save headers in an ordered dictionary

due to the usage of a hashmap to store headers, when relaying them
to the other side the order was not prevented.
even though correct from a standards point-of-view, this caused
issues with various programs, and it allows to fingerprint the use
of tinyproxy.

to implement this, i imported the MIT-licensed hsearch.[ch] from
https://github.com/rofl0r/htab which was originally taken from
musl libc. it's a simple and efficient hashtable implementation
with far better performance characteristic than the one previously
used by tinyproxy. additionally it has an API much more well-suited
for this purpose.

orderedmap.[ch] was implemented from scratch to address this issue.
behind the scenes it uses an sblist to store string values, and a htab
to store keys and the indices into the sblist.
this allows us to iterate linearly over the sblist and then find the
corresponding key in the hash table, so the headers can be reproduced
in the order they were received.

closes #73

1 files changed, 199 insertions, 0 deletions

diff --git a/src/hsearch.c b/src/hsearch.c
new file mode 100644
index 0000000..0d022a2
--- /dev/null
+++ b/src/hsearch.c
@@ -0,0 +1,199 @@
+/*
+musl license, hsearch.c originally written by Szabolcs Nagy
+
+Copyright © 2005-2020 Rich Felker, et al.
+
+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 <stdlib.h>
+#include <string.h>
+#include "hsearch.h"
+
+/*
+open addressing hash table with 2^n table size
+quadratic probing is used in case of hash collision
+tab indices and hash are size_t
+after resize fails with ENOMEM the state of tab is still usable
+*/
+
+typedef struct htab_entry {
+	char *key;
+	htab_value data;
+} htab_entry;
+
+struct elem {
+	htab_entry item;
+	size_t hash;
+};
+
+struct htab {
+	struct elem *elems;
+	size_t mask;
+	size_t used;
+};
+
+#define MINSIZE 8
+#define MAXSIZE ((size_t)-1/2 + 1)
+
+#define CASE_INSENSITIVE
+#ifdef CASE_INSENSITIVE
+#include <ctype.h>
+#include <strings.h>
+#define LOWER_OR_NOT(X) tolower(X)
+#define STRCMP(X, Y) strcasecmp(X, Y)
+#else
+#define LOWER_OR_NOT(X) X
+#define STRCMP(X, Y) strcmp(X, Y)
+#endif
+
+static size_t keyhash(const char *k)
+{
+	const unsigned char *p = (const void *)k;
+	size_t h = 0;
+
+	while (*p)
+		h = 31*h + LOWER_OR_NOT(*p++);
+	return h;
+}
+
+static int resize(struct htab *htab, size_t nel)
+{
+	size_t newsize;
+	size_t i, j;
+	struct elem *e, *newe;
+	struct elem *oldtab = htab->elems;
+	struct elem *oldend = htab->elems + htab->mask + 1;
+
+	if (nel > MAXSIZE)
+		nel = MAXSIZE;
+	for (newsize = MINSIZE; newsize < nel; newsize *= 2);
+	htab->elems = calloc(newsize, sizeof *htab->elems);
+	if (!htab->elems) {
+		htab->elems = oldtab;
+		return 0;
+	}
+	htab->mask = newsize - 1;
+	if (!oldtab)
+		return 1;
+	for (e = oldtab; e < oldend; e++)
+		if (e->item.key) {
+			for (i=e->hash,j=1; ; i+=j++) {
+				newe = htab->elems + (i & htab->mask);
+				if (!newe->item.key)
+					break;
+			}
+			*newe = *e;
+		}
+	free(oldtab);
+	return 1;
+}
+
+static struct elem *lookup(struct htab *htab, const char *key, size_t hash)
+{
+	size_t i, j;
+	struct elem *e;
+
+	for (i=hash,j=1; ; i+=j++) {
+		e = htab->elems + (i & htab->mask);
+		if (!e->item.key ||
+		    (e->hash==hash && STRCMP(e->item.key, key)==0))
+			break;
+	}
+	return e;
+}
+
+struct htab *htab_create(size_t nel)
+{
+	struct htab *r = calloc(1, sizeof *r);
+	if(r && !resize(r, nel)) {
+		free(r);
+		r = 0;
+	}
+	return r;
+}
+
+void htab_destroy(struct htab *htab)
+{
+	free(htab->elems);
+	free(htab);
+}
+
+static htab_entry *htab_find_item(struct htab *htab, const char* key)
+{
+	size_t hash = keyhash(key);
+	struct elem *e = lookup(htab, key, hash);
+
+	if (e->item.key) {
+		return &e->item;
+	}
+	return 0;
+}
+
+htab_value* htab_find(struct htab *htab, const char* key)
+{
+	htab_entry *i = htab_find_item(htab, key);
+	if(i) return &i->data;
+	return 0;
+}
+
+int htab_delete(struct htab *htab, const char* key)
+{
+	htab_entry *i = htab_find_item(htab, key);
+	if(!i) return 0;
+	i->key = 0;
+	return 1;
+}
+
+int htab_insert(struct htab *htab, char* key, htab_value value)
+{
+	size_t hash = keyhash(key);
+	struct elem *e = lookup(htab, key, hash);
+	if(e->item.key) {
+		/* it's not allowed to overwrite existing data */
+		return 0;
+	}
+
+	e->item.key = key;
+	e->item.data = value;
+	e->hash = hash;
+	if (++htab->used > htab->mask - htab->mask/4) {
+		if (!resize(htab, 2*htab->used)) {
+			htab->used--;
+			e->item.key = 0;
+			return 0;
+		}
+	}
+	return 1;
+}
+
+size_t htab_next(struct htab *htab, size_t iterator, char** key, htab_value **v)
+{
+	size_t i;
+	for(i=iterator;i<htab->mask+1;++i) {
+		struct elem *e = htab->elems + i;
+		if(e->item.key) {
+			*key = e->item.key;
+			*v = &e->item.data;
+			return i+1;
+		}
+	}
+	return 0;
+}