Fix #190 - Add subcommand output to logs (#417)

Summary:
Pull Request resolved: #417

The feature for writing output to a log file was incomplete in the initial stub implementation D44521651 and subsequent updates (#10) because it did not configure subcommands to write their output to the specified logFile

This has now been corrected - all output of the TTP, including subcommand stdout/stderr, should now write to the specified logfile

Reviewed By: nicolagiacchetta

Differential Revision: D51306975

fbshipit-source-id: a810eee5fcb19672788ef4f76bb7f395f6d022bf

pkg/blocks/iocapture.go

@@ -22,16 +22,45 @@ package blocks
 import (
 	"bytes"
 	"io"
-	"os"
 	"os/exec"
+
+	"github.com/facebookincubator/ttpforge/pkg/logging"
 )
 
+type zapWriter struct {
+	prefix string
+}
+
+func (z *zapWriter) Write(b []byte) (int, error) {
+	n := len(b)
+	// extra-defensive programming :P
+	if n <= 0 {
+		return 0, nil
+	}
+
+	// strip trailing newline
+	if b[n-1] == '\n' {
+		b = b[:n-1]
+	}
+
+	// split lines
+	lines := bytes.Split(b, []byte{'\n'})
+	for _, line := range lines {
+		logging.L().Info(z.prefix, string(line))
+	}
+	return n, nil
+}
+
 func streamAndCapture(cmd exec.Cmd, stdout, stderr io.Writer) (*ActResult, error) {
 	if stdout == nil {
-		stdout = os.Stdout
+		stdout = &zapWriter{
+			prefix: "[STDOUT] ",
+		}
 	}
 	if stderr == nil {
-		stderr = os.Stderr
+		stderr = &zapWriter{
+			prefix: "[STDERR] ",
+		}
 	}
 
 	var stdoutBuf, stderrBuf bytes.Buffer