text: package cat
  
  import (
  	"encoding/json"
  	"errors"
  	"fmt"
  )
  
  // SyntheticsHeader represents a decoded Synthetics header.
  type SyntheticsHeader struct {
  	Version    int
  	AccountID  int
  	ResourceID string
  	JobID      string
  	MonitorID  string
  }
  
  var (
  	errInvalidSyntheticsJSON       = errors.New("invalid synthetics JSON")
  	errInvalidSyntheticsVersion    = errors.New("version is not a float64")
  	errInvalidSyntheticsAccountID  = errors.New("account ID is not a float64")
  	errInvalidSyntheticsResourceID = errors.New("synthetics resource ID is not a string")
  	errInvalidSyntheticsJobID      = errors.New("synthetics job ID is not a string")
  	errInvalidSyntheticsMonitorID  = errors.New("synthetics monitor ID is not a string")
  )
  
  type errUnexpectedSyntheticsVersion int
  
  func (e errUnexpectedSyntheticsVersion) Error() string {
  	return fmt.Sprintf("unexpected synthetics header version: %d", e)
  }
  
  // UnmarshalJSON unmarshalls a SyntheticsHeader from raw JSON.
  func (s *SyntheticsHeader) UnmarshalJSON(data []byte) error {
  	var ok bool
  	var v interface{}
  
  	if err := json.Unmarshal(data, &v); err != nil {
  		return err
  	}
  
  	arr, ok := v.([]interface{})
  	if !ok {
  		return errInvalidSyntheticsJSON
  	}
  	if len(arr) != 5 {
  		return errUnexpectedArraySize{
  			label:    "unexpected number of application data elements",
  			expected: 5,
  			actual:   len(arr),
  		}
  	}
  
  	version, ok := arr[0].(float64)
  	if !ok {
  		return errInvalidSyntheticsVersion
  	}
  	s.Version = int(version)
  	if s.Version != 1 {
  		return errUnexpectedSyntheticsVersion(s.Version)
  	}
  
  	accountID, ok := arr[1].(float64)
  	if !ok {
  		return errInvalidSyntheticsAccountID
  	}
  	s.AccountID = int(accountID)
  
  	if s.ResourceID, ok = arr[2].(string); !ok {
  		return errInvalidSyntheticsResourceID
  	}
  
  	if s.JobID, ok = arr[3].(string); !ok {
  		return errInvalidSyntheticsJobID
  	}
  
  	if s.MonitorID, ok = arr[4].(string); !ok {
  		return errInvalidSyntheticsMonitorID
  	}
  
  	return nil
  }
  