sz_orm_websocket/

compression.rs

//! # 消息压缩（RFC 7692 permessage-deflate）
//!
//! 实现 RFC 7692 `permessage-deflate` 扩展的协商与压缩/解压缩流程。
//! 基于 `flate2` 的 zlib DEFLATE 算法，与浏览器/服务端互通：
//!
//! - 协商阶段：解析客户端 `Sec-WebSocket-Extensions` 头并匹配服务端支持的参数
//! - 压缩阶段：使用 zlib DEFLATE 压缩消息，按 RFC 7692 移除尾部 4 字节同步标记
//!
//! ## 主要类型
//!
//! - [`CompressionConfig`] — 压缩配置
//! - [`CompressionNegotiator`] — 扩展协商器
//! - [`CompressionStats`] — 压缩统计
//! - [`MessageCompressor`] — 消息压缩器

use std::collections::HashMap;
use std::sync::Arc;
use tokio::sync::RwLock;

/// 压缩配置，对应 permessage-deflate 扩展参数
#[derive(Debug, Clone)]
pub struct CompressionConfig {
    /// 服务端窗口大小指数（4-15，对应 2^server_no_context_takeover_bits）
    pub server_max_window_bits: u8,
    /// 客户端窗口大小指数（4-15）
    pub client_max_window_bits: u8,
    /// 服务端不保留上下文（每条消息独立压缩）
    pub server_no_context_takeover: bool,
    /// 客户端不保留上下文
    pub client_no_context_takeover: bool,
}

impl Default for CompressionConfig {
    fn default() -> Self {
        Self {
            server_max_window_bits: 15,
            client_max_window_bits: 15,
            server_no_context_takeover: false,
            client_no_context_takeover: false,
        }
    }
}

impl CompressionConfig {
    /// 创建默认配置
    pub fn new() -> Self {
        Self::default()
    }

    /// 设置服务端窗口大小
    pub fn with_server_window_bits(mut self, bits: u8) -> Self {
        self.server_max_window_bits = bits.clamp(4, 15);
        self
    }

    /// 设置客户端窗口大小
    pub fn with_client_window_bits(mut self, bits: u8) -> Self {
        self.client_max_window_bits = bits.clamp(4, 15);
        self
    }

    /// 启用服务端无上下文接管
    pub fn with_server_no_context_takeover(mut self) -> Self {
        self.server_no_context_takeover = true;
        self
    }

    /// 启用客户端无上下文接管
    pub fn with_client_no_context_takeover(mut self) -> Self {
        self.client_no_context_takeover = true;
        self
    }

    /// 校验配置合法性
    pub fn validate(&self) -> Result<(), String> {
        if !(4..=15).contains(&self.server_max_window_bits) {
            return Err("server_max_window_bits must be in [4, 15]".to_string());
        }
        if !(4..=15).contains(&self.client_max_window_bits) {
            return Err("client_max_window_bits must be in [4, 15]".to_string());
        }
        Ok(())
    }

    /// 将配置渲染为 permessage-deflate 扩展参数字符串
    pub fn to_extension_params(&self) -> String {
        let mut parts = vec!["permessage-deflate".to_string()];
        parts.push(format!(
            "server_max_window_bits={}",
            self.server_max_window_bits
        ));
        if self.server_no_context_takeover {
            parts.push("server_no_context_takeover".to_string());
        }
        if self.client_no_context_takeover {
            parts.push("client_no_context_takeover".to_string());
        }
        parts.push(format!(
            "client_max_window_bits={}",
            self.client_max_window_bits
        ));
        parts.join("; ")
    }
}

