本文分享自华为云社区《华为云短信服务教你用Zig实现Cmpp协议》，作者：张俭。

引言&协议概述

中国网络通信集团短信网关协议（CNGP）是中国网通为实现短信业务而制定的一种通信协议，全称叫做China Netcom Short Message Gateway Protocol，用于在PHS短消息网关（SMGW）和服务提供商（SP）之间、短消息网关（SMGW）和短消息网关（SMGW）之间通信。

Zig 是一种性能优异、安全性高的系统编程语言，适合用于实现底层网络协议。它提供了强大的类型系统、编译时计算和错误处理机制。

CNGP 协议基于客户端/服务端模型工作。由客户端（短信应用，如手机，应用程序等）先和短信网关（SMGW Short Message Gateway）建立起 TCP 长连接，并使用 CNGP 命令与SMGW进行交互，实现短信的发送和接收。在CNGP协议中，无需同步等待响应就可以发送下一个指令，实现者可以根据自己的需要，实现同步、异步两种消息传输模式，满足不同场景下的性能要求。

时序图

连接成功，发送短信

连接成功，从SMGW接收到短信

协议帧介绍

在CNGP协议中，每个PDU都包含两个部分：CNGP Header和CNGP Body

CNGP Header

Header包含以下字段，大小长度都是4字节

Total Length：整个PDU的长度，包括Header和Body。
Command ID：用于标识PDU的类型（例如，Login、Submit等）。
Common Status：命令状态
Sequence Id：序列号，用来匹配请求和响应。

使用Zig实现CNGP协议栈里的建立连接

.
├── src
│   └── bound_atomic.zig
│   ├── cngp_client.zig
│   ├── cngp_client_login_example.zig
│   ├── constant.zig
│   ├── protocol.zig

bound_atomic.zig：原子递增工具类，用来做SequenceId
cngp_client.zig：这个文件包含Cngp的定义，该类负责与CNGP服务进行通信，例如建立连接、发送短信等
cngp_client_login_example.zig：示例代码
constant.zig：存放常量
protocol.zig：这个文件包含 CNGP 协议相关的定义和实现，例如协议的命令 ID、PDU 格式等。

constant.zig存放相关commandId

pub const CommandId = enum(u32) {
    Login = 0x00000001,
    LoginResp = 0x80000001,
    Submit = 0x00000002,
    SubmitResp = 0x80000002,
    Deliver = 0x00000003,
    DeliverResp = 0x80000003,
    ActiveTest = 0x00000004,
    ActiveTestResp = 0x80000004,
    Exit = 0x00000006,
    ExitResp = 0x80000006,
};

protocol.zig协议编解码

const std = @import("std");
const io = std.io;
const CommandId = @import("constant.zig").CommandId;

pub const CngpLogin = struct {
    clientId: []const u8,
    authenticatorClient: []const u8,
    loginMode: u8,
    timeStamp: i32,
    version: u8,

    pub fn length(self: *const CngpLogin) usize {
        return self.clientId.len + self.authenticatorClient.len + 1 + 4 + 1;
    }

    pub fn encode(self: *const CngpLogin, writer: anytype) !void {
        try writer.writeAll(self.clientId);
        try writer.writeAll(self.authenticatorClient);
        try writer.writeByte(self.loginMode);
        try writer.writeIntBig(i32, self.timeStamp);
        try writer.writeByte(self.version);
    }
};

pub const CngpLoginResp = struct {
    authenticatorServer: []const u8,
    version: u8,

    pub fn decode(buffer: []u8) !CngpLoginResp {
        var stream = std.io.fixedBufferStream(buffer);
        var reader = stream.reader();
        var authenticatorServerBuffer: [16]u8 = undefined;
        var fixedSize = try reader.read(&authenticatorServerBuffer);
        if (fixedSize != 16) {
            return error.InvalidLength;
        }
        const version = try reader.readByte();
        return CngpLoginResp{
            .authenticatorServer = authenticatorServerBuffer[0..],
            .version = version,
        };
    }
};

pub const CngpHeader = struct {
    total_length: i32,
    command_id: CommandId,
    command_status: i32,
    sequence_id: i32,
};

pub const CngpBody = union(enum) {
    Login: CngpLogin,
    LoginResp: CngpLoginResp,
};

pub const CngpPdu = struct {
    header: CngpHeader,
    body: CngpBody,

    pub fn length(self: *const CngpPdu) usize {
        return 16 + switch (self.body) {
            .Login => |login| login.length(),
            else => 0,
        };
    }

    pub fn encode(self: *const CngpPdu) ![]u8 {
        const len = self.length();
        var buffer = try std.heap.page_allocator.alloc(u8, len);
        var stream = std.io.fixedBufferStream(buffer);
        var writer = stream.writer();
        try writer.writeInt(i32, @as(i32, @intCast(len)), .Big);
        try writer.writeInt(u32, @intFromEnum(self.header.command_id), .Big);
        try writer.writeInt(i32, self.header.command_status, .Big);
        try writer.writeInt(i32, self.header.sequence_id, .Big);
        switch (self.body) {
            .Login => |login| try login.encode(writer),
            else => unreachable,
        }
        return buffer;
    }

    pub fn decode_login_resp(buffer: []u8) !CngpPdu {
        var header: CngpHeader = undefined;
        header.total_length = 0;
        header.command_id = CommandId.LoginResp;
        header.command_status = std.mem.readIntLittle(i32, buffer[8..12]);
        header.sequence_id = std.mem.readIntLittle(i32, buffer[12..16]);

        const body = try CngpLoginResp.decode(buffer[12..]);
        return CngpPdu{
            .header = header,
            .body = CngpBody{ .LoginResp = body },
        };
    }
};

