Use RPC for friendbot when available

[leighmcculloch]

What

Use the RPC backend support of friendbot instead of Horizon. Update startup script to wait for either RPC or Horizon based on configuration. Remove hardcoded horizon_url from config and dynamically inject the appropriate backend URL. Allow friendbot to start when only RPC is enabled without requiring Horizon.

Why

Friendbot previously required Horizon to fund accounts. With RPC support, friendbot can operate in RPC-only deployments without needing Horizon running. RPC is the preferred integration point, because in the future Friendbot will support funding contracts, and so even if both RPC and Horizon are available it will default to RPC to be able to support contract functionality.

Merging

Dependent on:

• Add interface between app logic and horizon client for port to rpc friendbot#17
• Add RPC integration friendbot#20

Cannot be merged until all images are updated to use a version of friendbot that contains the two dependent changes above.

Testing

This change includes a new image, friendbot-with-rpc, temporarily just while in pull request that can be used for testing the dependent changes above.

Close stellar/friendbot#5
Close #791

[Copilot]

Pull request overview

This pull request enables friendbot to use RPC as its backend instead of requiring Horizon, supporting RPC-only deployments. The changes allow friendbot to dynamically configure either RPC or Horizon backends, with RPC being the preferred option when both are available to support future contract funding functionality.

• Removed hardcoded horizon_url from friendbot config and made backend URL injection dynamic based on which service is enabled
• Updated startup scripts to conditionally wait for either RPC or Horizon based on friendbot's configuration
• Removed the forced enabling of Horizon when RPC is enabled for local networks

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
start	Removed forced ENABLE_HORIZON when ENABLE_RPC is true; added dynamic backend URL injection in init_friendbot(); updated upgrade_local() to start friendbot when either RPC or Horizon is enabled
common/friendbot/etc/friendbot.cfg	Removed hardcoded horizon_url to allow dynamic backend configuration
common/friendbot/bin/start	Added conditional waiting logic for RPC and Horizon backends based on configuration file contents
images.json	Added temporary "friendbot-with-rpc" image for testing the dependent friendbot changes with specific commit reference

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[Copilot]

The init_friendbot() function should validate that at least one of ENABLE_RPC or ENABLE_HORIZON is true before proceeding. Without this check, friendbot could be initialized with no backend configured, which would cause it to fail when started. Consider adding a validation:

function init_friendbot() {
  if [ "$ENABLE_RPC" != "true" ] && [ "$ENABLE_HORIZON" != "true" ]; then
    echo "Warning: Friendbot requires either RPC or Horizon to be enabled"
    return 0
  fi

  pushd $FBHOME
  # ... rest of function

[Copilot]

Inconsistent indentation: this line uses 6 spaces while the codebase consistently uses 4 spaces for content inside if blocks (see lines 690-691, 695-696, 700, 704). Please adjust to 4 spaces:

if [ "$ENABLE_HORIZON" == "true" ] || [ "$ENABLE_RPC" == "true" ]; then
    supervisorctl start friendbot
fi

Suggested change

	supervisorctl start friendbot
	supervisorctl start friendbot