93 lines
3.1 KiB
Go
93 lines
3.1 KiB
Go
package catalogue
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// A five-field cron validator, enough to refuse a malformed schedule near its author
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// (novox/hq ADR 0053).
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//
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// **Validation only, and written rather than pulled in.** The control plane's part in a scheduled
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// step is small and exact: carry the field to the host unchanged, and refuse a `schedule` that is
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// not a well-formed cron here rather than on the machine — the same near-versus-far discipline the
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// manifest keeps for an action a module may not declare and a run-once that is not a boolean. What
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// *when to run it again* means is the host's to evaluate; the control plane only checks the string
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// is one it could. A cron library would be a dependency carried for evaluation nobody does here.
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//
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// The ordinary five fields — minute, hour, day-of-month, month, day-of-week — with `*`, lists
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// (`,`), ranges (`-`) and steps (`/`). No names (jan, mon): a numeric cron is what the host
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// evaluates, and refusing a name here is refusing it near whoever wrote it.
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import (
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"fmt"
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"strconv"
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"strings"
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)
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// validateCron reports why a string is not a five-field cron expression, or nil if it is one.
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func validateCron(expr string) error {
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fields := strings.Fields(expr)
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if len(fields) != 5 {
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return fmt.Errorf(
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"a schedule is a five-field cron expression (minute hour day-of-month month "+
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"day-of-week), and this has %d field(s)", len(fields))
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}
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bounds := []struct {
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name string
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min, max int
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}{
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{"minute", 0, 59},
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{"hour", 0, 23},
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{"day-of-month", 1, 31},
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{"month", 1, 12},
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{"day-of-week", 0, 7}, // 0 and 7 are both Sunday, the convention every cron keeps
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}
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for i, b := range bounds {
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if err := validateCronField(fields[i], b.min, b.max); err != nil {
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return fmt.Errorf("%s field: %w", b.name, err)
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}
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}
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return nil
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}
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// validateCronField checks one field's elements are within range and well-formed.
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func validateCronField(spec string, min, max int) error {
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if spec == "" {
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return fmt.Errorf("is empty")
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}
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for _, part := range strings.Split(spec, ",") {
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if part == "" {
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return fmt.Errorf("%q has an empty element between commas", spec)
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}
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rangePart := part
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if slash := strings.IndexByte(part, '/'); slash >= 0 {
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rangePart = part[:slash]
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n, err := strconv.Atoi(part[slash+1:])
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if err != nil || n < 1 {
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return fmt.Errorf("step in %q is not a positive number", part)
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}
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}
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switch {
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case rangePart == "*":
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// Any value; nothing to bound.
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case strings.IndexByte(rangePart, '-') >= 0:
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dash := strings.IndexByte(rangePart, '-')
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lo, errLo := strconv.Atoi(rangePart[:dash])
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hi, errHi := strconv.Atoi(rangePart[dash+1:])
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if errLo != nil || errHi != nil {
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return fmt.Errorf("range %q is not two numbers", rangePart)
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}
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if lo < min || hi > max || lo > hi {
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return fmt.Errorf("range %q is outside the allowed %d-%d", part, min, max)
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}
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default:
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v, err := strconv.Atoi(rangePart)
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if err != nil {
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return fmt.Errorf("%q is not a number", rangePart)
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}
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if v < min || v > max {
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return fmt.Errorf("%q is outside the allowed range %d-%d", part, min, max)
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}
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}
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}
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return nil
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}
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