Inititial commit

realip/realip.go

@@ -0,0 +1,89 @@
+package realip
+
+import (
+	"errors"
+	"net"
+	"net/http"
+	"strings"
+)
+
+var cidrs []*net.IPNet
+
+func init() {
+	maxCidrBlocks := []string{
+		"127.0.0.1/8",    // localhost
+		"10.0.0.0/8",     // 24-bit block
+		"172.16.0.0/12",  // 20-bit block
+		"192.168.0.0/16", // 16-bit block
+		"169.254.0.0/16", // link local address
+		"::1/128",        // localhost IPv6
+		"fc00::/7",       // unique local address IPv6
+		"fe80::/10",      // link local address IPv6
+	}
+
+	cidrs = make([]*net.IPNet, len(maxCidrBlocks))
+	for i, maxCidrBlock := range maxCidrBlocks {
+		_, cidr, _ := net.ParseCIDR(maxCidrBlock)
+		cidrs[i] = cidr
+	}
+}
+
+// isLocalAddress works by checking if the address is under private CIDR blocks.
+// List of private CIDR blocks can be seen on :
+//
+// https://en.wikipedia.org/wiki/Private_network
+//
+// https://en.wikipedia.org/wiki/Link-local_address
+func isPrivateAddress(address string) (bool, error) {
+	ipAddress := net.ParseIP(address)
+	if ipAddress == nil {
+		return false, errors.New("address is not valid")
+	}
+
+	for i := range cidrs {
+		if cidrs[i].Contains(ipAddress) {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+// FromRequest return client's real public IP address from http request headers.
+func FromRequest(r *http.Request) string {
+	// Fetch header value
+	xRealIP := r.Header.Get("X-Real-Ip")
+	xForwardedFor := r.Header.Get("X-Forwarded-For")
+
+	// If both empty, return IP from remote address
+	if xRealIP == "" && xForwardedFor == "" {
+		var remoteIP string
+
+		// If there are colon in remote address, remove the port number
+		// otherwise, return remote address as is
+		if strings.ContainsRune(r.RemoteAddr, ':') {
+			remoteIP, _, _ = net.SplitHostPort(r.RemoteAddr)
+		} else {
+			remoteIP = r.RemoteAddr
+		}
+
+		return remoteIP
+	}
+
+	// Check list of IP in X-Forwarded-For and return the first global address
+	for _, address := range strings.Split(xForwardedFor, ",") {
+		address = strings.TrimSpace(address)
+		isPrivate, err := isPrivateAddress(address)
+		if !isPrivate && err == nil {
+			return address
+		}
+	}
+
+	// If nothing succeed, return X-Real-IP
+	return xRealIP
+}
+
+// RealIP is depreciated, use FromRequest instead
+func RealIP(r *http.Request) string {
+	return FromRequest(r)
+}