HPACK Header Compression HTTP/2 minimalistic encoder

modules/access/http/Makefile.am

 hpack_test_SOURCES = access/http/hpack.c access/http/hpack.h
 hpack_test_CFLAGS = -DDEC_TEST
-check_PROGRAMS += hpack_test
-TESTS += hpack_test
+hpackenc_test_SOURCES = $(hpack_test_SOURCES) access/http/hpackenc.c
+hpackenc_test_CFLAGS = -DENC_TEST
+check_PROGRAMS += hpack_test hpackenc_test
+TESTS += hpack_test hpackenc_test

modules/access/http/hpack.h

@@ -25,3 +25,8 @@ void hpack_decode_destroy(struct hpack_decoder *);
 
 int hpack_decode(struct hpack_decoder *dec, const uint8_t *data,
                  size_t length, char *headers[][2], unsigned max);
+
+size_t hpack_encode_hdr_neverindex(uint8_t *restrict buf, size_t size,
+                                   const char *name, const char *value);
+size_t hpack_encode(uint8_t *restrict buf, size_t size,
+                    const char *const headers[][2], unsigned count);

modules/access/http/hpackenc.c

+/*****************************************************************************
+ * hpack.c: HPACK Header Compression for HTTP/2 encoder
+ *****************************************************************************
+ * Copyright (C) 2015 Rémi Denis-Courmont
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#ifdef ENC_TEST
+# undef NDEBUG
+#endif
+
+#include <assert.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "hpack.h"
+
+/*
+ * This is curently the simplest possible HPACK compressor: it does not
+ * compress anything and is stateless.
+ * TODO:
+ *  - use static Huffman compression when useful,
+ *  - use header names and values from the static HPACK table,
+ *  - become stateful and let the caller specify the indexed flag,
+ *  - let caller specify the never-indexed flag.
+ */
+
+static size_t hpack_encode_int(uint8_t *restrict buf, size_t size,
+                               uintmax_t value, unsigned n)
+{
+    assert(n >= 1 && n <= 8);
+
+    unsigned mask = (1 << n) - 1;
+    size_t ret = 1;
+
+    if (value < mask)
+    {
+        if (size > 0)
+            buf[0] |= value;
+        return 1;
+    }
+
+    if (size > 0)
+       *(buf++) |= mask;
+    value -= mask;
+
+    while (value >= 128)
+    {
+        if (ret++ < size)
+            *(buf++) = 0x80 | (value & 0x7F);
+        value >>= 7;
+    }
+
+    if (ret++ < size)
+        *(buf++) = value;
+    return ret;
+}
+
+static size_t hpack_encode_str_raw(uint8_t *restrict buf, size_t size,
+                                   const char *str)
+{
+    size_t len = strlen(str);
+
+    if (size > 0)
+        *buf = 0;
+
+    size_t ret = hpack_encode_int(buf, size, len, 7);
+    if (ret < size)
+    {
+        buf += ret;
+        size -= ret;
+
+        memcpy(buf, str, (len <= size) ? len : size);
+    }
+    ret += len;
+    return ret;
+}
+
+static size_t hpack_encode_str_raw_lower(uint8_t *restrict buf, size_t size,
+                                         const char *str)
+{
+    size_t len = strlen(str);
+
+    if (size > 0)
+        *buf = 0;
+
+    size_t ret = hpack_encode_int(buf, size, len, 7);
+    if (ret < size)
+    {
+        buf += ret;
+        size -= ret;
+
+        for (size_t i = 0; i < len && i < size; i++)
+            if (str[i] < 'A' || str[i] > 'Z')
+                buf[i] = str[i];
+            else
+                buf[i] = str[i] - 'A' + 'a';
+    }
+    ret += len;
+    return ret;
+}
+
+size_t hpack_encode_hdr_neverindex(uint8_t *restrict buf, size_t size,
+                                   const char *name, const char *value)
+{
+    size_t ret = 1, val;
+
+    if (size > 0)
+    {
+        *(buf++) = 0x10;
+        size--;
+    }
+
+    val = hpack_encode_str_raw_lower(buf, size, name);
+    if (size >= val)
+    {
+        buf += val;
+        size -= val;
+    }
+    else
+        size = 0;
+    ret += val;
+
+    val = hpack_encode_str_raw(buf, size, value);
+    if (size >= val)
+    {
+        buf += val;
+        size -= val;
