### Local Development Environment Variables

Source: https://crates.io/crates/serviceconf

Example environment variables for local development, setting direct values for API_KEY and PORT.

```bash
export API_KEY=dev-key-123
export PORT=3000

```

--------------------------------

### Configuration with Multiple File-Based Secrets

Source: https://crates.io/crates/serviceconf

Example Rust configuration struct using `#[conf(from_file)]` for both `api_key` and `database_password`. This setup is suitable for applications using Kubernetes Secrets mounted as files.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(from_file)]
    pub api_key: String,

    #[conf(from_file)]
    pub database_password: String,
}

```

--------------------------------

### Set Prefixed Environment Variables

Source: https://crates.io/crates/serviceconf/0.2.2

Example of setting environment variables that match a defined struct prefix.

```bash
export MYAPP_DATABASE_URL=postgres://localhost/db
export MYAPP_API_KEY=secret123
```

--------------------------------

### Environment Variables with Struct-Level Prefix

Source: https://crates.io/crates/serviceconf

Example environment variables demonstrating the use of a struct-level prefix. `MYAPP_DATABASE_URL` and `MYAPP_API_KEY` are read by the `Config` struct.

```bash
export MYAPP_DATABASE_URL=postgres://localhost/db
export MYAPP_API_KEY=secret123

```

--------------------------------

### Production Environment Variables for File-Based Secrets

Source: https://crates.io/crates/serviceconf

Example environment variables for production, specifying file paths for secrets like API_KEY_FILE and PORT.

```bash
export API_KEY_FILE=/run/secrets/api-key
export PORT=8080

```

--------------------------------

### Error Handling with `Result` from `from_env()`

Source: https://crates.io/crates/serviceconf

The `from_env()` method returns a `Result`. This example shows how to handle potential errors during configuration loading using a `match` statement.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: String,
}

match Config::from_env() {
    Ok(config) => println!("Config loaded successfully"),
    Err(e) => eprintln!("Failed to load config: {}", e),
}

```

--------------------------------

### Use Default Value with `#[conf(default)]`

Source: https://crates.io/crates/serviceconf

Apply `#[conf(default)]` to use `Default::default()` for a field if its corresponding environment variable is not set. For example, `u16` defaults to 0 and `String` defaults to an empty string.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default)]
    pub port: u16,  // Uses 0 (u16::default()) if PORT not set

    #[conf(default)]
    pub host: String,  // Uses "" (String::default()) if HOST not set
}

```

--------------------------------

### Combining Attributes: Prefix, Custom Name, From File, and Option

Source: https://crates.io/crates/serviceconf

Demonstrates combining multiple attributes: `#[conf(prefix = "APP_")]`, `#[conf(name = "DB_URL")]`, `#[conf(from_file)]`, and `Option<String>` for flexible configuration loading.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
#[conf(prefix = "APP_")]
struct Config {
    // Combines: prefix + custom name + from_file + Option
    #[conf(name = "DB_URL")]
    #[conf(from_file)]
    pub database_url: Option<String>,  // Reads from APP_DB_URL or APP_DB_URL_FILE

    // Combines: prefix + default
    #[conf(default = 8080)]
    pub port: u16,  // Reads from APP_PORT, defaults to 8080
}

```

--------------------------------

### Handle Configuration Errors

Source: https://crates.io/crates/serviceconf/0.2.2

Use the from_env() method to load configuration and handle potential errors.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: String,
}

match Config::from_env() {
    Ok(config) => println!("Config loaded successfully"),
    Err(e) => eprintln!("Failed to load config: {}", e),
}
```

--------------------------------

### Basic Configuration with ServiceConf

Source: https://crates.io/crates/serviceconf

Defines a configuration struct with a file-based secret and a default value. Use `Config::from_env().unwrap()` to load settings. Supports direct environment variables for local development and file paths for production.

