ucp

cmd/checkout/cart-client.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 	"time"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/cart"
@@ -14,12 +15,18 @@ import (
 type CartClient struct {
 	httpClient   *http.Client
 	baseUrl      string
+	agentProfile string // UCP-Agent profile URI
 }
 
 func NewCartClient(baseUrl string) *CartClient {
+	profile := os.Getenv("UCP_AGENT_PROFILE")
+	if profile == "" {
+		profile = "https://checkout.k6n.net/.well-known/ucp"
+	}
 	return &CartClient{
 		httpClient:   &http.Client{Timeout: 10 * time.Second},
 		baseUrl:      baseUrl,
+		agentProfile: profile,
 	}
 }
 
@@ -52,6 +59,7 @@ func (s *CartClient) getCartGrain(ctx context.Context, cartId cart.CartId) (*car
 	if err != nil {
 		return nil, err
 	}
+	req.Header.Set("UCP-Agent", `profile="`+s.agentProfile+`"`)
 	resp, err := s.httpClient.Do(req)
 	if err != nil {
 		return nil, err

cmd/checkout/order_client.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"os"
 	"time"
 )
 
@@ -18,13 +19,19 @@ import (
 type OrderClient struct {
 	httpClient   *http.Client
 	baseURL      string // e.g. "http://order-service:8092"
+	agentProfile string // UCP-Agent profile URI
 }
 
 // NewOrderClient returns a client that talks to the order service at baseURL.
 func NewOrderClient(baseURL string) *OrderClient {
+	profile := os.Getenv("UCP_AGENT_PROFILE")
+	if profile == "" {
+		profile = "https://cart.k6n.net/.well-known/ucp"
+	}
 	return &OrderClient{
 		httpClient:   &http.Client{Timeout: 30 * time.Second},
 		baseURL:      baseURL,
+		agentProfile: profile,
 	}
 }
 
@@ -91,6 +98,7 @@ func (c *OrderClient) CreateOrder(ctx context.Context, req CreateOrderReq, flowN
 		return nil, fmt.Errorf("order client: new request: %w", err)
 	}
 	httpReq.Header.Set("Content-Type", "application/json")
+	httpReq.Header.Set("UCP-Agent", `profile="`+c.agentProfile+`"`)
 