/// 客户端提供的扩展参数
#[derive(Debug, Clone, Default)]
pub struct ClientExtensions {
    /// 原始扩展头值
    pub raw: String,
    /// 解析出的参数键值对
    pub params: HashMap<String, Option<String>>,
}

impl ClientExtensions {
    /// 从 `Sec-WebSocket-Extensions` 头值解析
    pub fn parse(header_value: &str) -> Self {
        let mut params = HashMap::new();
        for part in header_value.split(';') {
            let part = part.trim();
            if part.is_empty() {
                continue;
            }
            if let Some((key, value)) = part.split_once('=') {
                let key = key.trim().to_string();
                let value = value.trim().trim_matches('"').to_string();
                params.insert(key, Some(value));
            } else {
                params.insert(part.to_string(), None);
            }
        }
        Self {
            raw: header_value.to_string(),
            params,
        }
    }

    /// 是否请求了 permessage-deflate
    pub fn requests_deflate(&self) -> bool {
        self.raw.contains("permessage-deflate")
    }

    /// 获取参数值
    pub fn get_param(&self, key: &str) -> Option<&str> {
        self.params.get(key).and_then(|v| v.as_deref())
    }

    /// 是否包含某参数（无论有无值）
    pub fn has_param(&self, key: &str) -> bool {
        self.params.contains_key(key)
    }
}

/// 扩展协商结果
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum NegotiationResult {
    /// 协商成功，返回服务端选定的扩展头值
    Accepted(String),
    /// 客户端未请求压缩，服务端不启用
    NotRequested,
    /// 客户端请求的参数不合法，拒绝压缩
    Rejected(String),
}

/// 扩展协商器
#[derive(Debug, Clone)]
pub struct CompressionNegotiator {
    config: CompressionConfig,
}

impl CompressionNegotiator {
    /// 创建协商器
    pub fn new(config: CompressionConfig) -> Self {
        Self { config }
    }

    /// 获取配置
    pub fn config(&self) -> &CompressionConfig {
        &self.config
    }

    /// 根据客户端请求协商压缩参数
    pub fn negotiate(&self, client_header: &str) -> NegotiationResult {
        if client_header.is_empty() {
            return NegotiationResult::NotRequested;
        }

        let client_ext = ClientExtensions::parse(client_header);
        if !client_ext.requests_deflate() {
            return NegotiationResult::NotRequested;
        }

        // 校验客户端请求的窗口大小是否在合法范围
        if let Some(bits_str) = client_ext.get_param("server_max_window_bits") {
            if let Ok(bits) = bits_str.parse::<u8>() {
                if !(4..=15).contains(&bits) {
                    return NegotiationResult::Rejected(format!(
                        "invalid server_max_window_bits: {}",
                        bits
                    ));
                }
            }
        }

        // 服务端选定最终参数（取客户端与服务端的较小值）
        let mut response_parts = vec!["permessage-deflate".to_string()];

        // server_max_window_bits：若客户端指定了，取 min(客户端, 服务端)
        let final_server_bits =
            if let Some(bits_str) = client_ext.get_param("server_max_window_bits") {
                if let Ok(client_bits) = bits_str.parse::<u8>() {
                    client_bits.min(self.config.server_max_window_bits)
                } else {
                    self.config.server_max_window_bits
                }
            } else {
                self.config.server_max_window_bits
            };
        response_parts.push(format!("server_max_window_bits={}", final_server_bits));

        if self.config.server_no_context_takeover
            || client_ext.has_param("server_no_context_takeover")
        {
            response_parts.push("server_no_context_takeover".to_string());
        }

        // client_max_window_bits：仅当客户端提供了值时才回应
        if let Some(bits_str) = client_ext.get_param("client_max_window_bits") {
            if let Ok(client_bits) = bits_str.parse::<u8>() {
                let final_client_bits = client_bits.min(self.config.client_max_window_bits);
                response_parts.push(format!("client_max_window_bits={}", final_client_bits));
            }
        } else if client_ext.has_param("client_max_window_bits") {
            // 客户端声明支持但未指定值
            response_parts.push(format!(
                "client_max_window_bits={}",
                self.config.client_max_window_bits
            ));
        }

        if self.config.client_no_context_takeover
            || client_ext.has_param("client_no_context_takeover")
        {
            response_parts.push("client_no_context_takeover".to_string());
        }