```rust
use serviceconf::ServiceConf;

#[derive(Debug, ServiceConf)]
struct Config {
    // File-based secret: reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,

    // Default value if not set
    #[conf(default = 8080)]
    pub port: u16,
}

let config = Config::from_env().unwrap();
println!("Port: {}", config.port);

```

--------------------------------

### Combining Attributes

Source: https://crates.io/crates/serviceconf/0.2.2

Demonstrates how to combine multiple attributes for flexible configuration loading.

```APIDOC
## Combining Attributes

Multiple attributes can be combined to create powerful configurations:

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
#[conf(prefix = "APP_")]
struct Config {
    // Combines: prefix + custom name + from_file + Option
    #[conf(name = "DB_URL")]
    #[conf(from_file)]
    pub database_url: Option<String>,  // Reads from APP_DB_URL or APP_DB_URL_FILE

    // Combines: prefix + default
    #[conf(default = 8080)]
    pub port: u16,  // Reads from APP_PORT, defaults to 8080
}
```

**Invalid combinations** (compile errors):
  * `Option<T>` + `#[conf(default)]` or `#[conf(default = value)]` → Option already defaults to None
```

--------------------------------

### Error Handling with `Result`

Source: https://crates.io/crates/serviceconf/0.2.2

Shows how to handle potential errors during configuration loading using the `Result` returned by `from_env()`.

```APIDOC
## Error Handling

The `from_env()` method returns a `Result` that can be handled appropriately:

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: String,
}

match Config::from_env() {
    Ok(config) => println!("Config loaded successfully"),
    Err(e) => eprintln!("Failed to load config: {}", e),
}
```

Example error messages:
  * `Environment variable 'DATABASE_URL' is required but not set`
  * `Failed to parse environment variable 'PORT' as u16: invalid digit found in string`
  * `Failed to read file '/etc/secrets/key' for environment variable 'API_KEY_FILE': No such file or directory`
```

--------------------------------

### Type Behavior Summary

Source: https://crates.io/crates/serviceconf/0.2.2

Overview of how different types and attributes affect configuration loading when environment variables are missing or set.

```APIDOC
## Type Behavior

Type | When Env Var Missing | When Env Var Set  
---|---|---
`T` (no attribute) | Error | Parsed with `FromStr`  
`T` + `#[conf(default)]` | `Default::default()` | Parsed with `FromStr`  
`T` + `#[conf(default = value)]` | Uses `value` | Parsed with `FromStr`  
`Option<T>` | `None` | `Some(parsed_value)`  
`T` + `#[conf(deserializer = "fn")]` | Error | Parsed with custom function  
```

--------------------------------

### Set Environment Variables for Development and Production

Source: https://crates.io/crates/serviceconf/0.2.2

Configure environment variables for local development or production environments using file-based secrets.

```bash
export API_KEY=dev-key-123
export PORT=3000
```

```bash
export API_KEY_FILE=/run/secrets/api-key
export PORT=8080
```

--------------------------------

### Define Configuration with ServiceConf

Source: https://crates.io/crates/serviceconf/0.2.2

Use the ServiceConf derive macro to define configuration structures with support for file-based secrets and default values.

```rust
use serviceconf::ServiceConf;

#[derive(Debug, ServiceConf)]
struct Config {
    // File-based secret: reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,

    // Default value if not set
    #[conf(default = 8080)]
    pub port: u16,
}

let config = Config::from_env().unwrap();
println!("Port: {}", config.port);
```

--------------------------------

### Load Secrets from File with `#[conf(from_file)]`

Source: https://crates.io/crates/serviceconf

Use `#[conf(from_file)]` to load secrets from a file specified by an environment variable (e.g., `API_KEY_FILE`). This is useful for Kubernetes and Docker secrets.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,
}

```

--------------------------------

### Apply Prefix to Configuration Fields

Source: https://crates.io/crates/serviceconf/0.2.2

Use the #[conf(prefix = "...")] attribute to automatically prepend a prefix to all environment variable lookups for a struct.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
#[conf(prefix = "MYAPP_")]
struct Config {
    pub database_url: String,  // Reads from MYAPP_DATABASE_URL
    pub api_key: String,       // Reads from MYAPP_API_KEY
}
```

--------------------------------

### Default Values with `#[conf(default)]`

Source: https://crates.io/crates/serviceconf/0.2.2

Use the `Default::default()` implementation for a type if the corresponding environment variable is not set.

