Proxy Core

FlowMind includes a Rust-based MITM (Man-in-the-Middle) proxy engine that supports HTTP/HTTPS/WebSocket traffic capture and parsing.

Proxy Architecture

flowchart LR
    Client[Client/Browser] --> Proxy[FlowMind Proxy]
    Proxy --> Target[Target Server]
    Proxy --> Store[FlowStore]
    Store --> UI[Frontend Interface]

Start & Stop

Start Proxy

1. Click the Start Proxy button in the title bar
2. Proxy starts listening on the configured address and port
3. Status bar shows: ● Proxy Running - 127.0.0.1:8080

Health Information

When the proxy is running, the following health metrics are displayed:

Metric	Description
Active Connections	Number of currently active connections
Total Requests	Total requests since proxy started

Configuration Options

Go to Settings → Proxy Configuration to adjust:

Option	Default	Description
Listen Address	127.0.0.1	IP address the proxy listens on
Listen Port	8080	Port the proxy listens on
Max Request Body Size	10 MB	Maximum size of a single request body
Max WebSocket Message Size	1 MB	Maximum WebSocket message size
Upstream Proxy	Empty	Optional upstream proxy, e.g. http://proxy.corp:8080

Port Conflict

If the configured port is already in use, the proxy will automatically try other ports and display the actual port in the status bar.

Upstream Proxy

FlowMind supports forwarding traffic through an upstream proxy, suitable for:

• Enterprise networks: Access external networks through corporate proxy
• Multi-layer proxy: Route traffic through other proxy tools
• Egress control: Control traffic exit through a specified proxy

Enter the proxy address (e.g. http://proxy.corp:8080) in the upstream proxy configuration, and the proxy engine will automatically forward captured traffic through the upstream proxy.

HTTPS MITM

How It Works

1. Client initiates HTTPS connection to proxy
2. Proxy dynamically generates certificate for target domain
3. Proxy establishes TLS connection with client
4. Proxy establishes TLS connection with target server
5. Proxy decrypts, records, and re-encrypts traffic

CA Certificate Management

Operation	Description
Export CA Certificate	Export CA certificate as file for client installation
Regenerate CA	Generate new CA key pair (old certificate will be invalid)
View CA SPKI	Display certificate's SPKI hash for certificate pinning

WebSocket Support

FlowMind fully supports WebSocket protocol:

• Connection Capture: Automatically identifies WebSocket upgrade requests
• Message Recording: Records all WebSocket messages (text/binary)
• Close Frames: Records WebSocket connection close information
• Detail View: View in Forwarder detail panel's WebSocket tab

Protocol Support

Protocol	Status	Notes
HTTP/1.0	✅ Full Support
HTTP/1.1	✅ Full Support	Auto-pools connections beyond 256
HTTPS	✅ Full Support	Decrypted via MITM
WebSocket	✅ Full Support	Including WSS
HTTP/2	⚠️ Partial	Currently HTTP/1 path based

Traffic Handling

Body Decompression

The proxy automatically decompresses compressed request/response bodies:

• gzip decompression
• Brotli decompression
• deflate decompression

View the decoded content in the Forwarder detail panel.

Domain Filtering

Configure domain exclusion rules in the Forwarder filter bar:

• Exact exclusion: api.example.com
• Wildcard exclusion: *.static.cdn.com

Excluded domains won't appear in the traffic list, useful for filtering static resources or health check requests.

Related Features

The proxy engine is the foundation for:

• Forwarder: View and analyze captured traffic
• Interceptor: Intercept and modify in-flight requests
• Match-Replace: Auto-modify in-transit requests/responses
• Plugins: Security check on captured traffic

Troubleshooting

Proxy Won't Start

1. Port in use: Change listen port or close program using the port
2. Insufficient permissions: Ports below 1024 need root on Linux/macOS
3. Firewall blocking: Check firewall settings

HTTPS Decryption Fails

1. CA certificate not installed: Export and install CA certificate
2. Certificate pinning: Target app uses certificate pinning
3. Mutual TLS: Client certificate scenarios not supported

Performance Issues

1. Many connections: Adjust max connection configuration
2. Large files: Increase request body size limit
3. Memory usage: Regularly clean Flow data