Golang dynamic sizing slice when reading a file using buffo.read

I have a problem where, I need to use bufio.read to read a tsv file line by line and I need to record how many bytes each line Ive read is.

The problem is, It seems like I can't just initialize an empty slice and pass it into bufio.read and expect the slice to contain the entire line of the file.

file, _ := os.Open("file.tsv")

reader := bufio.NewReader(file)

b := make([]byte, 10)
for {
	bytesRead, err:= reader.Read(b)
	fmt.Println(bytesRead, b)
	if err != nil {
		break
	}
}

So, for this example, since I specified the slice to be 10 bytes, the reader will read at most 10 bytes even if the line is bigger than 10 bytes.

However:

file, _ := os.Open("file.tsv")

reader := bufio.NewReader(file)

b := byte{} //or var b []byte
for {
	bytesRead, err:= reader.Read(b)
	fmt.Println(bytesRead, b)
	if err != nil {
		break
	}
}

This will always read 0 bytes and I assume its because the buffer is length 0 or capacity 0.

How do I read a file Line by line, save the entire line in a variable or buffer, and return exactly how many bytes Ive read?

Thanks!

If you want to read line by line, and you're using a buffered reader, use the buffered reader's ReadBytes method.

line,err := reader.ReadBytes('\n')

This will give you a full line, one line at a time, regardless of byte length.