+    }
+    else
+        size = 0;
+    ret += val;
+
+    return ret;
+}
+
+size_t hpack_encode(uint8_t *restrict buf, size_t size,
+                    const char *const headers[][2], unsigned count)
+{
+    size_t ret = 0;
+
+    while (count > 0)
+    {
+        size_t val = hpack_encode_hdr_neverindex(buf, size, headers[0][0],
+                                                 headers[0][1]);
+        if (size >= val)
+        {
+            buf += val;
+            size -= val;
+        }
+        else
+            size = 0;
+
+        ret += val;
+        headers++;
+        count--;
+    }
+    return ret;
+}
+
+/*** Test cases ***/
+#ifdef ENC_TEST
+# include <stdarg.h>
+# include <stdlib.h>
+# include <stdio.h>
+
+static void test_integer(unsigned n, uintmax_t value)
+{
+    uint8_t buf[3];
+    size_t ret;
+
+    for (unsigned i = 0; i < 3; i++)
+    {
+        ret = hpack_encode_int(buf, sizeof (buf), value, n);
+        assert(ret > 0);
+    }
+}
+
+static void test_integers(void)
+{
+    test_integer(5, 10);
+    test_integer(5, 1337);
+    test_integer(8, 42);
+}
+
+static void test_lowercase(const char *str)
+{
+    char c;
+
+    while ((c = *(str++)) != '\0')
+        assert(c < 'A' || c > 'Z');
+}
+
+static void test_block(const char *name, ...)
+{
+    const char *headers[16][2];
+    unsigned count = 0;
+    va_list ap;
+
+    va_start(ap, name);
+    while (name != NULL)
+    {
+        headers[count][0] = name;
+        headers[count][1] = va_arg(ap, const char *);
+        name = va_arg(ap, const char *);
+        count++;
+    }
+    va_end(ap);
+
+    printf(" %u header(s):\n", count);
+
+    uint8_t buf[1024];
+
+    size_t length = hpack_encode(NULL, 0, headers, count);
+
+    for (size_t i = 0; i < sizeof (buf); i++)
+        assert(hpack_encode(buf, i, headers, count) == length);
+
+    memset(buf, 0xAA, sizeof (buf));
+    assert(hpack_encode(buf, length, headers, count) == length);
+
+    char *eheaders[16][2];
+
+    struct hpack_decoder *dec = hpack_decode_init(4096);
+    assert(dec != NULL);
+
+    int ecount = hpack_decode(dec, buf, length, eheaders, 16);
+    assert((unsigned)ecount == count);
+
+    hpack_decode_destroy(dec);
+
+    for (unsigned i = 0; i < count; i++)
+    {
+        printf("  %s: %s\n", eheaders[i][0], eheaders[i][1]);
+        test_lowercase(eheaders[i][0]);
+        assert(!strcasecmp(eheaders[i][0], headers[i][0]));
+        assert(!strcmp(eheaders[i][1], headers[i][1]));
+        free(eheaders[i][1]);
+        free(eheaders[i][0]);
+    }
+}
+
+static void test_reqs(void)
+{
+    test_block(NULL);
+    test_block(":method", "GET", ":scheme", "http", ":path", "/",
+               ":authority", "www.example.com", NULL);
+    test_block(":method", "GET", ":scheme", "http", ":path", "/",
+               ":authority", "www.example.com", "Cache-Control", "no-cache",
+               NULL);
+    test_block(":method", "GET", ":scheme", "https", ":path", "/index.html",
+               ":authority", "www.example.com", "custom-key", "custom-value",
+               NULL);
+}
+
+static void test_resps(void)
+{
+    test_block(":status", "302", "Cache-Control", "private",
+               "Date", "Mon, 21 Oct 2013 20:13:21 GMT",
+               "Location", "https://www.example.com", NULL);
+    test_block(":status", "307", "Cache-Control", "private",
+               "Date", "Mon, 21 Oct 2013 20:13:21 GMT",
+               "Location", "https://www.example.com", NULL);
+    test_block(":status", "200", "Cache-Control", "private",
+               "Date", "Mon, 21 Oct 2013 20:13:22 GMT",
+               "Location", "https://www.example.com",
+               "Content-Encoding", "gzip",
+               "Set-Cookie", "foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; "
+                   "max-age=3600; version=1",
+               NULL);
+}
+
+int main(void)
+{
+    test_integers();
+    test_reqs();
+    test_resps();
+}
+#endif /* TEST */