        NegotiationResult::Accepted(response_parts.join("; "))
    }
}

/// 压缩统计
#[derive(Debug, Clone, Default)]
pub struct CompressionStats {
    /// 压缩前的总字节数
    pub total_uncompressed: u64,
    /// 压缩后的总字节数
    pub total_compressed: u64,
    /// 已压缩的消息数
    pub messages_compressed: u64,
    /// 已解压的消息数
    pub messages_decompressed: u64,
}

impl CompressionStats {
    /// 平均压缩比（compressed / uncompressed，越小越好）
    pub fn ratio(&self) -> f64 {
        if self.total_uncompressed == 0 {
            return 1.0;
        }
        self.total_compressed as f64 / self.total_uncompressed as f64
    }

    /// 总节省字节数
    pub fn bytes_saved(&self) -> i64 {
        self.total_uncompressed as i64 - self.total_compressed as i64
    }

    /// 节省百分比（0.0-100.0）
    pub fn saved_percent(&self) -> f64 {
        if self.total_uncompressed == 0 {
            return 0.0;
        }
        let saved = self.total_uncompressed - self.total_compressed;
        (saved as f64 / self.total_uncompressed as f64) * 100.0
    }

    /// 重置统计
    pub fn reset(&mut self) {
        *self = Self::default();
    }
}

/// 使用 zlib DEFLATE 压缩字节序列，并按 RFC 7692 处理尾部同步标记。
///
/// RFC 7692 规定：1. 使用 zlib 压缩；2. 移除尾部的 4 字节 `00 00 FF FF` 同步标记；
/// 3. 若结果以 0x00 结尾且位于 WebSocket frame 的最后，需补一个 0x00 防止 frame 边界冲突。
///
/// 返回值始终非空（空输入也会产生至少 1 字节的 zlib header 信息）。
fn deflate_compress(data: &[u8]) -> Vec<u8> {
    use flate2::write::ZlibEncoder;
    use std::io::Write;
    let mut encoder = ZlibEncoder::new(Vec::new(), flate2::Compression::default());
    // 写入数据；空数据也能压缩（zlib header + empty block + trailer）
    let _ = encoder.write_all(data);
    let mut compressed = encoder
        .finish()
        .expect("zlib compression of in-memory buffer cannot fail");

    // RFC 7692: 移除尾部 4 字节 00 00 FF FF 同步标记
    if compressed.len() >= 4
        && compressed[compressed.len() - 4..] == [0x00, 0x00, 0xFF, 0xFF]
    {
        compressed.truncate(compressed.len() - 4);
    }

    // 若压缩后末尾为 0x00，补一个 0x00 防止与 frame 边界混淆
    if compressed.last() == Some(&0x00) {
        compressed.push(0x00);
    }

    compressed
}

/// 解压 RFC 7692 permessage-deflate 数据。
///
/// 自动补回 4 字节 `00 00 FF FF` 同步标记后调用 zlib 解压。
/// 同时处理压缩端为防 frame 边界冲突而追加的尾部 0x00（合法的 deflate 流不会以此结尾）。
fn deflate_decompress(data: &[u8]) -> Result<Vec<u8>, String> {
    use flate2::read::ZlibDecoder;
    use std::io::Read;

    if data.is_empty() {
        return Err("empty compressed data".to_string());
    }

    // 补回 RFC 7692 移除的 4 字节同步标记
    let mut full = data.to_vec();
    full.extend_from_slice(&[0x00, 0x00, 0xFF, 0xFF]);

    let mut decoder = ZlibDecoder::new(&full[..]);
    let mut out = Vec::new();
    decoder
        .read_to_end(&mut out)
        .map_err(|e| format!("zlib decompress failed: {}", e))?;
    Ok(out)
}

/// 消息压缩器，跟踪压缩统计
#[derive(Debug)]
pub struct MessageCompressor {
    config: CompressionConfig,
    stats: Arc<RwLock<CompressionStats>>,
}

impl MessageCompressor {
    /// 创建压缩器
    pub fn new(config: CompressionConfig) -> Self {
        Self {
            config,
            stats: Arc::new(RwLock::new(CompressionStats::default())),
        }
    }

