postrust_graphql/

context.rs

//! GraphQL context containing auth, database pool, and schema cache.

use postrust_auth::AuthResult;
use postrust_core::schema_cache::SchemaCacheRef;
use sqlx::PgPool;
use std::collections::HashMap;
use std::sync::Arc;

/// The transaction every write in one operation shares.
///
/// A GraphQL mutation may name several root fields, and the specification
/// resolves them one after another. Hasura runs the whole set in one
/// transaction, so a mutation whose second root field violates a constraint
/// leaves nothing behind from its first -- which is what a client sending
/// "create the order and its lines" is relying on. Opening a transaction per
/// resolver, as this used to, half-applies that mutation and reports failure.
///
/// Opened lazily by the first write and settled once the operation is answered:
/// committed when the response carries no errors, rolled back otherwise. A
/// query never touches it.
pub type SharedWrite = Arc<tokio::sync::Mutex<Option<sqlx::Transaction<'static, sqlx::Postgres>>>>;

/// The `SET LOCAL` settings a request's session variables and role need.
///
/// Free of the context so it can be read on its own, which is also the only
/// way to test it: a [`GraphQLContext`] needs a connection pool and none of
/// this does.
///
/// The setting name is built from the variable's own name after it has been
/// checked, and the value is bound rather than interpolated: `set_config`
/// takes both as arguments, where `SET LOCAL` would need the value written
/// into the statement.
pub fn session_settings_for(
    session: &HashMap<String, String>,
    role: &str,
) -> Vec<(String, String)> {
    let mut settings: Vec<(String, String)> = session
        .iter()
        .filter(|(name, _)| {
            !name.is_empty() && name.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')
        })
        .map(|(name, value)| (format!("hasura.{}", name), value.clone()))
        .collect();
    // The whole session as one document, for a function that takes it.
    // A setting rather than a bound parameter because the places that call
    // such a function are projections and correlated subselects, which
    // assemble SQL without a parameter list to add to -- and because it is
    // then set exactly where the role is, once per transaction.
    settings.push((
        "hasura.session".to_string(),
        hasura_session_document(session, role).to_string(),
    ));
    // Beside the document, the role on its own, because a policy asking who is
    // calling should not have to parse JSON to find out.
    settings.push(("hasura.role".to_string(), role.to_string()));
    settings
}

/// The session as a function reading `hasura_session` expects it.
///
/// Hasura hands a function a JSON object of the caller's session variables
/// under the names they arrive as -- `x-hasura-role`, `x-hasura-user-id` --
/// which is what a function body indexes into. They are held stripped and
/// lowercased for the settings a row-level policy reads, so the prefix goes
/// back on here.
pub fn hasura_session_document(session: &HashMap<String, String>, role: &str) -> serde_json::Value {
    let mut object = serde_json::Map::new();
    for (name, value) in session {
        object.insert(
            format!("x-hasura-{}", name.replace('_', "-")),
            serde_json::Value::String(value.clone()),
        );
    }
    object.insert(
        "x-hasura-role".to_string(),
        serde_json::Value::String(role.to_string()),
    );
    serde_json::Value::Object(object)
}

/// Context available to all GraphQL resolvers.
pub struct GraphQLContext {
    /// Database connection pool.
    pub pool: PgPool,
    /// Schema cache for table/column metadata.
    pub schema_cache: SchemaCacheRef,
    /// Authentication result with role and claims.
    pub auth: AuthResult,
    /// Session variables carried into the transaction, without their
    /// `x-hasura-` prefix and lowercased: `user_id`, `org_id`.
    ///
    /// This is the half of Hasura's permission model that transfers. Its rules
    /// live in metadata and are compiled into every query; here permissions
    /// live in the database as roles and row level security, and what a policy
    /// needs is the caller's identity. A policy written against
    /// `current_setting('hasura.user_id')` sees what the Hasura permission
    /// would have seen.
    pub session: HashMap<String, String>,
    /// The role the caller speaks as, in Hasura's sense, where that is not the
    /// database role the transaction runs as.
    ///
    /// The two are different things and conflating them was the reason
    /// `hasura_session->>'x-hasura-role'` used to answer with the name of the
    /// connecting database user. Hasura's roles are labels -- `Artist`,
    /// `anonymous` -- that exist in no catalogue and could not be `SET ROLE`
    /// to; what they decide is which permissions apply and what a function
    /// reading the session document sees. Which database user the transaction
    /// runs as is [`AuthResult::role`], and it is settled separately.
    ///
    /// `None` when nothing named a Hasura role, in which case the database
    /// role stands in for it, as it did before the two were told apart.
    pub hasura_role: Option<String>,
    /// Whether the admin secret authenticated this request.
    ///
    /// Not the same question as whether the role is `admin`, which an
    /// administrator gives up as soon as it asks to be treated as someone
    /// else. What this gates is the fields a `backend_only` permission hides:
    /// reachable by a caller that proved it holds the secret, whatever role it
    /// then claims, and by no one else.
    pub elevated: bool,
    /// The transaction every write in this operation shares. See [`SharedWrite`].
    pub write: SharedWrite,
}

impl GraphQLContext {
    /// Create a new GraphQL context.
    pub fn new(pool: PgPool, schema_cache: SchemaCacheRef, auth: AuthResult) -> Self {
        Self {
            pool,
            schema_cache,
            auth,
            session: HashMap::new(),
            hasura_role: None,
            elevated: false,
            write: Arc::new(tokio::sync::Mutex::new(None)),
        }
    }

    /// Record who the caller is in Hasura's sense, and whether it proved it.
    pub fn with_identity(mut self, role: Option<String>, elevated: bool) -> Self {
        self.hasura_role = role;
        self.elevated = elevated;
        self
    }

