuvwxyz"), Ok(()));
+        assert_eq!(validate_name("ABCDEFGHIJKLMNOPQRSTUVWXYZ"), Ok(()));
+        assert_eq!(validate_name("0123456789_-"), Ok(()));
+
+        for c in "\n\t\r !@#$%^&*()+=[]{}|;:,.<>?/".chars() {
+            assert_eq!(
+                validate_name(&c.to_string()),
+                Err(NameValidationError::InvalidCharacters)
+            );
+        }
+
+        assert_eq!(validate_name(&"a".repeat(MAX_NAME_LENGTH)), Ok(()));
+
+        assert_eq!(
+            validate_name(&"a".repeat(MAX_NAME_LENGTH + 1)),
+            Err(NameValidationError::TooLong)
+        );
+    }
+
+    #[test]
+    fn test_validate_owner_by_prefixes() {
+        let prefixes = vec!["user".to_string(), "group".to_string()];
+
+        assert_eq!(
+            validate_ownership_by_prefixes("", &prefixes),
+            Err(OwnerValidationError::StringEmpty)
+        );
+
+        assert_eq!(
+            validate_ownership_by_prefixes("user", &prefixes),
+            Err(OwnerValidationError::MissingPostfix)
+        );
+        assert_eq!(
+            validate_ownership_by_prefixes("something", &prefixes),
+            Err(OwnerValidationError::MissingPostfix)
+        );
+        assert_eq!(
+            validate_ownership_by_prefixes("user-testdb", &prefixes),
+            Err(OwnerValidationError::MissingPostfix)
+        );
+
+        assert_eq!(
+            validate_ownership_by_prefixes("_testdb", &prefixes),
+            Err(OwnerValidationError::MissingPrefix)
+        );
+
+        assert_eq!(
+            validate_ownership_by_prefixes("user_testdb", &prefixes),
+            Ok(())
+        );
+        assert_eq!(
+            validate_ownership_by_prefixes("group_testdb", &prefixes),
+            Ok(())
+        );
+        assert_eq!(
+            validate_ownership_by_prefixes("group_test_db", &prefixes),
+            Ok(())
+        );
+        assert_eq!(
+            validate_ownership_by_prefixes("group_test-db", &prefixes),
+            Ok(())
+        );
+
+        assert_eq!(
+            validate_ownership_by_prefixes("nonexistent_testdb", &prefixes),
+            Err(OwnerValidationError::NoMatch)
+        );
+    }
+}

src/server/protocol.rs

@@ -0,0 +1,45 @@
+use serde::{Deserialize, Serialize};
+
+use super::{database_operations::{CreateDatabasesOutput, DropDatabasesOutput}, user_operations::{
+    CreateUsersOutput, DropUsersOutput, LockUsersOutput, SetPasswordOutput, UnlockUsersOutput,
+}};
+
+#[non_exhaustive]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum Request {
+    CreateDatabases(Vec<String>),
+    DropDatabases(Vec<String>),
+    ListDatabases,
+    ListPrivileges(Vec<String>),
+    ModifyPrivileges(()), // what data should be sent with this command? Who should calculate the diff?
+
+    CreateUsers(Vec<String>),
+    DropUsers(Vec<String>),
+    PasswdUser(String, String),
+    ListUsers(Option<Vec<String>>),
+    LockUsers(Vec<String>),
+    UnlockUsers(Vec<String>),
+}
+
+// TODO: include a generic "message" that will display a message to the user?
+
+#[non_exhaustive]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum Response {
+    // Specific data for specific commands
+    CreateDatabases(CreateDatabasesOutput),
+    DropDatabases(DropDatabasesOutput),
+    // ListDatabases(ListDatabasesOutput),
+    // ListPrivileges(ListPrivilegesOutput),
+    CreateUsers(CreateUsersOutput),
+    DropUsers(DropUsersOutput),
+    PasswdUser(SetPasswordOutput),
+    ListUsers(()), // what data should be sent with this response?
+    LockUsers(LockUsersOutput),
+    UnlockUsers(UnlockUsersOutput),
+
+    // Generic responses
+    OperationAborted,
+    Error(String),
+    Exit,
+}

src/server/user_operations.rs

@@ -0,0 +1,395 @@
+use std::collections::BTreeMap;
+
+use serde::{Deserialize, Serialize};
+
+use sqlx::prelude::*;
+use sqlx::MySqlConnection;
+
+use super::common::create_user_group_matching_regex;
+use super::common::UnixUser;
+use super::input_sanitization::{
+    quote_literal, validate_name, validate_ownership_by_unix_user, NameValidationError,
+    OwnerValidationError,
+};
+
+// NOTE: this function is unsafe because it does no input validation.
+async fn unsafe_user_exists(
+    db_user: &str,
+    connection: &mut MySqlConnection,
+) -> Result<bool, sqlx::Error> {
+    sqlx::query(
+        r#"
+          SELECT EXISTS(
+            SELECT 1
+            FROM `mysql`.`user`
+            WHERE `User` = ?
