Add query parameter parsing to ParseURL()

Before this change, ParseURL would only accept a very restricted
set of URLs (it returned an error, if it encountered any parameter).

This commit introduces the ability to process URLs like

	redis://localhost/1?dial_timeout=10s

and similar.

Go programs which were providing a configuration tunable (e.g.
CLI flag, config entry or environment variable) to configure
the Redis connection now don't need to perform this task
themselves.

options.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"net/url"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -192,9 +193,32 @@ func (opt *Options) clone() *Options {
 // Scheme is required.
 // There are two connection types: by tcp socket and by unix socket.
 // Tcp connection:
-// 		redis://<user>:<password>@<host>:<port>/<db_number>
+//		redis://<user>:<password>@<host>:<port>/<db_number>
 // Unix connection:
 //		unix://<user>:<password>@</path/to/redis.sock>?db=<db_number>
+// Most Option fields can be set using query parameters, with the following restrictions:
+//	- field names are mapped using snake-case conversion: to set MaxRetries, use max_retries
+//	- only scalar type fields are supported (bool, int, time.Duration)
+//	- for time.Duration fields, values must be a valid input for time.ParseDuration();
+//	  additionally a plain integer as value (i.e. without unit) is intepreted as seconds
+//	- to disable a duration field, use value less than or equal to 0; to use the default
+//	  value, leave the value blank or remove the parameter
+//	- only the last value is interpreted if a parameter is given multiple times
+//	- fields "network", "addr", "username" and "password" can only be set using other
+//	  URL attributes (scheme, host, userinfo, resp.), query paremeters using these
+//	  names will be treated as unknown parameters
+//	- unknown parameter names will result in an error
+// Examples:
+//		redis://user:password@localhost:6789/3?dial_timeout=3&db=1&read_timeout=6s&max_retries=2
+//		is equivalent to:
+//		&Options{
+//			Network:     "tcp",
+//			Addr:        "localhost:6789",
+//			DB:          1,               // path "/3" was overridden by "&db=1"
+//			DialTimeout: 3 * time.Second, // no time unit = seconds
+//			ReadTimeout: 6 * time.Second,
+//			MaxRetries:  2,
+//		}
 func ParseURL(redisURL string) (*Options, error) {
 	u, err := url.Parse(redisURL)
 	if err != nil {
@@ -216,10 +240,6 @@ func setupTCPConn(u *url.URL) (*Options, error) {
 
 	o.Username, o.Password = getUserPassword(u)
 
-	if len(u.Query()) > 0 {
-		return nil, errors.New("redis: no options supported")
-	}
-
 	h, p, err := net.SplitHostPort(u.Host)
 	if err != nil {
 		h = u.Host
@@ -250,7 +270,7 @@ func setupTCPConn(u *url.URL) (*Options, error) {
 		o.TLSConfig = &tls.Config{ServerName: h}
 	}
 
-	return o, nil
+	return setupConnParams(u, o)
 }
 
 func setupUnixConn(u *url.URL) (*Options, error) {
@@ -262,19 +282,122 @@ func setupUnixConn(u *url.URL) (*Options, error) {
 		return nil, errors.New("redis: empty unix socket path")
 	}
 	o.Addr = u.Path
-
 	o.Username, o.Password = getUserPassword(u)
+	return setupConnParams(u, o)
+}
 
-	dbStr := u.Query().Get("db")
-	if dbStr == "" {
-		return o, nil // if database is not set, connect to 0 db.
+type queryOptions struct {
+	q   url.Values
+	err error
+}
+
+func (o *queryOptions) string(name string) string {
+	vs := o.q[name]
+	if len(vs) == 0 {
+		return ""
+	}
+	delete(o.q, name) // enable detection of unknown parameters
+	return vs[len(vs)-1]
+}
+
+func (o *queryOptions) int(name string) int {
+	s := o.string(name)
+	if s == "" {
+		return 0
+	}
+	i, err := strconv.Atoi(s)
+	if err == nil {
+		return i
+	}
+	if o.err == nil {
+		o.err = fmt.Errorf("redis: invalid %s number: %s", name, err)
+	}
+	return 0
+}
+
+func (o *queryOptions) duration(name string) time.Duration {
+	s := o.string(name)
+	if s == "" {
+		return 0
+	}
+	// try plain number first
+	if i, err := strconv.Atoi(s); err == nil {
+		if i <= 0 {
+			// disable timeouts
+			return -1
+		}
+		return time.Duration(i) * time.Second
+	}
+	dur, err := time.ParseDuration(s)
+	if err == nil {
+		return dur
+	}
+	if o.err == nil {
+		o.err = fmt.Errorf("redis: invalid %s duration: %w", name, err)
+	}
+	return 0
+}
+
+func (o *queryOptions) bool(name string) bool {
+	switch s := o.string(name); s {
+	case "true", "1":
+		return true
+	case "false", "0", "":
+		return false
+	default:
+		if o.err == nil {
+			o.err = fmt.Errorf("redis: invalid %s boolean: expected true/false/1/0 or an empty string, got %q", name, s)
+		}
+		return false
+	}
+}
+
+func (o *queryOptions) remaining() []string {
+	if len(o.q) == 0 {
+		return nil
+	}
+	keys := make([]string, 0, len(o.q))
+	for k := range o.q {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+// setupConnParams converts query parameters in u to option value in o.
+func setupConnParams(u *url.URL, o *Options) (*Options, error) {
+	q := queryOptions{q: u.Query()}
+
+	// compat: a future major release may use q.int("db")
+	if tmp := q.string("db"); tmp != "" {
+		db, err := strconv.Atoi(tmp)
+		if err != nil {
+			return nil, fmt.Errorf("redis: invalid database number: %w", err)
+		}
+		o.DB = db
 	}
 
-	db, err := strconv.Atoi(dbStr)
-	if err != nil {
-		return nil, fmt.Errorf("redis: invalid database number: %w", err)
+	o.MaxRetries = q.int("max_retries")
+	o.MinRetryBackoff = q.duration("min_retry_backoff")
+	o.MaxRetryBackoff = q.duration("max_retry_backoff")
+	o.DialTimeout = q.duration("dial_timeout")
+	o.ReadTimeout = q.duration("read_timeout")
+	o.WriteTimeout = q.duration("write_timeout")
+	o.PoolFIFO = q.bool("pool_fifo")
+	o.PoolSize = q.int("pool_size")
+	o.MinIdleConns = q.int("min_idle_conns")
+	o.MaxConnAge = q.duration("max_conn_age")
+	o.PoolTimeout = q.duration("pool_timeout")
+	o.IdleTimeout = q.duration("idle_timeout")
+	o.IdleCheckFrequency = q.duration("idle_check_frequency")
+	if q.err != nil {
+		return nil, q.err
+	}
+
+	// any parameters left?
+	if r := q.remaining(); len(r) > 0 {
+		return nil, fmt.Errorf("redis: unexpected option: %s", strings.Join(r, ", "))
 	}
-	o.DB = db
 
 	return o, nil
 }