    /// The role the caller speaks as: the Hasura role where one was named, and
    /// the database role otherwise.
    pub fn acting_role(&self) -> &str {
        self.hasura_role.as_deref().unwrap_or(&self.auth.role)
    }

    /// Who is asking, for the SQL builders that have to narrow rows to them.
    ///
    /// The Hasura role rather than [`Self::acting_role`]: a permission is
    /// keyed by a role someone wrote into a document, and the database role
    /// standing in for a missing one would name no permission and read as
    /// unrestricted -- which is right, and is worth being explicit about.
    pub fn caller(&self) -> crate::role::Caller<'_> {
        crate::role::Caller {
            role: self.hasura_role.as_deref(),
            session: &self.session,
        }
    }

    /// Share one transaction with whoever is going to settle it.
    ///
    /// The caller keeps the other handle: it is the only thing that knows
    /// whether the operation ended in errors, and so the only thing that can
    /// decide between commit and rollback.
    pub fn with_write(mut self, write: SharedWrite) -> Self {
        self.write = write;
        self
    }

    /// Carry session variables into every transaction this request opens.
    pub fn with_session(mut self, session: HashMap<String, String>) -> Self {
        self.session = session;
        self
    }

    /// The `SET LOCAL` statements this request's session variables need.
    ///
    /// The setting name is built from the variable's own name after it has
    /// been checked, and the value is bound rather than interpolated:
    /// `set_config` takes both as arguments, where `SET LOCAL` would need the
    /// value written into the statement.
    pub fn session_settings(&self) -> Vec<(String, String)> {
        session_settings_for(&self.session, self.acting_role())
    }

    /// The session as a function reading `hasura_session` expects it.
    ///
    /// Hasura hands a function a JSON object of the caller's session
    /// variables, under the names they arrive as -- `x-hasura-role`,
    /// `x-hasura-user-id` -- which is what a function body indexes into.
    /// [`Self::session`] holds them stripped and lowercased for the settings a
    /// row-level policy reads, so the prefix goes back on here.
    ///
    /// The role is included and is not the caller's to choose: it is what
    /// authenticated the request, or the role an authenticated administrator
    /// asked to be treated as -- never a bare header.
    pub fn hasura_session(&self) -> serde_json::Value {
        hasura_session_document(&self.session, self.acting_role())
    }

    /// The database role this request's transaction runs as.
    ///
    /// Not [`Self::acting_role`], which is who the caller says it is. `SET
    /// LOCAL ROLE` takes this one, because it is the only one of the two that
    /// has to exist in the catalogue.
    pub fn role(&self) -> &str {
        &self.auth.role
    }

    /// Get a claim value.
    pub fn claim(&self, key: &str) -> Option<&serde_json::Value> {
        self.auth.claims.get(key)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn create_test_auth() -> AuthResult {
        let mut claims = HashMap::new();
        claims.insert("user_id".into(), serde_json::json!(123));
        claims.insert("role".into(), serde_json::json!("admin"));

        AuthResult {
            role: "authenticated".into(),
            claims,
        }
    }

    #[test]
    fn test_context_role() {
        let auth = create_test_auth();
        // Note: We can't fully test without a pool, but we can test the auth part
        assert_eq!(auth.role, "authenticated");
    }

    #[test]
    fn test_context_claim() {
        let auth = create_test_auth();
        assert_eq!(auth.claims.get("user_id"), Some(&serde_json::json!(123)));
    }

    fn session(pairs: &[(&str, &str)]) -> HashMap<String, String> {
        pairs
            .iter()
            .map(|(name, value)| (name.to_string(), value.to_string()))
            .collect()
    }

    fn setting<'a>(settings: &'a [(String, String)], name: &str) -> Option<&'a str> {
        settings
            .iter()
            .find(|(key, _)| key == name)
            .map(|(_, value)| value.as_str())
    }

    #[test]
    fn the_session_document_says_which_role_is_asking() {
        let document = hasura_session_document(&session(&[("user_id", "1")]), "user");
        assert_eq!(document["x-hasura-role"], serde_json::json!("user"));
        assert_eq!(document["x-hasura-user-id"], serde_json::json!("1"));
    }

    #[test]
    fn a_session_name_gets_its_dashes_back_in_the_document() {
        // `SET LOCAL` cannot carry a dash in a setting name, so the variables
        // are held with underscores -- and a function body indexes into the
        // document by the name the header arrived as.
        let document = hasura_session_document(&session(&[("infant_name", "Bittu")]), "infant");
        assert_eq!(document["x-hasura-infant-name"], serde_json::json!("Bittu"));
    }

    #[test]
    fn the_role_is_a_setting_of_its_own_beside_the_document() {
        let settings = session_settings_for(&session(&[("user_id", "1")]), "Artist");
        assert_eq!(setting(&settings, "hasura.role"), Some("Artist"));
        assert_eq!(setting(&settings, "hasura.user_id"), Some("1"));
        // And the document, for a function that takes the whole thing.
        let document: serde_json::Value =
            serde_json::from_str(setting(&settings, "hasura.session").unwrap()).unwrap();
        assert_eq!(document["x-hasura-role"], serde_json::json!("Artist"));
    }

    #[test]
    fn a_name_that_could_not_be_a_setting_is_dropped_rather_than_written() {
        // The name goes into the statement and the value is bound, so a name
        // that is not an identifier is the one thing here that could be an
        // injection. It never reaches SQL.
        let settings = session_settings_for(
            &session(&[("user_id", "1"), ("bad'; drop table t; --", "x")]),
            "user",
        );
        assert!(setting(&settings, "hasura.user_id").is_some());
        assert!(settings
            .iter()
            .all(|(name, _)| !name.contains("drop table")));
    }
}