+          )
+        "#,
+    )
+    .bind(db_user)
+    .fetch_one(connection)
+    .await
+    .map(|row| row.get::<bool, _>(0))
+}
+
+pub type CreateUsersOutput = BTreeMap<String, Result<(), CreateUserError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum CreateUserError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    UserAlreadyExists,
+    MySqlError(String),
+}
+
+pub async fn create_database_users(
+    db_users: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> CreateUsersOutput {
+    let mut results = BTreeMap::new();
+
+    for db_user in db_users {
+        if let Err(err) = validate_name(&db_user) {
+            results.insert(db_user, Err(CreateUserError::SanitizationError(err)));
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&db_user, unix_user) {
+            results.insert(db_user, Err(CreateUserError::OwnershipError(err)));
+            continue;
+        }
+
+        match unsafe_user_exists(&db_user, &mut *connection).await {
+            Ok(true) => {
+                results.insert(db_user, Err(CreateUserError::UserAlreadyExists));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(CreateUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        let result = sqlx::query(format!("CREATE USER {}@'%'", quote_literal(&db_user),).as_str())
+            .execute(&mut *connection)
+            .await
+            .map(|_| ())
+            .map_err(|err| CreateUserError::MySqlError(err.to_string()));
+
+        results.insert(db_user, result);
+    }
+
+    results
+}
+
+pub type DropUsersOutput = BTreeMap<String, Result<(), DropUserError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum DropUserError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    UserDoesNotExist,
+    MySqlError(String),
+}
+
+pub async fn drop_database_users(
+    db_users: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> DropUsersOutput {
+    let mut results = BTreeMap::new();
+
+    for db_user in db_users {
+        if let Err(err) = validate_name(&db_user) {
+            results.insert(db_user, Err(DropUserError::SanitizationError(err)));
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&db_user, unix_user) {
+            results.insert(db_user, Err(DropUserError::OwnershipError(err)));
+            continue;
+        }
+
+        match unsafe_user_exists(&db_user, &mut *connection).await {
+            Ok(false) => {
+                results.insert(db_user, Err(DropUserError::UserDoesNotExist));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(DropUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        let result = sqlx::query(format!("DROP USER {}@'%'", quote_literal(&db_user),).as_str())
+            .execute(&mut *connection)
+            .await
+            .map(|_| ())
+            .map_err(|err| DropUserError::MySqlError(err.to_string()));
+
+        results.insert(db_user, result);
+    }
+
+    results
+}
+
+pub type SetPasswordOutput = Result<(), SetPasswordError>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum SetPasswordError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    UserDoesNotExist,
+    MySqlError(String),
+}
+
+pub async fn set_password_for_database_user(
+    db_user: &str,
+    password: &str,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> SetPasswordOutput {
+    if let Err(err) = validate_name(db_user) {
+        return Err(SetPasswordError::SanitizationError(err));
+    }
+
+    if let Err(err) = validate_ownership_by_unix_user(db_user, unix_user) {
+        return Err(SetPasswordError::OwnershipError(err));
+    }
+
+    match unsafe_user_exists(db_user, &mut *connection).await {
+        Ok(false) => return Err(SetPasswordError::UserDoesNotExist),
+        Err(err) => return Err(SetPasswordError::MySqlError(err.to_string())),
+        _ => {}
+    }
+
+    sqlx::query(
+        format!(
+            "ALTER USER {}@'%' IDENTIFIED BY {}",
+            quote_literal(db_user),
+            quote_literal(password).as_str()
+        )
+        .as_str(),
+    )
+    .execute(&mut *connection)
+    .await
+    .map(|_| ())
+    .map_err(|err| SetPasswordError::MySqlError(err.to_string()))
+}
+
+// NOTE: this function is unsafe because it does no input validation.
+async fn database_user_is_locked_unsafe(
+    db_user: &str,
+    connection: &mut MySqlConnection,
+) -> Result<bool, sqlx::Error> {
+    sqlx::query(
+        r#"
+          SELECT JSON_EXTRACT(`mysql`.`global_priv`.`priv`, "$.account_locked") = 'true'
+          FROM `mysql`.`global_priv`
+          WHERE `User` = ?