```APIDOC
## `#[conf(default)]`

Use `Default::default()` if the environment variable is not set.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default)]
    pub port: u16,  // Uses 0 (u16::default()) if PORT not set

    #[conf(default)]
    pub host: String,  // Uses "" (String::default()) if HOST not set
}
```
```

--------------------------------

### Custom Deserialization with `#[conf(deserializer = "function")]` (JSON)

Source: https://crates.io/crates/serviceconf

Employ `#[conf(deserializer = "serde_json::from_str")]` to parse environment variable values using a specified function, such as `serde_json::from_str` for JSON data.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    // Parse JSON array
    #[conf(deserializer = "serde_json::from_str")]
    pub tags: Vec<String>,
}

```

--------------------------------

### Struct-Level Prefix for Environment Variables

Source: https://crates.io/crates/serviceconf

Applies a prefix to all environment variable names within a struct. Use `#[conf(prefix = "MYAPP_")]` to prepend `MYAPP_` to each variable.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
#[conf(prefix = "MYAPP_")]
struct Config {
    pub database_url: String,  // Reads from MYAPP_DATABASE_URL
    pub api_key: String,       // Reads from MYAPP_API_KEY
}


```

--------------------------------

### Explicit Default Values with `#[conf(default = value)]`

Source: https://crates.io/crates/serviceconf/0.2.2

Provide a specific default value to be used when the environment variable is not set.

```APIDOC
## `#[conf(default = value)]`

Specify an explicit default value when the environment variable is not set.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default = "127.0.0.1:8080".to_string())]
    pub server_addr: String,

    #[conf(default = 10)]
    pub max_connections: u32,

    #[conf(default = false)]
    pub enable_tls: bool,
}
```
```

--------------------------------

### Configure Kubernetes Secrets and Deployment

Source: https://crates.io/crates/serviceconf/0.2.2

Define Kubernetes secrets and mount them as files for use with the serviceconf library.

```yaml
apiVersion: v1
kind: Secret
metadata:
  name: app-secrets
type: Opaque
stringData:
  api-key: "prod-api-key-123"
  db-password: "secure-password"
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myservice
spec:
  template:
    spec:
      containers:
      - name: app
        image: myservice:latest
        env:
          - name: API_KEY_FILE
            value: /etc/secrets/api-key
          - name: DATABASE_PASSWORD_FILE
            value: /etc/secrets/db-password
        volumeMounts:
          - name: secrets
            mountPath: /etc/secrets
            readOnly: true
      volumes:
        - name: secrets
          secret:
            secretName: app-secrets
            items:
              - key: api-key
                path: api-key
              - key: db-password
                path: db-password
```

--------------------------------

### File-based Secrets with `#[conf(from_file)]`

Source: https://crates.io/crates/serviceconf/0.2.2

Load configuration values from files specified by environment variables ending in `_FILE`. This is useful for handling secrets in Kubernetes and Docker.

```APIDOC
## `#[conf(from_file)]` - File-based Secrets

Load from `{VAR_NAME}_FILE` in addition to the environment variable. This is the primary feature of `serviceconf` for handling file-based secrets in Kubernetes and Docker environments.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,
}
```
```

--------------------------------

### Apply Default Values

Source: https://crates.io/crates/serviceconf/0.2.2

Use Default::default() or an explicit value when the environment variable is missing.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default)]
    pub port: u16,  // Uses 0 (u16::default()) if PORT not set

    #[conf(default)]
    pub host: String,  // Uses "" (String::default()) if HOST not set
}
```

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default = "127.0.0.1:8080".to_string())]
    pub server_addr: String,

    #[conf(default = 10)]
    pub max_connections: u32,

    #[conf(default = false)]
    pub enable_tls: bool,
}
```

