vendor/github.com/Shopify/sarama/packet_decoder.go

package sarama

// PacketDecoder is the interface providing helpers for reading with Kafka's encoding rules.
// Types implementing Decoder only need to worry about calling methods like GetString,
// not about how a string is represented in Kafka.
type packetDecoder interface {
	// Primitives
	getInt8() (int8, error)
	getInt16() (int16, error)
	getInt32() (int32, error)
	getInt64() (int64, error)
	getVarint() (int64, error)
	getArrayLength() (int, error)
	getBool() (bool, error)

	// Collections
	getBytes() ([]byte, error)
	getVarintBytes() ([]byte, error)
	getRawBytes(length int) ([]byte, error)
	getString() (string, error)
	getNullableString() (*string, error)
	getInt32Array() ([]int32, error)
	getInt64Array() ([]int64, error)
	getStringArray() ([]string, error)

	// Subsets
	remaining() int
	getSubset(length int) (packetDecoder, error)
	peek(offset, length int) (packetDecoder, error) // similar to getSubset, but it doesn't advance the offset
	peekInt8(offset int) (int8, error)              // similar to peek, but just one byte

	// Stacks, see PushDecoder
	push(in pushDecoder) error
	pop() error
}

// PushDecoder is the interface for decoding fields like CRCs and lengths where the validity
// of the field depends on what is after it in the packet. Start them with PacketDecoder.Push() where
// the actual value is located in the packet, then PacketDecoder.Pop() them when all the bytes they
// depend upon have been decoded.
type pushDecoder interface {
	// Saves the offset into the input buffer as the location to actually read the calculated value when able.
	saveOffset(in int)

	// Returns the length of data to reserve for the input of this encoder (eg 4 bytes for a CRC32).
	reserveLength() int

	// Indicates that all required data is now available to calculate and check the field.
	// SaveOffset is guaranteed to have been called first. The implementation should read ReserveLength() bytes
	// of data from the saved offset, and verify it based on the data between the saved offset and curOffset.
	check(curOffset int, buf []byte) error
}

// dynamicPushDecoder extends the interface of pushDecoder for uses cases where the length of the
// fields itself is unknown until its value was decoded (for instance varint encoded length
// fields).
// During push, dynamicPushDecoder.decode() method will be called instead of reserveLength()
type dynamicPushDecoder interface {
	pushDecoder
	decoder
}