Sending System

Simple program for sending data from one computer to another.

The current version runs an HTTP/HTTPS server (CivetWeb) with two REST endpoints:

• POST /api/send — JSON messages (text, small base64 payloads, save-to-file requests)
• POST /api/upload — multipart/form-data file uploads, streamed without loading the file into memory

A WebSocket endpoint for real-time audio/binary streaming (/api/stream) is planned and partially wired; see src/handlers/.

The client is an Android app that talks to the server over HTTP or HTTPS using OkHttp. It can send text or a file picked via the system file chooser or the Android "Share" menu.

⚠️ ATTENTION!!!

Apple products (iPhone and other iOS devices) are not supported. Windows 7, 10 and 11 builds are targeted.

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🧩 Architecture

┌──────────────────┐        HTTP(S)         ┌────────────────────┐
│  Android client  │ ─────────────────────► │  Sending System    │
│  (OkHttp)        │  POST /api/send        │  (CivetWeb server) │
│                  │  POST /api/upload      │                    │
└──────────────────┘                        └────────────────────┘
                                                    │
                                                    ▼
                                            saves/ (file storage)

• The server listens on a single port (CONNECTION_PORT, default 5000).
  • When SSL_ENCRYPT = false → plain HTTP.
  • When SSL_ENCRYPT = true → HTTPS using the certificate/key in server.pem.
• The client switches between http:// and https:// via the SSL checkbox. The port stays the same; only the scheme changes.

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🛠 Dependencies

Linux Server

Library	Purpose
CivetWeb (fetched via CMake FetchContent)	HTTP/HTTPS/WebSocket server
cJSON v1.7.18 (fetched via FetchContent)	JSON parsing for /api/send
OpenSSL 3.x	TLS, pulled in by CivetWeb
libcurl	Query an external HTTPS service for the public IP
miniupnpc	Ask the local router for the public IP via UPnP
SQLite3	Persistence of messages (planned)

Ubuntu / Debian:

sudo apt install build-essential cmake libssl-dev \
                 libcurl4-openssl-dev libminiupnpc-dev

Fedora:

sudo dnf install gcc cmake openssl-devel \
                 libcurl-devel miniupnpc-devel

macOS:

brew install cmake openssl curl miniupnpc

Android Client

implementation("com.squareup.okhttp3:okhttp:4.12.0")
implementation("androidx.room:room-runtime:2.6.1")
annotationProcessor("androidx.room:room-compiler:2.6.1")

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🖼️ Program Appearance

Linux Server

Android Client

Screenshots may lag behind the current build. The current server prints a short startup banner and one line per request; the current client has a checkbox for SSL, two radio buttons (Text / File), and no progress bar yet.

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🏗 🚀 Building and launching

Linux server

1. Clone the repository

git clone https://github.com/ClassZak/SendingSystem.git
cd SendingSystem/Server/DesktopServer

2. Configure src/util/config.h

All server tunables live here. Defaults:

#define CONNECTION_PORT   5000
static const char* CONNECTION_IP = "0.0.0.0";

static const bool  SSL_ENCRYPT       = true;
static const char* PUBLIC_KEY_FILE   = "server.pem";

#define MAX_MESSAGE_SIZE   0x6400000   /*  100 MB — /api/send body limit */
#define MAX_UPLOAD_SIZE    0x64000000  /*    1 GB — /api/upload file limit */
#define REQUEST_TIMEOUT_MS 30000

If SSL_ENCRYPT = true, server.pem must exist and contain both the certificate and the private key, back to back. Generate it once:

# Either reuse an existing cert/key pair:
cat server.crt server.key > server.pem

# Or generate a self-signed pair from scratch:
openssl req -x509 -newkey rsa:2048 -nodes -days 3650 \
    -keyout server.key -out server.crt -subj "/CN=sending-system"
cat server.crt server.key > server.pem
chmod 600 server.pem

server.pem contains a private key — keep it out of git.

