从字节偏移开始读取文件的一行，直到换行

Question

I am using os.ReadAt() to read certain rows in a csv/tsv file. However, I don't know how many bytes are in that row, I just need to read the line starting at the byte offset I specify until the newline.

buffer = make([]byte, 46)
os.ReadAt(buffer, 64) //Read at byte offset 64 and put contents in buffer

However, this only allows me to read 46 bytes of the line in. Is there any way to read the entire line until the newline?

Thanks

Update:

I just create a struct that holds the offset and line length.. Should've done this in the beginning.. my bad

Answer 1

One way is use the bufio pkg. An example of this is the following:

fd, err := os.Open("your_file.csv")
if err != nil { //error handler
    log.Println(err)
    return
}

reader := bufio.NewReader(fd) // creates a new reader

_, err = reader.Discard(64) // discard the following 64 bytes
if err != nil { // error handler
    log.Println(err)
    return
}

// use isPrefix if is needed, this example doesn't use it
// read line until a new line is found
line, _, err := reader.ReadLine() 
if err != nil { // error handler
    log.Println(err)
    return
}
fmt.Println(string(line))

Another way to read the line, you can use fd.Seek(64,0) to jump to a specific byte like

_, err = fd.Seek(64, 0)  // Set the current position for the fd
if err != nil { // error handler
    log.Println(err)
    return
}

And afterward use the reader to read the line.

reader := bufio.NewReader(fd)

line, _, err := reader.ReadLine()
if err != nil {
    log.Println(err)
    return
}
fmt.Println(string(line))