Go Binary Protocols

Decode the length

AC 02 contributes 44 + (2 << 7) = 300.

• Low seven bits carry data.
• High bit requests another group.
• Payload length excludes the prefix.
• This complete frame consumes 302 bytes.

Tenth-byte boundary

• Nine groups use 63 bits.
• Tenth byte must terminate: only 00 or 01 is allowed.
• Nine 80 bytes: incomplete.
• Ten 80 bytes: malformed immediately.
• Non-minimal 80 00: valid zero in this contract.

Receive-buffer trace

For prefix 82 01, length is 130:

A retry receives the complete unconsumed buffer again.

Validate before slicing

1. Incomplete or malformed prefix?
2. Complete length over maxLen?
3. After safe conversion, length > len(buf)-prefixBytes?
4. Only then calculate the end and return a slice.

prefixBytes + length can overflow if checked too early.

One frame at a time

02 h i 01 ! contains two frames.

• First returns hi, consumed 3.
• Decode the remaining bytes after processing the alias.
• Second returns !, consumed 2.
• Every error returns nil,0,error.

Alias lifetime

• payload shares buf's backing array.
• Overwriting or pooling the buffer can change a saved payload.
• Process before reuse, transfer ownership, or copy deliberately.
• A short slice can retain a large allocation.

Measure correct implementations

• Compare custom parsing with an appropriately adapted standard helper.
• Allocate inputs before timing; preserve observable results.
• Measure lengths, partial inputs, errors, time, and allocations.
• Zero allocations alone does not establish speed or safe ownership.

Predict before implementing

85 01 encodes what length? What is the complete consumed count? Why does [05] with limit 4 differ from [80] with the same limit?

Check the lesson's reasoning, implement the decoder, then take the checkpoint.