Struct AppConfig 

pub struct AppConfig {
    pub name: String,
    pub version: String,
    pub debug: bool,
    pub max_body_size: usize,
    pub request_timeout_ms: u64,
    pub root_path: String,
    pub root_path_in_servers: bool,
    pub trailing_slash_mode: TrailingSlashMode,
    pub debug_config: DebugConfig,
}

Application configuration for the FastAPI Rust framework.

Controls application-level settings including naming, debug mode, body size limits, timeouts, and routing behavior.

Defaults

Setting	Default
name	"FastAPI"
version	"0.1.0"
debug	false
max_body_size	1 MB (1,048,576 bytes)
request_timeout_ms	30,000 ms
root_path	""
trailing_slash_mode	Strict

Example

use fastapi_core::AppConfig;

let config = AppConfig::default()
    .with_name("my-api")
    .with_version("2.0.0")
    .with_debug(true)
    .with_max_body_size(10 * 1024 * 1024); // 10 MB

Fields

name: String

Application name (used in logging and OpenAPI).

version: String

Application version.

debug: bool

Enable debug mode.

max_body_size: usize

Maximum request body size in bytes.

request_timeout_ms: u64

Default request timeout in milliseconds.

root_path: String

Root path prefix for apps behind a reverse proxy.

When the application is served behind a reverse proxy at a sub-path, this should be set to that sub-path. For example, if the app is proxied at /api/v1, set root_path = "/api/v1".

This affects:

• URL generation via url_for()
• OpenAPI servers list (if root_path_in_servers is true)

root_path_in_servers: bool

Whether to include the root_path in OpenAPI servers list.

When true and root_path is set, a server entry with the root_path will be added to the OpenAPI specification’s servers array.

trailing_slash_mode: TrailingSlashMode

Trailing slash handling mode.

Controls how the router handles trailing slashes in URLs:

• Strict (default): /users and /users/ are different routes
• Redirect: 308 redirect /users/ to /users
• RedirectWithSlash: 308 redirect /users to /users/
• MatchBoth: accept both forms without redirect

debug_config: DebugConfig

Debug mode configuration.

Controls whether error responses include additional diagnostic information such as source location, handler name, and route pattern. When a debug header and token are configured, debug info is only included for requests that present the correct token.

Implementations

impl AppConfig

pub fn new() -> Self

Creates a new configuration with defaults.

pub fn name(self, name: impl Into<String>) -> Self

Sets the application name.

pub fn version(self, version: impl Into<String>) -> Self

Sets the application version.

pub fn debug(self, debug: bool) -> Self

Enables or disables debug mode.

pub fn max_body_size(self, size: usize) -> Self

Sets the maximum request body size.

pub fn request_timeout_ms(self, timeout: u64) -> Self

Sets the default request timeout in milliseconds.

pub fn root_path(self, path: impl Into<String>) -> Self

Sets the root path for apps behind a reverse proxy.

When the application is served behind a reverse proxy at a sub-path, set this to that sub-path. For example, if the app is proxied at /api/v1, set root_path("/api/v1").

Example

let config = AppConfig::new().root_path("/api/v1");

pub fn root_path_in_servers(self, include: bool) -> Self

Sets whether to include root_path in OpenAPI servers list.

When true and root_path is set, a server entry with the root_path will be added to the OpenAPI specification’s servers array.

pub fn trailing_slash_mode(self, mode: TrailingSlashMode) -> Self

Sets the trailing slash handling mode.

Controls how the router handles trailing slashes in URLs.

Example

use fastapi_core::TrailingSlashMode;

let config = AppConfig::new()
    .trailing_slash_mode(TrailingSlashMode::Redirect);

pub fn debug_config(self, config: DebugConfig) -> Self

Sets the debug mode configuration.

Controls whether error responses include additional diagnostic information. Use with DebugConfig::new().enable().with_debug_header(...).

Example

use fastapi_core::{DebugConfig};

let config = AppConfig::new()
    .debug_config(DebugConfig::new()
        .enable()
        .with_debug_header("X-Debug-Token", "my-secret"));

pub fn from_env() -> Result<Self, ConfigError>

Load configuration from environment variables.

Variables (prefix FASTAPI_ by default):

• FASTAPI_NAME
• FASTAPI_VERSION
• FASTAPI_DEBUG (true/false/1/0/yes/no/on/off)
• FASTAPI_MAX_BODY_SIZE (bytes)
• FASTAPI_REQUEST_TIMEOUT_MS
• FASTAPI_ROOT_PATH (path prefix for reverse proxy)
• FASTAPI_ROOT_PATH_IN_SERVERS (true/false/1/0/yes/no/on/off)

pub fn from_env_with_prefix(prefix: &str) -> Result<Self, ConfigError>

Load configuration from environment variables using a custom prefix.

pub fn from_file(path: impl AsRef<Path>) -> Result<Self, ConfigError>

Load configuration from a JSON file.

Only JSON is supported for now to keep dependencies minimal.

pub fn from_env_and_file(path: impl AsRef<Path>) -> Result<Self, ConfigError>

Load configuration from a JSON file then override with environment variables.

pub fn openapi_server(&self) -> Option<(String, Option<String>)>

Returns the root_path as an OpenAPI server entry if configured.

Returns Some((url, description)) if:

• root_path is non-empty
• root_path_in_servers is true

Returns None otherwise.

Example

let config = AppConfig::new().root_path("/api/v1");
if let Some((url, description)) = config.openapi_server() {
    builder = builder.server(url, description);
}

pub fn validate(&self) -> Result<(), ConfigError>

Validate configuration values.

Trait Implementations

impl Clone for AppConfig

fn clone(&self) -> AppConfig

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for AppConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for AppConfig

fn default() -> Self

Returns the “default value” for a type.