feat: social graph features

pkg/geoip/geoip.go

@@ -0,0 +1,92 @@
+// Package geoip resolves a request to an ISO-3166-1 alpha-2 country code,
+// best-effort. Two sources, in priority order:
+//
+//  1. Cloudflare's CF-IPCountry header — instant, no network, present when
+//     the site is proxied through Cloudflare.
+//  2. A GeoIP lookup on the client IP via the free ip-api.com endpoint —
+//     the fallback for when we're not behind Cloudflare (the current
+//     deployment is DNS-only).
+//
+// Everything is fire-and-forget: every failure path returns "" and the
+// caller simply leaves the country unknown. Nothing here blocks a request
+// on the critical path — callers run LookupCountryByIP from a goroutine.
+package geoip
+
+import (
+	"context"
+	"encoding/json"
+	"net"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// CountryFromCloudflare reads the CF-IPCountry header. Cloudflare sets it
+// to a 2-letter code, or to a sentinel ("XX" unknown, "T1" Tor) we treat
+// as absent. Returns "" when the header isn't a usable country.
+func CountryFromCloudflare(r *http.Request) string {
+	cc := strings.ToUpper(strings.TrimSpace(r.Header.Get("CF-IPCountry")))
+	if len(cc) != 2 || cc == "XX" || cc == "T1" {
+		return ""
+	}
+	return cc
+}
+
+// ClientIP returns the best guess at the caller's IP. The chi RealIP
+// middleware already rewrites r.RemoteAddr from X-Forwarded-For /
+// X-Real-IP, so we just strip the port.
+func ClientIP(r *http.Request) string {
+	host, _, err := net.SplitHostPort(strings.TrimSpace(r.RemoteAddr))
+	if err != nil {
+		// RemoteAddr may already be bare (no port) behind some proxies.
+		return strings.TrimSpace(r.RemoteAddr)
+	}
+	return host
+}
+
+// LookupCountryByIP resolves an IP to a country code via ip-api.com.
+// Returns "" for empty / private / loopback IPs (no point asking) and on
+// any error, timeout, or non-success response. Respects ctx for
+// cancellation/timeout — callers should pass a short-timeout context.
+func LookupCountryByIP(ctx context.Context, ip string) string {
+	ip = strings.TrimSpace(ip)
+	if ip == "" {
+		return ""
+	}
+	parsed := net.ParseIP(ip)
+	if parsed == nil || parsed.IsLoopback() || parsed.IsPrivate() ||
+		parsed.IsLinkLocalUnicast() || parsed.IsUnspecified() {
+		return ""
+	}
+
+	// Free tier is HTTP-only; countryCode keeps the payload tiny.
+	url := "http://ip-api.com/json/" + ip + "?fields=status,countryCode"
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return ""
+	}
+	client := &http.Client{Timeout: 4 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return ""
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return ""
+	}
+	var body struct {
+		Status      string `json:"status"`
+		CountryCode string `json:"countryCode"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
+		return ""
+	}
+	if body.Status != "success" {
+		return ""
+	}
+	cc := strings.ToUpper(strings.TrimSpace(body.CountryCode))
+	if len(cc) != 2 {
+		return ""
+	}
+	return cc
+}