Extend nib API to allow reuse of underlying writer

README.md

@@ -34,6 +34,7 @@ The [`nib.Nib` interface][go-pkg-type-svengreb/nib#nib] consists of six function
 - `Infof(format string, args ...interface{})` — writes a message with `info` verbosity level for the given format and arguments.
 - `Successf(format string, args ...interface{})` — writes a message with `success` verbosity level for the given format and arguments.
 - `Warnf(format string, args ...interface{})` — writes a message with `warn` verbosity level for the given format and arguments.
+- `Writer() io.Writer` — returns the underlying [`io.Writer`][go-doc-type-io#writer].
 
 The [`pencil` package][go-pkg-svengreb/nib/pencil] implements this interface including [features like custom prefixes and verbosity level icons](#features).
 The [`inkpen` package][go-pkg-svengreb/nib/inkpen] composes [`pencil.Pencil`][go-pkg-type-svengreb/nib/pencil#pencil] and additionally [comes with additional features like colored output including automatic TTY and cross-platform terminal color support detection](#features).
@@ -276,6 +277,8 @@ func main() {
 }
 ```
 
+<!--lint enable no-tabs-->
+
 ### Prefixes
 
 By default only the verbosity level icons are printed as prefix before the given message format and arguments.
@@ -302,6 +305,8 @@ func main() {
 }
 ```
 
+<!--lint enable no-tabs-->
+
 ### Writer
 
 By default `pencil.Pencil` uses [`os.Stderr`][go-doc-os#pkg_vars] while `inkpen.Inkpen` uses `color.Output` which in turn is a exported variable that makes use of [github.com/mattn/go-colorable][mattn/go-colorable], a package for colored TTY output on multiple platforms.
@@ -332,6 +337,38 @@ func main() {
 
 <!--lint enable no-tabs-->
 
+<!--lint ignore no-duplicate-headings-->
+
+## Writer
+
+Both types [`pencil.Pencil`][go-pkg-type-svengreb/nib/pencil#pencil] and [`inkpen.Inkpen`][go-pkg-type-svengreb/nib/inkpen#inkpen] use recommended [`io.Writer`][go-doc-type-io#writer] by default to provide optimal compatibility for their specific features like colored output.
+To allow to either reuse the default or configured `io.Writer` the `Writer() io.Writer` method of the `nib.Nib` API interface can be used:
+
+<!--lint disable no-tabs-->
+
+```go
+package main
+
+import (
+	"os"
+
+	"github.com/svengreb/nib/inkpen"
+	"github.com/svengreb/nib/pencil"
+)
+
+func main() {
+	// Create a new pencil...
+	pen := pencil.New(pencil.WithWriter(os.Stderr))
+	// ... or inkpen.
+	ink := inkpen.New()
+
+	_, _ = fmt.Fprintln(pen.Writer(), "Brazil nuts are also a delicious and healthy snack between meals")
+	_, _ = fmt.Fprintln(ink.Writer(), "Brazil nuts are also a delicious and healthy snack between meals")
+}
+```
+
+<!--lint enable no-tabs-->
+
 ## Contributing
 
 _nib_ is an open source project and contributions are always welcome!

inkpen/inkpen.go

@@ -86,13 +86,17 @@ func (i *Inkpen) formatMsg(v nib.Verbosity, format string, args ...interface{})
 	return msg
 }
 
-// writef writes to the underlying writer and ensures a trailing newline for the given format.
+// writef writes to the underlying writer.
+// If an error occurs while writing to the underlying io.Writer the message is printed to os.Stdout instead.
+// When this also returns an error the error is written to os.Stderr instead.
 func (i *Inkpen) writef(v nib.Verbosity, format string, args ...interface{}) {
 	if i.Enabled(v) {
 		msg := i.formatMsg(v, format, args...)
 
-		if _, err := fmt.Fprint(i.opts.pencilOpts.Writer, msg); err != nil {
-			_, _ = fmt.Fprint(os.Stderr, msg)
+		if _, err := fmt.Fprint(i.Pencil.Writer(), msg); err != nil {
+			if _, err = fmt.Fprint(os.Stdout, msg); err != nil {
+				_, _ = fmt.Fprint(os.Stderr, err)
+			}
 		}
 	}
 }

nib.go

@@ -5,6 +5,8 @@
 // This package represents the currently latest API v0.
 package nib
 
+import "io"
+
 // Nib is a log-level based line printer for human-facing messages.
 type Nib interface {
 	// Compile compiles a message for the verbosity level using the given format and arguments.
@@ -21,4 +23,6 @@ type Nib interface {
 	Successf(format string, args ...interface{})
 	// Warnf writes a message with nib.WarnVerbosity level for the given format and arguments.
 	Warnf(format string, args ...interface{})
+	// Writer returns the underlying io.Writer.
+	Writer() io.Writer
 }

pencil/pencil.go

@@ -7,6 +7,7 @@ package pencil
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"strings"
 	"unicode"
@@ -76,6 +77,11 @@ func (p *Pencil) Warnf(format string, args ...interface{}) {
 	p.writef(nib.WarnVerbosity, format, args...)
 }
 
+// Writer returns the underlying io.Writer.
+func (p *Pencil) Writer() io.Writer {
+	return p.opts.Writer
+}
+
 // formatMsg formats the message and ensures a trailing newline for the given format.
 func (p *Pencil) formatMsg(v nib.Verbosity, format string, args ...interface{}) string {
 	if len(args) > 0 || !strings.HasSuffix(format, "\n") {
@@ -94,11 +100,15 @@ func (p *Pencil) formatMsg(v nib.Verbosity, format string, args ...interface{})
 }
 
 // writef writes to the underlying writer.
+// If an error occurs while writing to the underlying io.Writer the message is printed to os.Stdout instead.
+// When this also returns an error the error is written to os.Stderr instead.
 func (p *Pencil) writef(v nib.Verbosity, format string, args ...interface{}) {
 	if p.Enabled(v) {
 		msg := p.formatMsg(v, format, args...)
 		if _, err := fmt.Fprint(p.opts.Writer, msg); err != nil {
-			_, _ = fmt.Fprint(os.Stderr, msg)
+			if _, err = fmt.Fprint(os.Stdout, msg); err != nil {
+				_, _ = fmt.Fprint(os.Stderr, err)
+			}
 		}
 	}
 }