diff --git a/include/common/ist.h b/include/common/ist.h
new file mode 100644
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--- /dev/null
+++ b/include/common/ist.h
@@ -0,0 +1,412 @@
+/*
+ * include/common/ist.h
+ * Very simple indirect string manipulation functions.
+ *
+ * Copyright (C) 2014-2017 Willy Tarreau - w@1wt.eu
+ *
+ * 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_IST_H
+#define _COMMON_IST_H
+
+#include <string.h>
+
+#include <common/config.h>
+
+/* This string definition will most often be used to represent a read-only
+ * string returned from a function, based on the starting point and its length
+ * in bytes. No storage is provided, only a pointer and a length. The types
+ * here are important as we only want to have 2 native machine words there so
+ * that on modern architectures the compiler is capable of efficiently
+ * returning a register pair without having to allocate stack room from the
+ * caller. This is done with -freg-struct which is often enabled by default.
+ */
+struct ist {
+	char  *ptr;
+	size_t len;
+};
+
+/* makes an ist from a regular zero terminated string. Null has length 0.
+ * Constants are detected and replaced with constant initializers. Other values
+ * are measured by hand without strlen() as it's much cheaper and inlinable on
+ * small strings. The construct is complex because we must never call
+ * __builtin_strlen() with an expression otherwise it involves a real
+ * measurement.
+ */
+#if __GNUC__ >= 4
+// gcc >= 4 detects constant propagation of str through __x and resolves the
+// length of constant strings easily.
+#define ist(str) ({                                                    \
+	char *__x = (void *)(str);                                     \
+	(struct ist){                                                  \
+		.ptr = __x,                                            \
+		.len = __builtin_constant_p(str) ?                     \
+			((void *)str == (void *)0) ? 0 :               \
+			__builtin_strlen(__x) :                        \
+			({                                             \
+				size_t __l = 0;                        \
+				if (__x) for (__l--; __x[++__l]; ) ;   \
+				__l;                                   \
+			})                                             \
+	};                                                             \
+})
+#else
+// gcc < 4 can't do this, and the side effect is a warning each time a NULL is
+// passed to ist() due to the check on __builtin_strlen(). It doesn't have the
+// ability to know that this code is never called.
+#define ist(str) ({                                                    \
+	char *__x = (void *)(str);                                     \
+	(struct ist){                                                  \
+		.ptr = __x,                                            \
+		.len = __builtin_constant_p(str) ?                     \
+			((void *)str == (void *)0) ? 0 :               \
+			__builtin_strlen(str) :                        \
+			({                                             \
+				size_t __l = 0;                        \
+				if (__x) for (__l--; __x[++__l]; ) ;   \
+				__l;                                   \
+			})                                             \
+	};                                                             \
+})
+#endif
+
+/* makes an ist struct from a string and a length */
+static inline struct ist ist2(const void *ptr, size_t len)
+{
+	return (struct ist){ .ptr = (char *)ptr, .len = len };
+}
+
+/* returns the length of the string */
+static inline size_t istlen(const struct ist ist)
+{
+	return ist.len;
+}
+
+/* skips to next character in the string, always stops at the end */
+static inline struct ist istnext(const struct ist ist)
+{
+	struct ist ret = ist;
+
+	if (ret.len) {
+		ret.len--;
+		ret.ptr++;
+	}
+	return ret;
+}
+
+/* copies the contents from string <ist> to buffer <buf> and adds a trailing
+ * zero. The caller must ensure <buf> is large enough.
+ */
+static inline struct ist istpad(void *buf, const struct ist ist)
+{
+	struct ist ret = { .ptr = buf, .len = ist.len };
+
+	for (ret.len = 0; ret.len < ist.len; ret.len++)
+		ret.ptr[ret.len] = ist.ptr[ret.len];
+
+	ret.ptr[ret.len] = 0;
+	return ret;
+}
+
+/* trims string <ist> to no more than <size> characters. The string is
+ * returned.
