Print error messagge 'unable to open database' to stderr

Fixes #610

aptly/interfaces.go

@@ -109,6 +109,8 @@ type Progress interface {
 	Printf(msg string, a ...interface{})
 	// ColoredPrintf does printf in colored way + newline
 	ColoredPrintf(msg string, a ...interface{})
+	// PrintfStdErr does printf but in safe manner to stderr
+	PrintfStdErr(msg string, a ...interface{})
 }
 
 // Downloader is parallel HTTP fetcher

console/progress.go

@@ -2,6 +2,7 @@ package console
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/cheggaaa/pb"
@@ -11,6 +12,7 @@ import (
 
 const (
 	codePrint = iota
+	codePrintStdErr
 	codeProgress
 	codeHideProgress
 	codeStop
@@ -127,6 +129,11 @@ func (p *Progress) Printf(msg string, a ...interface{}) {
 	p.queue <- printTask{code: codePrint, message: fmt.Sprintf(msg, a...)}
 }
 
+// PrintfStdErr does printf but in safe manner to stderr
+func (p *Progress) PrintfStdErr(msg string, a ...interface{}) {
+	p.queue <- printTask{code: codePrintStdErr, message: fmt.Sprintf(msg, a...)}
+}
+
 // ColoredPrintf does printf in colored way + newline
 func (p *Progress) ColoredPrintf(msg string, a ...interface{}) {
 	if RunningOnTerminal() {
@@ -182,6 +189,12 @@ func (p *Progress) worker() {
 				p.barShown = false
 			}
 			fmt.Print(task.message)
+		case codePrintStdErr:
+			if p.barShown {
+				fmt.Print("\r\033[2K")
+				p.barShown = false
+			}
+			fmt.Fprint(os.Stderr, task.message)
 		case codeProgress:
 			if hasBar {
 				fmt.Print("\r" + task.message)

context/context.go

@@ -262,7 +262,7 @@ func (context *AptlyContext) _database() (database.Storage, error) {
 				delay = time.Second
 			}
 
-			context._progress().Printf("Unable to open database, sleeping %s, attempts left %d...\n", delay, tries)
+			context._progress().PrintfStdErr("Unable to open database, sleeping %s, attempts left %d...\n", delay, tries)
 			time.Sleep(delay)
 		}
 	}