Rename sds.{h,c} to yasl.{h,c}

1 files changed, 797 insertions, 0 deletions

diff --git a/src/yasl.c b/src/yasl.c
new file mode 100644
index 0000000..bd6d668
--- /dev/null
+++ b/src/yasl.c
@@ -0,0 +1,797 @@
+/* SDS (Simple Dynamic Strings), A C dynamic strings library.
+ *
+ * Copyright (c) 2006-2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <ctype.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "yasl.h"
+
+
+/// Initialization
+
+/* Create a new sds string with the content specified by the 'init' pointer
+ * and 'initlen'.
+ * If NULL is used for 'init' the string is initialized with zero bytes.
+ *
+ * The string is always null-termined (all the sds strings are, always) so
+ * even if you create an sds string with:
+ *
+ * mystring = sdsnew("abc", 3");
+ *
+ * You can print the string with printf() as there is an implicit \0 at the
+ * end of the string. However the string is binary safe and can contain
+ * \0 characters in the middle, as the length is stored in the sds header. */
+sds sdsnew(const void *init, size_t initlen) {
+	struct sdshdr *sh;
+
+	if (init) {
+		sh = malloc(sizeof(struct sdshdr) + initlen + 1);
+	} else {
+		sh = calloc(sizeof(struct sdshdr) + initlen + 1, 1);
+	}
+	if (sh == NULL) { return NULL; }
+
+	sh->len = initlen;
+	sh->free = 0;
+	if (initlen && init) {
+		memcpy(sh->buf, init, initlen);
+	}
+	sh->buf[initlen] = '\0';
+	return (char*)sh->buf;
+}
+
+/* Duplicate an sds string. */
+sds sdsdup(const sds s) {
+	return sdsnew(s, sdslen(s));
+}
+
+/* Create an empty (zero length) sds string. Even in this case the string
+ * always has an implicit null term. */
+sds sdsempty(void) {
+	return sdsnew("", 0);
+}
+
+/* Create an sds string from a long long value. It is much faster than:
+ *
+ * sdscatprintf(sdsempty(), "%lld\n", value);
+ */
+sds sdsfromlonglong(long long value) {
+	char buf[32], *p;
+	unsigned long long v;
+
+	v = (unsigned long long)((value < 0) ? -value : value);
+	p = buf + 31; /* point to the last character */
+	do {
+		*p-- = '0' + (v%10);
+		v /= 10;
+	} while(v);
+	if (value < 0) { *p-- = '-'; }
+	p++;
+	return sdsnew(p, (size_t)(32 - (p - buf)));
+}
+
+
+/// Querying
+
+/* Compare two sds strings s1 and s2 with memcmp().
+ *
+ * Return value:
+ *
+ *     1 if s1 > s2.
+ *    -1 if s1 < s2.
+ *     0 if s1 and s2 are exactly the same binary string.
+ *
+ * If two strings share exactly the same prefix, but one of the two has
+ * additional characters, the longer string is considered to be greater than
+ * the smaller one. */
+int sdscmp(const sds s1, const sds s2) {
+	size_t l1, l2, minlen;
+	int cmp;
+
+	l1 = sdslen(s1);
+	l2 = sdslen(s2);
+	minlen = (l1 < l2) ? l1 : l2;
+	cmp = memcmp(s1, s2, minlen);
+	if (cmp == 0) { return (int)(l1 - l2); }
+	return cmp;
+}
+
+
+/// Modification
+
+/* Modify an sds string on-place to make it empty (zero length).
+ * However all the existing buffer is not discarded but set as free space
+ * so that next append operations will not require allocations up to the
+ * number of bytes previously available. */
+void sdsclear(sds s) {
+	struct sdshdr *sh = sdsheader(s);
+	sh->free += sh->len;
+	sh->len = 0;
+	sh->buf[0] = '\0';
+}
+
+/* Grow the sds to have the specified length. Bytes that were not part of
+ * the original length of the sds will be set to zero.
