feat(admin): add atomic task claim leases

admin/internal/server/task_claims.go

@@ -0,0 +1,164 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"unicode/utf8"
+
+	"cmbuyer/admin/internal/deviceauth"
+	"cmbuyer/admin/internal/taskclaim"
+
+	"github.com/gin-gonic/gin"
+)
+
+const maxClaimJSONBytes = 4096
+
+func claimNext(options Options) gin.HandlerFunc {
+	return func(context *gin.Context) {
+		principal, ok := authenticateDevice(context, options)
+		if !ok {
+			return
+		}
+		var command taskclaim.ClaimCommand
+		if !decodeClaimJSON(context, &command) {
+			return
+		}
+		response, found, err := options.TaskClaims.ClaimNext(context.Request.Context(), principal.ID, command)
+		if err != nil {
+			writeTaskClaimError(context, err)
+			return
+		}
+		if !found {
+			context.Status(http.StatusNoContent)
+			return
+		}
+		context.JSON(http.StatusOK, response)
+	}
+}
+
+func renewLease(options Options) gin.HandlerFunc {
+	return func(context *gin.Context) {
+		principal, ok := authenticateDevice(context, options)
+		if !ok {
+			return
+		}
+		var command taskclaim.RenewCommand
+		if !decodeClaimJSON(context, &command) {
+			return
+		}
+		command.TaskID = context.Param("id")
+		response, err := options.TaskClaims.Renew(context.Request.Context(), principal.ID, command)
+		if err != nil {
+			writeTaskClaimError(context, err)
+			return
+		}
+		context.JSON(http.StatusOK, response)
+	}
+}
+
+// Authentication precedes path interpretation, Content-Type parsing and every body read. This
+// keeps rejected devices from using parsing differences as an oracle or making the server buffer data.
+func authenticateDevice(context *gin.Context, options Options) (deviceauth.Principal, bool) {
+	principal, err := options.DeviceAuthenticator.Authenticate(context.Request)
+	if errors.Is(err, deviceauth.ErrUnauthenticated) {
+		context.Header("WWW-Authenticate", "Bearer")
+		context.Status(http.StatusUnauthorized)
+		return deviceauth.Principal{}, false
+	}
+	if err != nil || !deviceauth.ValidDeviceID(principal.ID) {
+		context.Status(http.StatusServiceUnavailable)
+		return deviceauth.Principal{}, false
+	}
+	return principal, true
+}
+
+func decodeClaimJSON(context *gin.Context, target any) bool {
+	if !isJSONContentType(context.GetHeader("Content-Type")) {
+		writeFixedError(context, http.StatusUnsupportedMediaType, "unsupported_media_type")
+		return false
+	}
+	context.Request.Body = http.MaxBytesReader(context.Writer, context.Request.Body, maxClaimJSONBytes)
+	raw, err := io.ReadAll(context.Request.Body)
+	if err != nil {
+		var tooLarge *http.MaxBytesError
+		if errors.As(err, &tooLarge) {
+			writeFixedError(context, http.StatusRequestEntityTooLarge, "request_too_large")
+		} else {
+			writeFixedError(context, http.StatusBadRequest, "invalid_request")
+		}
+		return false
+	}
+	if len(raw) == 0 || !utf8.Valid(raw) {
+		writeFixedError(context, http.StatusBadRequest, "invalid_request")
+		return false
+	}
+	if !hasUniqueTopLevelJSONFields(raw) {
+		writeFixedError(context, http.StatusBadRequest, "invalid_request")
+		return false
+	}
+	decoder := json.NewDecoder(bytes.NewReader(raw))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(target); err != nil {
+		writeFixedError(context, http.StatusBadRequest, "invalid_request")
+		return false
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		writeFixedError(context, http.StatusBadRequest, "invalid_request")
+		return false
+	}
+	return true
+}
+
+func hasUniqueTopLevelJSONFields(raw []byte) bool {
+	decoder := json.NewDecoder(bytes.NewReader(raw))
+	first, err := decoder.Token()
+	if err != nil || first != json.Delim('{') {
+		return false
+	}
+	seen := make(map[string]struct{})
+	for decoder.More() {
+		key, err := decoder.Token()
+		name, ok := key.(string)
+		if err != nil || !ok {
+			return false
+		}
+		if _, duplicate := seen[name]; duplicate {
+			return false
+		}
+		seen[name] = struct{}{}
+		var value json.RawMessage
+		if err := decoder.Decode(&value); err != nil {
+			return false
+		}
+	}
+	last, err := decoder.Token()
+	return err == nil && last == json.Delim('}')
+}
+
+func writeTaskClaimError(context *gin.Context, err error) {
+	switch {
+	case errors.Is(err, taskclaim.ErrInvalid):
+		writeFixedError(context, http.StatusBadRequest, "invalid_request")
+	case errors.Is(err, taskclaim.ErrIdempotencyConflict):
+		writeFixedError(context, http.StatusConflict, "idempotency_conflict")
+	case errors.Is(err, taskclaim.ErrRequiresManual):
+		writeFixedError(context, http.StatusConflict, "claim_requires_manual")
+	case errors.Is(err, taskclaim.ErrNotCurrent):
+		writeFixedError(context, http.StatusConflict, "claim_not_current")
+	case errors.Is(err, taskclaim.ErrDeviceInactive):
+		context.Header("WWW-Authenticate", "Bearer")
+		context.Status(http.StatusUnauthorized)
+	default:
+		// Storage and transaction failures are intentionally bodyless: SQL, paths and candidate
+		// details are server-only and must not become a device-facing diagnostic oracle.
+		context.Status(http.StatusServiceUnavailable)
+	}
+}
+
+func writeFixedError(context *gin.Context, status int, code string) {
+	context.JSON(status, gin.H{"error": code})
+}