C Protocol Buffer Delimited I/O: Are There Java-Equivalent Functions?

Protocol Buffers Delimited I/O Functions: C Equivalents?

In an attempt to read and write multiple Protocol Buffers messages from files using both C and Java, it has been observed that Java provides a set of "Delimited" I/O functions for this purpose. However, it remains uncertain if C offers similar functionality.

The Java API functions are:

• parseDelimitedFrom
• mergeDelimitedFrom
• writeDelimitedTo

C Equivalents

As of version 3.3.0, Google has addressed this issue by introducing the following C equivalents in google/protobuf/util/delimited_message_util.h:

bool writeDelimitedTo(
    const google::protobuf::MessageLite& message,
    google::protobuf::io::ZeroCopyOutputStream* rawOutput) {
  // Code to write delimited messages
}

bool readDelimitedFrom(
    google::protobuf::io::ZeroCopyInputStream* rawInput,
    google::protobuf::MessageLite* message) {
  // Code to read delimited messages
}

Wire Format for Java Size Prefixes

For those seeking to parse the size-prefixed messages in C without using the official library, the wire format is as follows:

1. Size of the message is represented as a 32-bit variable-length integer.
2. A single byte is added after the size to ensure backward-compatibility.
3. The message data is appended after the size and compatibility byte.

Optimizations

The provided C implementations include optimizations that were missing from other responses. These optimizations ensure that the functions:

• Do not fail after 64MB of input.
• Enforce the 64MB limit on each individual message.
• Use a faster direct-to-array serialization path when possible.

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