agent+server: apply host bandwidth caps to restic invocations

P2R-13a. restic.Env gains LimitUploadKBps/LimitDownloadKBps which are
emitted as global --limit-upload/--limit-download flags before the
subcommand on every invocation. Agent dispatcher tracks host-wide
caps received via config.update; server pushes them on hello and
after PUT /api/hosts/{id}/bandwidth.

Also extends api.CommandRunPayload with optional per-job overrides
(BandwidthUpKBps/Down + PreHook/PostHook); the override consumers
land in T2/T6.

internal/agent/runner/runner.go

@@ -30,6 +30,12 @@ type Config struct {
 	RepoURL      string
 	RepoUsername string
 	RepoPassword string
+
+	// Bandwidth caps in KB/s applied to every restic invocation.
+	// <=0 means "no cap". Per-job override: callers that build a
+	// runner per-dispatch can pass the override value here directly.
+	LimitUploadKBps   int
+	LimitDownloadKBps int
 }
 
 // Runner owns the restic invocations.
@@ -54,10 +60,12 @@ func New(cfg Config, tx Sender, progressMinPeriod time.Duration) *Runner {
 // resticEnv builds the shared restic.Env from r.cfg.
 func (r *Runner) resticEnv() restic.Env {
 	return restic.Env{
-		Bin:          r.cfg.ResticBin,
-		RepoURL:      r.cfg.RepoURL,
-		RepoUsername: r.cfg.RepoUsername,
-		RepoPassword: r.cfg.RepoPassword,
+		Bin:               r.cfg.ResticBin,
+		RepoURL:           r.cfg.RepoURL,
+		RepoUsername:      r.cfg.RepoUsername,
+		RepoPassword:      r.cfg.RepoPassword,
+		LimitUploadKBps:   r.cfg.LimitUploadKBps,
+		LimitDownloadKBps: r.cfg.LimitDownloadKBps,
 	}
 }
 

internal/api/messages.go

@@ -130,6 +130,19 @@ type CommandRunPayload struct {
 	Tag                string        `json:"tag,omitempty"`
 	ForgetGroups       []ForgetGroup `json:"forget_groups,omitempty"`
 	RequiresAdminCreds bool          `json:"requires_admin_creds,omitempty"`
+
+	// Per-job bandwidth caps in KB/s. When nil, the agent uses the
+	// host-wide caps it received via config.update. When non-nil,
+	// the override wins for this job only — even a non-nil zero
+	// pointer means "no cap for this job" (caller's explicit choice).
+	BandwidthUpKBps   *int `json:"bandwidth_up_kbps,omitempty"`
+	BandwidthDownKBps *int `json:"bandwidth_down_kbps,omitempty"`
+
+	// Hooks run only for kind=backup. Server resolves source-group
+	// hook → host default → empty before dispatching, so the agent
+	// just executes whatever is here.
+	PreHook  string `json:"pre_hook,omitempty"`
+	PostHook string `json:"post_hook,omitempty"`
 }
 
 // CommandCancelPayload is the server → agent cancel signal.
@@ -306,6 +319,14 @@ type ConfigUpdatePayload struct {
 	RepoCredential string `json:"repo_credential,omitempty"` // sensitive (for rest server basic auth)
 	HookShell      string `json:"hook_shell,omitempty"`
 	Slot           string `json:"slot,omitempty"`
+
+	// Bandwidth caps in KB/s. Pointer semantics so the server can
+	// disambiguate "no change in this push" (nil → omitted on the
+	// wire) from "explicitly clear the cap" (zero or negative value).
+	// Applied to every restic invocation as --limit-upload /
+	// --limit-download. Per-job overrides ride on CommandRunPayload.
+	BandwidthUpKBps   *int `json:"bandwidth_up_kbps,omitempty"`
+	BandwidthDownKBps *int `json:"bandwidth_down_kbps,omitempty"`
 }
 
