feat(client): honor Retry-After on HTTP 429 responses#1965
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MukundaKatta wants to merge 2 commits intomodelcontextprotocol:mainfrom
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feat(client): honor Retry-After on HTTP 429 responses#1965MukundaKatta wants to merge 2 commits intomodelcontextprotocol:mainfrom
MukundaKatta wants to merge 2 commits intomodelcontextprotocol:mainfrom
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StreamableHTTPClientTransport now treats 429 Too Many Requests as a retryable signal. When the server returns 429 the transport parses the Retry-After header (delta-seconds or HTTP-date per RFC 7231 §7.1.3), waits for the indicated duration (clamped to a configurable ceiling), and retries the original POST/GET. After a configurable number of consecutive 429 responses the transport surfaces a typed SdkErrorCode.ClientHttpRateLimited so callers can react. Behaviour is configurable via the new rateLimitOptions transport option. Setting maxRetries to 0 disables automatic retries entirely for applications that want to handle rate limiting themselves. Closes modelcontextprotocol#1892.
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@modelcontextprotocol/client
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Why
Closes #1892.
StreamableHTTPClientTransportfalls through 429 to a genericSdkError, so any client talking to a server that rate-limits with429 Too Many Requests(e.g. theexpress-rate-limitdefault, the MiYo Kado MCP gateway, Cloudflare-fronted servers) crashes on the very first throttled response instead of waiting and retrying. Every consumer of this SDK has to reinvent client-side rate-limit handling.What
Retry-Afterheader on 429 (delta-seconds and HTTP-date forms per RFC 7231 §7.1.3) inside both the POST_sendpath and the GET_startOrAuthSsepath.defaultRetryAfterMswhen the header is missing or unparsable.SdkErrorCode.ClientHttpRateLimitedwith the originalRetry-Aftervalue attached toerror.dataso callers can react.rateLimitOptionstransport option (maxRetries,defaultRetryAfterMs,maxRetryAfterMs). Defaults: 3 retries, 1s fallback, 60s cap. SetmaxRetries: 0to opt out entirely.AbortControllersotransport.close()cancels in-flight Retry-After sleeps.Tested
vitestunit tests inpackages/client/test/client/streamableHttp.test.tscovering:Retry-After: 2waits ~2s then succeedsRetry-Afteris parsed and respectedRetry-Afterfalls back todefaultRetryAfterMsRetry-Afteris clamped tomaxRetryAfterMsClientHttpRateLimitedmaxRetries: 0disables retries_parseRetryAfterhelper across all input shapes (null, undefined, empty, garbage, integer, fractional, future/past HTTP-date)StreamableHTTPClientTransporttest suite still passes (no logic changes outside the new 429 branch).