n_http2.h File Reference

HTTP/2 (RFC 7540) wire framing plus HPACK header compression (RFC 7541) More...

#include <stddef.h>
#include <stdint.h>

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Data Structures
struct	N_H2_FRAME
	a parsed HTTP/2 frame; payload aliases the input buffer More...
struct	N_H2_HEADER
	one HPACK header field; after a decode both strings are owned (heap) More...
struct	N_H2_SETTING
	one SETTINGS parameter (identifier and value) More...

Macros
#define	N_H2_FRAME_HEADER_LEN   9
	length of the fixed frame header in bytes
#define	N_H2_HPACK_DEFAULT_TABLE_SIZE   4096
	the default HPACK dynamic table size (SETTINGS_HEADER_TABLE_SIZE default)
#define	N_H2_MAX_FRAME_PAYLOAD   16384
	largest frame payload the parser accepts (the default SETTINGS_MAX_FRAME_SIZE)
#define	N_H2_PREFACE   "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"
	the client connection preface sent before any HTTP/2 frame (RFC 7540 3.5)
HTTP/2 frame types (RFC 7540 6)
#define	N_H2_CONTINUATION   0x9
	CONTINUATION.
#define	N_H2_DATA   0x0
	DATA.
#define	N_H2_GOAWAY   0x7
	GOAWAY.
#define	N_H2_HEADERS   0x1
	HEADERS.
#define	N_H2_PING   0x6
	PING.
#define	N_H2_PRIORITY   0x2
	PRIORITY.
#define	N_H2_PUSH_PROMISE   0x5
	PUSH_PROMISE.
#define	N_H2_RST_STREAM   0x3
	RST_STREAM.
#define	N_H2_SETTINGS   0x4
	SETTINGS.
#define	N_H2_WINDOW_UPDATE   0x8
	WINDOW_UPDATE.
HTTP/2 frame flags (RFC 7540 6)
#define	N_H2_FLAG_ACK   0x1
	SETTINGS/PING: acknowledgement.
#define	N_H2_FLAG_END_HEADERS   0x4
	HEADERS/PUSH_PROMISE/CONTINUATION: header block complete.
#define	N_H2_FLAG_END_STREAM   0x1
	DATA/HEADERS: last frame of the stream.
#define	N_H2_FLAG_PADDED   0x8
	DATA/HEADERS/PUSH_PROMISE: a pad-length prefix is present.
#define	N_H2_FLAG_PRIORITY   0x20
	HEADERS: priority fields are present.
SETTINGS parameter identifiers (RFC 7540 6.5.2)
#define	N_H2_SETTINGS_ENABLE_PUSH   0x2
#define	N_H2_SETTINGS_HEADER_TABLE_SIZE   0x1
#define	N_H2_SETTINGS_INITIAL_WINDOW_SIZE   0x4
#define	N_H2_SETTINGS_MAX_CONCURRENT_STREAMS   0x3
#define	N_H2_SETTINGS_MAX_FRAME_SIZE   0x5
#define	N_H2_SETTINGS_MAX_HEADER_LIST_SIZE   0x6

Functions
size_t	n_http2_frame_build_header (unsigned char *out, size_t out_cap, uint32_t length, int type, int flags, uint32_t stream_id)
	write a 9-byte HTTP/2 frame header into out.
int	n_http2_frame_parse (const unsigned char *buf, size_t len, N_H2_FRAME *frame, size_t *consumed)
	parse one HTTP/2 frame from a byte buffer (stateless).
int	n_http2_hpack_decode (N_H2_HPACK *ctx, const unsigned char *block, size_t len, N_H2_HEADER *out, size_t max_out, size_t *count)
	decode an HPACK header block into out[] (owned name/value strings).
size_t	n_http2_hpack_encode (const N_H2_HEADER *headers, size_t n, unsigned char *out, size_t out_cap)
	encode a header list into a block using literal representations without indexing and without Huffman (a valid, interoperable, self-contained encoding that needs no dynamic-table state).
void	n_http2_hpack_free (N_H2_HPACK **ctx)
	free an HPACK codec context and NULL the caller's pointer
void	n_http2_hpack_headers_free (N_H2_HEADER *headers, size_t n)
	free the owned name/value strings of a decoded header array (does not free the array itself)
N_H2_HPACK *	n_http2_hpack_new (size_t max_table_size)
	create an HPACK codec context with the given dynamic table size limit (0 uses N_H2_HPACK_DEFAULT_TABLE_SIZE).
void	n_http2_hpack_set_max_size (N_H2_HPACK *ctx, size_t max_table_size)
	change the dynamic table size limit (a SETTINGS_HEADER_TABLE_SIZE change), evicting entries as needed so the table fits.
int	n_http2_settings_parse (const unsigned char *payload, size_t len, N_H2_SETTING *out, size_t max, size_t *count)
	parse a SETTINGS frame payload (6-byte id/value entries) into out.

