Rename the settings whose names do not say what they control (closes #234)

Applies the setting renames of the naming audit under the SWW_WAF_ and
SWW_RPROXY_ prefixes, with sneak's names for the IP reputation cache
time and the two time limits, which now take milliseconds. The rproxy
log field default_disposition becomes waf_backend_no_answer, and
config.Config and config.FromEnvironment become config.WAF and
config.WAFFromEnvironment. Go fields, test names and prose follow. No
aliases; nothing reads the old names.

Model: opus-5-5

internal/config/config.go

@@ -16,6 +16,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/spf13/viper"
 )
@@ -36,7 +37,9 @@ const (
 var (
 	errNotSize = errors.New(
 		"is not a size such as 512K, 100M or 5G, or off")
-	errNotPositive = errors.New("must be more than zero, or off")
+	errNotPositive     = errors.New("must be more than zero, or off")
+	errNotMilliseconds = errors.New(
+		"is not a whole number of milliseconds above zero, such as 2000")
 	errEmptyItem   = errors.New("has an empty item in its list")
 	errNotNetblock = errors.New(
 		"is not a netblock such as 10.0.0.0/8, or an address")
@@ -62,7 +65,8 @@ func Command(v *viper.Viper) (string, error) {
 	}
 }
 
-// environment is where FromEnvironment reads the settings: it notes each
+// environment is where WAFFromEnvironment and RProxyFromEnvironment read
+// the settings: it notes each
 // value for the log, and keeps the first error. It reads every setting
 // through v, the viper NewViper returns, and honours each setting's _FILE
 // form too.
@@ -162,6 +166,19 @@ func (e *environment) size(name, defaultValue string) int64 {
 	return size
 }
 
+// milliseconds reads a setting that is a whole number of milliseconds above
+// zero.
+func (e *environment) milliseconds(name, defaultValue string) time.Duration {
+	value := e.value(name, defaultValue)
+
+	duration, valid := parseMilliseconds(value)
+	if !valid {
+		e.check(name, fmt.Errorf("%q %w", value, errNotMilliseconds))
+	}
+
+	return duration
+}
+
 // parseSize reads a number of bytes with an optional K, M or G suffix, in
 // powers of 1024 (1K is 1024 bytes), or off.
 func parseSize(value string) (int64, error) {
@@ -198,6 +215,17 @@ func splitUnit(value string) (string, int64) {
 	}
 }
 
+// parseMilliseconds reads a whole number of milliseconds above zero, and
+// reports whether it is one.
+func parseMilliseconds(value string) (time.Duration, bool) {
+	n, err := strconv.ParseInt(value, 10, 64)
+	if err != nil || n <= 0 || n > math.MaxInt64/int64(time.Millisecond) {
+		return 0, false
+	}
+
+	return time.Duration(n) * time.Millisecond, true
+}
+
 // parseList splits a comma-separated list and trims the spaces around
 // each item. An empty value is an empty list.
 func parseList(value string) ([]string, error) {