compress,compress.gzip: add decompress_with_callback API (#24904)

vlib/compress/compress.c.v

@@ -51,3 +51,51 @@ pub fn decompress(data []u8, flags int) ![]u8 {
 		return ret
 	}
 }
+
+// ChunkCallback is used to receive decompressed chunks of maximum 32768 bytes.
+// After processing the chunk this function should return the chunk's length to indicate
+// the decompressor to send more chunks, otherwise the decompression stops.
+// The userdata parameter comes from the call to decompress_with_callback/4, and can be used
+// to pass arbitrary data, without having to create a closure.
+pub type ChunkCallback = fn (chunk []u8, userdata voidptr) int
+
+// decompress_with_callback decompresses an array of bytes based on the provided flags,
+// and a V fn callback to receive decompressed chunks, of at most 32 kilobytes each.
+// It returns the total decompressed length, or a decompression error.
+// NB: this is a low level api, a high level implementation like zlib/gzip should be preferred.
+pub fn decompress_with_callback(data []u8, cb ChunkCallback, userdata voidptr, flags int) !u64 {
+	cbdata := DecompressionCallBackData{
+		data:     data.data
+		size:     usize(data.len)
+		cb:       cb
+		userdata: userdata
+	}
+	status := C.tinfl_decompress_mem_to_callback(cbdata.data, &cbdata.size, c_cb_for_decompress_mem,
+		&cbdata, flags)
+	if status == 0 {
+		return error('decompression error')
+	}
+	return cbdata.decompressed_size
+}
+
+struct DecompressionCallBackData {
+mut:
+	data              voidptr
+	size              usize
+	decompressed_size u64
+	userdata          voidptr
+	cb                ChunkCallback = unsafe { nil }
+}
+
+fn c_cb_for_decompress_mem(buf &char, len int, pdcbd voidptr) int {
+	mut cbdata := unsafe { &DecompressionCallBackData(pdcbd) }
+	if cbdata.cb(unsafe { voidptr(buf).vbytes(len) }, cbdata.userdata) == len {
+		cbdata.decompressed_size += u64(len)
+		return 1 // continue decompressing
+	}
+	return 0 // stop decompressing
+}
+
+type DecompressCallback = fn (const_buffer voidptr, len int, userdata voidptr) int
+
+fn C.tinfl_decompress_mem_to_callback(const_input_buffer voidptr, psize &usize, put_buf_cb DecompressCallback, userdata voidptr, flags int) int

vlib/compress/gzip/gzip.v

@@ -203,7 +203,7 @@ pub fn validate(data []u8, params DecompressParams) !GzipHeader {
 	return header
 }
 
-// decompresses an array of bytes using zlib and returns the decompressed bytes in a new array
+// decompress an array of bytes using zlib and returns the decompressed bytes in a new array
 // Example: decompressed := gzip.decompress(b)!
 pub fn decompress(data []u8, params DecompressParams) ![]u8 {
 	gzip_header := validate(data, params)!
@@ -221,3 +221,20 @@ pub fn decompress(data []u8, params DecompressParams) ![]u8 {
 	}
 	return decompressed
 }
+
+// decompress_with_callback decompresses the given `data`, using zlib. It calls `cb` with each chunk of decompressed bytes.
+// A chunk is usually 32 KB or less. Note: the chunk data received by `cb` should be cloned, if you need to store it for later,
+// and not process it right away.
+// The callback function should return the chunk length, if it wants to continue decompressing, or 0, if it wants to abort the decompression early.
+// See also compress.ChunkCallback for more details.
+pub fn decompress_with_callback(data []u8, cb compr.ChunkCallback, userdata voidptr, params DecompressParams) !int {
+	gzip_header := validate(data, params)!
+	header_len := gzip_header.length
+	expected_len := int((u32(data[data.len - 1]) << 24) | (u32(data[data.len - 2]) << 16) | (u32(data[data.len - 3]) << 8) | data[data.len - 4])
+	body := data[header_len..data.len - 8]
+	chunks_len := int(compr.decompress_with_callback(body, cb, userdata, 0)!)
+	if params.verify_length && expected_len != chunks_len {
+		return error('Decompress error: expected length:${expected_len}, got:${chunks_len}')
+	}
+	return chunks_len
+}

vlib/compress/gzip/gzip_test.v

@@ -132,3 +132,18 @@ fn test_gzip_with_invalid_flags() {
 	compressed[3] |= 0b1000_0000
 	assert_decompress_error(compressed, 'reserved flags are set, unsupported field detected')!
 }
+
+fn test_gzip_decompress_callback() {
+	uncompressed := '321323'.repeat(10_000)
+	gz := compress(uncompressed.bytes())!
+	mut size := 0
+	mut ref := &size
+	decoded := decompress_with_callback(gz, fn (chunk []u8, ref &int) int {
+		unsafe {
+			*ref += chunk.len
+		}
+		return chunk.len
+	}, ref)!
+	assert decoded == size
+	assert decoded == uncompressed.len
+}