Maintenance: parallelize IP information fetch

internal/publicip/multi.go

@@ -0,0 +1,55 @@
+package publicip
+
+import (
+	"context"
+	"net"
+	"net/http"
+)
+
+// MultiInfo obtains the public IP address information for every IP
+// addresses provided and returns a slice of results with the corresponding
+// order as to the IP addresses slice order.
+// If an error is encountered, all the operations are canceled and
+// an error is returned, so the results returned should be considered
+// incomplete in this case.
+func MultiInfo(ctx context.Context, client *http.Client, ips []net.IP) (
+	results []Result, err error) {
+	ctx, cancel := context.WithCancel(ctx)
+
+	type asyncResult struct {
+		index  int
+		result Result
+		err    error
+	}
+	resultsCh := make(chan asyncResult)
+
+	for i, ip := range ips {
+		go func(index int, ip net.IP) {
+			aResult := asyncResult{
+				index: index,
+			}
+			aResult.result, aResult.err = Info(ctx, client, ip)
+			resultsCh <- aResult
+		}(i, ip)
+	}
+
+	results = make([]Result, len(ips))
+	for i := 0; i < len(ips); i++ {
+		aResult := <-resultsCh
+		if aResult.err != nil {
+			if err == nil {
+				// Cancel on the first error encountered
+				err = aResult.err
+				cancel()
+			}
+			continue // ignore errors after the first one
+		}
+
+		results[aResult.index] = aResult.result
+	}
+
+	close(resultsCh)
+	cancel()
+
+	return results, err
+}

internal/updater/providers/purevpn/servers.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
 	"net/http"
 	"strings"
 
@@ -73,15 +74,21 @@ func GetServers(ctx context.Context, client *http.Client,
 			ErrNotEnoughServers, len(servers), minServers)
 	}
 
-	// Dedup by location
+	// Get public IP address information
-	lts := make(locationToServer)
+	ipsToGetInfo := make([]net.IP, len(servers))
-	for _, server := range servers {
+	for i := range servers {
-		ipInfo, err := publicip.Info(ctx, client, server.IPs[0])
+		ipsToGetInfo[i] = servers[i].IPs[0]
+	}
+	ipsInfo, err := publicip.MultiInfo(ctx, client, ipsToGetInfo)
 	if err != nil {
 		return nil, warnings, err
 	}
 
+	// Dedup by location
+	lts := make(locationToServer)
+	for i, server := range servers {
 		// TODO split servers by host
+		ipInfo := ipsInfo[i]
 		lts.add(ipInfo.Country, ipInfo.Region, ipInfo.City, server.IPs)
 	}