Initial working implementation of HLS proxy

src/main/java/com/backend/hls/proxy/service/FetchService.java

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+package com.backend.hls.proxy.service;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+
+import org.springframework.cache.annotation.Cacheable;
+import org.springframework.stereotype.Service;
+
+import com.backend.hls.proxy.exception.FetchFailException;
+import com.backend.hls.proxy.model.SimpleResponse;
+
+@Service
+public class FetchService {
+    private final HttpClient httpClient;
+
+    public FetchService(HttpClient httpClient) {
+        this.httpClient = httpClient;
+    }
+
+    /**
+     * Fetch text content from URL
+     * 
+     * @throws FetchFailException
+     */
+    @Cacheable("hlsPlaylistContent")
+    public String fetchTextContent(String url) throws IOException, InterruptedException, FetchFailException {
+        HttpRequest request = HttpRequest.newBuilder()
+                .uri(URI.create(url))
+                .build();
+
+        HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
+
+        if (response.statusCode() != 200) {
+            throw new FetchFailException("Failed to fetch content from " + url + ", status: " + response.statusCode(),
+                    response);
+        }
+
+        return response.body();
+    }
+
+    /**
+     * Fetch binary content from URL
+     * 
+     * @throws FetchFailException
+     */
+    @Cacheable("playlistSegmentContent")
+    public SimpleResponse<byte[]> fetchBinaryContent(String url)
+            throws IOException, InterruptedException, FetchFailException {
+        return fetchBinaryContent(url, null);
+    }
+
+    /**
+     * Fetch binary content from URL
+     * 
+     * @throws FetchFailException
+     */
+    @Cacheable("playlistSegmentContent")
+    public SimpleResponse<byte[]> fetchBinaryContent(String url, String rangeHeader)
+            throws IOException, InterruptedException, FetchFailException {
+        HttpRequest.Builder builder = HttpRequest.newBuilder()
+                .uri(URI.create(url));
+
+        if (rangeHeader != null && !rangeHeader.isEmpty()) {
+            builder.header("Range", rangeHeader);
+        }
+
+        HttpResponse<byte[]> response = httpClient.send(builder.build(), HttpResponse.BodyHandlers.ofByteArray());
+
+        if (response.statusCode() >= 400) {
+            throw new FetchFailException("Failed to fetch content from " + url + ", status: " + response.statusCode(),
+                    response);
+        }
+
+        return new SimpleResponse<byte[]>(response.body(), response.headers());
+    }
+
+    /**
+     * Fetch content length
+     *
+     * @throws FetchFailException
+     */
+    public long getContentLength(String url)
+            throws IOException, InterruptedException, FetchFailException {
+
+        HttpRequest request = HttpRequest.newBuilder()
+                .uri(URI.create(url))
+                .method("HEAD", HttpRequest.BodyPublishers.noBody())
+                .timeout(Duration.ofSeconds(10))
+                .build();
+
+        HttpResponse<Void> response = httpClient.send(request,
+                HttpResponse.BodyHandlers.discarding());
+
+        if (response.statusCode() >= 400) {
+            throw new FetchFailException("HTTP " + response.statusCode(), response);
+        }
+
+        return response.headers()
+                .firstValueAsLong("Content-Length")
+                .orElse(-1L);
+    }
+
+}