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Stream: Handle streamID-related edge cases

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This commit solves several edge cases that are related to
exhausting the streamID limits: We should correctly calculate
the succeeding streamID instead of blindly incrementing 'seq'
This affects both XREAD and XADD.

Other (unrelated) changes:
Reply with a better error message when trying to add an entry
to a stream that has exhausted last_id
This commit is contained in:
Guy Benoish
2019-12-26 15:31:37 +05:30
parent 324e22accf
commit 1f75ce30df
4 changed files with 54 additions and 4 deletions
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28
src/t_stream.c
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@ -73,6 +73,21 @@ unsigned long streamLength(const robj *subject) {
return s->length;
}
/* Set 'id' to be its successor streamID */
void streamIncrID(streamID *id) {
if (id->seq == UINT64_MAX) {
if (id->ms == UINT64_MAX) {
/* Special case where 'id' is the last possible streamID... */
id->ms = id->seq = 0;
} else {
id->ms++;
id->seq = 0;
}
} else {
id->seq++;
}
}
/* Generate the next stream item ID given the previous one. If the current
* milliseconds Unix time is greater than the previous one, just use this
* as time part and start with sequence part of zero. Otherwise we use the
@ -83,8 +98,8 @@ void streamNextID(streamID *last_id, streamID *new_id) {
new_id->ms = ms;
new_id->seq = 0;
} else {
new_id->ms = last_id->ms;
new_id->seq = last_id->seq+1;
*new_id = *last_id;
streamIncrID(new_id);
}
}
@ -1220,6 +1235,13 @@ void xaddCommand(client *c) {
if ((o = streamTypeLookupWriteOrCreate(c,c->argv[1])) == NULL) return;
s = o->ptr;
/* Return ASAP if the stream has reached the last possible ID */
if (s->last_id.ms == UINT64_MAX && s->last_id.seq == UINT64_MAX) {
addReplyError(c,"The stream has exhausted the last possible ID, "
"unable to add more items");
return;
}
/* Append using the low level function and return the ID. */
if (streamAppendItem(s,c->argv+field_pos,(c->argc-field_pos)/2,
&id, id_given ? &id : NULL)
@ -1509,7 +1531,7 @@ void xreadCommand(client *c) {
* so start from the next ID, since we want only messages with
* IDs greater than start. */
streamID start = *gt;
start.seq++; /* uint64_t can't overflow in this context. */
streamIncrID(&start);
/* Emit the two elements sub-array consisting of the name
* of the stream and the data we extracted from it. */