+ */
+static inline struct ist isttrim(const struct ist ist, size_t size)
+{
+	struct ist ret = ist;
+
+	if (ret.len > size)
+		ret.len = size;
+	return ret;
+}
+
+/* trims string <ist> to no more than <size>-1 characters and ensures that a
+ * zero is placed after <ist.len> (possibly reduced by one) and before <size>,
+ * unless <size> is already zero. The string is returned. This is mostly aimed
+ * at building printable strings that need to be zero-terminated.
+ */
+static inline struct ist istzero(const struct ist ist, size_t size)
+{
+	struct ist ret = ist;
+
+	if (!size)
+		ret.len = 0;
+	else {
+		if (ret.len > size - 1)
+			ret.len = size - 1;
+		ret.ptr[ret.len] = 0;
+	}
+	return ret;
+}
+
+/* returns the ordinal difference between two strings :
+ *    < 0 if ist1 < ist2
+ *    = 0 if ist1 == ist2
+ *    > 0 if ist1 > ist2
+ */
+static inline int istdiff(const struct ist ist1, const struct ist ist2)
+{
+	struct ist l = ist1;
+	struct ist r = ist2;
+
+	do {
+		if (!l.len--)
+			return -r.len;
+		if (!r.len--)
+			return 1;
+	} while (*l.ptr++ == *r.ptr++);
+
+	return *(unsigned char *)(l.ptr - 1) - *(unsigned char *)(r.ptr - 1);
+}
+
+/* returns non-zero if <ist1> starts like <ist2> (empty strings do match) */
+static inline int istmatch(const struct ist ist1, const struct ist ist2)
+{
+	struct ist l = ist1;
+	struct ist r = ist2;
+
+	if (l.len < r.len)
+		return 0;
+
+	while (r.len--) {
+		if (*l.ptr++ != *r.ptr++)
+			return 0;
+	}
+	return 1;
+}
+
+/* returns non-zero if <ist1> starts like <ist2> on the first <count>
+ * characters (empty strings do match).
+ */
+static inline int istnmatch(const struct ist ist1, const struct ist ist2, size_t count)
+{
+	struct ist l = ist1;
+	struct ist r = ist2;
+
+	if (l.len > count)
+		l.len = count;
+	if (r.len > count)
+		r.len = count;
+	return istmatch(l, r);
+}
+
+/* returns non-zero if <ist1> equals <ist2> (empty strings are equal) */
+static inline int isteq(const struct ist ist1, const struct ist ist2)
+{
+	struct ist l = ist1;
+	struct ist r = ist2;
+
+	if (l.len != r.len)
+		return 0;
+
+	while (l.len--) {
+		if (*l.ptr++ != *r.ptr++)
+			return 0;
+	}
+	return 1;
+}
+
+/* returns non-zero if <ist1> equals <ist2> on the first <count> characters
+ * (empty strings are equal).
+ */
+static inline int istneq(const struct ist ist1, const struct ist ist2, size_t count)
+{
+	struct ist l = ist1;
+	struct ist r = ist2;
+
+	if (l.len > count)
+		l.len = count;
+	if (r.len > count)
+		r.len = count;
+	return isteq(l, r);
+}
+
+/* copies <src> over <dst> for a maximum of <count> bytes. Returns the number
+ * of characters copied (src.len), or -1 if it does not fit. In all cases, the
+ * contents are copied prior to reporting an error, so that the destination
+ * at least contains a valid but truncated string.
+ */
+static inline ssize_t istcpy(struct ist *dst, const struct ist src, size_t count)
+{
+	dst->len = 0;
+
+	if (count > src.len)
+		count = src.len;
+
+	while (dst->len < count) {
+		dst->ptr[dst->len] = src.ptr[dst->len];
+		dst->len++;
+	}
+
+	if (dst->len == src.len)
+		return src.len;
+
+	return -1;
+}
+
+/* copies <src> over <dst> for a maximum of <count> bytes. Returns the number
+ * of characters copied, or -1 if it does not fit. A (possibly truncated) valid
+ * copy of <src> is always left into <dst>, and a trailing \0 is appended as
+ * long as <count> is not null, even if that results in reducing the string by
+ * one character.
