ENT-12414: New network protocol v4 - SAFEGET #5621
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The current protocol (v3) uses a `STAT <FILENAME>` request to determine the file size (among other things), followed by a `GET <FILENAME>` request to fetch the file content. However, there is a race condition here. If the file size increases between the two requests, the client would think that the remaining data after the "file size" offset is a new response header. Here, we introduce a new protocol-version "safeget" to address the race condition. PDUs from the response following a `GET <FILENAME>` request now contain a protocol header consisting of a NULL-byte terminated string of four unsigned integers (`uint64_t`). We will refer to the four integers as ERROR_CODE, FILE_SIZE, FILE_OFFSET, and PAYLOAD_SIZE. The integers will appear in this order in the protocol header. Each integer is separated by a whitespace character. A non-zero ERROR_CODE signals that an error occurred. Furthermore, the exact value of ERROR_CODE specifies what went wrong on the server side. FILE_SIZE and FILE_OFFSET are mainly used to determine when the last PDU is received (i.e., when FILE_SIZE = FILE_OFFSET + PAYLOAD_SIZE). However, FILE_SIZE is also used to detect if the file is modified at the source during transmission. The payload starts immediately after the NULL-terminating byte in the protocol header and consists of PAYLOAD_SIZE bytes. Ticket: ENT-12414 Changelog: Fixed race condition when copying remote files. Signed-off-by: Lars Erik Wik <[email protected]>
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Superseded by #5629 |
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The current protocol (v3) uses a
STAT <FILENAME>request to determine the file size (among other things), followed by aGET <FILENAME>request to fetch the file content. However, there is a race condition here. If the file size increases between the two requests, the client would think that the remaining data after the "file size" offset is a new response header.Here, we introduce a new protocol-version "safeget" to address the race condition. PDUs from the response following a
GET <FILENAME>request now contain a protocol header consisting of a NULL-byte terminated string of four unsigned integers (uint64_t). We will refer to the four integers as ERROR_CODE, FILE_SIZE, FILE_OFFSET, and PAYLOAD_SIZE. The integers will appear in this order in the protocol header. Each integer is separated by a whitespace character.A non-zero ERROR_CODE signals that an error occurred. Furthermore, the exact value of ERROR_CODE specifies what went wrong on the server side. FILE_SIZE and FILE_OFFSET are mainly used to determine when the last PDU is received (i.e., when FILE_SIZE = FILE_OFFSET + PAYLOAD_SIZE). However, FILE_SIZE is also used to detect if the file is modified at the source during transmission. The payload starts immediately after the NULL-terminating byte in the protocol header and consists of PAYLOAD_SIZE bytes.