Add RSS parser implementation for IP extraction

parser/rss.go

@@ -0,0 +1,68 @@
+package parser
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// rssExtract defines the function signature for extracting IP addresses from a RSS item.
+type rssExtract func(decoder *xml.Decoder, start xml.StartElement) (string, error)
+
+// rssParser is a parser for RSS data.
+type rssParser struct {
+	// extract is the function that extracts an IP address from a RSS item.
+	extract rssExtract
+}
+
+// NewRss creates a new RSS parser.
+func NewRss(extract rssExtract) (Parser, error) {
+	if extract == nil {
+		return nil, fmt.Errorf("rss extract is nil")
+	}
+
+	return &rssParser{
+		extract: extract,
+	}, nil
+}
+
+// Parse parses the RSS data from the given reader.
+// It returns a slice of IP addresses and any errors that occurred during the process.
+func (p *rssParser) Parse(body io.Reader, validator IPValidator, limit uint) (IPs, error) {
+	decoder := xml.NewDecoder(body)
+	ips := make(IPs, 0)
+
+	for {
+		token, err := decoder.Token()
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+
+			return nil, fmt.Errorf("parse rss: %w", err)
+		}
+
+		start, ok := token.(xml.StartElement)
+		if !ok {
+			continue
+		}
+
+		ip, err := p.extract(decoder, start)
+		if err != nil {
+			return nil, fmt.Errorf("extract rss ip: %w", err)
+		}
+
+		ip = strings.TrimSpace(ip)
+		if !validator.IsValid(ip) {
+			continue
+		}
+
+		ips = append(ips, ip)
+		if limit > 0 && uint(len(ips)) >= limit {
+			break
+		}
+	}
+
+	return ips, nil
+}