comparison rust/hg-core/src/revlog/mod.rs @ 50508:39ed7b2953bb

rust: mostly avoid streaming zstd decompression

Streaming ZStd decompression seems slightly slower, and
the API we use makes it very inconvenient to re-use the
decompression context.

Instead of using that, use the buffer-backed version,
because we can give a reasonable-ish size estimate.

50507:d1cab48354bc

            Ok(buf)
        }
    }

    fn uncompressed_zstd_data(&self) -> Result<Vec<u8>, HgError> {
        if self.is_delta() {
            let mut buf = Vec::with_capacity(self.compressed_len as usize);
            zstd::stream::copy_decode(self.bytes, &mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            Ok(buf)
        } else {
            let cap = self.uncompressed_len.max(0) as usize;
            let mut buf = Vec::with_capacity(cap);
            let len = zstd_decompress_to_buffer(self.bytes, &mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            if len != self.uncompressed_len as usize {
                Err(corrupted("uncompressed length does not match"))

50508:39ed7b2953bb

            Ok(buf)
        }
    }

    fn uncompressed_zstd_data(&self) -> Result<Vec<u8>, HgError> {
        let cap = self.uncompressed_len.max(0) as usize;
        if self.is_delta() {
            // [cap] is usually an over-estimate of the space needed because
            // it's the length of delta-decoded data, but we're interested
            // in the size of the delta.
            // This means we have to [shrink_to_fit] to avoid holding on
            // to a large chunk of memory, but it also means we must have a
            // fallback branch, for the case when the delta is longer than
            // the original data (surprisingly, this does happen in practice)
            let mut buf = Vec::with_capacity(cap);
            match zstd_decompress_to_buffer(self.bytes, &mut buf) {
                Ok(_) => buf.shrink_to_fit(),
                Err(_) => {
                    buf.clear();
                    zstd::stream::copy_decode(self.bytes, &mut buf)
                        .map_err(|e| corrupted(e.to_string()))?;
                }
            };
            Ok(buf)
        } else {
            let mut buf = Vec::with_capacity(cap);
            let len = zstd_decompress_to_buffer(self.bytes, &mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            if len != self.uncompressed_len as usize {
                Err(corrupted("uncompressed length does not match"))