README.md

@@ -44,7 +44,7 @@ level — folders, then the category (a JSON file), then fields.
 | `-d`, `--data-path D` | a directory to layer over the shipped data; repeatable, the last wins a name clash |
 | `--no-shipped-data` | load only the `--data-path` directories |
 | `-s`, `--seed N` | reproducible output |
-| `-n`, `--repeat N` | render the path N times, each an independent draw |
+| `-n`, `--repeat N` | render the path N times (up to 1048576), each an independent draw, streamed |
 | `--separator S` | between repeated values (default a newline) |
 | `--list` | print every path, then exit |
 | `--version`, `-h`, `--help` | print, then exit |

builtins.go

@@ -14,7 +14,7 @@ import (
 // fat-fingered or overflowing argument fails at New instead of trying to allocate
 // gigabytes — or panicking — at render.
 const (
-	maxLen      = 1 << 20 // 1,048,576 chars/bytes
+	maxLen      = MaxRepeat
 	maxDecimals = 1024
 )
 

cmd/fejkdata/main.go

@@ -8,6 +8,7 @@
 package main
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"io"
@@ -27,7 +28,7 @@ const usage = `Usage: fejkdata [flags] <path>
   -h, --help             print this help, then exit
       --list             list the paths the data offers, then exit
       --no-shipped-data  load only the --data-path directories
-  -n, --repeat N         render the path N times (default 1)
+  -n, --repeat N         render the path N times, 1..1048576 (default 1)
   -s, --seed N           seed for reproducible output
       --separator S      string between repeated values (default newline)
       --version          print the version, then exit
@@ -43,9 +44,11 @@ type invocation struct {
 	noShipped    bool
 	paths        []string
 	repeat       int
+	repeatSet    bool
 	seed         uint64
 	seeded       bool
 	separator    string
+	separatorSet bool
 	version      bool
 }
 
@@ -63,10 +66,10 @@ var flagDefs = []flagDef{
 	{"no-shipped-data", "", false, func(in *invocation, _ string) error { in.noShipped = true; return nil }},
 	{"repeat", "n", true, func(in *invocation, v string) error {
 		n, err := strconv.Atoi(v)
-		if err != nil || n < 1 {
-			return fmt.Errorf("--repeat needs a positive integer, got %q", v)
+		if err != nil || n < 1 || n > fejkdata.MaxRepeat {
+			return fmt.Errorf("--repeat needs an integer in 1..%d, got %q", fejkdata.MaxRepeat, v)
 		}
-		in.repeat = n
+		in.repeat, in.repeatSet = n, true
 		return nil
 	}},
 	{"seed", "s", true, func(in *invocation, v string) error {
@@ -77,7 +80,7 @@ var flagDefs = []flagDef{
 		in.seed, in.seeded = n, true
 		return nil
 	}},
-	{"separator", "", true, func(in *invocation, v string) error { in.separator = v; return nil }},
+	{"separator", "", true, func(in *invocation, v string) error { in.separator, in.separatorSet = v, true; return nil }},
 	{"version", "", false, func(in *invocation, _ string) error { in.version = true; return nil }},
 }
 
@@ -124,8 +127,8 @@ func splitFlags(arg string) ([]flagArg, error) {
 	}
 	var flags []flagArg
 	letters := arg[1:]
-	for i := 0; i < len(letters); i++ {
-		letter := letters[i : i+1]
+	for i, r := range letters {
+		letter := string(r)
 		def := flagByShort(letter)
 		if def == nil {
 			return nil, fmt.Errorf("unknown flag -%s", letter)
@@ -134,7 +137,7 @@ func splitFlags(arg string) ([]flagArg, error) {
 			flags = append(flags, flagArg{def: def})
 			continue
 		}
-		rest := letters[i+1:]
+		rest := letters[i+len(letter):]
 		if strings.HasPrefix(rest, "=") {
 			return nil, fmt.Errorf("-%s takes its value attached (-%s%s) or next (-%s %s); = belongs to --%s=%s",
 				letter, letter, rest[1:], letter, rest[1:], def.long, rest[1:])
@@ -188,6 +191,9 @@ func (in invocation) check() error {
 	if in.list && len(in.paths) > 0 {
 		return errors.New("--list takes no path")
 	}
+	if in.list && (in.repeatSet || in.separatorSet) {
+		return errors.New("--list takes no --repeat or --separator")
+	}
 	if !in.list && len(in.paths) != 1 {
 		return fmt.Errorf("expected one path, got %d", len(in.paths))
 	}
@@ -208,17 +214,23 @@ func (in invocation) options() []fejkdata.Option {
 	return opts
 }
 
-// values renders the path repeat times, joined by the separator.
-func (in invocation) values(f *fejkdata.Generator) (string, error) {
-	vals := make([]string, in.repeat)
-	for i := range vals {
+// write streams the path's renders to w, repeat of them joined by the separator
+// and ended by a newline. A path that renders once renders every time, so the only
+// failure comes before anything is written.
+func (in invocation) write(f *fejkdata.Generator, w io.Writer) error {
+	out := bufio.NewWriter(w)
+	for i := 0; i < in.repeat; i++ {
 		v, err := f.Fake(in.paths[0])
 		if err != nil {
-			return "", err
+			return err
 		}
-		vals[i] = v
+		if i > 0 {
+			out.WriteString(in.separator)
 		}
-	return strings.Join(vals, in.separator), nil
+		out.WriteString(v)
+	}
+	out.WriteString("\n")
+	return out.Flush()
 }
 
 func main() { os.Exit(run(os.Args[1:], os.Stdout, os.Stderr)) }
@@ -254,12 +266,10 @@ func run(args []string, stdout, stderr io.Writer) int {
 		}
 		return 0
 	}
-	out, err := in.values(f)
-	if err != nil {
+	if err := in.write(f, stdout); err != nil {
 		fmt.Fprintln(stderr, err)
 		return 1
 	}
-	fmt.Fprintln(stdout, out)
 	return 0
 }
 

fejkdata.go

@@ -28,6 +28,9 @@ import (
 //go:embed data
 var shippedFS embed.FS
 
+// MaxRepeat caps a repeat, and the renders nested repeats multiply to along any path.
+const MaxRepeat = 1 << 20
+
 // ErrNoData is returned by New when no source is loaded at all.
 var ErrNoData = errors.New("no data: WithoutShippedData needs at least one WithDataPath or WithDataFS")