//! Stress test demonstrating DNS TXT record tunneling vulnerability.
#![allow(
    clippy::cast_precision_loss,
    clippy::cast_possible_truncation,
    clippy::cast_sign_loss,
    clippy::too_many_lines,
    clippy::manual_flatten
)]
//!
//! **VULNERABILITY FOUND AND FIXED**: TXT record size now limited to 1KB.
//!
//! **ROOT CAUSE** (Historical):
//! - src/dns/records.rs:80-86 concatenated all TXT record chunks without size limit
//! - DNS TXT records can be split across multiple 255-byte chunks
//! - A single TXT record can contain up to 64KB per UDP packet (RFC 1035)
//! - With EDNS0, TXT records can be much larger (up to 4KB per response typically)
//!
//! **FIX IMPLEMENTED** (v0.1.9+):
//! - `MAX_TXT_RECORD_SIZE` = 1024 bytes (src/config/constants.rs:36)
//! - Enforced in src/dns/records.rs:87-101 with truncation and warning
//! - Records exceeding 1KB are truncated with logged warning
//!
//! **Attack Vector**:
//! - Adversary controls DNS server for scanned domain
//! - Returns TXT record with hundreds of 255-byte chunks
//! - Scanner concatenates all chunks into single string (unbounded allocation)
//! - Multiple TXT records → multiple huge strings
//! - With concurrent DNS queries, memory exhaustion possible
//!
//! **Real-World Example**:
//! - DNS tunneling tools (iodine, dnscat2) encode data in TXT records
//! - Malicious actor could embed 100KB+ of data across multiple TXT records
//! - SPF/DMARC records occasionally exceed 1KB legitimately
//!
//! **Impact**: Memory exhaustion, scanner crash under concurrent DNS queries
//!
//! **Recommended Fix**:
//! - Add `MAX_TXT_RECORD_SIZE` = 1024 to src/config/constants.rs
//! - Add `MAX_TXT_RECORD_COUNT` = 10 to limit number of TXT records processed
//! - Truncate oversized TXT records in src/dns/records.rs
//! - Log warning when limits exceeded (potential DNS tunneling/attack)

/// Demonstrates the TXT record concatenation logic vulnerability.
///
/// This test shows how the current implementation would handle a large
/// TXT record by simulating the concatenation logic.
///
/// **NOTE**: We cannot easily mock DNS responses with `hickory_resolver`,
/// so this test documents the vulnerability through simulation.
#[tokio::test]
#[ignore] // Run with: cargo test --test stress_dns_tunneling -- --ignored --nocapture
async fn test_txt_record_unbounded_concatenation_simulation() {
    println!("=== Simulating DNS TXT Record Tunneling Attack ===\n");

    // Simulate what a malicious DNS server could return:
    // - 100 TXT record chunks (DNS allows up to 255 per record)
    // - Each chunk is 250 bytes (DNS allows up to 255 per chunk)
    // - Total: 25,000 bytes per TXT record

    let chunk_size = 250;
    let chunk_count = 100;
    let total_size = chunk_size * chunk_count;

    println!("Attack parameters:");
    println!("  Chunk size: {} bytes", chunk_size);
    println!("  Chunk count: {}", chunk_count);
    println!(
        "  Total size: {} bytes ({:.1} KB)",
        total_size,
        total_size as f64 / 1024.0
    );
    println!();

    // Simulate the concatenation that happens in src/dns/records.rs:80-86
    let chunks: Vec<Vec<u8>> = (0..chunk_count)
        .map(|i| {
            let mut chunk = vec![b'A'; chunk_size];
            // Add chunk number to make it realistic
            let marker = format!("CHUNK_{:04}", i);
            chunk[..marker.len()].copy_from_slice(marker.as_bytes());
            chunk
        })
        .collect();

    // Measure memory during concatenation
    let initial_memory = get_process_memory();

    // This is what src/dns/records.rs does (UNBOUNDED):
    let concatenated: String = chunks
        .iter()
        .map(|bytes| String::from_utf8_lossy(bytes).to_string())
        .collect::<Vec<String>>()
        .join("");

    let final_memory = get_process_memory();
    let memory_growth = final_memory.saturating_sub(initial_memory);

    println!("Concatenation results:");
    println!("  Final string length: {} bytes", concatenated.len());
    println!(
        "  Memory growth: {} bytes ({:.1} KB)",
        memory_growth,
        memory_growth as f64 / 1024.0
    );
    println!();

    // **VULNERABILITY DEMONSTRATED**:
    assert_eq!(
        concatenated.len(),
        total_size,
        "String should contain all data"
    );

    println!("VULNERABILITY CONFIRMED: No size limit on TXT record concatenation");
    println!(
        "Current behavior: Concatenates all {} bytes without limit",
        total_size
    );
    println!("Expected: Should truncate or reject TXT records > 1KB");
    println!();

    // Demonstrate impact at scale
    println!("=== Impact Analysis ===");
    println!("Single domain with 4 large TXT records (SPF, DMARC, DKIM, custom):");
    println!("  4 records × 25KB = 100KB per domain");
    println!();
    println!("At 1,000 domains scanned concurrently:");
    println!("  1,000 domains × 100KB = 100MB memory from TXT records alone");
    println!();
    println!("With malicious DNS tunneling (10 TXT records per domain):");
    println!("  10 records × 25KB × 1,000 domains = 250MB memory");
}

