131 lines
3.3 KiB
Markdown
131 lines
3.3 KiB
Markdown
|
# httprc
|
||
|
|
||
|
`httprc` is a HTTP "Refresh" Cache. Its aim is to cache a remote resource that
|
||
|
can be fetched via HTTP, but keep the cached content up-to-date based on periodic
|
||
|
refreshing.
|
||
|
|
||
|
# SYNOPSIS
|
||
|
|
||
|
<!-- INCLUDE(httprc_example_test.go) -->
|
||
|
```go
|
||
|
package httprc_test
|
||
|
|
||
|
import (
|
||
|
"context"
|
||
|
"fmt"
|
||
|
"net/http"
|
||
|
"net/http/httptest"
|
||
|
"sync"
|
||
|
"time"
|
||
|
|
||
|
"github.com/lestrrat-go/httprc"
|
||
|
)
|
||
|
|
||
|
const (
|
||
|
helloWorld = `Hello World!`
|
||
|
goodbyeWorld = `Goodbye World!`
|
||
|
)
|
||
|
|
||
|
func ExampleCache() {
|
||
|
var mu sync.RWMutex
|
||
|
|
||
|
msg := helloWorld
|
||
|
|
||
|
srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
|
||
|
w.Header().Set(`Cache-Control`, fmt.Sprintf(`max-age=%d`, 2))
|
||
|
w.WriteHeader(http.StatusOK)
|
||
|
mu.RLock()
|
||
|
fmt.Fprint(w, msg)
|
||
|
mu.RUnlock()
|
||
|
}))
|
||
|
defer srv.Close()
|
||
|
|
||
|
ctx, cancel := context.WithCancel(context.Background())
|
||
|
defer cancel()
|
||
|
|
||
|
errSink := httprc.ErrSinkFunc(func(err error) {
|
||
|
fmt.Printf("%s\n", err)
|
||
|
})
|
||
|
|
||
|
c := httprc.NewCache(ctx,
|
||
|
httprc.WithErrSink(errSink),
|
||
|
httprc.WithRefreshWindow(time.Second), // force checks every second
|
||
|
)
|
||
|
|
||
|
c.Register(srv.URL,
|
||
|
httprc.WithHTTPClient(srv.Client()), // we need client with TLS settings
|
||
|
httprc.WithMinRefreshInterval(time.Second), // allow max-age=1 (smallest)
|
||
|
)
|
||
|
|
||
|
payload, err := c.Get(ctx, srv.URL)
|
||
|
if err != nil {
|
||
|
fmt.Printf("%s\n", err)
|
||
|
return
|
||
|
}
|
||
|
|
||
|
if string(payload.([]byte)) != helloWorld {
|
||
|
fmt.Printf("payload mismatch: %s\n", payload)
|
||
|
return
|
||
|
}
|
||
|
|
||
|
mu.Lock()
|
||
|
msg = goodbyeWorld
|
||
|
mu.Unlock()
|
||
|
|
||
|
time.Sleep(4 * time.Second)
|
||
|
|
||
|
payload, err = c.Get(ctx, srv.URL)
|
||
|
if err != nil {
|
||
|
fmt.Printf("%s\n", err)
|
||
|
return
|
||
|
}
|
||
|
|
||
|
if string(payload.([]byte)) != goodbyeWorld {
|
||
|
fmt.Printf("payload mismatch: %s\n", payload)
|
||
|
return
|
||
|
}
|
||
|
|
||
|
cancel()
|
||
|
|
||
|
// OUTPUT:
|
||
|
}
|
||
|
```
|
||
|
source: [httprc_example_test.go](https://github.com/lestrrat-go/jwx/blob/main/httprc_example_test.go)
|
||
|
<!-- END INCLUDE -->
|
||
|
|
||
|
# Sequence Diagram
|
||
|
|
||
|
```mermaid
|
||
|
sequenceDiagram
|
||
|
autonumber
|
||
|
actor User
|
||
|
participant httprc.Cache
|
||
|
participant httprc.Storage
|
||
|
User->>httprc.Cache: Fetch URL `u`
|
||
|
activate httprc.Storage
|
||
|
httprc.Cache->>httprc.Storage: Fetch local cache for `u`
|
||
|
alt Cache exists
|
||
|
httprc.Storage-->httprc.Cache: Return local cache
|
||
|
httprc.Cache-->>User: Return data
|
||
|
Note over httprc.Storage: If the cache exists, there's nothing more to do.<br />The cached content will be updated periodically in httprc.Refresher
|
||
|
deactivate httprc.Storage
|
||
|
else Cache does not exist
|
||
|
activate httprc.Fetcher
|
||
|
httprc.Cache->>httprc.Fetcher: Fetch remote resource `u`
|
||
|
httprc.Fetcher-->>httprc.Cache: Return fetched data
|
||
|
deactivate httprc.Fetcher
|
||
|
httprc.Cache-->>User: Return data
|
||
|
httprc.Cache-)httprc.Refresher: Enqueue into auto-refresh queue
|
||
|
activate httprc.Refresher
|
||
|
loop Refresh Loop
|
||
|
Note over httprc.Storage,httprc.Fetcher: Cached contents are updated synchronously
|
||
|
httprc.Refresher->>httprc.Refresher: Wait until next refresh
|
||
|
httprc.Refresher-->>httprc.Fetcher: Request fetch
|
||
|
httprc.Fetcher->>httprc.Refresher: Return fetched data
|
||
|
httprc.Refresher-->>httprc.Storage: Store new version in cache
|
||
|
httprc.Refresher->>httprc.Refresher: Enqueue into auto-refresh queue (again)
|
||
|
end
|
||
|
deactivate httprc.Refresher
|
||
|
end
|
||
|
```
|