feat: add 1px transparent image in RSS item descriptions for telemetry content views (#44)

### What this PR does?

传统网站即使使用 Umami 等访问统计工具，也难以覆盖 RSS 订阅用户的阅读行为，导致访问量数据不完整，影响对内容表现的准确评估。为解决这一短板，我们新增了在 RSS 订阅中统计访问量的功能支持。

通过在每个 RSS 条目的内容中插入 1 像素透明图片，系统可匿名统计订阅内容的实际阅读量。这种轻量化设计不会影响用户体验，帮助内容创作者更全面的了解内容阅读量情况。

Umami 适配参考 halo-sigs/plugin-umami#30

```release-note
为 RSS 订阅内容统计访问量提供扩展支持，本插件并不提供任何存储和分析访问量的功能但允许其他插件扩展并获取访问量数据上报给诸如 Umami 之类的应用
```

Author: guqing

api/src/main/java/run/halo/feed/TelemetryEventInfo.java

@@ -0,0 +1,45 @@
+package run.halo.feed;
+
+import java.util.Objects;
+import lombok.Data;
+import lombok.Getter;
+import lombok.experimental.Accessors;
+import org.springframework.http.HttpHeaders;
+import org.springframework.lang.NonNull;
+
+@Data
+@Accessors(chain = true)
+public class TelemetryEventInfo {
+    private String pageUrl;
+    private String screen;
+    private String language;
+    private String languageRegion;
+    private String title;
+    private String referrer;
+    private String ip;
+    private String userAgent;
+    private String browser;
+    private String os;
+
+    @Getter(onMethod_ = @NonNull)
+    private HttpHeaders headers;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        TelemetryEventInfo that = (TelemetryEventInfo) o;
+        return Objects.equals(pageUrl, that.pageUrl) && Objects.equals(title, that.title)
+            && Objects.equals(referrer, that.referrer) && Objects.equals(ip, that.ip)
+            && Objects.equals(userAgent, that.userAgent);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(pageUrl, title, referrer, ip, userAgent);
+    }
+}

api/src/main/java/run/halo/feed/TelemetryRecorder.java

@@ -0,0 +1,8 @@
+package run.halo.feed;
+
+import org.pf4j.ExtensionPoint;
+
+public interface TelemetryRecorder extends ExtensionPoint {
+
+    void record(TelemetryEventInfo eventInfo);
+}

app/src/main/java/run/halo/feed/RssCacheManager.java

@@ -35,22 +35,23 @@ public Mono<String> get(String key, Mono<RSS2> loader) {
     }
 
     private Mono<String> generateRssXml(Mono<RSS2> loader) {
-        var builder = new RssXmlBuilder();
+        var builder = new RssXmlBuilder()
+            .withGenerator("Halo v2.0");
+
         var rssMono = loader.doOnNext(builder::withRss2);
-        var generatorMono = getRssGenerator()
-            .doOnNext(builder::withGenerator);
+
+        var generatorMono = systemInfoGetter.get()
+            .doOnNext(info -> builder.withExternalUrl(info.getUrl().toString())
+                .withGenerator("Halo v" + info.getVersion().toStableVersion().toString())
+            );
+
         var extractTagsMono = BasicProp.getBasicProp(settingFetcher)
             .doOnNext(prop -> builder.withExtractRssTags(prop.getRssExtraTags()));
+
         return Mono.when(rssMono, generatorMono, extractTagsMono)
             .then(Mono.fromSupplier(builder::toXmlString));
     }
 
-    private Mono<String> getRssGenerator() {
-        return systemInfoGetter.get()
-            .map(info -> "Halo v" + info.getVersion().toStableVersion().toString())
-            .defaultIfEmpty("Halo v2.0");
-    }
-
     @EventListener(PluginConfigUpdatedEvent.class)
     public void onPluginConfigUpdated() {
         cache.invalidateAll();

app/src/main/java/run/halo/feed/RssXmlBuilder.java

@@ -2,6 +2,7 @@
 
 import com.google.common.base.Throwables;
 import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
 import java.time.Instant;
 import java.time.ZoneOffset;
 import java.time.format.DateTimeFormatter;
@@ -14,13 +15,17 @@
 import org.dom4j.Element;
 import org.dom4j.io.SAXReader;
 import org.springframework.util.CollectionUtils;
+import org.springframework.web.util.UriComponentsBuilder;
+import org.springframework.web.util.UriUtils;
+import run.halo.feed.telemetry.TelemetryEndpoint;
 
 @Slf4j
 public class RssXmlBuilder {
     private RSS2 rss2;
     private String generator = "Halo v2.0";
     private String extractRssTags;
     private Instant lastBuildDate = Instant.now();
+    private String externalUrl;
 
     public RssXmlBuilder withRss2(RSS2 rss2) {
         this.rss2 = rss2;
@@ -48,6 +53,11 @@ RssXmlBuilder withLastBuildDate(Instant lastBuildDate) {
         return this;
     }
 