Detailed Description

HTTP/2 (RFC 7540) wire framing plus HPACK header compression (RFC 7541)

Author

Castagnier Mickael

Version

1.0

Date

2026

The framing layer of HTTP/2: the client connection preface, the frame-type and flag constants, a 9-byte frame-header parse/build, and a SETTINGS payload reader. The frame codec is stateless and does no allocation, so a caller drives its own reassembly buffer.

On top of the framing sits HPACK (RFC 7541): an N_H2_HPACK codec context with a per-direction dynamic table, a full decoder (indexed and literal fields, the static and dynamic tables, Huffman-coded and literal strings, and dynamic table size updates), and a self-contained encoder (literal fields without indexing, no Huffman) that needs no shared state. The stream/connection state machine builds on these two layers.

Definition in file n_http2.h.

---

Data Structure Documentation

N_H2_FRAME

struct N_H2_FRAME

a parsed HTTP/2 frame; payload aliases the input buffer

Examples

ex_http2.c.

Definition at line 91 of file n_http2.h.

Collaboration diagram for N_H2_FRAME:

Data Fields
int	flags	frame flags
uint32_t	length	payload length (24-bit)
const unsigned char *	payload	pointer into the input buffer (may be NULL when length is 0)
uint32_t	stream_id	stream identifier (31-bit; the reserved bit is cleared)
int	type	frame type (N_H2_*)

N_H2_HEADER

struct N_H2_HEADER

one HPACK header field; after a decode both strings are owned (heap)

Examples

ex_http2.c.

Definition at line 123 of file n_http2.h.

Collaboration diagram for N_H2_HEADER:

Data Fields
char *	name	header field name (owned after decode)
char *	value	header field value (owned after decode)

N_H2_SETTING

struct N_H2_SETTING

one SETTINGS parameter (identifier and value)

Examples

ex_http2.c.

Definition at line 100 of file n_http2.h.

Collaboration diagram for N_H2_SETTING:

Data Fields
uint16_t	id	parameter identifier (N_H2_SETTINGS_*)
uint32_t	value	parameter value

Macro Definition Documentation

N_H2_CONTINUATION

#define N_H2_CONTINUATION   0x9

CONTINUATION.

Definition at line 68 of file n_http2.h.

N_H2_DATA

#define N_H2_DATA   0x0

DATA.

Examples

ex_http2.c.

Definition at line 59 of file n_http2.h.

N_H2_FLAG_ACK

#define N_H2_FLAG_ACK   0x1

SETTINGS/PING: acknowledgement.

Definition at line 74 of file n_http2.h.

N_H2_FLAG_END_HEADERS

#define N_H2_FLAG_END_HEADERS   0x4

HEADERS/PUSH_PROMISE/CONTINUATION: header block complete.

Examples

ex_http2.c.

Definition at line 75 of file n_http2.h.

N_H2_FLAG_END_STREAM

#define N_H2_FLAG_END_STREAM   0x1

DATA/HEADERS: last frame of the stream.

Examples

ex_http2.c.

Definition at line 73 of file n_http2.h.

N_H2_FLAG_PADDED

#define N_H2_FLAG_PADDED   0x8

DATA/HEADERS/PUSH_PROMISE: a pad-length prefix is present.

Definition at line 76 of file n_http2.h.

N_H2_FLAG_PRIORITY

#define N_H2_FLAG_PRIORITY   0x20

HEADERS: priority fields are present.

Definition at line 77 of file n_http2.h.

N_H2_FRAME_HEADER_LEN

#define N_H2_FRAME_HEADER_LEN   9

length of the fixed frame header in bytes

Examples

ex_http2.c.

Definition at line 53 of file n_http2.h.

N_H2_GOAWAY

#define N_H2_GOAWAY   0x7

GOAWAY.

Definition at line 66 of file n_http2.h.

N_H2_HEADERS

#define N_H2_HEADERS   0x1

HEADERS.

Examples

ex_http2.c.

Definition at line 60 of file n_http2.h.

