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Creating a robust, zero-config SFTP testing environment on different platforms

Technical Summary

1. Project Objective

To build an automated testing suite for the sftpR package that functions seamlessly across three distinct environments without manual configuration or security interruptions.

2. The Core Challenges

A. SSH Security Handshakes (The “Interactive” Problem)

  • Host Key Fingerprints: Docker containers generate new SSH keys on every start. Standard clients detect this change and abort the connection to prevent “Man-in-the-Middle” attacks.
  • Prompt Hanging: In CI/CD (GitHub Actions/act), there is no terminal user to type “yes” to the “Trust this host?” prompt, causing tests to time out or crash.

B. Network Architecture Conflicts (The “Port” Problem)

  • Local/Cloud VM: The R process runs outside the Docker engine. It must use Port Mapping (127.0.0.1:2222 or 2223) to reach the container.
  • act (Local CI): The R process runs inside a container on the same Docker network. It sees the SFTP container as a “neighbor” and must use the Internal IP/Port (sftp:22).
  • Port Clashing: Using port 2222 for both local dev and CI tests causes failures if a local container is already active.

3. Implemented Solutions

Layer 1: R6 Class “Blindfold” (Security Bypass)

Modified the R handle initialization to bypass strict SSH checks. * ssh_knownhosts = NULL: Instructs libcurl to ignore the system known_hosts file. * ssl_verifyhost = 0: Prevents connection drops if the IP/Host doesn’t match the certificate/key exactly.

Layer 2: Environment-Aware Routing (helper-sftp.R)

Implemented a logic gate that detects the runner environment and selects the correct connection string: * act Logic: Connects to sftp on Port 22. * Cloud Logic: Connects to 127.0.0.1 on Port 2223. * Local Logic: Connects to 127.0.0.1 on Port 2222.

Layer 3: Dynamic Infrastructure (R-CMD-check.yaml)

  • Isolation: Shifted the CI port to 2223 to prevent interference with local dev.
  • DNS Injection: Used docker inspect to grab the internal IP and added it to /etc/hosts as sftp.
  • Network Discovery: Added logic to identify the specific Docker network name used by act to ensure containers can “see” each other.

4. Modified Files & Impact

File Change Impact
R/sftp_connection.R Added bypass options to curl handle. Eliminates “Host Key not OK” errors and interactive prompts.
tests/testthat/helper-sftp.R Created get_conn_info(). Switches between Internal (22) and External (2223) ports automatically.
.github/workflows/R-CMD-check.yaml Reordered steps and added network/IP exports. Ensures the SFTP server is ready and reachable before R tests begin.

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.
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