Implementation

TODO: This section is under development. Basic implementation patterns are outlined below.

Overview

This guide covers practical implementation of concurrency control in SCIM Server, including ETag generation, version tracking, and conditional operations.

ETag Generation

Basic ETag Implementation

#![allow(unused)]
fn main() {
use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};
use chrono::{DateTime, Utc};

#[derive(Debug, Clone)]
pub struct ETag {
    value: String,
    weak: bool,
}

impl ETag {
    pub fn from_content(content: &[u8]) -> Self {
        let mut hasher = DefaultHasher::new();
        content.hash(&mut hasher);
        let hash = hasher.finish();
        
        ETag {
            value: format!("\"{}\"", hash),
            weak: false,
        }
    }
    
    pub fn from_timestamp(timestamp: DateTime<Utc>) -> Self {
        ETag {
            value: format!("\"{}\"", timestamp.timestamp()),
            weak: true,
        }
    }
    
    pub fn weak() -> Self {
        ETag {
            value: format!("\"{}\"", uuid::Uuid::new_v4()),
            weak: true,
        }
    }
}
}

Version Tracking

Database Schema

-- Add versioning columns to resource tables
ALTER TABLE users ADD COLUMN version INTEGER DEFAULT 1;
ALTER TABLE users ADD COLUMN etag VARCHAR(64);
ALTER TABLE users ADD COLUMN last_modified TIMESTAMPTZ DEFAULT NOW();

-- Create index for efficient lookups
CREATE INDEX idx_users_etag ON users(tenant_id, id, etag);

Provider Implementation

#![allow(unused)]
fn main() {
impl ResourceProvider for DatabaseProvider {
    async fn conditional_update(
        &self,
        resource_type: &str,
        id: &str,
        data: serde_json::Value,
        expected_etag: &ETag,
        context: &RequestContext,
    ) -> Result<ConditionalResult<VersionedResource>, ProviderError> {
        let mut tx = self.pool.begin().await?;
        
        // Check current version
        let current = sqlx::query!(
            "SELECT etag, version FROM users WHERE tenant_id = $1 AND id = $2",
            context.tenant_id(),
            id
        )
        .fetch_optional(&mut *tx)
        .await?;
        
        let Some(current) = current else {
            return Ok(ConditionalResult::NotFound);
        };
        
        // Verify ETag matches
        if current.etag != expected_etag.value() {
            return Ok(ConditionalResult::VersionMismatch(VersionConflict {
                resource_id: id.to_string(),
                expected_version: expected_etag.clone(),
                current_version: ETag::from_str(&current.etag)?,
            }));
        }
        
        // Update with new version
        let new_version = current.version + 1;
        let new_etag = ETag::from_content(&serde_json::to_vec(&data)?);
        
        sqlx::query!(
            "UPDATE users SET data = $1, version = $2, etag = $3, last_modified = NOW() 
             WHERE tenant_id = $4 AND id = $5",
            data,
            new_version,
            new_etag.value(),
            context.tenant_id(),
            id
        )
        .execute(&mut *tx)
        .await?;
        
        tx.commit().await?;
        
        let updated = self.get_resource(resource_type, id, context).await?
            .ok_or(ProviderError::NotFound)?;
            
        Ok(ConditionalResult::Success(VersionedResource::new(updated, new_etag)))
    }
}
}

HTTP Headers

Request Headers

#![allow(unused)]
fn main() {
use axum::http::HeaderMap;

fn extract_if_match(headers: &HeaderMap) -> Option<ETag> {
    headers.get("If-Match")
        .and_then(|h| h.to_str().ok())
        .and_then(|s| ETag::from_str(s).ok())
}

fn extract_if_none_match(headers: &HeaderMap) -> Option<ETag> {
    headers.get("If-None-Match")
        .and_then(|h| h.to_str().ok())
        .and_then(|s| ETag::from_str(s).ok())
}
}

Response Headers

#![allow(unused)]
fn main() {
use axum::response::{Response, IntoResponse};
use axum::http::{StatusCode, HeaderValue};

fn add_etag_header(mut response: Response, etag: &ETag) -> Response {
    response.headers_mut().insert(
        "ETag",
        HeaderValue::from_str(etag.value()).unwrap()
    );
    response
}

fn not_modified_response(etag: &ETag) -> impl IntoResponse {
    let mut response = Response::new("".into());
    *response.status_mut() = StatusCode::NOT_MODIFIED;
    add_etag_header(response, etag)
}
}

Performance Considerations

1. ETag Caching

TODO: Implement efficient ETag caching strategies.

2. Database Optimization

TODO: Add database-specific optimization patterns.

3. Memory Usage

TODO: Document memory usage patterns for large-scale deployments.

Testing

#![allow(unused)]
fn main() {
#[cfg(test)]
mod tests {
    use super::*;
    
    #[tokio::test]
    async fn test_conditional_update_success() {
        // TODO: Implement comprehensive test cases
    }
    
    #[tokio::test]
    async fn test_version_mismatch() {
        // TODO: Test conflict detection
    }
}
}

TODO: Add more comprehensive implementation examples and patterns.