N_H2_HPACK_DEFAULT_TABLE_SIZE

#define N_H2_HPACK_DEFAULT_TABLE_SIZE   4096

the default HPACK dynamic table size (SETTINGS_HEADER_TABLE_SIZE default)

Definition at line 120 of file n_http2.h.

N_H2_MAX_FRAME_PAYLOAD

#define N_H2_MAX_FRAME_PAYLOAD   16384

largest frame payload the parser accepts (the default SETTINGS_MAX_FRAME_SIZE)

Definition at line 55 of file n_http2.h.

N_H2_PING

#define N_H2_PING   0x6

PING.

Examples

ex_http2.c.

Definition at line 65 of file n_http2.h.

N_H2_PREFACE

#define N_H2_PREFACE   "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"

the client connection preface sent before any HTTP/2 frame (RFC 7540 3.5)

Examples

ex_http2.c.

Definition at line 51 of file n_http2.h.

N_H2_PRIORITY

#define N_H2_PRIORITY   0x2

PRIORITY.

Definition at line 61 of file n_http2.h.

N_H2_PUSH_PROMISE

#define N_H2_PUSH_PROMISE   0x5

PUSH_PROMISE.

Definition at line 64 of file n_http2.h.

N_H2_RST_STREAM

#define N_H2_RST_STREAM   0x3

RST_STREAM.

Definition at line 62 of file n_http2.h.

N_H2_SETTINGS

#define N_H2_SETTINGS   0x4

SETTINGS.

Definition at line 63 of file n_http2.h.

N_H2_SETTINGS_ENABLE_PUSH

#define N_H2_SETTINGS_ENABLE_PUSH   0x2

Definition at line 83 of file n_http2.h.

N_H2_SETTINGS_HEADER_TABLE_SIZE

#define N_H2_SETTINGS_HEADER_TABLE_SIZE   0x1

Definition at line 82 of file n_http2.h.

N_H2_SETTINGS_INITIAL_WINDOW_SIZE

#define N_H2_SETTINGS_INITIAL_WINDOW_SIZE   0x4

Examples

ex_http2.c.

Definition at line 85 of file n_http2.h.

N_H2_SETTINGS_MAX_CONCURRENT_STREAMS

#define N_H2_SETTINGS_MAX_CONCURRENT_STREAMS   0x3

Examples

ex_http2.c.

Definition at line 84 of file n_http2.h.

N_H2_SETTINGS_MAX_FRAME_SIZE

#define N_H2_SETTINGS_MAX_FRAME_SIZE   0x5

Definition at line 86 of file n_http2.h.

N_H2_SETTINGS_MAX_HEADER_LIST_SIZE

#define N_H2_SETTINGS_MAX_HEADER_LIST_SIZE   0x6

Definition at line 87 of file n_http2.h.

N_H2_WINDOW_UPDATE

#define N_H2_WINDOW_UPDATE   0x8

WINDOW_UPDATE.

Examples

ex_http2.c.

Definition at line 67 of file n_http2.h.

Function Documentation

n_http2_frame_build_header()

size_t n_http2_frame_build_header	(	unsigned char *	out,
		size_t	out_cap,
		uint32_t	length,
		int	type,
		int	flags,
		uint32_t	stream_id
	)

write a 9-byte HTTP/2 frame header into out.

Returns N_H2_FRAME_HEADER_LEN, or 0 when out_cap is too small or length exceeds 24 bits.

Definition at line 52 of file n_http2.c.

References N_H2_FRAME_HEADER_LEN.

Referenced by test_boundaries(), and test_roundtrip().

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n_http2_frame_parse()

int n_http2_frame_parse	(	const unsigned char *	buf,
		size_t	len,
		N_H2_FRAME *	frame,
		size_t *	consumed
	)

parse one HTTP/2 frame from a byte buffer (stateless).

Returns 1 and fills frame + *consumed (header + payload) on a complete frame, 0 when more bytes are needed, -1 when the payload exceeds N_H2_MAX_FRAME_PAYLOAD.

Definition at line 32 of file n_http2.c.

References N_H2_FRAME::flags, N_H2_FRAME::length, N_H2_FRAME_HEADER_LEN, N_H2_MAX_FRAME_PAYLOAD, N_H2_FRAME::payload, N_H2_FRAME::stream_id, and N_H2_FRAME::type.

Referenced by test_boundaries(), and test_roundtrip().

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n_http2_hpack_decode()

int n_http2_hpack_decode	(	N_H2_HPACK *	ctx,
		const unsigned char *	block,
		size_t	len,
		N_H2_HEADER *	out,
		size_t	max_out,
		size_t *	count
	)

decode an HPACK header block into out[] (owned name/value strings).