 // AgentUpdateAvailablePayload — informational only; the agent does

internal/restic/runner.go

@@ -47,6 +47,37 @@ type Env struct {
 	RepoPassword string            // doubles as RESTIC_PASSWORD and (for rest:) HTTP basic-auth password
 	ExtraEnv     map[string]string // any other RESTIC_* / passthrough
 	WorkDir      string            // CWD; default = current
+
+	// Bandwidth caps in KB/s. <=0 means "no cap" (omit the flag).
+	// Emitted as restic global flags --limit-upload / --limit-download
+	// before the subcommand on every invocation.
+	LimitUploadKBps   int
+	LimitDownloadKBps int
+}
+
+// globalArgs returns restic's pre-subcommand global flags derived
+// from the Env. Currently just bandwidth caps.
+func (e Env) globalArgs() []string {
+	var out []string
+	if e.LimitUploadKBps > 0 {
+		out = append(out, "--limit-upload", fmt.Sprintf("%d", e.LimitUploadKBps))
+	}
+	if e.LimitDownloadKBps > 0 {
+		out = append(out, "--limit-download", fmt.Sprintf("%d", e.LimitDownloadKBps))
+	}
+	return out
+}
+
+// resticCmd builds an exec.Cmd with bandwidth-limit globals prefixed
+// before the supplied subcommand args. Centralizing this so every
+// command (backup/forget/prune/check/unlock/init/stats) honors
+// the caps without each call site having to remember.
+func (e Env) resticCmd(ctx context.Context, sub ...string) *exec.Cmd {
+	args := append(e.globalArgs(), sub...)
+	cmd := exec.CommandContext(ctx, e.Bin, args...)
+	cmd.Env = e.envSlice()
+	cmd.Dir = e.WorkDir
+	return cmd
 }
 
 // EventKind enumerates what we care about in restic's --json output
@@ -110,9 +141,7 @@ func (e Env) RunBackup(ctx context.Context, paths, excludes, tags []string, hand
 	}
 	args = append(args, paths...)
 
-	cmd := exec.CommandContext(ctx, e.Bin, args...)
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
+	cmd := e.resticCmd(ctx, args...)
 
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {
@@ -215,9 +244,7 @@ func (e Env) RunForget(ctx context.Context, groups []ForgetGroup, handle LineHan
 		}
 		args := []string{"forget", "--json", "--tag", g.Tag}
 		args = append(args, g.Policy.args()...)
-		cmd := exec.CommandContext(ctx, e.Bin, args...)
-		cmd.Env = e.envSlice()
-		cmd.Dir = e.WorkDir
+		cmd := e.resticCmd(ctx, args...)
 		if err := runWithPump(cmd, handle); err != nil {
 			return err
 		}
@@ -232,9 +259,7 @@ func (e Env) RunForget(ctx context.Context, groups []ForgetGroup, handle LineHan
 // <id> at <url>" on success, "config file already exists" on a
 // re-init attempt, etc.).
 func (e Env) RunInit(ctx context.Context, handle LineHandler) error {
-	cmd := exec.CommandContext(ctx, e.Bin, "init")
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
+	cmd := e.resticCmd(ctx, "init")
 
 	// Sniff for "config file already exists" on stderr; if we see it
 	// we'll treat the non-zero exit as a soft success — running init
@@ -272,10 +297,7 @@ func (e Env) RunInit(ctx context.Context, handle LineHandler) error {
 // support that's useful for our purposes). We tee everything to the
 // handler so the live log is the operator's progress bar.
 func (e Env) RunPrune(ctx context.Context, handle LineHandler) error {
-	cmd := exec.CommandContext(ctx, e.Bin, "prune")
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
-	return runWithPump(cmd, handle)
+	return runWithPump(e.resticCmd(ctx, "prune"), handle)
 }
 
 // runWithPump starts the configured cmd, fans stdout+stderr into
@@ -313,10 +335,7 @@ func runWithPump(cmd *exec.Cmd, handle LineHandler) error {
 
