feat: Add SpringerDownloadService

AoU-Common/src/main/java/ch/unige/aou/service/SpringerDownloadService.java

+package ch.unige.aou.service;
+
+import java.net.URI;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Consumer;
+
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferUtils;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import ch.unige.solidify.util.StringTool;
+
+@Service
+public class SpringerDownloadService {
+
+  private static final int MAX_REDIRECT = 10;
+
+  public void download(URI uri, Path path) {
+    final WebClient client = WebClient.create();
+    ResponseEntity<Void> responseEntity;
+    URI location = uri;
+    Map<String, String> cookies = new HashMap<>();
+    int nbRedirect = 0;
+
+    // Follow redirects
+    do {
+      responseEntity = getClientResponse(client, location, cookies);
+      URI newLocation = responseEntity.getHeaders().getLocation();
+      if(newLocation != null) {
+        location = newLocation;
+      }
+      List<String> receivedCookies = responseEntity.getHeaders().get("Set-Cookie");
+      if(receivedCookies != null) {
+        for (String cookieToMerge : receivedCookies) {
+          final String cookieNameValue = cookieToMerge.substring(0, cookieToMerge.indexOf(';'));
+          final String cookieName = cookieNameValue.substring(0, cookieNameValue.indexOf('='));
+          final String cookieValue = cookieNameValue.substring(cookieNameValue.indexOf('=') + 1);
+          cookies.put(cookieName, cookieValue);
+        }
+      }
+      nbRedirect++;
+    } while(responseEntity.getStatusCode().is3xxRedirection() && nbRedirect < MAX_REDIRECT);
+
+    // Trigger download
+    Flux<DataBuffer> dataBufferFlux = client.get()
+            .uri(location)
+            .headers(this.getCookieConsumer(cookies))
+            .retrieve()
+            .bodyToFlux(DataBuffer.class);
+    DataBufferUtils.write(dataBufferFlux, path, StandardOpenOption.CREATE).block();
+  }
+
+  private ResponseEntity<Void> getClientResponse(WebClient client, URI uri, Map<String, String> cookies) {
+    return client.get()
+            .uri(uri)
+            .headers(this.getCookieConsumer(cookies))
+            .retrieve()
+            .onStatus(status -> true, response -> Mono.empty())
+            .toBodilessEntity()
+            .block();
+  }
+
+  private String getCookieString(Map<String, String> cookies) {
+    StringBuilder cookieString = new StringBuilder();
+    for(Map.Entry<String, String> cookieNameValue : cookies.entrySet()) {
+      cookieString.append(cookieNameValue.getKey())
+                  .append("=")
+                  .append(cookieNameValue.getValue())
+                  .append("; ");
+    }
+    return cookieString.toString();
+  }
+
+  private Consumer<HttpHeaders> getCookieConsumer(Map<String,String> cookies) {
+    return headers -> {
+      final String cookieString = this.getCookieString(cookies);
+      if (!StringTool.isNullOrEmpty(cookieString)) {
+        headers.set("Cookie", cookieString);
+      }
+    };
+  }
+
+}