parser/gotest: Create interface for reading lines with metadata

parser/gotest/internal/reader/reader.go

@@ -6,6 +6,16 @@ import (
 	"io"
 )
 
+// LineReader is an interface to read lines with optional Metadata.
+type LineReader interface {
+	ReadLine() (string, *Metadata, error)
+}
+
+// Metadata contains metadata that belongs to a line.
+type Metadata struct {
+	Package string
+}
+
 // 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.
@@ -14,6 +24,8 @@ type LimitedLineReader struct {
 	limit int
 }
 
+var _ LineReader = &LimitedLineReader{}
+
 // NewLimitedLineReader returns a LimitedLineReader to read lines from r with a
 // maximum line size of limit.
 func NewLimitedLineReader(r io.Reader, limit int) *LimitedLineReader {
@@ -23,14 +35,14 @@ func NewLimitedLineReader(r io.Reader, limit int) *LimitedLineReader {
 // 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) {
+func (r *LimitedLineReader) ReadLine() (string, *Metadata, error) {
 	line, isPrefix, err := r.r.ReadLine()
 	if err != nil {
-		return "", err
+		return "", nil, err
 	}
 
 	if !isPrefix {
-		return string(line), nil
+		return string(line), nil, nil
 	}
 
 	// Line is incomplete, keep reading until we reach the end of the line.
@@ -39,7 +51,7 @@ func (r *LimitedLineReader) ReadLine() (string, error) {
 	for isPrefix {
 		line, isPrefix, err = r.r.ReadLine()
 		if err != nil {
-			return "", err
+			return "", nil, err
 		}
 
 		if buf.Len() >= r.limit {
@@ -54,5 +66,5 @@ func (r *LimitedLineReader) ReadLine() (string, error) {
 	if buf.Len() > r.limit {
 		buf.Truncate(r.limit)
 	}
-	return buf.String(), nil
+	return buf.String(), nil, nil
 }