Fix nil panic in UpdateCache when listapisresponse is empty (#211)

[rohanmishra29]

Fixes #211

Problem

When the CloudStack management server returns an empty listapisresponse (i.e., {"listapisresponse":{}}), the sync command panics with:
panic: interface conversion: interface {} is nil, not []interface {}
This happens in config/cache.go at the type assertion response["api"].([]interface{}) when response["api"] is nil.

Fix

Added a nil check for response["api"] before the type assertion. If the API list is empty, the function now returns nil with a clear error message instead of panicking.

Testing

Built successfully with go build ./.... The nil check prevents the panic when an empty listapisresponse is received.

[borisstoyanov]

@rohanmishra29 thanks for this fix, I'll include it in the milestone

[Copilot]

🟡 Changes recommended

The new early-return path can still produce confusing CLI output and may wipe existing in-memory caches before validation, so the error handling should be adjusted to be safe and consistent.

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Pull request overview

This PR addresses a crash in CloudMonkey’s API discovery/cache update path when the CloudStack listApis response contains an empty listapisresponse (missing the api field), by adding a guard before the []interface{} type assertion.

Changes:

• Add a nil check for response["api"] in Config.UpdateCache to prevent a panic on empty listapisresponse.
• Print an error message and return early when the API list is missing.

File summaries

File	Description
config/cache.go	Adds a guard in UpdateCache to avoid panicking when listApis returns an empty response payload.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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[borisstoyanov]

This nil check stops the original panic, but a few things are still off:

1. The error goes to stdout, not stderr.
2. The message hard-codes "sync", but UpdateCache is also called from LoadCache.
3. apiCache/apiVerbMap are already cleared before the early return, so a transient bad response wipes a cache that was previously fine.
4. If response["api"] is non-nil but not a []interface{}, the type assertion still panics.

A safe type assertion placed before the reset covers all four. Returning 0 instead of nil also keeps sync from printing Discovered APIs. Suggested top of the function (note the two reset lines move down):

func (c *Config) UpdateCache(response map[string]interface{}) interface{} {
	apiList, valid := response["api"].([]interface{})
	if !valid || len(apiList) == 0 {
		fmt.Fprintln(os.Stderr, "Error: no APIs found in the discovery response, keeping the existing API cache. Please run 'sync'.")
		return 0
	}

	apiCache = make(map[string]*API)
	apiVerbMap = nil

	count := response["count"]

	for _, node := range apiList {

os is already imported in this file, so no import change is needed.

Tested locally with a cache file of {"count":0}, {"count":1,"api":"boom"} and {"count":0,"api":[]} — all three print the error to stderr instead of panicking, and go vet ./config/ is clean.