 	resp, err := c.httpClient.Do(httpReq)
 	if err != nil {

internal/ucp/agent.go

@@ -0,0 +1,151 @@
+package ucp
+
+import (
+	"context"
+	"net/http"
+	"strings"
+)
+
+// ---------------------------------------------------------------------------
+// UCP-Agent header parsing (RFC 8941 Dictionary Structured Field)
+// ---------------------------------------------------------------------------
+
+// ucpAgentProfileKey is the context key for the UCP-Agent profile URI.
+type ucpAgentProfileKey struct{}
+
+// UCPAgentProfileFromContext returns the UCP-Agent profile URI stored in the
+// request context, or empty string if none was advertised.
+func UCPAgentProfileFromContext(ctx context.Context) string {
+	v, _ := ctx.Value(ucpAgentProfileKey{}).(string)
+	return v
+}
+
+// parseUCPAgentProfile parses a single "profile" member value from an RFC 8941
+// Dictionary Structured Field header. It only handles the string-value form:
+//
+//	UCP-Agent: profile="https://agent.example/profiles/shopping-agent.json"
+//
+// Returns the profile URI (without surrounding quotes) or empty string.
+func parseUCPAgentProfile(header string) string {
+	if header == "" {
+		return ""
+	}
+
+	// Walk the dictionary entries looking for "profile".
+	// RFC 8941 §3.1.2: Dict = ((im-key | key) value) *(SP "," ((im-key | key) value))
+	i := 0
+	bs := []byte(header)
+	n := len(bs)
+
+	for i < n {
+		// Skip whitespace.
+		for i < n && (bs[i] == ' ' || bs[i] == '\t') {
+			i++
+		}
+		if i >= n {
+			break
+		}
+
+		// Read key (im-key or key). Lowercase letters, digits, "_", "-", "*".
+		start := i
+		for i < n && isKeyChar(bs[i]) {
+			i++
+		}
+		if i == start {
+			// No key found; skip to next comma or end.
+			for i < n && bs[i] != ',' {
+				i++
+			}
+			i++ // skip comma
+			continue
+		}
+		key := string(bs[start:i])
+
+		// Check for "=" separator. RFC 8941 allows bare names (boolean true)
+		// when "=? " follows — but we only care about key=value entries.
+		if i < n && bs[i] == '=' {
+			i++ // skip '='
+
+			// Read the value. For our case it's a string (starts with '"').
+			if i < n && bs[i] == '"' {
+				i++ // skip opening quote
+				valStart := i
+				for i < n && bs[i] != '"' {
+					if bs[i] == '\\' {
+						i++ // skip escape
+					}
+					i++
+				}
+				val := string(bs[valStart:i])
+				if i < n {
+					i++ // skip closing quote
+				}
+				if strings.EqualFold(key, "profile") {
+					return val
+				}
+			}
+		}
+
+		// Skip to next comma or end.
+		for i < n && bs[i] != ',' {
+			i++
+		}
+		i++ // skip comma
+	}
+
+	return ""
+}
+
+// isKeyChar reports whether b is valid in an RFC 8941 key (lc-ltr, DIGIT, "_", "-", "*").
+func isKeyChar(b byte) bool {
+	return (b >= 'a' && b <= 'z') || (b >= '0' && b <= '9') || b == '_' || b == '-' || b == '*'
+}
+
+// WithUCPAgent is HTTP middleware that reads the UCP-Agent header from incoming
+// requests, parses it per RFC 8941, and stores the profile URI in the request
+// context so downstream handlers can inspect the calling platform's identity.
+//
+// Usage:
+//
+//	mux.Handle("/ucp/v1/carts", ucp.WithUCPAgent(ucp.CartHandler(pool)))
+func WithUCPAgent(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if profile := parseUCPAgentProfile(r.Header.Get("UCP-Agent")); profile != "" {
+			ctx := context.WithValue(r.Context(), ucpAgentProfileKey{}, profile)
+			r = r.WithContext(ctx)
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+// DefaultUCPAgentProfile is the profile URI sent on outgoing requests from
+// this commerce platform. Override via SetDefaultUCPAgentProfile or the
+// UCP_AGENT_PROFILE environment variable at init time.
+var DefaultUCPAgentProfile = "https://cart.k6n.net/.well-known/ucp"
+
+// SetDefaultUCPAgentProfile overrides the default profile URI used for outgoing
+// UCP-Agent headers.
+func SetDefaultUCPAgentProfile(profile string) {
+	if profile != "" {
+		DefaultUCPAgentProfile = profile
+	}
+}
+
+// UCPAgentHeaderValue returns the RFC 8941 Dictionary value for the UCP-Agent
+// header, encoding the given profile URI.
+func UCPAgentHeaderValue(profile string) string {
+	if profile == "" {
+		profile = DefaultUCPAgentProfile
+	}
+	return `profile="` + profile + `"`
+}
+
+// WithUCPAgentOnRequest adds the UCP-Agent header to an outgoing HTTP request.
+// It sets the header to the default profile unless a custom profile is provided.
+func WithUCPAgentOnRequest(req *http.Request, profile ...string) {
+	p := DefaultUCPAgentProfile
+	if len(profile) > 0 && profile[0] != "" {
+		p = profile[0]
+	}
+	req.Header.Set("UCP-Agent", `profile="`+p+`"`)
+}

internal/ucp/checkout.go

@@ -5,7 +5,9 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
+	"os"
 	"time"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/checkout"
@@ -61,17 +63,52 @@ func (s *CheckoutServer) handleCreateCheckout(w http.ResponseWriter, r *http.Req
 		return
 	}
 
-	// Initialize checkout with cart reference.
+	// Fetch cart state from cart service
+	cartBaseURL := os.Getenv("CART_INTERNAL_URL")
+	if cartBaseURL == "" {
+		cartBaseURL = "http://cart:8080"
+	}
+	url := fmt.Sprintf("%s/cart/byid/%s", cartBaseURL, cartId.String())
+
+	client := &http.Client{Timeout: 10 * time.Second}
+	cartReq, err := http.NewRequestWithContext(r.Context(), "GET", url, nil)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to create cart request: "+err.Error())
+		return
+	}
+
+	profile := os.Getenv("UCP_AGENT_PROFILE")
+	if profile == "" {
+		profile = DefaultUCPAgentProfile
+	}
+	cartReq.Header.Set("UCP-Agent", `profile="`+profile+`"`)
+
+	cartResp, err := client.Do(cartReq)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to fetch cart: "+err.Error())
+		return
+	}
+	defer cartResp.Body.Close()
+
+	if cartResp.StatusCode != http.StatusOK {
+		writeError(w, http.StatusBadRequest, fmt.Sprintf("cart service returned status: %d", cartResp.StatusCode))
+		return
+	}
+
+	cartStateBytes, err := io.ReadAll(cartResp.Body)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to read cart state: "+err.Error())
+		return
+	}
+
+	// Initialize checkout with cart reference and state.
 	initMsg := &checkoutMessages.InitializeCheckout{
 		OrderId: "",
 		CartId:  uint64(cartId),
-	}
-	if req.Country != "" {
-		// Pass country through the cart state snapshot (minimal).
-		initMsg.CartState = &anypb.Any{
-			TypeUrl: "request/country",
-			Value:   []byte(req.Country),
-		}
+		CartState: &anypb.Any{
+			TypeUrl: "type.googleapis.com/cart.CartGrain",
+			Value:   cartStateBytes,
+		},
 	}
 
 	if _, err := s.applier.Apply(r.Context(), uint64(checkoutId), initMsg); err != nil {
@@ -290,14 +327,22 @@ func (s *CheckoutServer) handleCancelCheckout(w http.ResponseWriter, r *http.Req
 type OrderHTTPClient struct {
 	baseURL    string
 	httpClient *http.Client
+	agentProfile string // UCP-Agent profile URI
 }
 
