package cachecontrol
import (
"time"
"github.com/Southclaws/opt"
)
type ETag struct {
Value string
Time time.Time
}
func NewETag(t time.Time) *ETag {
return &ETag{
Value: "t-" + t.UTC().Format(time.RFC3339Nano),
Time: t,
}
}
func ParseETag(t string) ETag {
// Strip quotes if present (ETags are quoted in HTTP headers)
if len(t) >= 2 && t[0] == '"' && t[len(t)-1] == '"' {
t = t[1 : len(t)-1]
}
// expected format: t-<time in RFC3339Nano>
if len(t) < 3 || t[:2] != "t-" {
return ETag{}
}
parsedTime, err := time.Parse(time.RFC3339Nano, t[2:])
if err != nil {
return ETag{}
}
return ETag{
Value: t,
Time: parsedTime,
}
}
func (t ETag) String() string {
// Return quoted ETag for HTTP header
return `"` + t.Value + `"`
}
// Query represents a HTTP conditional request query.
type Query struct {
ETag opt.Optional[ETag]
ModifiedSince opt.Optional[time.Time]
}
// NewQuery must be constructed from a HTTP request's conditional headers.
func NewQuery(ifNoneMatch opt.Optional[string], ifModifiedSince opt.Optional[time.Time]) Query {
return Query{
ETag: opt.Map(ifNoneMatch, ParseETag),
ModifiedSince: ifModifiedSince,
}
}
// NotModified takes the current updated date of a resource and returns true if
// the cache control query includes a Is-Modified-Since header and the resource
// updated date is not after the header value. True means a 304 response header.
func (q Query) Check(fn func() *time.Time) (*ETag, bool) {
resourceUpdated := fn()
if resourceUpdated == nil {
return nil, false
}
if etag, ok := q.ETag.Get(); ok {
modified := resourceUpdated.Compare(etag.Time)
return NewETag(*resourceUpdated), modified <= 0
}
if ms, ok := q.ModifiedSince.Get(); ok {
// truncate the resourceUpdated to the nearest second because the actual
// HTTP header is already truncated but the DB time is in nanoseconds.
// If we didn't do this the resource time will always be slightly ahead.
truncated := resourceUpdated.Truncate(time.Second)
// If the resource update time is ahead of the HTTP Last-Modified check,
// modified = 1, meaning the resource has been modified since the last
// request and should be returned from the DB, instead of a 304 status.
modified := truncated.Compare(ms)
return NewETag(*resourceUpdated), modified <= 0
}
return NewETag(*resourceUpdated), false
}