利用原子类型实现sequenceId递增

const std = @import("std");

pub const BoundAtomic = struct {
    min: i32,
    max: i32,
    integer: std.atomic.Atomic(i32),

    pub fn new(min: i32, max: i32) BoundAtomic {
        return BoundAtomic{
            .min = min,
            .max = max,
            .integer = std.atomic.Atomic(i32).init(min),
        };
    }

    pub fn nextVal(self: *BoundAtomic) i32 {
        while (true) {
            const current = self.integer.load(.SeqCst);
            const next = if (current == self.max) self.min else current + 1;
            if (self.integer.compareAndSwap(current, next, .SeqCst, .SeqCst) == null) {
                return next;
            }
        }
    }
};

实现client以及login方法

const std = @import("std");
const net = std.net;
const CngpBody = @import("protocol.zig").CngpBody;
const CngpLogin = @import("protocol.zig").CngpLogin;
const CngpPdu = @import("protocol.zig").CngpPdu;
const CommandId = @import("constant.zig").CommandId;
const BoundAtomic = @import("bound_atomic.zig").BoundAtomic;

pub const CngpClient = struct {
    host: []const u8,
    port: u16,
    sequenceId: BoundAtomic,
    stream: ?std.net.Stream,

    pub fn init(host: []const u8, port: u16) CngpClient {
        return CngpClient{
            .host = host,
            .port = port,
            .sequenceId = BoundAtomic.new(1, 0x7FFFFFFF),
            .stream = null,
        };
    }

    pub fn connect(self: *CngpClient) !void {
        const peer = try net.Address.parseIp4(self.host, self.port);
        self.stream = try net.tcpConnectToAddress(peer);
    }

    pub fn login(self: *CngpClient, body: CngpLogin) !CngpPdu {
        const sequenceId = self.sequenceId.nextVal();
        const pdu = CngpPdu{
            .header = .{
                .total_length = 0, // Will be calculated in encode method
                .command_id = CommandId.Login,
                .command_status = 0,
                .sequence_id = sequenceId,
            },
            .body = CngpBody{ .Login = body },
        };
        const data = try pdu.encode();
        if (self.stream) |s| {
            const size = try s.write(data);
            if (size != data.len) {
                return error.WriteFailed;
            }

            var buffer: [4]u8 = undefined;
            const readLengthSize = try s.read(buffer[0..]);
            if (readLengthSize != 4) {
                return error.ReadFailed;
            }
            const remainLength = std.mem.readInt(u32, buffer[0..], .Big) - 4;

            var responseBuffer = try std.heap.page_allocator.alloc(u8, remainLength);
            defer std.heap.page_allocator.free(responseBuffer);

            var reader = s.reader();
            const readSize = try reader.read(responseBuffer[0..remainLength]);
            if (readSize != remainLength) {
                return error.ReadFailed;
            }

            const response = try CngpPdu.decode_login_resp(responseBuffer);
            return response;
        } else {
            return error.UnexpectedNull;
        }
    }

    pub fn close(self: *CngpClient) void {
        if (self.stream) |s| {
            s.close();
            self.stream = null;
        }
    }
};

运行Example，验证连接成功

const std = @import("std");
const CngpClient = @import("cngp_client.zig").CngpClient;
const CngpLogin = @import("protocol.zig").CngpLogin;

pub fn main() !void {
    const host = "127.0.0.1";
    const port: u16 = 9890;

    var client = CngpClient.init(host, port);
    defer client.close();

    const clientId = "1234567890";
    const authenticatorClient = "1234567890123456";
    const loginMode: u8 = 1;
    const timeStamp: i32 = 123456789;
    const version: u8 = 1;

    const loginBody = CngpLogin{
        .clientId = clientId,
        .authenticatorClient = authenticatorClient,
        .loginMode = loginMode,
        .timeStamp = timeStamp,
        .version = version,
    };

    try client.connect();
    const response = try client.login(loginBody);
    try std.io.getStdOut().writer().print("Login response: {}\n", .{response});
}

总结

本文简单对CNGP协议进行了介绍，并尝试用zig实现协议栈，但实际商用发送短信往往更加复杂，面临诸如流控、运营商对接、传输层安全等问题，可以选择华为云消息&短信（Message & SMS）服务，华为云短信服务是华为云携手全球多家优质运营商和渠道，为企业用户提供的通信服务。企业调用API或使用群发助手，即可使用验证码、通知短信服务。

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教你如何使用Zig实现Cmpp协议