pim
d63ffd6a3a
Reusable, generics-based CLI extracted from vpp-evpn's cmd/evpnc: a declarative command tree (Node[C]) from which dispatch, '?'-help and TAB-completion are derived, an interactive Shell[C], dynamic slot resolvers (context-dependent via captured args), text-or-JSON output (Emit), and color helpers (Paint/Label/KV). Builds on Linux and OpenBSD (readline termios override). Includes a self-contained example and a design proposal under docs/. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
65 lines
2.3 KiB
Go
65 lines
2.3 KiB
Go
// SPDX-FileCopyrightText: (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
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// SPDX-License-Identifier: Apache-2.0
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package cli
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import (
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"encoding/json"
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"fmt"
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"os"
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)
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// Format selects how command results are rendered. It is process-global,
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// toggled once at startup via SetFormat (parallel to SetColor), so command
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// functions can stay simple: they describe a result once and the framework
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// renders it the chosen way.
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type Format int
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const (
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// FormatText renders the human-readable string a command passes to Emit.
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FormatText Format = iota
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// FormatJSON marshals the machine value a command passes to Emit and
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// ignores the text. Color is irrelevant in this mode.
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FormatJSON
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)
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var outputFormat Format
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// SetFormat selects the output format for Emit. Call it once at startup, e.g.
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// from a -json flag.
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func SetFormat(f Format) { outputFormat = f }
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// OutputFormat reports the current output format.
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func OutputFormat() Format { return outputFormat }
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// IsJSON reports whether output is in JSON mode. Commands can use it to skip
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// building the (then-unused) text representation, or to suppress banners.
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func IsJSON() bool { return outputFormat == FormatJSON }
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// Emit renders one command result to stdout. In FormatText mode it prints text
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// — which the caller may have colorized with Paint/Label/KV — followed by a
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// newline. In FormatJSON mode it marshals v (indented) and ignores text. The
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// caller supplies both: text is the human form, v is the machine form. This is
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// the single seam that lets the same command serve "show foo" and "-json show
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// foo". Returns an error only if JSON marshaling fails.
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//
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// For multi-record output, marshal a slice as v and join the text yourself;
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// Emit is one call per logical result so the JSON stays a single document.
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func Emit(text string, v any) error {
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if outputFormat == FormatJSON {
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b, err := json.MarshalIndent(v, "", " ")
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if err != nil {
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return fmt.Errorf("marshal json: %w", err)
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}
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_, _ = fmt.Fprintln(os.Stdout, string(b))
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return nil
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}
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_, _ = fmt.Fprintln(os.Stdout, text)
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return nil
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}
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// KV renders "key=value" with the key (and the '=') painted blue when color is
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// enabled, leaving the value in normal font. It is the building block for
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// one-line text output and pairs with Emit's text argument.
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func KV(key, value string) string { return Label(key+"=") + value }
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