This HEX file parser analyses each byte by using state machine method.
The fields of Intel HEX records includes: 
 
Start code
 
Byte count
 
Address
 
Record type
 
Data
 
Checksum
For example:
If the input string is ":020000040800F2:10"
The parser will iterate through the string, the last character will be recognized as "Byte count last nibble" field.
Then, the parser will save current state and return back to the caller function.
If the 2nd input string is "8000000804002001810008C582000871810008" The parser will parse the string based on previous saved state. Hence, the first character will be recognized as "Address" field.
bool testcase_long_str()
{
    printf("=== testcase_long_str\n");
    const uint8_t ihex_long0[] = ":020000040800F2\n:108000000804002001810008C582000871810008";
    const uint8_t ihex_long1[] = "71\n:10801000C38200086D8100089583000800000000FD\r\n:1080";
    const uint8_t ihex_long2[] = "2000000000000000000000000000C9820008FD\n:10803000";
    const uint8_t ihex_long3[] = "6F81000800000000C7820008CB82";
    const uint8_t ihex_long4[] = "0008A2\r\n:108040001B8100081B8100081B8100081B810008";
    const uint8_t ihex_long5[] = "A0\n:08847000A683000800A24A04E3\n:04000005080080ED82\n:00000001FF";
    if (!ihex_parser(ihex_long0, sizeof(ihex_long0)))
    {
        printf("Parse error long0\n");
        return false;
    }
    if (!ihex_parser(ihex_long1, sizeof(ihex_long1)))
    {
        printf("Parse error long1\n");
        return false;
    }
    if (!ihex_parser(ihex_long2, sizeof(ihex_long2)))
    {
        printf("Parse error long2\n");
        return false;
    }
    if (!ihex_parser(ihex_long3, sizeof(ihex_long3)))
    {
        printf("Parse error long3\n");
        return false;
    }
    if (!ihex_parser(ihex_long4, sizeof(ihex_long4)))
    {
        printf("Parse error long4\n");
        return false;
    }
    if (!ihex_parser(ihex_long5, sizeof(ihex_long5)))
    {
        printf("Parse error long5\n");
        return false;
    }
    return true;
}Set Linear Address:08000000 
WriteData (0x08008000):0804002001810008C582000871810008 
WriteData (0x08008010):C38200086D8100089583000800000000 
WriteData (0x08008020):000000000000000000000000C9820008 
WriteData (0x08008030):6F81000800000000C7820008CB820008 
WriteData (0x08008040):1B8100081B8100081B8100081B810008 
WriteData (0x08008470):A683000800A24A04 
Start linear address 
EOF
    ihex_set_callback_func(write_flash_data);
    ihex_reset_state();
    
    /* Open HEX file, read per 256 byte block size*/
    bool return_status = false;
    uint8_t fbuf[256];
    size_t readcount = 0;
    FILE *fp = fopen("test.hex", "r");
    if (fp == NULL)
    {
        printf("fopen: cannot open hex file\n");
        goto EXIT;
    }
    
    while ((readcount = fread(fbuf, 1, sizeof(fbuf), fp)) > 0)
    {
        if (readcount < sizeof(fbuf))
        {
            fbuf[readcount] = '\0';     // Add null teminated char
        }
        if (!ihex_parser(fbuf, sizeof(fbuf)))
        {
            printf("parse failed\n");
            goto EXIT;
        }
    }
    
    return_status = true;
EXIT:
    if (fp)
        fclose(fp);
    return return_status;