+          AND `Host` = '%'
+        "#,
+    )
+    .bind(db_user)
+    .fetch_one(connection)
+    .await
+    .map(|row| row.get::<bool, _>(0))
+}
+
+pub type LockUsersOutput = BTreeMap<String, Result<(), LockUserError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum LockUserError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    UserDoesNotExist,
+    UserIsAlreadyLocked,
+    MySqlError(String),
+}
+
+pub async fn lock_database_users(
+    db_users: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> LockUsersOutput {
+    let mut results = BTreeMap::new();
+
+    for db_user in db_users {
+        if let Err(err) = validate_name(&db_user) {
+            results.insert(db_user, Err(LockUserError::SanitizationError(err)));
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&db_user, unix_user) {
+            results.insert(db_user, Err(LockUserError::OwnershipError(err)));
+            continue;
+        }
+
+        match unsafe_user_exists(&db_user, &mut *connection).await {
+            Ok(false) => {
+                results.insert(db_user, Err(LockUserError::UserDoesNotExist));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(LockUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        match database_user_is_locked_unsafe(&db_user, &mut *connection).await {
+            Ok(true) => {
+                results.insert(db_user, Err(LockUserError::UserIsAlreadyLocked));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(LockUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        let result = sqlx::query(
+            format!("ALTER USER {}@'%' ACCOUNT LOCK", quote_literal(&db_user),).as_str(),
+        )
+        .execute(&mut *connection)
+        .await
+        .map(|_| ())
+        .map_err(|err| LockUserError::MySqlError(err.to_string()));
+
+        results.insert(db_user, result);
+    }
+
+    results
+}
+
+pub type UnlockUsersOutput = BTreeMap<String, Result<(), UnlockUserError>>;
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum UnlockUserError {
+    SanitizationError(NameValidationError),
+    OwnershipError(OwnerValidationError),
+    UserDoesNotExist,
+    UserIsAlreadyUnlocked,
+    MySqlError(String),
+}
+
+pub async fn unlock_database_user(
+    db_users: Vec<String>,
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> UnlockUsersOutput {
+    let mut results = BTreeMap::new();
+
+    for db_user in db_users {
+        if let Err(err) = validate_name(&db_user) {
+            results.insert(db_user, Err(UnlockUserError::SanitizationError(err)));
+            continue;
+        }
+
+        if let Err(err) = validate_ownership_by_unix_user(&db_user, unix_user) {
+            results.insert(db_user, Err(UnlockUserError::OwnershipError(err)));
+            continue;
+        }
+
+        match unsafe_user_exists(&db_user, &mut *connection).await {
+            Ok(false) => {
+                results.insert(db_user, Err(UnlockUserError::UserDoesNotExist));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(UnlockUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        match database_user_is_locked_unsafe(&db_user, &mut *connection).await {
+            Ok(false) => {
+                results.insert(db_user, Err(UnlockUserError::UserIsAlreadyUnlocked));
+                continue;
+            }
+            Err(err) => {
+                results.insert(db_user, Err(UnlockUserError::MySqlError(err.to_string())));
+                continue;
+            }
+            _ => {}
+        }
+
+        let result = sqlx::query(
+            format!("ALTER USER {}@'%' ACCOUNT UNLOCK", quote_literal(&db_user),).as_str(),
+        )
+        .execute(&mut *connection)
+        .await
+        .map(|_| ())
+        .map_err(|err| UnlockUserError::MySqlError(err.to_string()));
+
+        results.insert(db_user, result);
+    }
+
+    results
+}
+
+/// This struct contains information about a database user.
+/// This can be extended if we need more information in the future.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, FromRow)]
+pub struct DatabaseUser {
+    #[sqlx(rename = "User")]
+    pub user: String,
+
+    #[allow(dead_code)]
+    #[serde(skip)]
+    #[sqlx(rename = "Host")]
+    pub host: String,
+
+    #[sqlx(rename = "has_password")]
+    pub has_password: bool,
+
+    #[sqlx(rename = "is_locked")]
+    pub is_locked: bool,
+}
+
+const DB_USER_SELECT_STATEMENT: &str = r#"
+SELECT
+  `mysql`.`user`.`User`,
+  `mysql`.`user`.`Host`,
+  `mysql`.`user`.`Password` != '' OR `mysql`.`user`.`authentication_string` != '' AS `has_password`,
+  COALESCE(
+    JSON_EXTRACT(`mysql`.`global_priv`.`priv`, "$.account_locked"),
+    'false'
+  ) != 'false' AS `is_locked`
+FROM `mysql`.`user`
+JOIN `mysql`.`global_priv` ON
+  `mysql`.`user`.`User` = `mysql`.`global_priv`.`User`
+  AND `mysql`.`user`.`Host` = `mysql`.`global_priv`.`Host`
+"#;
+
+pub async fn get_all_database_users_for_unix_user(
+    unix_user: &UnixUser,
+    connection: &mut MySqlConnection,
+) -> Result<Vec<DatabaseUser>, sqlx::Error> {
+    sqlx::query_as::<_, DatabaseUser>(
+        &(DB_USER_SELECT_STATEMENT.to_string() + "WHERE `mysql`.`user`.`User` REGEXP ?"),
+    )
+    .bind(create_user_group_matching_regex(unix_user))
+    .fetch_all(connection)
+    .await
+}
+
+// /// This function fetches a database user if it exists.
+// pub async fn get_database_user_for_user(
+//     username: &str,
+//     connection: &mut MySqlConnection,
+// ) -> anyhow::Result<Option<DatabaseUser>> {
+//     let user = sqlx::query_as::<_, DatabaseUser>(
+//         &(DB_USER_SELECT_STATEMENT.to_string() + "WHERE `mysql`.`user`.`User` = ?"),
+//     )
+//     .bind(username)
+//     .fetch_optional(connection)
+//     .await?;
+
+//     Ok(user)
+// }
+
+// /// NOTE: It is very critical that this function validates the database name
+// ///       properly. MySQL does not seem to allow for prepared statements, binding
+// ///       the database name as a parameter to the query. This means that we have
+// ///       to validate the database name ourselves to prevent SQL injection.