 // NewOrderHTTPClient returns an order applier that creates orders by calling
-// the order service at baseURL (e.g. "http://order-service:8092").
+// the order service at baseURL (e.g. "http://order-service:8092"). It reads
+// the UCP_AGENT_PROFILE env var for the profile URI, falling back to
+// DefaultUCPAgentProfile from the ucp package.
 func NewOrderHTTPClient(baseURL string) *OrderHTTPClient {
+	profile := os.Getenv("UCP_AGENT_PROFILE")
+	if profile == "" {
+		profile = DefaultUCPAgentProfile
+	}
 	return &OrderHTTPClient{
 		baseURL:    baseURL,
 		httpClient: &http.Client{Timeout: 30 * time.Second},
+		agentProfile: profile,
 	}
 }
 
@@ -381,6 +426,8 @@ func (c *OrderHTTPClient) CreateOrder(ctx context.Context, checkoutID uint64, g
 		return "", fmt.Errorf("order: new request: %w", err)
 	}
 	httpReq.Header.Set("Content-Type", "application/json")
+	// Advertise this platform's UCP profile on all outgoing requests.
+	WithUCPAgentOnRequest(httpReq, c.agentProfile)
 
 	resp, err := c.httpClient.Do(httpReq)
 	if err != nil {

internal/ucp/handler.go

@@ -23,7 +23,7 @@ func OrderHandler(applier OrderReadApplier) http.Handler {
 	mux.HandleFunc("POST /{id}/fulfillments", s.handleCreateFulfillment)
 	mux.HandleFunc("POST /{id}/returns", s.handleRequestReturn)
 	mux.HandleFunc("POST /{id}/refunds", s.handleIssueRefund)
-	return mux
+	return withUCPAgent(withJSONContentType(mux))
 }
 
 // ---------------------------------------------------------------------------
@@ -46,7 +46,7 @@ func CartHandler(applier CartApplier) http.Handler {
 	mux.HandleFunc("GET /{id}", s.handleGetCart)
 	mux.HandleFunc("PUT /{id}", s.handleUpdateCart)
 	mux.HandleFunc("POST /{id}/cancel", s.handleCancelCart)
-	return mux
+	return withUCPAgent(withJSONContentType(mux))
 }
 
 // ---------------------------------------------------------------------------
@@ -70,7 +70,7 @@ func CheckoutHandler(applier CheckoutApplier, orderSvc ...OrderApplier) http.Han
 	mux.HandleFunc("PUT /{id}", s.handleUpdateCheckout)
 	mux.HandleFunc("POST /{id}/complete", s.handleCompleteCheckout)
 	mux.HandleFunc("POST /{id}/cancel", s.handleCancelCheckout)
-	return mux
+	return withUCPAgent(withJSONContentType(mux))
 }
 
 // ---------------------------------------------------------------------------
@@ -113,5 +113,18 @@ func Handler(cartApplier CartApplier, opts Options) http.Handler {
 		mux.HandleFunc("POST /checkout-sessions/{id}/cancel", checkoutSrv.handleCancelCheckout)
 	}
 
-	return mux
+	return withUCPAgent(withJSONContentType(mux))
+}
+
+// withUCPAgent wraps a handler with UCP-Agent header parsing middleware.
+func withUCPAgent(next http.Handler) http.Handler {
+	return WithUCPAgent(next)
+}
+
+// withJSONContentType is a middleware that ensures all responses have Content-Type: application/json.
+func withJSONContentType(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		next.ServeHTTP(w, r)
+	})
 }

pkg/cart/mcp/tools.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/cart"
 	messages "git.k6n.net/mats/go-cart-actor/proto/cart"
@@ -26,6 +27,12 @@ func (s *Server) callTool(req *rpcRequest) *rpcResponse {
 	if err := json.Unmarshal(req.Params, &p); err != nil {
 		return errorResponse(req.ID, codeInvalidParams, "invalid params")
 	}
+
+	// Extract UCP meta from arguments (UCP-Agent profile advertisement).
+	// Per the UCP spec, meta is a sibling key inside arguments:
+	//   "arguments": { "meta": { "ucp-agent": { "profile": "..." } }, ... }
+	args := extractUCPAgentMeta(&p.Arguments)
+
 	var t *tool
 	for i := range s.tools {
 		if s.tools[i].Name == p.Name {
@@ -36,13 +43,48 @@ func (s *Server) callTool(req *rpcRequest) *rpcResponse {
 	if t == nil {
 		return errorResponse(req.ID, codeInvalidParams, "unknown tool: "+p.Name)
 	}
-	out, err := t.invoke(p.Arguments)
+	out, err := t.invoke(args)
 	if err != nil {
 		return result(req.ID, toolError(err))
 	}
 	return result(req.ID, toolText(out))
 }
 
