Examples

Each example walks through building a complete, working parser for a real network protocol using Hammer. The examples are self-contained and introduce Hammer concepts as they're needed, with links back to the Fundamentals and Quick Reference for more detail.

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Available Examples

NTP (Network Time Protocol)

Difficulty	Beginner
Source	ntp.c, hex.c, main.c
Packet size	48 bytes minimum, variable with extensions
What you'll build	A validator for NTP packets (RFC 5905)

Hammer concepts covered:

Concept	Combinator	What NTP Teaches You
Sub-byte fields	h_bits	Parsing 2-bit and 3-bit header fields
Value constraints	h_int_range	Rejecting invalid version numbers
Ordered fields	h_sequence	Composing header, timestamps, etc.
Alternatives	h_choice	Matching different packet types
Repetition	h_many	Zero or more extension fields
Length-prefixed data	h_put_value, h_free_value, h_length_value	Variable-length extension field values
Semantic actions	h_action, H_ARULE	Adjusting lengths, hex-to-byte conversion
Parse tree walking	h_seq_index, H_MAKE_*	Building transformed results
End-of-input assertion	h_end_p, h_left	Ensuring no trailing garbage

Pages:

1. NTP Overview - Protocol intro, project structure, quick start
2. Parsing the Header - h_bits, h_int_range, h_sequence
3. Parsing Data Fields - Timestamps, fixed-point numbers
4. Extension Fields and MAC - h_put_value, h_length_value, h_many
5. Assembling the Parser - h_choice, h_left, h_end_p
6. Hex Input Preprocessing - h_ch_range, h_repeat_n, H_ARULE
7. Running and Testing - Build, run, test with real packets

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DNS (Domain Name System)

Difficulty	Intermediate
Source	dns.c, dns.h, main.c
Packet size	12-byte header + variable-length body
What you'll build	A structural validator for DNS query and response packets RFC 1035

Hammer concepts covered:

Concept	Combinator	What DNS Teaches You
Sub-byte fields	h_bits	Parsing packed DNS flag bits (QR, Opcode, AA, etc.)
Grammar-level invariants	h_attr_bool	Enforcing reserved Z bits = 0, validating TYPE/CLASS
Ordered fields	h_sequence	Composing header and resource record structure
Alternatives	h_choice	Handling label-only, pointer-only, and label+pointer names
Length-prefixed data	h_length_value	Parsing labels and RDATA fields
Context-driven parsing	h_action	Storing header counts for body parsing
Position awareness	h_tell	Validating compression pointer offsets
Failure propagation	(automatic)	Rejecting malformed packets immediately

Pages:

1. DNS Overview - Protocol intro, project structure, quick start
2. Parsing the Header - h_bits, h_attr_bool, h_sequence
3. Parsing the Body - Labels, compression pointers, h_length_value, h_repeat_n
4. Assembling the Parser - Context wiring via DNSContext, h_parse flow
5. Running and Testing - Manual testing and automated suite with runtests.py

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TFTP (Trivial File Transfer Protocol)

Difficulty	Beginner
Source	tftp.c, main.c
Packet size	Variable (up to 516 bytes for data packets)
What you'll build	A parser for TFTP request, data, ACK, and error packets (RFC 1350)

Hammer concepts covered:

Concept	Combinator	What TFTP Teaches You
Value constraints	h_int_range	Validating opcodes, error codes, block numbers
String matching	h_token	Matching exact mode strings ("netascii", "octet", "mail")
Character parsing	h_ch_range	Parsing printable ASCII filenames and error messages
Variable-length data	h_many, h_many1	Filenames, error messages, data payloads
Alternatives	h_choice	Dispatching to the correct packet type parser
Null termination	h_int_range(h_uint8(), 0, 0)	Validating \x00 terminators
End-of-input	h_end_p	Ensuring all bytes are consumed

Pages:

1. TFTP Overview - Protocol intro, project structure, quick start
2. RRQ/WRQ Packets - h_int_range, h_ch_range, h_token, h_many1
3. DATA Packets - h_many, h_end_p
4. ACK Packets - h_int_range, h_sequence
5. ERROR Packets - h_ch_range, h_many1
6. Assembling the Parser - h_choice, h_parse
7. Running and Testing - Build, run, and test

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Adding Your Own Example

Have a protocol you'd like to parse with Hammer? See Adding a New Example for a template and guidelines.