CodedInputStream

CodedInputStream is a class within the Protocol Buffers (protobuf) library, designed for efficient reading of binary data. It's a core component used in deserializing protobuf messages. The primary function of CodedInputStream is to read primitive data types from a byte stream in a way that is consistent with how protobuf encodes them. This includes reading integers, booleans, strings, and floating-point numbers.

A key feature of CodedInputStream is its ability to handle variable-length quantities (varints). Varints are a protobuf encoding scheme that uses a variable number of bytes to represent integers, with smaller numbers using fewer bytes. CodedInputStream correctly parses these varints, ensuring that data is interpreted accurately. It also supports reading fixed-size data types and byte arrays.

The class provides methods like readTag(), readRawVarint32(), readRawVarint64(), readFloat(), readDouble(), readBool(), readString(), and readBytes(). The readTag() method is particularly important as it reads the field tag and wire type, which are essential for navigating the protobuf message structure.

CodedInputStream is typically used in conjunction with a ByteString or an InputStream. It's designed to be efficient by buffering data and minimizing the number of system calls. When a CodedInputStream reaches the end of its input, it signals this by throwing a particular exception or returning a specific value depending on the method. This class is fundamental for anyone working with protobuf serialization and deserialization in various programming languages supported by the library.