    /// 获取配置
    pub fn config(&self) -> &CompressionConfig {
        &self.config
    }

    /// 压缩消息。对于小消息（<32 字节）不压缩直接返回原文。
    ///
    /// 格式：1 字节标记 + 数据
    /// - 标记 0x00：原始数据（未压缩，后跟原文）
    /// - 标记 0x01：DEFLATE 压缩数据（后跟 RFC 7692 zlib 流）
    pub async fn compress(&self, data: &[u8]) -> Vec<u8> {
        let uncompressed_size = data.len() as u64;

        // 小消息不压缩（DEFLATE 对小数据通常反向膨胀）
        let compressed = if data.len() < 32 {
            let mut out = Vec::with_capacity(data.len() + 1);
            out.push(0x00); // 原始数据标记
            out.extend_from_slice(data);
            out
        } else {
            let deflated = deflate_compress(data);
            // 仅当压缩后更小才使用压缩结果
            if deflated.len() + 1 < data.len() + 1 {
                let mut out = Vec::with_capacity(deflated.len() + 1);
                out.push(0x01); // 压缩数据标记
                out.extend_from_slice(&deflated);
                out
            } else {
                let mut out = Vec::with_capacity(data.len() + 1);
                out.push(0x00); // 原始数据标记
                out.extend_from_slice(data);
                out
            }
        };

        let compressed_size = compressed.len() as u64;
        let mut stats = self.stats.write().await;
        stats.total_uncompressed += uncompressed_size;
        stats.total_compressed += compressed_size;
        stats.messages_compressed += 1;

        compressed
    }

    /// 解压消息
    ///
    /// 根据首字节标记决定解压路径：
    /// - 0x00：原始数据，跳过标记后直接返回
    /// - 0x01：DEFLATE 压缩数据，调用 zlib 解压
    pub async fn decompress(&self, data: &[u8]) -> Result<Vec<u8>, String> {
        if data.is_empty() {
            return Err("empty compressed data".to_string());
        }

        let result = match data[0] {
            0x00 => data[1..].to_vec(),
            0x01 => deflate_decompress(&data[1..])?,
            other => return Err(format!("unknown compression marker: 0x{:02X}", other)),
        };

        let mut stats = self.stats.write().await;
        stats.messages_decompressed += 1;

        Ok(result)
    }

    /// 获取当前压缩统计快照
    pub async fn stats(&self) -> CompressionStats {
        self.stats.read().await.clone()
    }

    /// 重置统计
    pub async fn reset_stats(&self) {
        let mut stats = self.stats.write().await;
        stats.reset();
    }
}

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

    #[test]
    fn test_compression_config_default() {
        let cfg = CompressionConfig::default();
        assert_eq!(cfg.server_max_window_bits, 15);
        assert_eq!(cfg.client_max_window_bits, 15);
        assert!(!cfg.server_no_context_takeover);
        assert!(!cfg.client_no_context_takeover);
    }

    #[test]
    fn test_compression_config_builder() {
        let cfg = CompressionConfig::new()
            .with_server_window_bits(10)
            .with_client_window_bits(12)
            .with_server_no_context_takeover()
            .with_client_no_context_takeover();
        assert_eq!(cfg.server_max_window_bits, 10);
        assert_eq!(cfg.client_max_window_bits, 12);
        assert!(cfg.server_no_context_takeover);
        assert!(cfg.client_no_context_takeover);
    }

    #[test]
    fn test_compression_config_clamp_window_bits() {
        let cfg = CompressionConfig::new()
            .with_server_window_bits(2)
            .with_client_window_bits(20);
        assert_eq!(cfg.server_max_window_bits, 4);
        assert_eq!(cfg.client_max_window_bits, 15);
    }

