runes: introduce Feeder

Signed-off-by: Alejandro Mery <amery@jpi.io>

runes/feeder.go

@@ -0,0 +1,131 @@
+package runes
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"strings"
+	"sync"
+)
+
+// feeder is a generic implementation of the output interfaces of Feeder
+type Feeder struct {
+	sync.Mutex
+
+	in  io.RuneReader
+	out []rune
+	sz  []int
+	err error
+}
+
+// NewFeederBytes creates a new Feeder using an slice of bytes as input
+func NewFeederBytes(b []byte) *Feeder {
+	return &Feeder{in: bytes.NewReader(b)}
+}
+
+// NewFeederString creates a new Feeder using a string as input
+func NewFeederString(s string) *Feeder {
+	return &Feeder{in: strings.NewReader(s)}
+}
+
+// NewFeederString creates a new Feeder using a string as input
+func NewFeeder(in io.Reader) *Feeder {
+	return &Feeder{in: bufio.NewReader(in)}
+}
+
+// Skip drops n runes from the head of the buffer
+func (f *Feeder) Skip(n int) (int, bool) {
+	f.Lock()
+	defer f.Unlock()
+
+	if l := f.skip(n); l > 0 {
+		return l, true
+	} else {
+		return 0, false
+	}
+}
+func (f *Feeder) skip(n int) int {
+	if l := len(f.out); l > n {
+		f.out = f.out[n:]
+		f.sz = f.sz[n:]
+		return l - n
+	} else {
+		f.out = f.out[:0]
+		f.sz = f.sz[:0]
+		return 0
+	}
+}
+
+// ReadRune returns the next rune
+func (f *Feeder) ReadRune() (r rune, size int, err error) {
+	f.Lock()
+	defer f.Unlock()
+
+	if f.atLeast(1) {
+		r = f.out[0]
+		size = f.sz[0]
+
+		f.skip(1)
+	}
+
+	err = f.Err()
+	return
+}
+
+// AtLeast blocks until there are at least n runes on the buffer, or an error or EOF has occurred
+func (f *Feeder) AtLeast(n int) (out []rune, err error) {
+	f.Lock()
+	defer f.Unlock()
+
+	if !f.atLeast(n) {
+		err = f.err
+	}
+
+	if len(f.out) > 0 {
+		out = f.out
+	}
+
+	return
+}
+
+func (f *Feeder) atLeast(n int) bool {
+	for len(f.out) < n {
+		r, size, err := f.in.ReadRune()
+		if err != nil && f.err == nil {
+			// store first error
+			f.err = err
+		}
+
+		if size > 0 {
+			f.out = append(f.out, r)
+			f.sz = append(f.sz, size)
+		} else if f.err != nil {
+			break
+		}
+	}
+
+	return len(f.out) >= n
+}
+
+// Currently buffered runes
+func (f *Feeder) Buffered() []rune {
+	return f.out
+}
+
+// Count of currently buffered runes
+func (f *Feeder) Len() int {
+	return len(f.out)
+}
+
+// Feeder has reached EOF
+func (f *Feeder) EOF() bool {
+	return f.err == io.EOF
+}
+
+// Feeder encountered an error
+func (f *Feeder) Err() error {
+	if f.err == io.EOF {
+		return nil
+	}
+	return f.err
+}