+// extractUCPAgentMeta checks if the JSON arguments contain a "meta" key with
+// a nested "ucp-agent.profile" field. If found, it logs the profile (for
+// observability) and strips the "meta" key before returning the cleaned
+// arguments to the tool handler, so the meta object does not leak into the
+// tool's argument namespace.
+func extractUCPAgentMeta(arguments *json.RawMessage) json.RawMessage {
+	if arguments == nil || len(*arguments) == 0 {
+		return *arguments
+	}
+	var obj map[string]json.RawMessage
+	if err := json.Unmarshal(*arguments, &obj); err != nil {
+		return *arguments
+	}
+	metaRaw, hasMeta := obj["meta"]
+	if !hasMeta {
+		return *arguments
+	}
+	// Try to extract the profile for observability.
+	var meta struct {
+		UCPAgent *struct {
+			Profile string `json:"profile"`
+		} `json:"ucp-agent"`
+	}
+	if err := json.Unmarshal(metaRaw, &meta); err == nil && meta.UCPAgent != nil && meta.UCPAgent.Profile != "" {
+		log.Printf("ucp-agent: profile=%s", meta.UCPAgent.Profile)
+	}
+	// Strip meta from arguments before passing to the tool handler.
+	delete(obj, "meta")
+	cleaned, err := json.Marshal(obj)
+	if err != nil {
+		return *arguments
+	}
+	return cleaned
+}
+
 func (s *Server) buildTools() []tool {
 	return []tool{
 		{

pkg/order/mcp/tools.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log"
 	"time"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/order"
@@ -27,6 +28,12 @@ func (s *Server) callTool(req *rpcRequest) *rpcResponse {
 	if err := json.Unmarshal(req.Params, &p); err != nil {
 		return errorResponse(req.ID, codeInvalidParams, "invalid params")
 	}
+
+	// Extract UCP meta from arguments (UCP-Agent profile advertisement).
+	// Per the UCP spec, meta is a sibling key inside arguments:
+	//   "arguments": { "meta": { "ucp-agent": { "profile": "..." } }, ... }
+	args := extractUCPAgentMeta(&p.Arguments)
+
 	var t *tool
 	for i := range s.tools {
 		if s.tools[i].Name == p.Name {
@@ -37,13 +44,48 @@ func (s *Server) callTool(req *rpcRequest) *rpcResponse {
 	if t == nil {
 		return errorResponse(req.ID, codeInvalidParams, "unknown tool: "+p.Name)
 	}
-	out, err := t.invoke(p.Arguments)
+	out, err := t.invoke(args)
 	if err != nil {
 		return result(req.ID, toolError(err))
 	}
 	return result(req.ID, toolText(out))
 }
 
+// extractUCPAgentMeta checks if the JSON arguments contain a "meta" key with
+// a nested "ucp-agent.profile" field. If found, it logs the profile (for
+// observability) and strips the "meta" key before returning the cleaned
+// arguments to the tool handler, so the meta object does not leak into the
+// tool's argument namespace.
+func extractUCPAgentMeta(arguments *json.RawMessage) json.RawMessage {
+	if arguments == nil || len(*arguments) == 0 {
+		return *arguments
+	}
+	var obj map[string]json.RawMessage
+	if err := json.Unmarshal(*arguments, &obj); err != nil {
+		return *arguments
+	}
+	metaRaw, hasMeta := obj["meta"]
+	if !hasMeta {
+		return *arguments
+	}
+	// Try to extract the profile for observability.
+	var meta struct {
+		UCPAgent *struct {
+			Profile string `json:"profile"`
+		} `json:"ucp-agent"`
+	}
+	if err := json.Unmarshal(metaRaw, &meta); err == nil && meta.UCPAgent != nil && meta.UCPAgent.Profile != "" {
+		log.Printf("ucp-agent: profile=%s", meta.UCPAgent.Profile)
+	}
+	// Strip meta from arguments before passing to the tool handler.
+	delete(obj, "meta")
+	cleaned, err := json.Marshal(obj)
+	if err != nil {
+		return *arguments
+	}
+	return cleaned
+}
+
 func (s *Server) buildTools() []tool {
 	return []tool{
 		{