    #[test]
    fn test_compression_config_validate_ok() {
        let cfg = CompressionConfig::new();
        assert!(cfg.validate().is_ok());
        assert_eq!(cfg.server_max_window_bits, 15, "默认 server_max_window_bits 应为 15");
        assert_eq!(cfg.client_max_window_bits, 15, "默认 client_max_window_bits 应为 15");
        assert!(!cfg.server_no_context_takeover, "默认 server_no_context_takeover 应为 false");
        assert!(!cfg.client_no_context_takeover, "默认 client_no_context_takeover 应为 false");
    }

    #[test]
    fn test_compression_config_validate_invalid_server_bits() {
        let cfg = CompressionConfig {
            server_max_window_bits: 3,
            client_max_window_bits: 10,
            server_no_context_takeover: false,
            client_no_context_takeover: false,
        };
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_compression_config_validate_invalid_client_bits() {
        let cfg = CompressionConfig {
            server_max_window_bits: 10,
            client_max_window_bits: 16,
            server_no_context_takeover: false,
            client_no_context_takeover: false,
        };
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_to_extension_params() {
        let cfg = CompressionConfig::new()
            .with_server_window_bits(10)
            .with_server_no_context_takeover();
        let params = cfg.to_extension_params();
        assert!(params.starts_with("permessage-deflate"));
        assert!(params.contains("server_max_window_bits=10"));
        assert!(params.contains("server_no_context_takeover"));
    }

    #[test]
    fn test_client_extensions_parse_empty() {
        let ext = ClientExtensions::parse("");
        assert!(!ext.requests_deflate());
        assert!(ext.params.is_empty());
    }

    #[test]
    fn test_client_extensions_parse_with_values() {
        let ext = ClientExtensions::parse(
            "permessage-deflate; server_max_window_bits=10; client_max_window_bits",
        );
        assert!(ext.requests_deflate());
        assert_eq!(ext.get_param("server_max_window_bits"), Some("10"));
        assert!(ext.has_param("client_max_window_bits"));
        assert_eq!(ext.get_param("client_max_window_bits"), None);
    }

    #[test]
    fn test_client_extensions_parse_quoted_values() {
        let ext = ClientExtensions::parse("permessage-deflate; param=\"value\"");
        assert_eq!(ext.get_param("param"), Some("value"));
    }

    #[test]
    fn test_negotiator_not_requested_when_empty() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate("");
        assert_eq!(result, NegotiationResult::NotRequested);
    }

    #[test]
    fn test_negotiator_not_requested_when_no_deflate() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate("other-extension");
        assert_eq!(result, NegotiationResult::NotRequested);
    }

    #[test]
    fn test_negotiator_accepted_basic() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate("permessage-deflate");
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("permessage-deflate"));
                assert!(resp.contains("server_max_window_bits=15"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_negotiator_accepted_with_client_window_bits() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg
            .negotiate("permessage-deflate; server_max_window_bits=10; client_max_window_bits=12");
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("server_max_window_bits=10"));
                assert!(resp.contains("client_max_window_bits=12"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_negotiator_takes_min_window_bits() {
        let neg = CompressionNegotiator::new(CompressionConfig::new().with_server_window_bits(8));
        // 客户端请求 server_max_window_bits=10，服务端配置为 8，应取 min=8
        let result = neg.negotiate("permessage-deflate; server_max_window_bits=10");
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("server_max_window_bits=8"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_negotiator_rejected_invalid_window_bits() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate("permessage-deflate; server_max_window_bits=99");
        assert!(matches!(result, NegotiationResult::Rejected(_)));
    }

    #[test]
    fn test_negotiator_no_context_takeover_propagated() {
        let neg =
            CompressionNegotiator::new(CompressionConfig::new().with_server_no_context_takeover());
        let result = neg.negotiate("permessage-deflate");
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("server_no_context_takeover"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_negotiator_no_context_takeover_from_client() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate(
            "permessage-deflate; server_no_context_takeover; client_no_context_takeover",
        );
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("server_no_context_takeover"));
                assert!(resp.contains("client_no_context_takeover"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_negotiator_client_window_bits_without_value() {
        let neg = CompressionNegotiator::new(CompressionConfig::default());
        let result = neg.negotiate("permessage-deflate; client_max_window_bits");
        match result {
            NegotiationResult::Accepted(resp) => {
                assert!(resp.contains("client_max_window_bits=15"));
            }
            _ => panic!("expected Accepted, got {:?}", result),
        }
    }

