felhom-agent/internal/localapi/escrow_recover.go

package localapi

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"net/http"
	"strings"
	"time"

	"gitea.dooplex.hu/admin/felhom-agent/internal/escrow"
)

// R-199 (agent v0.125.0) — the in-guest controller asks the agent to recover the offsite repository
// password from the hub's sealed bundle, using the customer's recovery code R.
//
// WHY THE AGENT AND NOT THE CONTROLLER. Three reasons, all structural: the unsealing binary (`age`)
// is an agent runtime dependency and is deliberately absent from the controller image; the sealed
// blob is a HOST-scoped object whose only writer is this agent under the per-host key, so the read is
// that write's mirror; and the controller is a trust tier down — it should receive one field, not a
// bundle it has no use for.
//
// R'S HANDLING, WHICH IS THE TIGHTEST RULE IN THIS FLOW. R is the one secret in the system that
// cannot be rotated, re-issued or recovered — it exists only in the customer's hands. Here it:
//   - arrives in the request body over the already-pinned local-API channel (the operator accepted
//     that crossing on 2026-08-04; the acceptance covers the CHANNEL, not carelessness at either end);
//   - is held in memory for the duration of one call and cleared on BOTH paths;
//   - is never written to disk, never an argument in a process list, and never logged at any level,
//     including inside an error;
//   - is never echoed: no response this endpoint can emit contains it.
//
// The request-level DEBUG middleware logs method/path/status/duration and never bodies — see
// `logRequests`. Do not add a body dump.
//
// THE RESPONSE CARRIES THE PASSWORD AND ITS HASH. The hash is what this session's proof compares
// (compare by hash, never by value). The password itself is present because the next link — placing a
// recovered password so the existing repository opens — needs it, and building a hash-only seam now
// would have to be torn out to add it. The controller's diagnostic reads only the hash.

type recoverOffsitePasswordRequest struct {
	VMID int `json:"vmid"`
	// RecoveryCode is the customer's R. NEVER logged, never persisted, never echoed.
	RecoveryCode string `json:"recovery_code"`
}

// handleRecoverOffsitePassword fetches this host's sealed bundle, unseals it with R and returns only
// the offsite repository password (plus its sha256, for hash-only comparison by the caller).
func (s *Server) handleRecoverOffsitePassword(w http.ResponseWriter, r *http.Request, vmid int) {
	var req recoverOffsitePasswordRequest
	if !decodeBody(w, r, &req) {
		return
	}
	if !s.scopedFromBody(w, req.VMID, vmid, r.URL.Path) {
		return
	}
	R := strings.TrimSpace(req.RecoveryCode)
	req.RecoveryCode = "" // drop the decoded copy immediately
	if R == "" {
		writeErr(w, http.StatusBadRequest, "recovery_code is required")
		return
	}
	if s.escrowRecovery == nil {
		R = ""
		writeErr(w, http.StatusServiceUnavailable, "offsite key recovery is not configured on this agent (no hub client)")
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 60*time.Second)
	defer cancel()
	s.logger.Info("local-api: recovering the offsite repository password from the sealed escrow (R via body, never logged/persisted)", "vmid", vmid)

	pw, err := s.escrowRecovery.RecoverOffsiteRepoPassword(ctx, R)
	R = "" // cleared on BOTH paths, before anything else can happen
	if err != nil {
		// Each situation gets its own status and its own words. None of them names a secret.
		switch {
		// ── R-224 (2026-08-06) — THE FETCH FAILURE IS NOT A WRONG CODE. ────────────────────────
		//
		// This case did not exist, and its absence is the defect. A failed fetch fell through to the
		// `default` below and was answered with "the recovery code did not open the sealed bundle" —
		// so a hub that could not be reached was reported to the customer as a bad recovery code, on
		// the one screen whose whole purpose is to be believed about their backups.
		//
		// Measured live 2026-08-05 (CAMPAIGN-11 F3 and F4): a CORRECT current code returned that
		// message in 0.0556 s with the hub firewalled off, and in 0.0299 s with this agent stopped —
		// against ~1.0 s for a genuine unseal. No unseal was attempted in either case.
		//
		// 502 rather than 400: 4xx says "your request was bad", and the request was not bad — an
		// upstream dependency failed. The status is the machine-readable half; the controller
		// classifies on it and must never parse this sentence.
		//
		// ⚠ THE CODE WAS NOT USED. Nothing may be said about it — not that it was wrong, and not
		// that it was right.
		case errors.Is(err, escrow.ErrBundleFetch):
			s.logger.Warn("local-api: offsite key recovery: the sealed bundle could not be FETCHED — the recovery code was never used", "vmid", vmid, "err", err)
			writeErr(w, http.StatusBadGateway, "the sealed recovery bundle could not be fetched from the hub — the recovery code was NOT used and nothing was written")
		case errors.Is(err, escrow.ErrNoEscrowBlob):
			s.logger.Warn("local-api: offsite key recovery: the hub holds no sealed bundle for this host", "vmid", vmid)
			writeErr(w, http.StatusNotFound, "the hub holds no sealed recovery bundle for this host — no escrow ceremony has run")
		case errors.Is(err, escrow.ErrNoResticPassword):
			s.logger.Warn("local-api: offsite key recovery: the bundle opened but predates the repository-password field", "vmid", vmid)
			writeErr(w, http.StatusConflict, "the recovery code opened the bundle, but it carries NO offsite repository password (sealed before that field existed; it cannot be retro-fitted)")
		default:
			// The fail-closed WRONG-CODE case, and only it: the bundle was fetched and `age -d`
			// refused it. Every other situation above has its own status. The agent log records the
			// STEP, never the code.
			s.logger.Warn("local-api: offsite key recovery: the fetched bundle did not open with the supplied recovery code", "vmid", vmid, "err", err)
			writeErr(w, http.StatusBadRequest, "the recovery code did not open the sealed bundle — nothing was written")
		}
		return
	}

	sum := sha256.Sum256([]byte(strings.TrimSpace(pw)))
	// §8.6's lesson, applied: say exactly WHAT was recovered and what was NOT, so nobody reading this
	// concludes the wrong thing about the bundle's contents (which is how link 8 came to be missing).
	s.logger.Info("local-api: offsite repository password RECOVERED from the sealed escrow — returning that field ONLY "+
		"(the tunnel token, the PBS token and the WG key stay inside the agent and are not returned)",
		"vmid", vmid, "restic_pw_sha256", hex.EncodeToString(sum[:]))
	writeOK(w, map[string]any{
		"restic_repo_password": pw,
		"restic_pw_sha256":     hex.EncodeToString(sum[:]),
	})
}