 // RunUnlock executes `restic unlock`. Returns nil on a clean exit.
 func (e Env) RunUnlock(ctx context.Context, handle LineHandler) error {
-	cmd := exec.CommandContext(ctx, e.Bin, "unlock")
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
-	return runWithPump(cmd, handle)
+	return runWithPump(e.resticCmd(ctx, "unlock"), handle)
 }
 
 // RepoStats mirrors `restic stats --json --mode raw-data` output.
@@ -333,9 +352,7 @@ type RepoStats struct {
 // caller can still log it. Returns an error if no JSON-shaped line
 // arrived on stdout.
 func (e Env) RunStats(ctx context.Context, handle LineHandler) (*RepoStats, error) {
-	cmd := exec.CommandContext(ctx, e.Bin, "stats", "--json", "--mode", "raw-data")
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
+	cmd := e.resticCmd(ctx, "stats", "--json", "--mode", "raw-data")
 	var out *RepoStats
 	capture := func(stream, line string, ev any) {
 		if stream == "stdout" && strings.HasPrefix(line, "{") {
@@ -378,9 +395,7 @@ func (e Env) RunCheck(ctx context.Context, subsetPct int, handle LineHandler) (C
 	if subsetPct > 0 {
 		args = append(args, "--read-data-subset", fmt.Sprintf("%d%%", subsetPct))
 	}
-	cmd := exec.CommandContext(ctx, e.Bin, args...)
-	cmd.Env = e.envSlice()
-	cmd.Dir = e.WorkDir
+	cmd := e.resticCmd(ctx, args...)
 
 	var res CheckResult
 	sniff := func(stream, line string, ev any) {

internal/restic/runner_test.go

@@ -174,6 +174,43 @@ func TestRunStatsErrorsWithoutJSON(t *testing.T) {
 	}
 }
 
+func TestBandwidthLimitFlagsInjected(t *testing.T) {
+	// Script echoes its argv to stdout. Each variant should produce
+	// the right --limit-* flags before the subcommand.
+	cases := []struct {
+		name string
+		env  Env
+		want []string
+	}{
+		{"both caps", Env{LimitUploadKBps: 1024, LimitDownloadKBps: 512}, []string{"--limit-upload 1024", "--limit-download 512"}},
+		{"only upload", Env{LimitUploadKBps: 256}, []string{"--limit-upload 256"}},
+		{"zero means omit", Env{LimitUploadKBps: 0, LimitDownloadKBps: 0}, nil},
+		{"negative means omit", Env{LimitUploadKBps: -1}, nil},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			bin := setupScriptBin(t, `echo "$@"`)
+			env := c.env
+			env.Bin = bin
+			lines, h := captureLines()
+			if err := env.RunUnlock(context.Background(), h); err != nil {
+				t.Fatalf("RunUnlock: %v", err)
+			}
+			joined := strings.Join(*lines, "\n")
+			for _, want := range c.want {
+				if !strings.Contains(joined, want) {
+					t.Fatalf("want %q in argv; got: %s", want, joined)
+				}
+			}
+			if len(c.want) == 0 {
+				if strings.Contains(joined, "--limit-upload") || strings.Contains(joined, "--limit-download") {
+					t.Fatalf("expected no limit flags; got: %s", joined)
+				}
+			}
+		})
+	}
+}
+
 func TestRunStatsZeroSnapshots(t *testing.T) {
 	// Confirms RunStats succeeds and returns a valid *RepoStats when the
 	// repo has no snapshots (snapshots_count=0). A regression that

internal/server/http/host_bandwidth.go

@@ -58,5 +58,10 @@ func (s *Server) handleUpdateHostBandwidth(w stdhttp.ResponseWriter, r *stdhttp.
 		writeJSONError(w, stdhttp.StatusInternalServerError, "internal", err.Error())
 		return
 	}
+	// Fan out to the agent if connected. Errors are non-fatal — the
+	// next reconnect's onAgentHello will resync.
+	if s.deps.Hub != nil && s.deps.Hub.Connected(hostID) {
+		_ = s.pushBandwidthToAgent(r.Context(), hostID, req.BandwidthUpKBps, req.BandwidthDownKBps)
+	}
 	writeJSON(w, stdhttp.StatusOK, hostBandwidthView(req))
 }

