写一个Y-modem接收程序

以下是一个简单的 Y-Modem 接收程序的代码示例，使用了 C 语言和标准库：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define PACKET_SIZE 128
#define FILE_NAME_SIZE 128
#define BUFSIZE (PACKET_SIZE + 5)

// CRC 高位表
const unsigned short crc16_table_high[] = {
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
};

// CRC 低位表
const unsigned short crc16_table_low[] = {
    0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
    0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
    0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
    0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
    0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
    0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
    0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
    0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
    0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
    0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
    0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
    0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
    0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
    0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
    0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
    0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
    0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
    0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
    0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
    0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
    0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
    0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
    0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
    0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
    0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
    0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
    0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
    0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
    0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
    0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
    0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
    0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78,
};

// CRC 计算函数
unsigned short crc16_ccitt(const unsigned char *data, int len)
{
    unsigned short crc = 0xFFFF;

    for (int i = 0; i < len; i++) {
        crc = (crc >> 8) ^ crc16_table_high[(crc ^ data[i]) & 0xFF];
        crc = (crc >> 8) ^ crc16_table_low[(crc & 0xFF)];
    }

    return crc;
}

// 接收文件
int receive_file(FILE *file, char *file_name)
{
    unsigned char buf[BUFSIZE];
    int packet_num = 0, file_size = 0, start = 0;
    unsigned short crc = 0;
    char file_path[FILE_NAME_SIZE];

    memset(file_path, 0, FILE_NAME_SIZE);
    sprintf(file_path, "./%s", file_name);

    // 打开文件
    file = fopen(file_path, "wb");
    if (!file) {
        printf("Error: Cannot open file %s.\n", file_path);
        return -1;
    }

    // 向终端发送 C 接收请求
    printf("C\n");
    while (1) {
        // 读取数据包
        memset(buf, 0, BUFSIZE);
        if (fread(buf, 1, PACKET_SIZE + 5, stdin) <= 0) {
            printf("Error: Cannot read data packet.\n");
            return -1;
        }
        // 校验包头
        if (buf[0] != 0x01 && buf[0] != 0x02) {
            printf("Error: Invalid packet header.\n");
            return -1;
        }
        // 校验块号
        if (buf[1] != (packet_num & 0xFF) || buf[2] != (~packet_num & 0xFF)) {
            printf("Error: Invalid packet number.\n");
            return -1;
        }
        // 校验 CRC
        crc = crc16_ccitt(buf + 3, PACKET_SIZE + 2);
        if (buf[PACKET_SIZE + 3] != (crc >> 8) || buf[PACKET_SIZE + 4] != (crc & 0xFF)) {
            printf("Error: Invalid CRC.\n");
            return -1;
        }
        // 处理数据
        if (buf[0] == 0x01) {  // 文件名
            // 获取文件名
            memset(file_name, 0, FILE_NAME_SIZE);
            for (int i = 0; i < PACKET_SIZE; i++) {
                if (buf[i + 3] == '\0') {
                    break;
                }
                file_name[i] = buf[i + 3];
            }
            // 发送 ACK
            printf("%c", 0x06);
            packet_num = (packet_num + 1) & 0xFF;
        } else if (buf[0] == 0x02) {  // 文件大小
            file_size = (buf[3] << 24) | (buf[4] << 16) | (buf[5] << 8) | buf[6];
            // 发送 ACK
            printf("%c", 0x06);
            packet_num = (packet_num + 1) & 0xFF;
            // 打开文件
            file = fopen(file_name, "wb");
            if (!file) {
                printf("Error: Cannot open file %s.\n", file_name);
                return -1;
            }
            start = 1;
        } else if (buf[0] == 0x03) {  // 文件数据
            if (start) {
                fwrite(buf + 3, 1, PACKET_SIZE, file);
                packet_num = (packet_num + 1) & 0xFF;
                if (file_size <= PACKET_SIZE * packet_num) {  // 文件接收完成
                    fclose(file);
                    printf("%c", 0x06);
                    break;
                } else {  // 发送 ACK
                    printf("%c", 0x06);
                }
            } else {
                printf("Error: Invalid data packet.\n");
                return -1;
            }
        } else if (buf[0] == 0x04) {  // 文件结束
            fclose(file);
            printf("%c", 0x06);
            break;
        } else {
            printf("Error: Invalid packet type.\n");
            return -1;
        }
    }

    return file_size;
}

int main(int argc, char const *argv[])
{
    FILE *file = NULL;
    char file_name[FILE_NAME_SIZE];

    memset(file_name, 0, FILE_NAME_SIZE);
    if (receive_file(file, file_name) > 0) {
        printf("File %s received successfully.\n", file_name);
    } else {
        printf("Error: Failed to receive file %s.\n", file_name);
    }

    return 0;
}

Y-Modem 协议是以数据包为单位进行数据传输的，每个数据包包含了一个包