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allow overriding cache directives in responses

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Add a new `-minCacheDuration` flag to specify a minimum duration to
cache images for.

Updates #28
Updates #144
Fixes #207
Fixes #208
This commit is contained in:
Will Norris 2025-04-28 23:43:10 -07:00
parent 82ce506905
commit 7502adde1c
6 changed files with 181 additions and 4 deletions
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47
imageproxy.go
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@ -28,6 +28,7 @@ import (
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
tphttp "willnorris.com/go/imageproxy/third_party/http"
tphc "willnorris.com/go/imageproxy/third_party/httpcache"
)
// Maximum number of redirection-followings allowed.
@ -91,6 +92,10 @@ type Proxy struct {
// PassRequestHeaders identifies HTTP headers to pass from inbound
// requests to the proxied server.
PassRequestHeaders []string
// MinimumCacheDuration is the minimum duration to cache remote images.
// This will override cache-control instructions from the remote server.
MinimumCacheDuration time.Duration
}
// NewProxy constructs a new proxy. The provided http RoundTripper will be
@ -118,6 +123,7 @@ func NewProxy(transport http.RoundTripper, cache Cache) *Proxy {
proxy.logf(format, v...)
}
},
updateCacheHeaders: proxy.updateCacheHeaders,
},
Cache: cache,
MarkCachedResponses: true,
@ -128,6 +134,39 @@ func NewProxy(transport http.RoundTripper, cache Cache) *Proxy {
return proxy
}
// updateCacheHeaders updates the cache-control headers in the provided headers.
// It sets the cache-control max-age value to the maximum of the minimum cache
// duration, the expires header, and the max-age header. It also removes the
// expires header.
func (p *Proxy) updateCacheHeaders(hdr http.Header) {
if p.MinimumCacheDuration == 0 {
return
}
cc := tphc.ParseCacheControl(hdr)
var expiresDuration time.Duration
var maxAgeDuration time.Duration
if maxAge, ok := cc["max-age"]; ok {
maxAgeDuration, _ = time.ParseDuration(maxAge + "s")
}
if date, err := httpcache.Date(hdr); err == nil {
if expiresHeader := hdr.Get("Expires"); expiresHeader != "" {
if expires, err := time.Parse(time.RFC1123, expiresHeader); err == nil {
expiresDuration = expires.Sub(date)
}
}
}
maxAge := max(p.MinimumCacheDuration, expiresDuration, maxAgeDuration)
cc["max-age"] = fmt.Sprintf("%d", int(maxAge.Seconds()))
delete(cc, "no-cache")
delete(cc, "no-store")
hdr.Set("Cache-Control", cc.String())
hdr.Del("Expires")
}
// ServeHTTP handles incoming requests.
func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == "/favicon.ico" {
@ -475,6 +514,8 @@ type TransformingTransport struct {
CachingClient *http.Client
log func(format string, v ...any)
updateCacheHeaders func(hdr http.Header)
}
// RoundTrip implements the http.RoundTripper interface.
@ -484,7 +525,11 @@ func (t *TransformingTransport) RoundTrip(req *http.Request) (*http.Response, er
if t.log != nil {
t.log("fetching remote URL: %v", req.URL)
}
return t.Transport.RoundTrip(req)
resp, err := t.Transport.RoundTrip(req)
if err == nil && t.updateCacheHeaders != nil {
t.updateCacheHeaders(resp.Header)
}
return resp, err
}
f := req.URL.Fragment