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Tweak caching edge case of reading message ply's backwards

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This commit is contained in:
Jeremy Lakeman 2017-02-14 14:55:36 +10:30
parent 8571de4848
commit f60704b3e1
1 changed files with 17 additions and 5 deletions
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22
rhizome_store.c
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@ -1237,13 +1237,25 @@ ssize_t rhizome_read_buffered(struct rhizome_read *read, struct rhizome_read_buf
}
}
// ok, so we need to read a new buffer to fulfill the request.
// ok, so we need to read at least one buffer to fulfill the request.
// remember the requested read offset so we can put it back
uint64_t ofs = read->offset;
buffer->offset = read->offset = ofs & ~(RHIZOME_CRYPT_PAGE_SIZE -1);
ssize_t r = rhizome_read(read, buffer->data, sizeof buffer->data);
read->offset = ofs;
uint64_t original_ofs = read->offset;
// round down to the previous block boundary
uint64_t read_offset = original_ofs & ~(RHIZOME_CRYPT_PAGE_SIZE -1);
if (read->length != RHIZOME_SIZE_UNSET && original_ofs + len == read->length){
// if more than one PAGE is being requested, and the end of the requested range lines up with the end of the file
// we should probably read the last block first.
// That way, if the reader is scanning a payload backwards,
// we will end up caching part of the previous block for the next buffered read
read_offset = (read->length -1) & ~(RHIZOME_CRYPT_PAGE_SIZE -1);
}
buffer->len = 0;
buffer->offset = read->offset = read_offset;
ssize_t r = rhizome_read(read, buffer->data, sizeof buffer->data);
read->offset = original_ofs;
if (r == -1)
return -1;
buffer->len = (size_t) r;