From 15a60b747e4f0e0d11353f8e89bc9ce7b36c5512 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Mon, 8 Apr 2024 14:16:59 +0200 Subject: reftable/block: open-code call to `uncompress2()` The reftable format stores log blocks in a compressed format. Thus, whenever we want to read such a block we first need to decompress it. This is done by calling the convenience function `uncompress2()` of the zlib library, which is a simple wrapper that manages the lifecycle of the `zstream` structure for us. While nice for one-off inflation of data, when iterating through reflogs we will likely end up inflating many such log blocks. This requires us to reallocate the state of the `zstream` every single time, which adds up over time. It would thus be great to reuse the `zstream` instead of discarding it after every inflation. Open-code the call to `uncompress2()` such that we can start reusing the `zstream` in the subsequent commit. Note that our open-coded variant is different from `uncompress2()` in two ways: - We do not loop around `inflate()` until we have processed all input. As our input is limited by the maximum block size, which is 16MB, we should not hit limits of `inflate()`. - We use `Z_FINISH` instead of `Z_NO_FLUSH`. Quoting the `inflate()` documentation: "inflate() should normally be called until it returns Z_STREAM_END or an error. However if all decompression is to be performed in a single step (a single call of inflate), the parameter flush should be set to Z_FINISH." Furthermore, "Z_FINISH also informs inflate to not maintain a sliding window if the stream completes, which reduces inflate's memory footprint." Other than that this commit is expected to be functionally equivalent and does not yet reuse the `zstream`. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/block.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) diff --git a/reftable/block.c b/reftable/block.c index 9460273290..435922b569 100644 --- a/reftable/block.c +++ b/reftable/block.c @@ -195,10 +195,10 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block, } if (typ == BLOCK_TYPE_LOG) { - int block_header_skip = 4 + header_off; - uLongf dst_len = sz - block_header_skip; /* total size of dest - buffer. */ - uLongf src_len = block->len - block_header_skip; + uint32_t block_header_skip = 4 + header_off; + uLong dst_len = sz - block_header_skip; + uLong src_len = block->len - block_header_skip; + z_stream stream = {0}; /* Log blocks specify the *uncompressed* size in their header. */ REFTABLE_ALLOC_GROW(br->uncompressed_data, sz, @@ -207,15 +207,33 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block, /* Copy over the block header verbatim. It's not compressed. */ memcpy(br->uncompressed_data, block->data, block_header_skip); - /* Uncompress */ - if (Z_OK != - uncompress2(br->uncompressed_data + block_header_skip, &dst_len, - block->data + block_header_skip, &src_len)) { + err = inflateInit(&stream); + if (err != Z_OK) { err = REFTABLE_ZLIB_ERROR; goto done; } - if (dst_len + block_header_skip != sz) { + stream.next_in = block->data + block_header_skip; + stream.avail_in = src_len; + stream.next_out = br->uncompressed_data + block_header_skip; + stream.avail_out = dst_len; + + /* + * We know both input as well as output size, and we know that + * the sizes should never be bigger than `uInt_MAX` because + * blocks can at most be 16MB large. We can thus use `Z_FINISH` + * here to instruct zlib to inflate the data in one go, which + * is more efficient than using `Z_NO_FLUSH`. + */ + err = inflate(&stream, Z_FINISH); + inflateEnd(&stream); + if (err != Z_STREAM_END) { + err = REFTABLE_ZLIB_ERROR; + goto done; + } + err = 0; + + if (stream.total_out + block_header_skip != sz) { err = REFTABLE_FORMAT_ERROR; goto done; } @@ -224,7 +242,7 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block, reftable_block_done(block); block->data = br->uncompressed_data; block->len = sz; - full_block_size = src_len + block_header_skip; + full_block_size = src_len + block_header_skip - stream.avail_in; } else if (full_block_size == 0) { full_block_size = sz; } else if (sz < full_block_size && sz < block->len && -- cgit 1.2.3-korg