--------------------------------

### Custom Deserializers with `#[conf(deserializer = "function")]`

Source: https://crates.io/crates/serviceconf/0.2.2

Use a custom function to deserialize environment variable values, enabling complex parsing logic.

```APIDOC
## `#[conf(deserializer = "function")]`

Use a custom deserializer function for complex types or custom parsing logic.
The deserializer function must have the signature:
```rust
fn deserialize(s: &str) -> Result<T, impl std::fmt::Display>
```

**Example with JSON:**
```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    // Parse JSON array
    #[conf(deserializer = "serde_json::from_str")]
    pub tags: Vec<String>,
}
```

Environment variable:
```bash
export TAGS='["prod","api","v2"]'
```

**Example with custom function:**
```rust
use serviceconf::ServiceConf;

// Custom comma-separated parser
fn comma_separated(s: &str) -> Result<Vec<String>, String> {
    Ok(s.split(',').map(|s| s.trim().to_string()).collect())
}

#[derive(ServiceConf)]
struct Config {
    #[conf(deserializer = "comma_separated")]
    pub features: Vec<String>,
}
```

Environment variable:
```bash
export FEATURES=feature1,feature2,feature3
```
```

--------------------------------

### Handle Optional Fields

Source: https://crates.io/crates/serviceconf/0.2.2

Use Option<T> to allow fields to be missing without triggering an error.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: Option<String>,  // None if API_KEY not set
    pub max_retries: Option<u32>, // None if MAX_RETRIES not set
}
```

--------------------------------

### Combine Configuration Attributes

Source: https://crates.io/crates/serviceconf/0.2.2

Stack multiple attributes to define complex loading behavior for a single field.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
#[conf(prefix = "APP_")]
struct Config {
    // Combines: prefix + custom name + from_file + Option
    #[conf(name = "DB_URL")]
    #[conf(from_file)]
    pub database_url: Option<String>,  // Reads from APP_DB_URL or APP_DB_URL_FILE

    // Combines: prefix + default
    #[conf(default = 8080)]
    pub port: u16,  // Reads from APP_PORT, defaults to 8080
}
```

--------------------------------

### Custom Deserialization with `#[conf(deserializer = "function")]` (Custom Function)

Source: https://crates.io/crates/serviceconf

Define and use custom deserializer functions, like `comma_separated`, for parsing environment variables into specific types, such as a `Vec<String>` from a comma-delimited string.

```rust
use serviceconf::ServiceConf;

// Custom comma-separated parser
fn comma_separated(s: &str) -> Result<Vec<String>, String> {
    Ok(s.split(',').map(|s| s.trim().to_string()).collect())
}

#[derive(ServiceConf)]
struct Config {
    #[conf(deserializer = "comma_separated")]
    pub features: Vec<String>,
}

```

--------------------------------

### Load File-based Secrets

Source: https://crates.io/crates/serviceconf/0.2.2

Use the from_file attribute to read secrets from a file path specified by an environment variable suffixed with _FILE.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,
}
```

--------------------------------

### Optional Fields with `Option<T>`

Source: https://crates.io/crates/serviceconf

Utilize `Option<T>` for fields to make them optional. If the corresponding environment variable is not set, the field will be `None`.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: Option<String>,  // None if API_KEY not set
    pub max_retries: Option<u32>, // None if MAX_RETRIES not set
}

```

--------------------------------

### Optional Fields with `Option<T>`

Source: https://crates.io/crates/serviceconf/0.2.2

Define fields as optional using `Option<T>`. If the environment variable is not set, the field will be `None`.

```APIDOC
## Optional Fields

Use `Option<T>` for optional fields. Returns `None` if the environment variable is not set.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    pub api_key: Option<String>,  // None if API_KEY not set
    pub max_retries: Option<u32>, // None if MAX_RETRIES not set
}
```
```

--------------------------------

### Specify Explicit Default Value with `#[conf(default = value)]`

Source: https://crates.io/crates/serviceconf

Use `#[conf(default = value)]` to set an explicit default value for a field when the environment variable is absent. The value must be a valid Rust expression.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(default = "127.0.0.1:8080".to_string())]
    pub server_addr: String,

    #[conf(default = 10)]
    pub max_connections: u32,

    #[conf(default = false)]
    pub enable_tls: bool,
}

