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net/http: add context cancellation reason for server handlers #70850

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net/http: add context cancellation reason for server handlers #70850

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124f0d2
net/http: add context cancellation reason for server handlers
sgielen Dec 15, 2024
29c5a17
Update error names and descriptions based on feedback & insights.
sgielen Dec 15, 2024
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26 changes: 20 additions & 6 deletions src/net/http/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,17 @@ var (
// anything in the net/http package. Callers should not
// compare errors against this variable.
ErrWriteAfterFlush = errors.New("unused")

// TODO: expose once proposal is accepted
// errConnectionClosed is used as a context Cause for contexts
// cancelled because the client closed their connection while
// a request was being handled.
errConnectionClosed = errors.New("connection closed by client")

// TODO: expose once proposal is accepted
// errRequestHandlerReturned is used as a context Cause for contexts
// cancelled because the request handler already returned.
errRequestHandlerReturned = errors.New("request handler returned")
)

// A Handler responds to an HTTP request.
Expand Down Expand Up @@ -257,7 +268,7 @@ type conn struct {
server *Server

// cancelCtx cancels the connection-level context.
cancelCtx context.CancelFunc
cancelCtx context.CancelCauseFunc

// rwc is the underlying network connection.
// This is never wrapped by other types and is the value given out
Expand Down Expand Up @@ -754,8 +765,11 @@ func (cr *connReader) hitReadLimit() bool { return cr.remain <= 0 }
// down its context.
//
// It may be called from multiple goroutines.
func (cr *connReader) handleReadError(_ error) {
cr.conn.cancelCtx()
func (cr *connReader) handleReadError(err error) {
if errors.Is(err, io.EOF) {
err = errConnectionClosed
}
cr.conn.cancelCtx(err)
cr.closeNotify()
}

Expand Down Expand Up @@ -2005,9 +2019,9 @@ func (c *conn) serve(ctx context.Context) {

// HTTP/1.x from here on.

ctx, cancelCtx := context.WithCancel(ctx)
ctx, cancelCtx := context.WithCancelCause(ctx)
c.cancelCtx = cancelCtx
defer cancelCtx()
defer cancelCtx(errRequestHandlerReturned)

c.r = &connReader{conn: c}
c.bufr = newBufioReader(c.r)
Expand Down Expand Up @@ -4021,7 +4035,7 @@ func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
n, err = w.c.rwc.Write(p)
if err != nil && w.c.werr == nil {
w.c.werr = err
w.c.cancelCtx()
w.c.cancelCtx(err)
}
return
}
Expand Down