io: fix detection of end_of_stream, when reading files through io.new_buffered_reader(reader: io.make_reader(f))

examples/buf_reader.v

@@ -5,17 +5,15 @@ import io
 
 fn main() {
 	// Make a new connection
-	mut conn := net.dial_tcp('google.com:80')?
+	mut conn := net.dial_tcp('google.com:80') ?
 	// Simple http HEAD request for a file
-	conn.write_str('GET /index.html HTTP/1.0\r\n\r\n')?
+	conn.write_str('GET /index.html HTTP/1.0\r\n\r\n') ?
 	// Wrap in a buffered reader
 	mut r := io.new_buffered_reader(reader: io.make_reader(conn))
 	for {
-		l := r.read_line() or {
-			break
-		}
+		l := r.read_line() or { break }
 		println('$l')
 		// Make it nice and obvious that we are doing this line by line
-		time.sleep_ms(10)
+		time.sleep_ms(100)
 	}
 }

vlib/io/buffered_reader.v

@@ -3,19 +3,21 @@ module io
 // BufferedReader provides a buffered interface for a reader
 struct BufferedReader {
 mut:
-	reader        Reader
-	buf           []byte
-	// current offset in the buffer
-	offset        int
-	len           int
-	// Whether we reached the end of the upstream reader
-	end_of_stream bool
+	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
+	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
@@ -26,6 +28,7 @@ pub fn new_buffered_reader(o BufferedReaderConfig) &BufferedReader {
 		reader: o.reader
 		buf: []byte{len: o.cap, cap: o.cap}
 		offset: 0
+		mfails: o.retries
 	}
 	return r
 }
@@ -59,6 +62,17 @@ fn (mut r BufferedReader) fill_buffer() bool {
 		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
 }

vlib/io/os_file_reader_test.v

@@ -0,0 +1,29 @@
+import os
+import io
+
+fn read_file(file string, cap int) []string {
+	mut lines := []string{}
+	mut f := os.open(file) or { panic(err) }
+	defer {
+		f.close()
+	}
+	mut r := io.new_buffered_reader(reader: io.make_reader(f), cap: cap)
+	for {
+		l := r.read_line() or { break }
+		lines << l
+		// println('Line: $l')
+	}
+	assert lines.len > 0
+	assert r.end_of_stream == true
+	println('------------------------------------------------ cap: ${cap:6}; read: ${lines.len:3} lines')
+	return lines
+}
+
+fn test_file_reader() {
+	for cap := 64; cap <= 10000; cap += 256 {
+		lines := read_file(@FILE, cap)
+		assert lines.last() == '// my last line'
+	}
+}
+
+// my last line