Handles indexed fields (static and dynamic table), the three literal forms (with/without/never indexing), Huffman-coded and literal strings, and dynamic table size updates. On success *count holds the number of headers written (<= max_out) and the dynamic table is updated. Returns 0 on success, -1 on a malformed block or when more than max_out headers are produced. Free the decoded headers with n_http2_hpack_headers_free.

Parameters

ctx	codec context (its dynamic table is read and updated)
block	the header block fragment bytes
len	length of block
out	array receiving the decoded headers
max_out	capacity of out
count	receives the number of headers decoded

Returns

0 on success, -1 on error

Definition at line 472 of file n_http2.c.

References hpack_dyn_add(), hpack_evict(), hpack_int_decode(), hpack_lookup(), hpack_str_decode(), N_H2_HPACK::limit, N_H2_HPACK::max_size, n_http2_hpack_headers_free(), N_H2_HEADER::name, and N_H2_HEADER::value.

Referenced by test_hpack_guards(), test_hpack_overflow(), test_hpack_rfc_huffman(), test_hpack_rfc_requests(), and test_hpack_roundtrip().

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n_http2_hpack_encode()

size_t n_http2_hpack_encode	(	const N_H2_HEADER *	headers,
		size_t	n,
		unsigned char *	out,
		size_t	out_cap
	)

encode a header list into a block using literal representations without indexing and without Huffman (a valid, interoperable, self-contained encoding that needs no dynamic-table state).

Returns the number of bytes written, or 0 when out_cap is too small or an argument is invalid.

Parameters

headers	the header fields to encode (name/value C strings)
n	number of headers
out	destination buffer
out_cap	capacity of out

Returns

bytes written, or 0 on error

Definition at line 554 of file n_http2.c.

References hpack_str_encode().

Referenced by test_hpack_roundtrip().

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n_http2_hpack_free()

void n_http2_hpack_free

(

N_H2_HPACK **

ctx

)

free an HPACK codec context and NULL the caller's pointer

Definition at line 375 of file n_http2.c.

References N_H2_HPACK::ents, H2_DYN_ENTRY::name, N_H2_HPACK::nents, and H2_DYN_ENTRY::value.

Referenced by test_hpack_guards(), test_hpack_overflow(), test_hpack_rfc_huffman(), test_hpack_rfc_requests(), and test_hpack_roundtrip().

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n_http2_hpack_headers_free()

void n_http2_hpack_headers_free	(	N_H2_HEADER *	headers,
		size_t	n
	)

free the owned name/value strings of a decoded header array (does not free the array itself)

Definition at line 460 of file n_http2.c.

References N_H2_HEADER::name, and N_H2_HEADER::value.

Referenced by n_http2_hpack_decode(), test_hpack_rfc_huffman(), test_hpack_rfc_requests(), and test_hpack_roundtrip().

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n_http2_hpack_new()

N_H2_HPACK * n_http2_hpack_new

(

size_t

max_table_size

)

create an HPACK codec context with the given dynamic table size limit (0 uses N_H2_HPACK_DEFAULT_TABLE_SIZE).

Returns NULL on allocation failure.

Definition at line 353 of file n_http2.c.

References N_H2_HPACK::limit, N_H2_HPACK::max_size, and N_H2_HPACK_DEFAULT_TABLE_SIZE.

Referenced by test_hpack_guards(), test_hpack_overflow(), test_hpack_rfc_huffman(), test_hpack_rfc_requests(), and test_hpack_roundtrip().

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n_http2_hpack_set_max_size()

void n_http2_hpack_set_max_size	(	N_H2_HPACK *	ctx,
		size_t	max_table_size
	)

change the dynamic table size limit (a SETTINGS_HEADER_TABLE_SIZE change), evicting entries as needed so the table fits.

Definition at line 390 of file n_http2.c.

References hpack_evict(), N_H2_HPACK::limit, and N_H2_HPACK::max_size.

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n_http2_settings_parse()

int n_http2_settings_parse	(	const unsigned char *	payload,
		size_t	len,
		N_H2_SETTING *	out,
		size_t	max,
		size_t *	count
	)

parse a SETTINGS frame payload (6-byte id/value entries) into out.

Returns 0 on success (*count set, <= max), -1 when the payload length is not a multiple of 6.

Definition at line 70 of file n_http2.c.

References N_H2_SETTING::id, and N_H2_SETTING::value.

Referenced by test_settings().

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