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HandlerWithKey:recover panic in callback #2

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HandlerWithKey:recover panic in callback #2

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2c09a97
HandlerWithKey:recover panic in callback
AgrimPrasad Aug 20, 2020
43cd1d9
HandlerWithKey: handle panic error separately for stacktrace
AgrimPrasad Aug 20, 2020
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22 changes: 20 additions & 2 deletions http.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"io"
"io/ioutil"
"net/http"
"runtime/debug"
"strings"
"time"
)
Expand Down Expand Up @@ -76,10 +77,22 @@ func HandlerWithKey(cacheSize int, ttl time.Duration, keyFunc ...func(r *http.Re
}

// mark the request that actually processes the response
first := false
var (
err error
panicErr error
first bool
val interface{}
)

// process request (single flight)
val, err := cache.GetFresh(r.Context(), key, func(ctx context.Context) (interface{}, error) {
val, err = cache.GetFresh(r.Context(), key, func(ctx context.Context) (interface{}, error) {
defer func() {
// need a panic recoverer as separate recoverer middleware can't catch panics in new goroutine
if r := recover(); r != nil {
panicErr = fmt.Errorf("recovered panicking request:%#v, stack:%s", r, string(debug.Stack()))
}
}()

first = true
buf := bytes.NewBuffer(nil)
ww := &responseWriter{ResponseWriter: w, tee: buf}
Expand All @@ -94,6 +107,11 @@ func HandlerWithKey(cacheSize int, ttl time.Duration, keyFunc ...func(r *http.Re
return val, nil
})

// handle panic for first or other listeners
if panicErr != nil {
panic(fmt.Sprintf("stampede: encountered unexpected panic, %v", panicErr))
}

// the first request to trigger the fetch should return as it's already
// responded to the client
if first {
Expand Down