telnet: honor CURLOPT_TIMEOUT in send_telnet_data()#21685
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The poll-before-write loop used -1 (infinite) as the Curl_poll timeout, so a peer that stops reading could stall the transfer indefinitely, bypassing CURLOPT_TIMEOUT. Use Curl_timeleft_ms() instead and return CURLE_OPERATION_TIMEDOUT when the deadline is reached or exceeded.
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The poll-before-write loop used -1 (infinite) as the Curl_poll timeout, so a peer that stops reading could stall the transfer indefinitely, bypassing CURLOPT_TIMEOUT. Use Curl_timeleft_ms() instead and return CURLE_OPERATION_TIMEDOUT when the deadline is reached or exceeded. Closes curl#21685
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The poll-before-write loop in
send_telnet_data()passed-1toCurl_poll(), making the wait infinite. A peer that accepts theconnection but stops reading fills the TCP send buffer, causing
Curl_poll()to block indefinitely and bypassingCURLOPT_TIMEOUT.Fix: use
Curl_timeleft_ms()for the poll timeout and returnCURLE_OPERATION_TIMEDOUTwhen the deadline is reached.