+ */
+static inline ssize_t istscpy(struct ist *dst, const struct ist src, size_t count)
+{
+	dst->len = 0;
+
+	if (!count)
+		goto fail;
+
+	if (count > src.len)
+		count = src.len + 1;
+
+	while (dst->len < count - 1) {
+		dst->ptr[dst->len] = src.ptr[dst->len];
+		dst->len++;
+	}
+
+	dst->ptr[dst->len] = 0;
+	if (dst->len == src.len)
+		return src.len;
+ fail:
+	return -1;
+}
+
+/* appends <src> after <dst> for a maximum of <count> total bytes in <dst> after
+ * the copy. <dst> is assumed to be <count> or less before the call. The new
+ * string's length is returned, or -1 if a truncation happened. In all cases,
+ * the contents are copied prior to reporting an error, so that the destination
+ * at least contains a valid but truncated string.
+ */
+static inline ssize_t istcat(struct ist *dst, const struct ist src, size_t count)
+{
+	const char *s = src.ptr;
+
+	while (dst->len < count && s != src.ptr + src.len)
+		dst->ptr[dst->len++] = *s++;
+
+	if (s == src.ptr + src.len)
+		return dst->len;
+
+	return -1;
+}
+
+/* appends <src> after <dst> for a maximum of <count> total bytes in <dst> after
+ * the copy. <dst> is assumed to be <count> or less before the call. The new
+ * string's length is returned, or -1 if a truncation happened. In all cases,
+ * the contents are copied prior to reporting an error, so that the destination
+ * at least contains a valid but truncated string.
+ */
+static inline ssize_t istscat(struct ist *dst, const struct ist src, size_t count)
+{
+	const char *s = src.ptr;
+
+	if (!count)
+		goto fail;
+
+	while (dst->len < count - 1 && s != src.ptr + src.len) {
+		dst->ptr[dst->len++] = *s++;
+	}
+
+	dst->ptr[dst->len] = 0;
+	if (s == src.ptr + src.len)
+		return dst->len;
+ fail:
+	return -1;
+}
+
+/* looks for first occurrence of character <chr> in string <ist>. Returns the
+ * pointer if found, or NULL if not found.
+ */
+static inline char *istchr(const struct ist ist, char chr)
+{
+	char *s = ist.ptr;
+
+	do {
+		if (s >= ist.ptr + ist.len)
+			return NULL;
+	} while (*s++ != chr);
+	return s - 1;
+}
+
+/* looks for first occurrence of character <chr> in string <ist> and returns
+ * the tail of the string starting with this character, or (ist.end,0) if not
+ * found.
+ */
+static inline struct ist istfind(const struct ist ist, char chr)
+{
+	struct ist ret = ist;
+
+	while (ret.len--) {
+		if (*ret.ptr++ == chr)
+			return ist2(ret.ptr - 1, ret.len + 1);
+	}
+	return ist2(ret.ptr, 0);
+}
+
+/* looks for first occurrence of character different from <chr> in string <ist>
+ * and returns the tail of the string starting at this character, or (ist_end,0)
+ * if not found.
+ */
+static inline struct ist istskip(const struct ist ist, char chr)
+{
+	struct ist ret = ist;
+
+	while (ret.len--) {
+		if (*ret.ptr++ != chr)
+			return ist2(ret.ptr - 1, ret.len + 1);
+	}
+	return ist2(ret.ptr, 0);
+}
+
+/* looks for first occurrence of string <pat> in string <ist> and returns the
+ * tail of the string starting at this position, or (NULL,0) if not found. The
+ * empty pattern is found everywhere.
+ */
+static inline struct ist istist(const struct ist ist, const struct ist pat)
+{
+	struct ist ret = ist;
+	size_t pos;
+
+	if (!pat.len)
+		return ret;
+
+	while (1) {
+	loop:
+		ret = istfind(ret, *pat.ptr);
+		if (ret.len < pat.len)
+			break;
+
+		/* ret.len >= 1, pat.len >= 1 and *ret.ptr == *pat.ptr */
+
+		ret = istnext(ret);
+		for (pos = 0; pos < pat.len - 1; ) {
+			++pos;
+			if (ret.ptr[pos - 1] != pat.ptr[pos])
+				goto loop;
+		}
+		return ist2(ret.ptr - 1, ret.len + 1);
+	}
+	return ist2(NULL, 0);
+}
+
+#endif