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BACKPORT: Improve logging of long log lines
Upstream reference: moby#22982 This change updates how we handle long lines of output from the container. The previous logic used a bufio reader to read entire lines of output from the container through an intermediate BytesPipe, and that allowed the container to cause dockerd to consume an unconstrained amount of memory as it attempted to collect a whole line of output, by outputting data without newlines. To avoid that, we replace the bufio reader with our own buffering scheme that handles log lines up to 16k in length, breaking up anything longer than that into multiple chunks. If we can dispense with noting this detail properly at the end of output, we can switch from using ReadBytes() to using ReadLine() instead. We add a field ("Partial") to the log message structure to flag when we pass data to the log driver that did not end with a newline. The Line member of Message structures that we pass to log drivers is now a slice into data which can be overwritten between calls to the log driver's Log() method, so drivers which batch up Messages before processing them need to take additional care: we add a function (logger.CopyMessage()) that can be used to create a deep copy of a Message structure, and modify the awslogs driver to use it. We update the jsonfile log driver to append a "\n" to the data that it logs to disk only when the Partial flag is false (it previously did so unconditionally), to make its "logs" output correctly reproduce the data as we received it. Likewise, we modify the journald log driver to add a data field with value CONTAINER_PARTIAL_MESSAGE=true to entries when the Partial flag is true, and update its "logs" reader to refrain from appending a "\n" to the data that it retrieves if it does not see this field/value pair (it also previously did this unconditionally). Signed-off-by: Nalin Dahyabhai <nalin@redhat.com> (github: nalind) Signed-off-by: Antonio Murdaca <runcom@redhat.com>
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