internal/server/http/host_bandwidth_push.go

@@ -0,0 +1,78 @@
+// host_bandwidth_push.go — server → agent fan-out of host-wide
+// bandwidth caps via config.update.
+//
+// Two entry points: pushBandwidthOnHello (called from onAgentHello,
+// always pushes the current state so the agent picks up edits made
+// while it was offline) and pushBandwidthToAgent (called after the
+// PUT bandwidth handler succeeds, so an online agent re-arms within
+// seconds).
+//
+// We always send pointer fields (zero-valued when uncapped) so the
+// agent can distinguish "no change" (nil → field absent on the wire)
+// from "explicitly cleared" (non-nil zero pointer). See
+// api.ConfigUpdatePayload doc for the wire semantics.
+package http
+
+import (
+	"context"
+	"log/slog"
+	"time"
+
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/api"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/server/ws"
+)
+
+// pushBandwidthOnHello ships the host's current bandwidth caps as a
+// config.update on the supplied conn. Silent no-op on lookup error.
+func (s *Server) pushBandwidthOnHello(ctx context.Context, hostID string, conn *ws.Conn) {
+	host, err := s.deps.Store.GetHost(ctx, hostID)
+	if err != nil {
+		slog.Warn("on-hello: load host for bandwidth", "host_id", hostID, "err", err)
+		return
+	}
+	payload := bandwidthPayload(host.BandwidthUpKBps, host.BandwidthDownKBps)
+	env, err := api.Marshal(api.MsgConfigUpdate, "", payload)
+	if err != nil {
+		slog.Error("on-hello: marshal bandwidth config.update", "host_id", hostID, "err", err)
+		return
+	}
+	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	if err := conn.Send(sendCtx, env); err != nil {
+		slog.Warn("on-hello: send bandwidth config.update", "host_id", hostID, "err", err)
+	}
+}
+
+// pushBandwidthToAgent ships the supplied caps via the hub. Caller is
+// expected to check Hub.Connected first when it matters.
+func (s *Server) pushBandwidthToAgent(ctx context.Context, hostID string, up, down *int) error {
+	env, err := api.Marshal(api.MsgConfigUpdate, "", bandwidthPayload(up, down))
+	if err != nil {
+		return err
+	}
+	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	return s.deps.Hub.Send(sendCtx, hostID, env)
+}
+
+// bandwidthPayload builds a ConfigUpdatePayload with only the
+// bandwidth fields populated. Pointers are passed through verbatim;
+// callers wanting to clear a cap should pass a non-nil pointer to 0.
+// On the on-hello path we materialize zero-valued pointers when the
+// host record has no cap set, so the agent's stored state is always
+// in sync (rather than retaining whatever value it last received).
+func bandwidthPayload(up, down *int) api.ConfigUpdatePayload {
+	zero := 0
+	upPtr := up
+	if upPtr == nil {
+		upPtr = &zero
+	}
+	downPtr := down
+	if downPtr == nil {
+		downPtr = &zero
+	}
+	return api.ConfigUpdatePayload{
+		BandwidthUpKBps:   upPtr,
+		BandwidthDownKBps: downPtr,
+	}
+}

internal/server/http/host_credentials.go

@@ -399,6 +399,10 @@ func (s *Server) pushAdminCredsToAgent(ctx context.Context, hostID string) error
 // don't race a brand-new register against an old still-closing conn.
 func (s *Server) onAgentHello(ctx context.Context, hostID string, conn *ws.Conn) {
 	s.pushRepoCredsOnHello(ctx, hostID, conn)
+	// Bandwidth caps are sent unconditionally so an agent that
+	// reconnects after a cap edit picks up the new state without
+	// waiting for the next bandwidth PUT.
+	s.pushBandwidthOnHello(ctx, hostID, conn)
 	// Push the current schedule set in the same on-hello window so
 	// the agent's local cron is in sync before any command.run lands.
 	// An empty schedule list is a valid push: it tells the agent to