client: add minimal client api for the http api

.gitignore

@@ -1,2 +1,2 @@
-geoipapi
+./geoipapi
 *~

client/geoipapi/geoipclient.go

@@ -0,0 +1,77 @@
+package geoipapi
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net"
+	"net/http"
+	"net/netip"
+	"net/url"
+	"os"
+	"time"
+
+	"github.com/oschwald/geoip2-golang"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+)
+
+var client http.Client
+
+func init() {
+	netTransport := &http.Transport{
+		Dial: (&net.Dialer{
+			Timeout: 5 * time.Second,
+		}).Dial,
+		TLSHandshakeTimeout: 5 * time.Second,
+	}
+	client = http.Client{
+		Timeout:   time.Second * 10,
+		Transport: netTransport,
+	}
+}
+
+func GetCity(ctx context.Context, ip netip.Addr) (*geoip2.City, error) {
+	ctx, span := otel.Tracer("geoipapi").Start(ctx, "geoip.GetCity")
+	defer span.End()
+
+	baseURL := os.Getenv("geoip_service")
+	if len(baseURL) == 0 {
+		return nil, fmt.Errorf("geoip_service not configured")
+	}
+
+	q := url.Values{}
+	q.Set("ip", ip.String())
+
+	span.SetAttributes(attribute.String("ip", ip.String()))
+
+	reqURL, err := url.Parse(fmt.Sprintf("http://%s/api/json?%s", baseURL, q.Encode()))
+	if err != nil {
+		span.RecordError(err)
+		return nil, err
+	}
+
+	req, err := http.NewRequestWithContext(ctx, "GET", reqURL.String(), nil)
+	if err != nil {
+		span.RecordError(err)
+		return nil, err
+	}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		span.RecordError(err)
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	dec := json.NewDecoder(resp.Body)
+
+	city := geoip2.City{}
+	err = dec.Decode(&city)
+	if err != nil {
+		span.RecordError(err)
+		return nil, err
+	}
+
+	return &city, nil
+}