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mcp: export session missing error (#771)

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Fix: #715

- export session missing error
- modify `errSessionMissing` to `ErrSessionMissing`
- add unit test about session missing error
This commit is contained in:
FanOne 2026-02-03 22:46:49 +08:00 • committed by GitHub
commit 7ecd8049c6
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1 changed files with 55 additions and 18 deletions
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19
mcp/streamable.go
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@ -1540,17 +1540,6 @@ type streamableClientConn struct {
sessionID string
}
// errSessionMissing distinguishes if the session is known to not be present on
// the server (see [streamableClientConn.fail]).
//
// TODO(rfindley): should we expose this error value (and its corresponding
// API) to the user?
//
// The spec says that if the server returns 404, clients should reestablish
// a session. For now, we delegate that to the user, but do they need a way to
// differentiate a 'NotFound' error from other errors?
var errSessionMissing = errors.New("session not found")
var _ clientConnection = (*streamableClientConn)(nil)
func (c *streamableClientConn) sessionUpdated(state clientSessionState) {
@ -1629,7 +1618,7 @@ func (c *streamableClientConn) connectStandaloneSSE() {
// If err is non-nil, it is terminal, and subsequent (or pending) Reads will
// fail.
//
// If err wraps errSessionMissing, the failure indicates that the session is no
// If err wraps ErrSessionMissing, the failure indicates that the session is no
// longer present on the server, and no final DELETE will be performed when
// closing the connection.
func (c *streamableClientConn) fail(err error) {
@ -1896,9 +1885,9 @@ func (c *streamableClientConn) checkResponse(requestSummary string, resp *http.R
// which it MUST respond to requests containing that session ID with HTTP
// 404 Not Found."
if resp.StatusCode == http.StatusNotFound {
// Return an errSessionMissing to avoid sending a redundant DELETE when the
// Return an ErrSessionMissing to avoid sending a redundant DELETE when the
// session is already gone.
return fmt.Errorf("%s: failed to connect (session ID: %v): %w", requestSummary, c.sessionID, errSessionMissing)
return fmt.Errorf("%s: failed to connect (session ID: %v): %w", requestSummary, c.sessionID, ErrSessionMissing)
}
// Transient server errors (502, 503, 504, 429) should not break the connection.
// Wrap them with ErrRejected so the jsonrpc2 layer doesn't set writeErr.
@ -2055,7 +2044,7 @@ func (c *streamableClientConn) connectSSE(ctx context.Context, lastEventID strin
// Close implements the [Connection] interface.
func (c *streamableClientConn) Close() error {
c.closeOnce.Do(func() {
if errors.Is(c.failure(), errSessionMissing) {
if errors.Is(c.failure(), ErrSessionMissing) {
// If the session is missing, no need to delete it.
} else {
req, err := http.NewRequestWithContext(c.ctx, http.MethodDelete, c.url, nil)