MEDIUM: hpack: implement basic hpack encoding

For now it only supports literals and a bit of static header table
references for the 9 most common header field names (date, server,
content-type, content-length, last-modified, accept-ranges, etag,
cache-control, location).

A previous incarnation of this commit used to strip the forbidden H2
header names (connection, proxy-connection, upgrade, transfer-encoding,
keep-alive) but this is no longer the case as this filtering is irrelevant
to HPACK encoding and is specific to H2, so this will have to be done by
the caller.

It's quite not optimal but works fine enough to prepare some valid and
partially compressed responses during development.

Makefile

@@ -848,7 +848,7 @@ OBJS = src/cfgparse.o src/proto_http.o src/stats.o src/server.o src/stream.o \
        src/haproxy.o src/stream_interface.o src/tcp_rules.o src/proxy.o \
        src/listener.o src/acl.o src/flt_http_comp.o src/filters.o src/dns.o \
        src/cli.o src/flt_trace.o src/connection.o src/session.o src/vars.o \
-       src/hpack-dec.o src/hpack-tbl.o src/hpack-huff.o \
+       src/hpack-dec.o src/hpack-enc.o src/hpack-tbl.o src/hpack-huff.o \
        src/map.o src/payload.o src/namespace.o src/compression.o \
        src/mailers.o src/auth.o src/proto_udp.o src/memory.o src/freq_ctr.o \
        src/signal.o src/uri_auth.o src/buffer.o src/task.o src/chunk.o \

include/common/hpack-enc.h

@@ -0,0 +1,38 @@
+/*
+ * HPACK compressor (RFC7541)
+ *
+ * Copyright (C) 2014-2017 Willy Tarreau <willy@haproxy.org>
+ * Copyright (C) 2017 HAProxy Technologies
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef _COMMON_HPACK_ENC_H
+#define _COMMON_HPACK_ENC_H
+
+#include <stdint.h>
+#include <common/chunk.h>
+#include <common/config.h>
+#include <common/ist.h>
+
+int hpack_encode_header(struct chunk *out, const struct ist n, const struct ist v);
+
+#endif /* _COMMON_HPACK_ENC_H */

src/hpack-enc.c

@@ -0,0 +1,133 @@
+/*
+ * HPACK decompressor (RFC7541)
+ *
+ * Copyright (C) 2014-2017 Willy Tarreau <willy@haproxy.org>
+ * Copyright (C) 2017 HAProxy Technologies
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <common/hpack-enc.h>
+#include <common/http-hdr.h>
+#include <common/ist.h>
+
+#include <types/global.h>
+
+/* returns the number of bytes required to encode the string length <len>. The
+ * number of usable bits is an integral multiple of 7 plus 6 for the last byte.
+ * The maximum number of bytes returned is 4 (2097279 max length). Larger values
+ * return 0.
+ */
+static inline int len_to_bytes(size_t len)
+{
+	if (len < 127)
+		return 1;
+	if (len < 127 + (1 << 7))
+		return 2;
+	if (len < 127 + (1 << 14))
+		return 3;
+	if (len < 127 + (1 << 21))
+		return 4;
+	return 0;
+}
+
+/* Encode <len> into <out>+<pos> and return the new position. The caller is
+ * responsible for checking for available room using len_to_bytes() first.
+ */
+static inline int hpack_encode_len(char *out, int pos, int len)
+{
+	int code = len - 127;
+
+	if (code < 0) {
+		out[pos++] = len;
+	} else {
+		out[pos++] = 127;
+		for (; code >= 128; code >>= 7)
+			out[pos++] = code | 128;
+		out[pos++] = code;
+	}
+	return pos;
+}
+
+
+/* Tries to encode header whose name is <n> and value <v> into the chunk <out>.
+ * Returns non-zero on success, 0 on failure (buffer full).
+ */
+int hpack_encode_header(struct chunk *out, const struct ist n, const struct ist v)
+{
+	int len = out->len;
+	int size = out->size;
+
+	if (len >= size)
+		return 0;
+
+	/* check a few very common response header fields to encode them using
+	 * the static header table. The tests are sorted by size to help the
+	 * compiler factor out the common sizes.
+	 */
+	if (isteq(n, ist("date")))
+		out->str[len++] = 0x61; // literal with indexing -- name="date" (idx 33)
+	else if (isteq(n, ist("etag")))
+		out->str[len++] = 0x62; // literal with indexing -- name="etag" (idx 34)
+	else if (isteq(n, ist("server")))
+		out->str[len++] = 0x76; // literal with indexing -- name="server" (idx 54)
+	else if (isteq(n, ist("location")))
+		out->str[len++] = 0x6e; // literal with indexing -- name="location" (idx 46)
+	else if (isteq(n, ist("content-type")))
+		out->str[len++] = 0x5f; // literal with indexing -- name="content-type" (idx 31)
+	else if (isteq(n, ist("last-modified")))
+		out->str[len++] = 0x6c; // literal with indexing -- name="last-modified" (idx 44)
+	else if (isteq(n, ist("accept-ranges")))
+		out->str[len++] = 0x51; // literal with indexing -- name="accept-ranges" (idx 17)
+	else if (isteq(n, ist("cache-control")))
+		out->str[len++] = 0x58; // literal with indexing -- name="cache-control" (idx 24)
+	else if (isteq(n, ist("content-length")))
+		out->str[len++] = 0x5c; // literal with indexing -- name="content-length" (idx 28)
+	else if (len_to_bytes(n.len) && len + len_to_bytes(n.len) + n.len <= size) {
+		out->str[len++] = 0x00;      /* literal without indexing -- new name */
+
+		len = hpack_encode_len(out->str, len, n.len);
+		memcpy(out->str + len, n.ptr, n.len);
+		len += n.len;
+	}
+	else {
+		/* header field name too large for the buffer */
+		return 0;
+	}
+
+	/* copy literal header field value */
+	if (!len_to_bytes(v.len) || len + len_to_bytes(v.len) + v.len > size) {
+		/* header value too large for the buffer */
+		return 0;
+	}
+
+	len = hpack_encode_len(out->str, len, v.len);
+	memcpy(out->str + len, v.ptr, v.len);
+	len += v.len;
+
+	out->len = len;
+	return 1;
+}