parser/gotest: Create LimitedLineReader

parser/gotest/internal/reader/reader.go

@@ -0,0 +1,58 @@
+package reader
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+)
+
+// LimitedLineReader reads lines from an io.Reader object with a configurable
+// line size limit. Lines exceeding the limit will be truncated, but read
+// completely from the underlying io.Reader.
+type LimitedLineReader struct {
+	r     *bufio.Reader
+	limit int
+}
+
+// NewLimitedLineReader returns a LimitedLineReader to read lines from r with a
+// maximum line size of limit.
+func NewLimitedLineReader(r io.Reader, limit int) *LimitedLineReader {
+	return &LimitedLineReader{r: bufio.NewReader(r), limit: limit}
+}
+
+// ReadLine returns the next line from the underlying reader. The length of the
+// line will not exceed the configured limit. ReadLine either returns a line or
+// it returns an error, never both.
+func (r *LimitedLineReader) ReadLine() (string, error) {
+	line, isPrefix, err := r.r.ReadLine()
+	if err != nil {
+		return "", err
+	}
+
+	if !isPrefix {
+		return string(line), nil
+	}
+
+	// Line is incomplete, keep reading until we reach the end of the line.
+	var buf bytes.Buffer
+	buf.Write(line) // ignore err, always nil
+	for isPrefix {
+		line, isPrefix, err = r.r.ReadLine()
+		if err != nil {
+			return "", err
+		}
+
+		if buf.Len() >= r.limit {
+			// Stop writing to buf if we exceed the limit. We continue reading
+			// however to make sure we consume the entire line.
+			continue
+		}
+
+		buf.Write(line) // ignore err, always nil
+	}
+
+	if buf.Len() > r.limit {
+		buf.Truncate(r.limit)
+	}
+	return buf.String(), nil
+}