io: migrate the Reader API to Result instead of Option (#15229)

vlib/io/buffered_reader.v

@@ -36,20 +36,23 @@ pub fn new_buffered_reader(o BufferedReaderConfig) &BufferedReader {
 }
 
 // read fufills the Reader interface
-pub fn (mut r BufferedReader) read(mut buf []u8) ?int {
+pub fn (mut r BufferedReader) read(mut buf []u8) !int {
 	if r.end_of_stream {
-		return none
+		return IError(Eof{})
 	}
 	// read data out of the buffer if we dont have any
 	if r.needs_fill() {
 		if !r.fill_buffer() {
 			// end of stream
-			return none
+			return IError(Eof{})
 		}
 	}
 	read := copy(mut buf, r.buf[r.offset..r.len])
 	if read == 0 {
-		return none
+		return IError(NotExpected{
+			cause: 'invalid copy of buffer'
+			code: -1
+		})
 	}
 	r.offset += read
 	return read

vlib/io/custom_string_reading_test.v

@@ -10,12 +10,12 @@ fn imin(a int, b int) int {
 	return if a < b { a } else { b }
 }
 
-fn (mut s StringReader) read(mut buf []u8) ?int {
+fn (mut s StringReader) read(mut buf []u8) !int {
 	$if debug {
 		eprintln('>>>> StringReader.read output buf.len: $buf.len')
 	}
 	if s.place > s.text.len + 1 {
-		return none
+		return IError(io.Eof{})
 	}
 	mut howmany := imin(buf.len, s.text.len - s.place)
 	xxx := s.text[s.place..s.place + howmany].bytes()

vlib/io/io_test.v

@@ -12,9 +12,9 @@ pub mut:
 	bytes []u8
 }
 
-fn (mut b Buf) read(mut buf []u8) ?int {
+fn (mut b Buf) read(mut buf []u8) !int {
 	if !(b.i < b.bytes.len) {
-		return none
+		return IError(io.Eof{})
 	}
 	n := copy(mut buf, b.bytes[b.i..])
 	b.i += n

vlib/io/reader.v

@@ -1,13 +1,32 @@
 module io
 
+/// Eof error means that we reach the end of the stream.
+pub struct Eof {
+	Error
+}
+
+// NotExpected is a generic error that means that we receave a not expecte error.
+pub struct NotExpected {
+	cause string
+	code  int
+}
+
+fn (err NotExpected) msg() string {
+	return err.cause
+}
+
+fn (err NotExpected) code() int {
+	return err.code
+}
+
 // Reader represents a stream of data that can be read
 pub interface Reader {
 	// read reads up to buf.len bytes and places
 	// them into buf.
 	// A type that implements this should return
-	// `none` on end of stream (EOF) instead of just returning 0
+	// `io.Eof` on end of stream (EOF) instead of just returning 0
 mut:
-	read(mut buf []u8) ?int
+	read(mut buf []u8) !int
 }
 
 const (
@@ -50,7 +69,7 @@ pub fn read_any(mut r Reader) ?[]u8 {
 	mut b := []u8{len: io.read_all_len}
 	mut read := 0
 	for {
-		new_read := r.read(mut b[read..]) or { break }
+		new_read := r.read(mut b[read..]) or { return none }
 		read += new_read
 		if new_read == 0 {
 			break

vlib/io/reader_test.v

@@ -7,9 +7,9 @@ mut:
 	i int
 }
 
-fn (mut b Buf) read(mut buf []u8) ?int {
+fn (mut b Buf) read(mut buf []u8) !int {
 	if !(b.i < b.bytes.len) {
-		return none
+		return IError(Eof{})
 	}
 	n := copy(mut buf, b.bytes[b.i..])
 	b.i += n
@@ -44,9 +44,9 @@ mut:
 	place int
 }
 
-fn (mut s StringReader) read(mut buf []u8) ?int {
+fn (mut s StringReader) read(mut buf []u8) !int {
 	if s.place >= s.text.len {
-		return none
+		return IError(Eof{})
 	}
 	read := copy(mut buf, s.text[s.place..].bytes())
 	s.place += read

vlib/io/readerwriter.v

@@ -14,7 +14,7 @@ mut:
 	w Writer
 }
 
-pub fn (mut r ReaderWriterImpl) read(mut buf []u8) ?int {
+pub fn (mut r ReaderWriterImpl) read(mut buf []u8) !int {
 	return r.r.read(mut buf)
 }