3. Build

cmake --list-presets
cmake --preset linux-debug
cmake --build build --preset linux-debug

The binary is at build/SendingSystem.

CMake fetches CivetWeb and cJSON automatically. libcurl and miniupnpc must be installed on the system (see Dependencies above).

4. Run

./build/SendingSystem

Expected startup log:

[INFO] Local IP addresses (3):
[INFO]   192.168.1.42/24
[INFO]   127.0.0.1/8
[INFO]   fe80::1c2b:3fff:fe4a:1234/64
***  ... mg_start2: ... [listening_ports] -> [5000s]
***  ... mg_start2: ... [ssl_certificate] -> [server.pem]
[SUCCESS] Server started
[INFO]   POST http://0.0.0.0:5000/api/send
[INFO]   POST http://0.0.0.0:5000/api/upload
[INFO]   HTTPS/WSS on port 5000 (cert: server.pem)
[INFO] Public IP (UPnP): 203.0.113.42       # or (HTTP): … or "unknown"

The local-IP and public-IP lines are produced by a background thread — server startup is not blocked by network lookups.

5. Smoke-test with curl

Text message:

# plain HTTP
curl -v -X POST http://127.0.0.1:5000/api/send \
     -H "Content-Type: application/json" \
     -d '{"type":"RAW_DATA","data":"hello"}'

# HTTPS (self-signed)
curl -kv -X POST https://127.0.0.1:5000/api/send \
     -H "Content-Type: application/json" \
     -d '{"type":"RAW_DATA","data":"hello"}'

Expected body: {"type":"message","data":"OK"}.

File upload:

curl -kv -F "file=@record.aac" https://127.0.0.1:5000/api/upload

Expected body: {"type":"message","data":"File(s) received"} and the file appears under saves/.

Android client

1. Open the project in Android Studio

The client source lives under app/src/main/java/com/example/sendingsystemclient/.

2. Sync Gradle

Android Studio will download OkHttp and Room automatically.

3. Run

adb uninstall com.example.sendingsystemclient    # ensure a clean install
./gradlew installDebug

4. First run

1. Enter the server's IP (the one printed by get_server_ip_addresses, e.g. 192.168.1.42) and port (5000).
2. Tick or untick SSL to match the server's SSL_ENCRYPT setting.
3. Pick Text or File, fill in the field(s), press Send.

HTTP cleartext on Android 9+

If you set SSL_ENCRYPT = false and the client tries to use http://, Android will refuse the connection with

CLEARTEXT communication to <ip> not permitted by network security policy

Either enable HTTPS on the server (SSL_ENCRYPT = true) or add the following to AndroidManifest.xml:

<application
    android:usesCleartextTraffic="true"
    ...>

(For development only. Do not ship a production build with this flag on.)

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🔌 API

POST /api/send

JSON body:

{
  "type":       "RAW_DATA" | "FILE" | "<any>",
  "data":       "<plain text, or base64-encoded file>",
  "saveToPath": "<optional file name>"
}

• Without saveToPath: message is logged and the server replies OK.
• With saveToPath and type = "FILE": data is base64-decoded and saved.
• With saveToPath and any other type: data is written verbatim.

Response: {"type": "message", "data": "..."} on success, {"type": "error", "data": "..."} on failure.

POST /api/upload

multipart/form-data with one or more file parts. Each part is streamed to saves/<sanitised-name>; memory usage is independent of file size.

Response: {"type": "message", "data": "File(s) received"}.

WS /api/stream (planned)

Bidirectional WebSocket for real-time audio chunks. Not part of the stable API yet.

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🧪 Status

Feature	Status
HTTP server (/api/send)	✅
HTTPS server (/api/send)	✅
Multipart upload (/api/upload)	✅
Public-IP detection (UPnP + HTTP)	✅
Local-IP enumeration	✅
WebSocket (/api/stream)	🚧 in progress
Android client (OkHttp)	✅
Android client progress bar	🚧 not wired to UI yet
Authentication	❌ (planned)
Windows build	🚧 untested

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📄 License

See LICENSE.txt.