module io // BufferedReader provides a buffered interface for a reader struct BufferedReader { mut: reader Reader buf []byte offset int // current offset in the buffer len int fails int // how many times fill_buffer has read 0 bytes in a row mfails int // maximum fails, after which we can assume that the stream has ended pub mut: end_of_stream bool // whether we reached the end of the upstream reader } // BufferedReaderConfig are options that can be given to a reader pub struct BufferedReaderConfig { reader Reader cap int = 128 * 1024 // large for fast reading of big(ish) files retries int = 2 // how many times to retry before assuming the stream ended } // new_buffered_reader creates new BufferedReader pub fn new_buffered_reader(o BufferedReaderConfig) &BufferedReader { assert o.cap >= 2 // create r := &BufferedReader{ reader: o.reader buf: []byte{len: o.cap, cap: o.cap} offset: 0 mfails: o.retries } return r } // read fufills the Reader interface pub fn (mut r BufferedReader) read(mut buf []byte) ?int { // read data out of the buffer if we dont have any if r.needs_fill() { if !r.fill_buffer() { // end of stream return none } } read := copy(buf, r.buf[r.offset..r.len]) r.offset += read return read } // fill_buffer attempts to refill the internal buffer // and returns whether it got any data fn (mut r BufferedReader) fill_buffer() bool { if r.end_of_stream { // we know we have already reached the end of stream // so return early return true } r.offset = 0 r.len = 0 r.len = r.reader.read(mut r.buf) or { // end of stream was reached r.end_of_stream = true return false } if r.len == 0 { r.fails++ } else { r.fails = 0 } if r.fails >= r.mfails { // When reading 0 bytes several times in a row, assume the stream has ended. // This prevents infinite loops ¯\_(ツ)_/¯ ... r.end_of_stream = true return false } // we got some data return true } // needs_fill returns whether the buffer needs refilling fn (r BufferedReader) needs_fill() bool { return r.offset >= r.len - 1 } // end_of_stream returns whether the end of the stream was reached pub fn (r BufferedReader) end_of_stream() bool { return r.end_of_stream } // read_line attempts to read a line from the buffered reader // it will read until it finds a new line character (\n) or // the end of stream pub fn (mut r BufferedReader) read_line() ?string { if r.end_of_stream { return none } mut line := []byte{} for { if r.needs_fill() { // go fetch some new data if !r.fill_buffer() { // We are at the end of the stream if line.len == 0 { // we had nothing so return nothing return none } return line.bytestr() } } // try and find a newline character mut i := r.offset for ; i < r.len; i++ { c := r.buf[i] if c == `\n` { // great, we hit something // do some checking for whether we hit \r\n or just \n if i != 0 && r.buf[i - 1] == `\r` { x := i - 1 line << r.buf[r.offset..x] } else { line << r.buf[r.offset..i] } r.offset = i + 1 return line.bytestr() } } line << r.buf[r.offset..i] r.offset = i } return none }