const (
    // BypassQuotaAuthHeader is the header key used by the frontend server to know
    // that a request can bypass the quota server.
    BypassQuotaAuthHeader = "X-Go-Discovery-Auth-Bypass-Quota"

    // BypassCacheAuthHeader is the header key used by the frontend server to
    // know that a request can bypass cache.
    BypassCacheAuthHeader = "X-Go-Discovery-Auth-Bypass-Cache"
)

const AppVersionFormat = "20060102t150405"

const SourceTimeout = 1 * time.Minute

const StatementTimeout = 10 * time.Minute

const TaskIDChangeIntervalFrontend = 30 * time.Minute

type Config struct {
    // AuthValues is the set of values that could be set on the AuthHeader, in
    // order to bypass checks by the cache.
    AuthValues []string

    // Discovery environment variables
    ProxyURL, IndexURL string

    // Ports used for hosting. 'DebugPort' is used for serving HTTP debug pages.
    Port, DebugPort string

    // AppEngine identifiers
    ProjectID, ServiceID, VersionID, ZoneID, InstanceID, LocationID string

    // ServiceAccount is the email of the service account that this process
    // is running as when on GCP.
    ServiceAccount string

    // QueueURL is the URL that the Cloud Tasks queue should send requests to.
    // It should be used when the worker is not on AppEngine.
    QueueURL string

    // QueueAudience is used to allow the Cloud Tasks queue to authorize itself
    // to the worker. It should be the OAuth 2.0 client ID associated with the
    // IAP that is gating access to the worker.
    QueueAudience string

    // GoogleTagManagerID is the ID used for GoogleTagManager. It has the
    // structure GTM-XXXX.
    GoogleTagManagerID string

    // MonitoredResource represents the resource that is running the current binary.
    // It might be a Google AppEngine app or a Kubernetes pod.
    // See https://cloud.google.com/monitoring/api/resources for more
    // details:
    // "An object representing a resource that can be used for monitoring, logging,
    // billing, or other purposes. Examples include virtual machine instances,
    // databases, and storage devices such as disks.""
    MonitoredResource *mrpb.MonitoredResource

    // FallbackVersionLabel is used as the VersionLabel when not hosting on
    // AppEngine.
    FallbackVersionLabel string

    DBSecret, DBUser, DBHost, DBPort, DBName string
    DBSecondaryHost                          string // DB host to use if first one is down
    DBPassword                               string `json:"-"`
    DBDriver                                 string

    // Configuration for redis page cache.
    RedisCacheHost, RedisCachePort string

    // Configuration for redis autocompletion. This is different from the page
    // cache instance as it has different availability requirements.
    RedisHAHost, RedisHAPort string

    // UseProfiler specifies whether to enable Stackdriver Profiler.
    UseProfiler bool

    Quota QuotaSettings

    // Teeproxy sepcifies the configuration values for the teeproxy.
    Teeproxy TeeproxySettings

    // Minimum log level below which no logs will be printed.
    // Possible values are [debug, info, error, fatal].
    // In case of invalid/empty value, all logs will be printed.
    LogLevel string

    // DynamicConfigLocation is the location (either a file or gs://bucket/object) for
    // dynamic configuration.
    DynamicConfigLocation string

    // ServeStats determines whether the server has an endpoint that serves statistics for
    // benchmarking or other purposes.
    ServeStats bool

    // DisableErrorReporting disables sending errors to the GCP ErrorReporting system.
    DisableErrorReporting bool
}

type QuotaSettings struct {
    Enable     bool
    QPS        int // allowed queries per second, per IP block
    Burst      int // maximum requests per second, per block; the size of the token bucket
    MaxEntries int // maximum number of entries to keep track of
    // Record data about blocking, but do not actually block.
    // This is a *bool, so we can distinguish "not present" from "false" in an override
    RecordOnly *bool
    // AuthValues is the set of values that could be set on the AuthHeader, in
    // order to bypass checks by the quota server.
    AuthValues []string
    HMACKey    []byte `json:"-"` // key for obfuscating IPs
}

type TeeproxySettings struct {
    AuthKey          string
    AuthValue        string
    Hosts            []string
    Rate             float64
    Burst            int
    FailsToRed       int
    FailureThreshold float64
    GreenInterval    time.Duration
    MinTimeout       time.Duration
    MaxTimeout       time.Duration
    SuccsToGreen     int
}