removed tinyurl logic added support for new short code logic

MOBILE.md

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+# Mobile Integration Guide
+
+This document outlines the requirements for mobile applications to integrate with the Simple File Upload Server.
+
+## API Endpoints
+
+### Upload File
+**Endpoint:** `POST /upload`  
+**Content-Type:** `multipart/form-data`
+
+**Request Parameters:**
+```
+file: File (required) - The file to upload
+max_downloads: Integer (optional) - Maximum number of downloads allowed (default: 1)
+expiry_hours: Integer (optional) - Hours until file expires (default: 24, max: 24)
+```
+
+**Example Request (Swift):**
+```swift
+let url = URL(string: "http://your-server:7777/upload")!
+var request = URLRequest(url: url)
+request.httpMethod = "POST"
+
+let boundary = "Boundary-\(UUID().uuidString)"
+request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
+
+var body = Data()
+// Add file data
+body.append("--\(boundary)\r\n")
+body.append("Content-Disposition: form-data; name=\"file\"; filename=\"log.txt\"\r\n")
+body.append("Content-Type: text/plain\r\n\r\n")
+body.append(fileData)
+body.append("\r\n")
+// Add parameters
+body.append("--\(boundary)\r\n")
+body.append("Content-Disposition: form-data; name=\"max_downloads\"\r\n\r\n")
+body.append("3\r\n")
+body.append("--\(boundary)\r\n")
+body.append("Content-Disposition: form-data; name=\"expiry_hours\"\r\n\r\n")
+body.append("24\r\n")
+body.append("--\(boundary)--\r\n")
+
+request.httpBody = body
+```
+
+**Example Request (Kotlin):**
+```kotlin
+val file = File("log.txt")
+val requestBody = MultipartBody.Builder()
+    .setType(MultipartBody.FORM)
+    .addFormDataPart(
+        "file",
+        file.name,
+        file.asRequestBody("application/octet-stream".toMediaType())
+    )
+    .addFormDataPart("max_downloads", "3")
+    .addFormDataPart("expiry_hours", "24")
+    .build()
+
+val request = Request.Builder()
+    .url("http://your-server:7777/upload")
+    .post(requestBody)
+    .build()
+```
+
+**Success Response:**
+```json
+{
+    "code": "ABC123"
+}
+```
+
+**Error Responses:**
+```json
+{
+    "error": "No file part"
+}
+```
+Status: 400 Bad Request
+
+```json
+{
+    "error": "No selected file"
+}
+```
+Status: 400 Bad Request
+
+### Download File
+**Endpoint:** `GET /download/{code}`
+
+**Parameters:**
+- `code`: 6-character alphanumeric code received from upload
+
+**Example Request (Swift):**
+```swift
+let code = "ABC123"
+let url = URL(string: "http://your-server:7777/download/\(code)")!
+let task = URLSession.shared.downloadTask(with: url) { localURL, response, error in
+    guard let localURL = localURL else { return }
+    // Handle downloaded file
+}
+task.resume()
+```
+
+**Example Request (Kotlin):**
+```kotlin
+val code = "ABC123"
+val request = Request.Builder()
+    .url("http://your-server:7777/download/$code")
+    .get()
+    .build()
+
+client.newCall(request).enqueue(object : Callback {
+    override fun onResponse(call: Call, response: Response) {
+        // Handle downloaded file
+    }
+    override fun onFailure(call: Call, e: IOException) {
+        // Handle error
+    }
+})
+```
+
+**Success Response:**
+- Status: 200 OK
+- Content-Type: application/octet-stream
+- Content-Disposition: attachment; filename="original_filename.ext"
+
+**Error Responses:**
+- Status: 404 Not Found
+- Content-Type: application/json
+
+Various error messages:
+```json
+{
+    "error": "Invalid or expired code"
+}
+```
+```json
+{
+    "error": "File expired"
+}
+```
+```json
+{
+    "error": "Download limit reached"
+}
+```
+```json
+{
+    "error": "File not found"
+}
+```
+
+## Implementation Requirements
+
+### File Upload
+1. Implement proper error handling for network issues
+2. Show upload progress to user
+3. Handle timeout scenarios (recommended timeout: 60 seconds)
+4. Store received code securely if needed
+5. Validate file size before upload (max size: 16MB)
+6. Implement retry logic for failed uploads
+
+### File Download
+1. Handle all error scenarios gracefully
+2. Show download progress to user
+3. Validate downloaded file integrity
+4. Implement proper file saving logic
+5. Handle interrupted downloads with resume capability if possible
+
+### Security Considerations
+1. Use HTTPS for all API calls in production
+2. Don't store sensitive files for extended periods
+3. Implement proper error messages without exposing server details
+4. Sanitize all user inputs
+5. Handle session timeouts appropriately
+
+## Testing Requirements
+1. Test with various file types and sizes
+2. Verify all error scenarios
+3. Test network condition variations:
+    - Slow network
+    - Intermittent connectivity
+    - Network switches (WiFi to Cellular)
+4. Test concurrent uploads/downloads
+5. Verify proper cleanup of temporary files
+
+## Sample Status Codes
+- 200: Success
+- 400: Bad Request (invalid parameters)
+- 404: Not Found (invalid code or expired file)
+- 413: Payload Too Large (file size exceeded)
+- 500: Server Error
+
+## Rate Limiting
+- Maximum 10 requests per minute per IP
+- Implement exponential backoff for retries
+
+## Migration Notes
+If upgrading from previous versions:
+1. Update API endpoint URLs
+2. Implement new error handling
+3. Update file size limits
+4. Add support for download codes
+5. Remove old URL-based download logic