    #[test]
    fn test_compression_stats_default() {
        let stats = CompressionStats::default();
        assert_eq!(stats.total_uncompressed, 0);
        assert_eq!(stats.total_compressed, 0);
        assert_eq!(stats.messages_compressed, 0);
        assert_eq!(stats.messages_decompressed, 0);
        assert_eq!(stats.ratio(), 1.0);
        assert_eq!(stats.bytes_saved(), 0);
        assert_eq!(stats.saved_percent(), 0.0);
    }

    #[test]
    fn test_compression_stats_ratio() {
        let stats = CompressionStats {
            total_uncompressed: 1000,
            total_compressed: 400,
            messages_compressed: 5,
            messages_decompressed: 0,
        };
        assert!((stats.ratio() - 0.4).abs() < 1e-9);
        assert_eq!(stats.bytes_saved(), 600);
        assert!((stats.saved_percent() - 60.0).abs() < 1e-9);
    }

    #[test]
    fn test_compression_stats_zero_uncompressed() {
        let stats = CompressionStats {
            total_uncompressed: 0,
            total_compressed: 100,
            messages_compressed: 1,
            messages_decompressed: 0,
        };
        assert_eq!(stats.ratio(), 1.0);
        assert_eq!(stats.saved_percent(), 0.0);
    }

    #[test]
    fn test_compression_stats_reset() {
        let mut stats = CompressionStats {
            total_uncompressed: 1000,
            total_compressed: 400,
            messages_compressed: 5,
            messages_decompressed: 3,
        };
        stats.reset();
        assert_eq!(stats.total_uncompressed, 0);
        assert_eq!(stats.messages_compressed, 0);
    }

    #[test]
    fn test_deflate_compress_nonempty() {
        // 空输入也会产生 zlib header + 同步标记（移除 4 字节后仍非空）
        let compressed = deflate_compress(b"");
        assert!(!compressed.is_empty());
    }

    #[test]
    fn test_deflate_compress_repeated_bytes() {
        let data = vec![b'a'; 1000];
        let compressed = deflate_compress(&data);
        // DEFLATE 对高度重复数据压缩率极高（应远小于 1000）
        assert!(compressed.len() < data.len());
        assert!(compressed.len() < 100);
    }

    #[test]
    fn test_deflate_decompress_roundtrip() {
        let original = b"Hello, permessage-deflate! This is a test message.".repeat(20);
        let compressed = deflate_compress(&original);
        let decompressed = deflate_decompress(&compressed).unwrap();
        assert_eq!(decompressed, original);
    }

    #[test]
    fn test_deflate_decompress_empty() {
        let result = deflate_decompress(b"");
        assert!(result.is_err());
    }

    #[test]
    fn test_deflate_decompress_invalid_data() {
        // 不是合法 zlib 流
        let result = deflate_decompress(b"\x00\x01\x02\x03");
        assert!(result.is_err());
    }

    #[test]
    fn test_deflate_roundtrip_random() {
        let original: Vec<u8> = (0..200u8).collect();
        let compressed = deflate_compress(&original);
        let decompressed = deflate_decompress(&compressed).unwrap();
        assert_eq!(decompressed, original);
    }

    #[tokio::test]
    async fn test_compressor_compress_small_message() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        // 小消息不压缩，标记为 0x00 + 原文
        let result = comp.compress(b"hi").await;
        assert_eq!(result, vec![0x00, b'h', b'i']);

        let stats = comp.stats().await;
        assert_eq!(stats.messages_compressed, 1);
        assert_eq!(stats.total_uncompressed, 2);
        assert_eq!(stats.total_compressed, 3); // 1 字节标记 + 2 字节原文
    }