```

--------------------------------

### Specify Custom Environment Variable Name with `#[conf(name)]`

Source: https://crates.io/crates/serviceconf

Use `#[conf(name = "CUSTOM_NAME")]` to map a struct field to a different environment variable name than its own name.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Load from REDIS_URL environment variable
    #[conf(name = "REDIS_URL")]
    pub redis_connection_string: String,
}

```

--------------------------------

### Implement File-based Secrets in Rust

Source: https://crates.io/crates/serviceconf/0.2.2

Use the #[conf(from_file)] attribute to map fields to file-based secrets in your Rust struct.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    #[conf(from_file)]
    pub api_key: String,

    #[conf(from_file)]
    pub database_password: String,
}
```

--------------------------------

### Kubernetes Secret and Deployment Configuration

Source: https://crates.io/crates/serviceconf

Defines a Kubernetes Secret and a Deployment to mount secrets into the application container. The `env` section maps secret file paths, and `volumeMounts` specifies where to access them.

```yaml
apiVersion: v1
kind: Secret
metadata:
  name: app-secrets
type: Opaque
stringData:
  api-key: "prod-api-key-123"
  db-password: "secure-password"
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myservice
spec:
  template:
    spec:
      containers:
      - name: app
        image: myservice:latest
        env:
          - name: API_KEY_FILE
            value: /etc/secrets/api-key
          - name: DATABASE_PASSWORD_FILE
            value: /etc/secrets/db-password
        volumeMounts:
          - name: secrets
            mountPath: /etc/secrets
            readOnly: true
      volumes:
        - name: secrets
          secret:
            secretName: app-secrets
            items:
              - key: api-key
                path: api-key
              - key: db-password
                path: db-password

```

--------------------------------

### Custom Environment Variable Names with `#[conf(name = "CUSTOM_NAME")]`

Source: https://crates.io/crates/serviceconf/0.2.2

Specify a custom environment variable name that differs from the struct field name.

```APIDOC
## `#[conf(name = "CUSTOM_NAME")]`

Specify an environment variable name different from the field name.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Load from REDIS_URL environment variable
    #[conf(name = "REDIS_URL")]
    pub redis_connection_string: String,
}
```
```

--------------------------------

### Specify Custom Environment Variable Names

Source: https://crates.io/crates/serviceconf/0.2.2

Map a struct field to a specific environment variable name using the name attribute.

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
pub struct Config {
    // Load from REDIS_URL environment variable
    #[conf(name = "REDIS_URL")]
    pub redis_connection_string: String,
}
```

--------------------------------

### Define Custom Deserializers

Source: https://crates.io/crates/serviceconf/0.2.2

Implement custom parsing logic for complex types using a function reference.

```rust
fn deserialize(s: &str) -> Result<T, impl std::fmt::Display>
```

```rust
use serviceconf::ServiceConf;

#[derive(ServiceConf)]
struct Config {
    // Parse JSON array
    #[conf(deserializer = "serde_json::from_str")]
    pub tags: Vec<String>,
}
```

```bash
export TAGS='["prod","api","v2"]'
```

```rust
use serviceconf::ServiceConf;

// Custom comma-separated parser
fn comma_separated(s: &str) -> Result<Vec<String>, String> {
    Ok(s.split(',').map(|s| s.trim().to_string()).collect())
}

#[derive(ServiceConf)]
struct Config {
    #[conf(deserializer = "comma_separated")]
    pub features: Vec<String>,
}
```

```bash
export FEATURES=feature1,feature2,feature3
```

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