Fix boundary value extraction for form-data requests

android/capacitor/src/main/java/com/getcapacitor/plugin/util/CapacitorHttpUrlConnection.java

@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.UUID;
 import javax.net.ssl.HttpsURLConnection;
 import javax.net.ssl.SSLSocketFactory;
 import org.json.JSONException;
@@ -224,7 +225,16 @@ public void setRequestBody(PluginCall call, JSValue body, String bodyType) throw
                 this.writeRequestBody(body.toString());
             }
         } else if (bodyType != null && bodyType.equals("formData")) {
-            this.writeFormDataRequestBody(contentType, body.toJSArray());
+            String boundary = extractBoundaryFromContentType(contentType);
+            if (boundary == null) {
+                // If no boundary is provided, generate a random one and set the Content-Type header accordingly
+                // or otherwise servers will not be able to parse the request body. Browsers do this automatically
+                // but here we need to do this manually in order to comply with browser api behavior.
+                boundary = UUID.randomUUID().toString();
+                connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
+            }
+
+            this.writeFormDataRequestBody(boundary, body.toJSArray());
         } else {
             this.writeRequestBody(body.toString());
         }
@@ -260,9 +270,8 @@ private void writeObjectRequestBody(JSObject object) throws IOException, JSONExc
         }
     }
 
-    private void writeFormDataRequestBody(String contentType, JSArray entries) throws IOException, JSONException {
+    private void writeFormDataRequestBody(String boundary, JSArray entries) throws IOException, JSONException {
         try (DataOutputStream os = new DataOutputStream(connection.getOutputStream())) {
-            String boundary = contentType.split(";")[1].split("=")[1];
             String lineEnd = "\r\n";
             String twoHyphens = "--";
 
@@ -303,6 +312,39 @@ private void writeFormDataRequestBody(String contentType, JSArray entries) throw
         }
     }
 
+    /**
+     * Extracts the boundary value from the `Content-Type` header for multipart/form-data requests, if provided.
+     *
+     * The boundary value might be surrounded by double quotes (") which will be stripped away.
+     *
+     * @param contentType The `Content-Type` header string.
+     * @return The boundary value if found, otherwise `null`.
+     */
+    public static String extractBoundaryFromContentType(String contentType) {
+        String boundaryPrefix = "boundary=";
+        int boundaryIndex = contentType.indexOf(boundaryPrefix);
+        if (boundaryIndex == -1) {
+            return null;
+        }
+
+        // Extract the substring starting right after "boundary="
+        String boundary = contentType.substring(boundaryIndex + boundaryPrefix.length());
+
+        // Find the end of the boundary value by looking for the next ";"
+        int endIndex = boundary.indexOf(";");
+        if (endIndex != -1) {
+            boundary = boundary.substring(0, endIndex);
+        }
+
+        // Remove surrounding double quotes if present
+        boundary = boundary.trim();
+        if (boundary.startsWith("\"") && boundary.endsWith("\"")) {
+            boundary = boundary.substring(1, boundary.length() - 1);
+        }
+
+        return boundary;
+    }
+
     /**
      * Opens a communications link to the resource referenced by this
      * URL, if such a connection has not already been established.

ios/Capacitor/Capacitor/Plugins/CapacitorUrlRequest.swift

@@ -66,7 +66,7 @@ open class CapacitorUrlRequest: NSObject, URLSessionTaskDelegate {
 
         var data = Data()
         var boundary = UUID().uuidString
-        if contentType.contains("="), let contentBoundary = contentType.components(separatedBy: "=").last {
+        if contentType.contains("boundary="), let contentBoundary = extractBoundary(from: contentType)  {
             boundary = contentBoundary
         } else {
             overrideContentType(boundary)
@@ -86,6 +86,27 @@ open class CapacitorUrlRequest: NSObject, URLSessionTaskDelegate {
         request.setValue(contentType, forHTTPHeaderField: "Content-Type")
         headers["Content-Type"] = contentType
     }
+
+    /**
+     Extracts the boundary value of the `content-type` header for multiplart/form-data requests, if provided
+     The boundary value might be surrounded by double quotes (") which will be stripped away.
+     */
+    private func extractBoundary(from contentType: String) -> String? {
+        if let boundaryRange = contentType.range(of: "boundary=") {
+            var boundary = contentType[boundaryRange.upperBound...]
+            if let endRange = boundary.range(of: ";") {
+                boundary = boundary[..<endRange.lowerBound]
+            }
+
+            if boundary.hasPrefix("\"") && boundary.hasSuffix("\"") {
+                return String(boundary.dropFirst().dropLast())
+            } else {
+                return String(boundary)
+            }
+        }
+
+        return nil
+    }
 
     public func getRequestDataAsString(_ data: JSValue) throws -> Data {
         guard let stringData = data as? String else {
@@ -110,7 +131,7 @@ open class CapacitorUrlRequest: NSObject, URLSessionTaskDelegate {
         }
         var data = Data()
         var boundary = UUID().uuidString
-        if contentType.contains("="), let contentBoundary = contentType.components(separatedBy: "=").last {
+        if contentType.contains("boundary="), let contentBoundary = extractBoundary(from: contentType) {    
             boundary = contentBoundary
         } else {
             overrideContentType(boundary)