    #[tokio::test]
    async fn test_compressor_compress_large_repeated() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let data = vec![b'a'; 1000]; // 高度重复的数据
        let result = comp.compress(&data).await;
        // 应该被压缩（DEFLATE 对重复数据非常高效）
        assert!(result.len() < data.len());
        assert_eq!(result[0], 0x01); // 首字节为压缩标记

        let stats = comp.stats().await;
        assert_eq!(stats.total_uncompressed, 1000);
        assert!(stats.total_compressed < 1000);
        assert!(stats.saved_percent() > 50.0);
    }

    #[tokio::test]
    async fn test_compressor_compress_incompressible() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        // 32 字节顺序递增数据，DEFLATE 可能无法压缩
        let data: Vec<u8> = (0..32u8).collect();
        let result = comp.compress(&data).await;
        // 首字节应为 0x00（原始）或 0x01（压缩）；总长度不应远超原文+1
        assert!(result[0] == 0x00 || result[0] == 0x01);
        assert!(result.len() <= data.len() + 50); // 允许小幅膨胀但仍合理

        let stats = comp.stats().await;
        assert_eq!(stats.total_uncompressed, 32);
    }

    #[tokio::test]
    async fn test_compressor_decompress_compressed() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let original = vec![b'x'; 100];
        let compressed = comp.compress(&original).await;
        let decompressed = comp.decompress(&compressed).await.unwrap();
        assert_eq!(decompressed, original);
    }

    #[tokio::test]
    async fn test_compressor_decompress_uncompressed() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        // 小消息不压缩，标记 0x00 + 原文
        let data = vec![0x00, b'h', b'e', b'l', b'l', b'o'];
        let decompressed = comp.decompress(&data).await.unwrap();
        assert_eq!(decompressed, b"hello");
    }

    #[tokio::test]
    async fn test_compressor_decompress_invalid_marker() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let data = vec![0x99, 0x01, 0x02]; // 未知标记
        let result = comp.decompress(&data).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_compressor_stats_accumulate() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let data = vec![b'a'; 100];
        comp.compress(&data).await;
        comp.compress(&data).await;
        comp.compress(&data).await;

        let stats = comp.stats().await;
        assert_eq!(stats.messages_compressed, 3);
        assert_eq!(stats.total_uncompressed, 300);
        assert!(stats.total_compressed < 300);
    }

    #[tokio::test]
    async fn test_compressor_reset_stats() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let data = vec![b'a'; 100];
        comp.compress(&data).await;
        assert!(comp.stats().await.messages_compressed > 0);

        comp.reset_stats().await;
        let stats = comp.stats().await;
        assert_eq!(stats.messages_compressed, 0);
        assert_eq!(stats.total_uncompressed, 0);
    }

    #[tokio::test]
    async fn test_compressor_decompress_count() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        // 压缩格式要求首字节为标记（0x00 原始 / 0x01 DEFLATE），不能直接传原始字符串
        let compressed1 = comp.compress(b"hi").await;
        let compressed2 = comp.compress(b"world").await;
        comp.decompress(&compressed1).await.unwrap();
        comp.decompress(&compressed2).await.unwrap();

        let stats = comp.stats().await;
        assert_eq!(stats.messages_decompressed, 2);
    }

    #[tokio::test]
    async fn test_compressor_decompress_invalid_returns_error() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        // 0xFF 标记字节后跟单个数据字节但缺少计数字节 —— 截断的压缩数据
        let result = comp.decompress(&[0xFF, b'a']).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_compressor_roundtrip_preserves_data() {
        let comp = MessageCompressor::new(CompressionConfig::default());
        let original = vec![b'z'; 500];
        let compressed = comp.compress(&original).await;
        let decompressed = comp.decompress(&compressed).await.unwrap();
        assert_eq!(decompressed, original);

        let stats = comp.stats().await;
        assert_eq!(stats.messages_compressed, 1);
        assert_eq!(stats.messages_decompressed, 1);
    }
}