fix: `exec` template func should not throw away stdout when stdin is non empty (#1151)

Fixes #1149

go.mod

@@ -35,6 +35,7 @@ require (
 	go.uber.org/zap v1.9.1
 	golang.org/x/crypto v0.0.0-20191029031824-8986dd9e96cf // indirect
 	golang.org/x/net v0.0.0-20191028085509-fe3aa8a45271 // indirect
+	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
 	golang.org/x/sys v0.0.0-20191029155521-f43be2a4598c // indirect
 	golang.org/x/time v0.0.0-20191024005414-555d28b269f0 // indirect
 	google.golang.org/api v0.13.0 // indirect

pkg/tmpl/context_funcs.go

@@ -2,6 +2,7 @@ package tmpl
 
 import (
 	"fmt"
+	"golang.org/x/sync/errgroup"
 	"gopkg.in/yaml.v2"
 	"io"
 	"os"
@@ -58,60 +59,54 @@ func (c *Context) Exec(command string, args []interface{}, inputs ...string) (st
 	cmd := exec.Command(command, strArgs...)
 	cmd.Dir = c.basePath
 
-	writeErrs := make(chan error)
-	cmdErrs := make(chan error)
-	cmdOuts := make(chan []byte)
+	g := errgroup.Group{}
 
 	if len(input) > 0 {
 		stdin, err := cmd.StdinPipe()
 		if err != nil {
 			return "", err
 		}
-		go func(input string, stdin io.WriteCloser) {
+
+		g.Go(func() error {
 			defer stdin.Close()
-			defer close(writeErrs)
 
 			size := len(input)
 
-			var n int
-			var err error
 			i := 0
+
 			for {
-				n, err = io.WriteString(stdin, input[i:])
+				n, err := io.WriteString(stdin, input[i:])
 				if err != nil {
-					writeErrs <- fmt.Errorf("failed while writing %d bytes to stdin of \"%s\": %v", len(input), command, err)
-					break
+					return fmt.Errorf("failed while writing %d bytes to stdin of \"%s\": %v", len(input), command, err)
 				}
+
 				i += n
-				if n == size {
-					break
+
+				if i == size {
+					return nil
 				}
 			}
-		}(input, stdin)
+		})
 	}
 
-	go func() {
-		defer close(cmdOuts)
-		defer close(cmdErrs)
+	var bytes []byte
 
-		bytes, err := cmd.Output()
+	g.Go(func() error {
+		bs, err := cmd.Output()
 		if err != nil {
-			cmdErrs <- fmt.Errorf("exec cmd=%s args=[%s] failed: %v", command, strings.Join(strArgs, ", "), err)
-		} else {
-			cmdOuts <- bytes
+			return fmt.Errorf("exec cmd=%s args=[%s] failed: %v", command, strings.Join(strArgs, ", "), err)
+		}
+
+		bytes = bs
+
+		return nil
+	})
+
+	if err := g.Wait(); err != nil {
+		return "", err
 	}
-	}()
 
-	for {
-		select {
-		case bytes := <-cmdOuts:
 	return string(bytes), nil
-		case err := <-cmdErrs:
-			return "", err
-		case err := <-writeErrs:
-			return "", err
-		}
-	}
 }
 
 func (c *Context) ReadFile(filename string) (string, error) {