+    RssXmlBuilder withExternalUrl(String externalUrl) {
+        this.externalUrl = externalUrl;
+        return this;
+    }
+
     public String toXmlString() {
         Document document = DocumentHelper.createDocument();
 
@@ -127,18 +137,19 @@ private Element parseXmlString(String xml) throws DocumentException {
         }
     }
 
-    private static void createItemElementsToChannel(Element channel, List<RSS2.Item> items) {
+    private void createItemElementsToChannel(Element channel, List<RSS2.Item> items) {
         if (CollectionUtils.isEmpty(items)) {
             return;
         }
         items.forEach(item -> createItemElementToChannel(channel, item));
     }
 
-    private static void createItemElementToChannel(Element channel, RSS2.Item item) {
+    private void createItemElementToChannel(Element channel, RSS2.Item item) {
         Element itemElement = channel.addElement("item");
         itemElement.addElement("title").addCDATA(item.getTitle());
         itemElement.addElement("link").addText(item.getLink());
-        itemElement.addElement("description").addCDATA(item.getDescription());
+        var description = getDescriptionWithTelemetry(item);
+        itemElement.addElement("description").addCDATA(description);
         itemElement.addElement("guid")
             .addAttribute("isPermaLink", "false")
             .addText(item.getGuid());
@@ -201,6 +212,29 @@ private static void createItemElementToChannel(Element channel, RSS2.Item item)
         });
     }
 
+    private String getDescriptionWithTelemetry(RSS2.Item item) {
+        if (StringUtils.isBlank(externalUrl)) {
+            return item.getDescription();
+        }
+        var uri = UriComponentsBuilder.fromUriString(item.getLink())
+            .build();
+        var telemetryBaseUri = externalUrl + TelemetryEndpoint.TELEMETRY_PATH;
+        var telemetryUri = UriComponentsBuilder.fromUriString(telemetryBaseUri)
+            .queryParam("title", UriUtils.encode(item.getTitle(), StandardCharsets.UTF_8))
+            .queryParam("url", uri.getPath())
+            .build(true)
+            .toUriString();
+
+        // Build the telemetry image HTML
+        var telemetryImageHtml = String.format(
+            "<img src=\"%s\" width=\"1\" height=\"1\" alt=\"\" style=\"opacity:0;\" />",
+            telemetryUri
+        );
+
+        // Append telemetry image to description
+        return telemetryImageHtml + item.getDescription();
+    }
+
     static <T> List<T> nullSafeList(List<T> list) {
         return list == null ? List.of() : list;
     }

app/src/main/java/run/halo/feed/telemetry/AcceptLanguageParser.java

@@ -0,0 +1,72 @@
+package run.halo.feed.telemetry;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+import lombok.experimental.UtilityClass;
+import org.springframework.lang.NonNull;
+
+@UtilityClass
+public class AcceptLanguageParser {
+
+    public record Language(String code, String script, String region, double quality) {
+        @Override
+        public String toString() {
+            return "Language{" +
+                "code='" + code + '\'' +
+                ", script='" + script + '\'' +
+                ", region='" + region + '\'' +
+                ", quality=" + quality +
+                '}';
+        }
+    }
+
+    private static final Pattern REGEX = Pattern.compile(
+        "((([a-zA-Z]+(-[a-zA-Z0-9]+){0,2})|\\*)(;q=[0-1](\\.[0-9]+)?)?)*");
+
+    @NonNull
+    public static List<Language> parseAcceptLanguage(String acceptLanguage) {
+        if (acceptLanguage == null || acceptLanguage.isEmpty()) {
+            return Collections.emptyList();
+        }
+
+        List<Language> languages = new ArrayList<>();
+        Matcher matcher = REGEX.matcher(acceptLanguage);
+
+        while (matcher.find()) {
+            String match = matcher.group();
+            if (match == null || match.isEmpty()) {
+                continue;
+            }
+
+            String[] parts = match.split(";");
+            String ietfTag = parts[0];
+            String[] ietfComponents = ietfTag.split("-");
+            String code = ietfComponents[0];
+            String script = ietfComponents.length == 3 ? ietfComponents[1] : null;
+            String region = ietfComponents.length == 3 ? ietfComponents[2]
+                : ietfComponents.length == 2 ? ietfComponents[1] : null;
+
+            double quality = 1.0;
+            if (parts.length > 1 && parts[1].startsWith("q=")) {
+                try {
+                    quality = Double.parseDouble(parts[1].substring(2));
+                } catch (NumberFormatException e) {
+                    // ignore
+                }
+            }
+
+            languages.add(new Language(code, script, region, quality));
+        }
+
+        return languages.stream()
+            .filter(Objects::nonNull)
+            .sorted(Comparator.comparingDouble((Language l) -> l.quality).reversed())
+            .collect(Collectors.toList());
+    }
+}