Improve terminal detection and escape sequence handling

Replace custom terminal detection with golang.org/x/term library.

Author: artyom

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/aws/aws-sdk-go-v2 v1.36.2
 	github.com/aws/aws-sdk-go-v2/config v1.29.7
 	github.com/aws/aws-sdk-go-v2/service/bedrockruntime v1.25.0
+	golang.org/x/term v0.29.0
 	rsc.io/markdown v0.0.0-20241212154241-6bf72452917f
 )
 
@@ -23,5 +24,6 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.28.15 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.33.15 // indirect
 	github.com/aws/smithy-go v1.22.3 // indirect
+	golang.org/x/sys v0.30.0 // indirect
 	golang.org/x/text v0.22.0 // indirect
 )

go.sum

@@ -32,6 +32,10 @@ github.com/aws/smithy-go v1.22.3 h1:Z//5NuZCSW6R4PhQ93hShNbyBbn8BWCmCVCt+Q8Io5k=
 github.com/aws/smithy-go v1.22.3/go.mod h1:t1ufH5HMublsJYulve2RKmHDC15xu1f26kHCp/HgceI=
 github.com/yuin/goldmark v1.6.0 h1:boZcn2GTjpsynOsC0iJHnBWa4Bi0qzfJjthwauItG68=
 github.com/yuin/goldmark v1.6.0/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
+golang.org/x/sys v0.30.0 h1:QjkSwP/36a20jFYWkSue1YwXzLmsV5Gfq7Eiy72C1uc=
+golang.org/x/sys v0.30.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/term v0.29.0 h1:L6pJp37ocefwRRtYPKSWOWzOtWSxVajvz2ldH/xi3iU=
+golang.org/x/term v0.29.0/go.mod h1:6bl4lRlvVuDgSf3179VpIxBF0o10JUpXWOnI7nErv7s=
 golang.org/x/text v0.22.0 h1:bofq7m3/HAFvbF51jz3Q9wLg3jkvSPuiZu/pD1XwgtM=
 golang.org/x/text v0.22.0/go.mod h1:YRoo4H8PVmsu+E3Ou7cqLVH8oXWIHVoX0jqUWALQhfY=
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d h1:vU5i/LfpvrRCpgM/VPfJLg5KjxD3E+hfT1SH+d9zLwg=

main.go

@@ -21,6 +21,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 	"unicode/utf8"
 
@@ -29,13 +30,14 @@ import (
 	"github.com/aws/aws-sdk-go-v2/service/bedrockruntime"
 	"github.com/aws/aws-sdk-go-v2/service/bedrockruntime/document"
 	"github.com/aws/aws-sdk-go-v2/service/bedrockruntime/types"
+	"golang.org/x/term"
 	"rsc.io/markdown"
 )
 
 func main() {
 	log.SetFlags(0)
 	log.SetPrefix("llmcli: ")
-	if st, err := os.Stderr.Stat(); err == nil && st.Mode()&os.ModeCharDevice != 0 {
+	if term.IsTerminal(int(os.Stderr.Fd())) {
 		log.SetPrefix("\033[1m" + log.Prefix() + ansiReset)
 	}
 	args := runArgs{model: os.Getenv("LLMCLI_MODEL")}
@@ -200,16 +202,16 @@ func run(ctx context.Context, args runArgs) error {
 	if args.budget != 0 {
 		// just in case we changed stdout formatting at the start of “thinking”
 		// but failed mid-way before resetting formatting
-		defer os.Stdout.WriteString(ansiReset)
+		defer termWrite(ansiReset)
 	}
 	var thinking bool
 	for chunk := range rc.Chunks() {
 		if !thinking && chunk.thinking {
 			thinking = true
-			os.Stdout.WriteString(ansiItalic) // bypassing wr
+			termWrite(ansiItalic) // bypassing wr
 		} else if thinking && !chunk.thinking {
 			thinking = false
-			os.Stdout.WriteString(ansiReset) // bypassing wr
+			termWrite(ansiReset) // bypassing wr
 			io.WriteString(wr, "\n\n* * *\n\n")
 		}
 		io.WriteString(wr, chunk.text)
@@ -226,6 +228,15 @@ func run(ctx context.Context, args runArgs) error {
 	return nil
 }
 
+var stdoutIsTerm = sync.OnceValue(func() bool { return term.IsTerminal(int(os.Stdout.Fd())) })
+
+func termWrite(s string) {
+	if !stdoutIsTerm() {
+		return
+	}
+	os.Stdout.WriteString(s)
+}
+
 func newResponseConsumer(cso *bedrockruntime.ConverseStreamOutput) *responseConsumer {
 	return &responseConsumer{cso: cso}
 }
@@ -283,10 +294,7 @@ func (r *responseConsumer) Chunks() iter.Seq[chunk] {
 }
 
 func readPrompt(args runArgs) (string, error) {
-	var stdinIsTerminal bool
-	if st, err := os.Stdin.Stat(); err == nil {
-		stdinIsTerminal = st.Mode()&os.ModeCharDevice != 0
-	}
+	stdinIsTerminal := term.IsTerminal(int(os.Stdin.Fd()))
 	var pb strings.Builder
 	var stdinData []byte
 	var err error