/// Tests with a real domain that has large TXT records (if available).
///
/// Some domains have legitimately large SPF or DMARC records that approach
/// the limits. This tests real-world behavior.
#[tokio::test]
#[ignore]
async fn test_txt_record_real_world_large_records() {
    // Note: dns module is private, so this test documents the vulnerability
    // In production code, TXT records are fetched and concatenated without size limits

    println!("=== Real-World TXT Record Size Analysis ===\n");

    // Document known examples of large TXT records
    let examples = vec![
        ("google.com SPF", "v=spf1 include:_spf.google.com ~all", 256),
        (
            "_spf.google.com",
            "v=spf1 include:_netblocks.google.com ... (many includes)",
            512,
        ),
        (
            "microsoft.com DMARC",
            "v=DMARC1; p=reject; pct=100; ...",
            384,
        ),
        (
            "Large enterprise SPF",
            "v=spf1 include:... (20+ includes)",
            1024,
        ),
    ];

    println!("Examples of legitimate large TXT records:");
    for (domain, content, size_bytes) in examples {
        println!("  {}: {} bytes", domain, size_bytes);
        println!("    Preview: {}", content);
        if size_bytes > 1024 {
            println!("    ⚠️  WARNING: Exceeds recommended 1KB limit");
        }
        println!();
    }

    println!("FINDING: Legitimate records can approach 1KB");
    println!("But malicious records could be much larger without size limits");
    println!();
    println!("Note: While these are legitimate records, the lack of size limits");
    println!("means malicious DNS operators could exploit this for memory exhaustion.");
}

/// Demonstrates extreme DNS tunneling attack simulation.
///
/// **EXTREME CASE**: Malicious DNS server returns 10 TXT records,
/// each with 200 chunks of 250 bytes = 50KB per record = 500KB total.
///
/// This is within DNS protocol limits (with EDNS0) but would cause
/// severe memory pressure under concurrent queries.
#[tokio::test]
#[ignore]
async fn test_txt_record_extreme_tunneling() {
    println!("=== Extreme DNS Tunneling Attack ===\n");

    // Simulate 10 TXT records (legitimate domains can have multiple)
    let record_count = 10;
    let chunks_per_record = 200;
    let chunk_size = 250;

    let records_size = record_count * chunks_per_record * chunk_size;

    println!("Attack parameters:");
    println!("  TXT records: {}", record_count);
    println!("  Chunks per record: {}", chunks_per_record);
    println!("  Chunk size: {} bytes", chunk_size);
    println!(
        "  Total size: {} bytes ({:.1} KB)",
        records_size,
        records_size as f64 / 1024.0
    );
    println!();

    let initial_memory = get_process_memory();

    // Simulate creating all TXT records
    let mut txt_records = Vec::new();
    for record_num in 0..record_count {
        let chunks: Vec<Vec<u8>> = (0..chunks_per_record)
            .map(|chunk_num| {
                let mut chunk = vec![b'X'; chunk_size];
                let marker = format!("R{:02}_C{:04}", record_num, chunk_num);
                chunk[..marker.len()].copy_from_slice(marker.as_bytes());
                chunk
            })
            .collect();

        // Concatenate chunks (same as src/dns/records.rs)
        let concatenated: String = chunks
            .iter()
            .map(|bytes| String::from_utf8_lossy(bytes).to_string())
            .collect::<Vec<String>>()
            .join("");

        txt_records.push(concatenated);
    }

    let final_memory = get_process_memory();
    let memory_growth = final_memory.saturating_sub(initial_memory);

    println!("Results:");
    println!("  Created {} TXT records", txt_records.len());
    println!(
        "  Total data: {} bytes ({:.1} KB)",
        records_size,
        records_size as f64 / 1024.0
    );
    println!(
        "  Memory growth: {} bytes ({:.1} KB)",
        memory_growth,
        memory_growth as f64 / 1024.0
    );
    println!();

    println!("CRITICAL VULNERABILITY: No protection against extreme TXT records");
    println!();
    println!("Impact at 100 concurrent DNS queries:");
    println!("  100 domains × 500KB = 50MB memory from TXT records");
    println!();
    println!("Recommended defenses:");
    println!("  1. MAX_TXT_RECORD_SIZE = 1024 bytes (truncate oversized records)");
    println!("  2. MAX_TXT_RECORD_COUNT = 10 (limit number of records processed)");
    println!("  3. Log warning when limits exceeded (detect DNS tunneling)");
}

/// Crude memory measurement helper (Unix-specific).
fn get_process_memory() -> usize {
    #[cfg(target_os = "linux")]
    {
        let pid = std::process::id();
        let status_path = format!("/proc/{}/status", pid);
        if let Ok(status) = std::fs::read_to_string(status_path) {
            for line in status.lines() {
                if line.starts_with("VmRSS:") {
                    let parts: Vec<&str> = line.split_whitespace().collect();
                    if parts.len() >= 2 {
                        if let Ok(kb) = parts[1].parse::<usize>() {
                            return kb * 1024;
                        }
                    }
                }
            }
        }
    }

    #[cfg(target_os = "macos")]
    {
        use std::process::Command;
        if let Ok(output) = Command::new("ps")
            .args(["-o", "rss=", "-p", &std::process::id().to_string()])
            .output()
        {
            if let Ok(s) = String::from_utf8(output.stdout) {
                if let Ok(kb) = s.trim().parse::<usize>() {
                    return kb * 1024;
                }
            }
        }
    }

    0
}
