feat(protocol): job messages, protocol version and job model (#7)

internal/protocol/protocol.go

@@ -1,33 +1,66 @@
 // Package protocol defines the messages agents and the master exchange over
 // their WebSocket connection. Every message is an Envelope whose Payload is
 // one of the payload types below, selected by Type.
+//
+// Both sides close the connection on a message they cannot parse (bad JSON,
+// or a known Type whose payload does not decode). A message with an unknown
+// Type is logged and ignored, so a newer peer can add message types without
+// breaking an older one.
 package protocol
 
 import (
 	"encoding/json"
 	"fmt"
+	"time"
 )
 
+// Version is the protocol version this build speaks. Agents send it in
+// Hello. Phase-1 agents do not send the field, which reads as 0.
+const Version = 2
+
+// MinJobVersion is the lowest agent protocol version the master sends jobs to.
+const MinJobVersion = 2
+
+// MaxJobOutput caps the job output an agent keeps and the master stores, in
+// bytes. Only the tail is kept. With JSON escaping (worst case 6 bytes per
+// byte) a JobResult carrying this much output still fits the 1 MiB read limit.
+const MaxJobOutput = 128 << 10
+
 // Message types sent from agent to master.
 const (
-	TypeHello    = "hello"
-	TypeSnapshot = "snapshot"
-	TypeUpsert   = "upsert"
-	TypeRemove   = "remove"
+	TypeHello       = "hello"
+	TypeSnapshot    = "snapshot"
+	TypeUpsert      = "upsert"
+	TypeRemove      = "remove"
+	TypeJobProgress = "job.progress"
+	TypeJobResult   = "job.result"
 )
 
-// Envelope wraps every message on the wire.
+// Message types sent from master to agent.
+const (
+	TypeJobStart = "job.start"
+	TypeJobAck   = "job.ack"
+)
+
+// Envelope wraps every message on the wire. ID is the job ID (decimal) on
+// job.* messages and empty on inventory messages.
 type Envelope struct {
 	Type    string          `json:"type"`
+	ID      string          `json:"id,omitempty"`
 	Payload json.RawMessage `json:"payload,omitempty"`
 }
 
 // Hello is the first message an agent sends on every connection.
 type Hello struct {
-	AgentVersion   string `json:"agent_version"`
-	Hostname       string `json:"hostname"`
-	SwarmManager   bool   `json:"swarm_manager"`
-	SwarmClusterID string `json:"swarm_cluster_id,omitempty"`
+	AgentVersion    string `json:"agent_version"`
+	ProtocolVersion int    `json:"protocol_version,omitempty"`
+	Hostname        string `json:"hostname"`
+	SwarmManager    bool   `json:"swarm_manager"`
+	SwarmClusterID  string `json:"swarm_cluster_id,omitempty"`
+	// KnownJobs lists every job ID the agent holds: queued, running, or
+	// finished but not yet acknowledged. The master fails its queued and
+	// running jobs for this agent that are not listed ("lost").
+	KnownJobs []string `json:"known_jobs,omitempty"`
 }
 
 // Kind says how a service is deployed.
@@ -47,12 +80,16 @@ type Service struct {
 	ComposeProject string `json:"compose_project,omitempty"`
 	ComposeService string `json:"compose_service,omitempty"`
 	WorkingDir     string `json:"working_dir,omitempty"`
-	SwarmService   string `json:"swarm_service,omitempty"`
-	ContainerName  string `json:"container_name,omitempty"`
-	Image          string `json:"image"`
-	Digest         string `json:"digest,omitempty"`
-	Status         string `json:"status"`
-	Self           bool   `json:"self,omitempty"`
+	// ConfigFiles is the raw com.docker.compose.project.config_files label:
+	// absolute host paths joined by ",". Kept as a string so Service stays
+	// comparable with ==.
+	ConfigFiles   string `json:"config_files,omitempty"`
+	SwarmService  string `json:"swarm_service,omitempty"`
+	ContainerName string `json:"container_name,omitempty"`
+	Image         string `json:"image"`
+	Digest        string `json:"digest,omitempty"`
+	Status        string `json:"status"`
+	Self          bool   `json:"self,omitempty"`
 }
 
 // Key identifies the service within one agent's report. It is stable across
@@ -83,6 +120,50 @@ type Remove struct {
 	Key string `json:"key"`
 }
 
+// JobStart asks the agent to deploy Ref to one service. Ref is "repo:tag";
+// the agent resolves the tag's current digest and deploys "repo:tag@digest".
+// The agent reads the Compose working directory and config files from its
+// own Docker daemon, not from this message.
+type JobStart struct {
+	Kind           Kind   `json:"kind"`
+	ComposeProject string `json:"compose_project,omitempty"`
+	ComposeService string `json:"compose_service,omitempty"`
+	SwarmClusterID string `json:"swarm_cluster_id,omitempty"`
+	SwarmService   string `json:"swarm_service,omitempty"`
+	Ref            string `json:"ref"`
+}
+
+// JobProgress carries output produced since the previous JobProgress for the
+// same job. The first JobProgress of a job (Output may be empty) tells the
+// master the job is running.
+type JobProgress struct {
+	Output string `json:"output"`
+}
+
+// Job result statuses.
+const (
+	ResultSucceeded = "succeeded"
+	ResultFailed    = "failed"
+)
+
+// JobResult is a job's outcome. The agent keeps it until the master sends
+// JobAck for the same ID, and resends it after every reconnect until then.
+type JobResult struct {
+	Status string `json:"status"`        // ResultSucceeded or ResultFailed
+	Ref    string `json:"ref,omitempty"` // deployed "repo:tag@digest", set on success
+	Error  string `json:"error,omitempty"`
+	// Output is the job's complete output, tail-capped at MaxJobOutput. It
+	// replaces whatever the master assembled from JobProgress messages.
+	Output          string    `json:"output"`
+	OutputTruncated bool      `json:"output_truncated,omitempty"`
+	StartedAt       time.Time `json:"started_at"`
+	FinishedAt      time.Time `json:"finished_at"`
+}
+
+// JobAck tells the agent the master has stored the JobResult with the same
+// ID. It has no fields.
+type JobAck struct{}
+
 // Encode wraps payload in an Envelope of the given type.
 func Encode(typ string, payload any) (Envelope, error) {
 	raw, err := json.Marshal(payload)
@@ -92,6 +173,16 @@ func Encode(typ string, payload any) (Envelope, error) {
 	return Envelope{Type: typ, Payload: raw}, nil
 }
 
+// EncodeJob wraps a job message's payload in an Envelope carrying the job ID.
+func EncodeJob(typ, jobID string, payload any) (Envelope, error) {
+	env, err := Encode(typ, payload)
+	if err != nil {
+		return Envelope{}, err
+	}
+	env.ID = jobID
+	return env, nil
+}
+
 // Decode unpacks env's payload into T.
 func Decode[T any](env Envelope) (T, error) {
 	var v T