mongoproxy

mongoproxy is a lightweight, programmable TCP proxy for MongoDB. It sits between your client and a real MongoDB server and allows you to simulate broken or delayed network behavior — useful for testing retry logic, timeouts, and error handling in database drivers or applications.

• Inject millisecond-level delays into server responses
• Send only part of a reply (sendBytes)
• Flush the rest after a delay (sendAll)
• Simulate mid-stream disconnects
• Easily trigger timeouts, EOFs, or corrupted reads

📦 Installation

To install the latest version:

go install github.com/prestonvasquez/mongoproxy/cmd/mongoproxy@latest

Or build it locally in bin/mongoproxy:

bash build.sh

Running tests requires Docker:

go test ./...

🔧 Usage

To simulate network-level faults during testing, you can include a special proxyTest field in your command document. This field should contain an actions array to instruct the proxy how to manipulate the server’s reply.

Action	Parameter	Description
delayMs	number	Pause forwarding for the specified milliseconds.
sendBytes	number	Forward exactly that many bytes from the response.
sendAll	boolean	Forward all remaining bytes in the response.

Example:

{
  "ping": 1,
  "proxyTest": {
    "actions": [
      { "sendBytes": 1 },    // send only the first byte of the server response
      { "delay": 200 },      // wait 200 milliseconds
      { "sendAll": true }    // then send the remainder of the message
    ]
  }
}

This simulates a partial response followed by a delay, then a full flush — useful for testing client behavior during slow or fragmented network reads.

⚠️ These fields are intercepted by mongoproxy and do not reach the MongoDB server. They are intended for use in integration tests, not production.