adding read() and eof() for line by line read from stdin (#270)

extensions/extension.go

@@ -136,6 +136,7 @@ func initInternal(c *Config) error {
 	if c.UnrestrictedIOs {
 		createShellFunctions()
 	}
+	createIOFunctions()
 	return nil
 }
 

extensions/io.go

@@ -0,0 +1,63 @@
+package extensions
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"strings"
+
+	"grol.io/grol/eval"
+	"grol.io/grol/object"
+)
+
+var seenEOF = object.FALSE
+
+func createIOFunctions() {
+	// This can hang so not to be used in wasm/discord/...
+	ioFn := object.Extension{
+		Name:    "read",
+		MinArgs: 0,
+		MaxArgs: 0,
+		Help:    "Reads one line from stdin",
+		Callback: func(env any, _ string, _ []object.Object) object.Object {
+			s := env.(*eval.State)
+			if s.Term != nil {
+				s.Term.Suspend()
+				//nolint:fatcontext // we do need to update/reset the context and its cancel function.
+				s.Context, s.Cancel = context.WithCancel(context.Background()) // no timeout.
+			}
+			var linebuf strings.Builder
+			// reading one byte at a time is pretty inefficient, but necessary because of the terminal raw mode switch/switchback.
+			var b [1]byte
+			for {
+				n, err := os.Stdin.Read(b[:])
+				if n == 1 {
+					linebuf.WriteByte(b[0])
+				}
+				if errors.Is(err, io.EOF) {
+					seenEOF = object.TRUE
+					break
+				}
+				if b[0] == '\n' {
+					break
+				}
+				if err != nil {
+					return s.Error(err)
+				}
+			}
+			if s.Term != nil {
+				s.Context, s.Cancel = s.Term.Resume(context.Background())
+			}
+			return object.String{Value: linebuf.String()}
+		},
+		DontCache: true,
+	}
+	MustCreate(ioFn)
+	ioFn.Name = "eof"
+	ioFn.Help = "Returns true if a previous read hit the end of file for stdin"
+	ioFn.Callback = func(_ any, _ string, _ []object.Object) object.Object {
+		return seenEOF
+	}
+	MustCreate(ioFn)
+}