+ *
+ * if the specified length is smaller than the current length, no operation
+ * is performed. */
+sds sdsgrowzero(sds s, size_t len) {
+	struct sdshdr *sh = sdsheader(s);
+	size_t totlen, curlen = sh->len;
+
+	if (len <= curlen) { return s; }
+	s = sdsMakeRoomFor(s, len - curlen);
+	if (s == NULL) { return NULL; }
+
+	/* Make sure added region doesn't contain garbage */
+	sh = sdsheader(s);
+	memset(s + curlen, 0, (len - curlen + 1)); /* also set trailing \0 byte */
+	totlen = sh->len + sh->free;
+	sh->len = len;
+	sh->free = totlen - sh->len;
+	return s;
+}
+
+/* Destructively modify the sds string 's' to hold the specified binary
+ * safe string pointed by 't' of length 'len' bytes. */
+sds sdscpylen(sds s, const char *t, size_t len) {
+	struct sdshdr *sh = sdsheader(s);
+	size_t totlen = sh->free + sh->len;
+
+	if (totlen < len) {
+		s = sdsMakeRoomFor(s, len - sh->len);
+		if (s == NULL) { return NULL; }
+		sh = sdsheader(s);
+		totlen = sh->free + sh->len;
+	}
+	memcpy(s, t, len);
+	s[len] = '\0';
+	sh->len = len;
+	sh->free = totlen - len;
+	return s;
+}
+
+/* Like sdscpylen() but 't' must be a null-termined string so that the length
+ * of the string is obtained with strlen(). */
+sds sdscpy(sds s, const char *t) {
+	return sdscpylen(s, t, strlen(t));
+}
+
+/* Join an array of C strings using the specified separator (also a C string).
+ * Returns the result as an sds string. */
+sds sdsjoin(char **argv, int argc, char *sep, size_t seplen) {
+	sds join = sdsempty();
+
+	for (int j = 0; j < argc; j++) {
+		join = sdscat(join, argv[j]);
+		if (j != argc - 1) { join = sdscatlen(join, sep, seplen); }
+	}
+	return join;
+}
+
+/* Like sdsjoin, but joins an array of SDS strings. */
+sds sdsjoinsds(sds *argv, int argc, const char *sep, size_t seplen) {
+	sds join = sdsempty();
+
+	for (int j = 0; j < argc; j++) {
+		join = sdscatsds(join, argv[j]);
+		if (j != argc - 1) { join = sdscatlen(join, sep, seplen); }
+	}
+	return join;
+}
+
+/* Modify the string substituting all the occurrences of the set of
+ * characters specified in the 'from' string to the corresponding character
+ * in the 'to' array.
+ *
+ * For instance: sdsmapchars(mystring, "ho", "01", 2)
+ * will have the effect of turning the string "hello" into "0ell1".
+ *
+ * The function returns the sds string pointer, that is always the same
+ * as the input pointer since no resize is needed. */
+sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {
+	for (size_t j = 0; j < sdslen(s); j++) {
+		for (size_t i = 0; i < setlen; i++) {
+			if (s[j] == from[i]) {
+				s[j] = to[i];
+				break;
+			}
+		}
+	}
+	return s;
+}
+
+/* Turn the string into a smaller (or equal) string containing only the
+ * substring specified by the 'start' and 'end' indexes.
+ *
+ * start and end can be negative, where -1 means the last character of the
+ * string, -2 the penultimate character, and so forth.
+ *
+ * The interval is inclusive, so the start and end characters will be part
+ * of the resulting string.
+ *
+ * The string is modified in-place.
+ *
+ * Example:
+ *
+ * s = sdsauto("Hello World");
+ * sdsrange(s, 1, -1); => "ello World"
+ */
+void sdsrange(sds s, ptrdiff_t start, ptrdiff_t end) {
+	struct sdshdr *sh = sdsheader(s);
+	size_t newlen, len = sdslen(s);
+
+	if (len == 0) { return; }
+	if (start < 0) {
+		start = (ptrdiff_t)len + start;
+		if (start < 0) { start = 0; }
+	}
+	if (end < 0) {
+		end = (ptrdiff_t)len + end;
+		if (end < 0) { end = 0; }
+	}
+	newlen = (size_t)((start > end) ? 0 : (end - start) + 1);
+	if (newlen != 0) {
+		if ((size_t)start >= len) {
+			newlen = 0;
+		} else if ((size_t)end >= len) {
+			end = (ptrdiff_t)len - 1;
+			newlen = (size_t)((start > end) ? 0 : (end - start) + 1);
+		}
+	} else {
+		start = 0;
+	}
+	if (start && newlen) { memmove(sh->buf, sh->buf + start, newlen); }
+	sh->buf[newlen] = 0;
+	sh->free = sh->free + (sh->len - newlen);
+	sh->len = newlen;
+}
+
+/* Apply tolower() to every character of the sds string 's'. */
+void sdstolower(sds s) {
+	for (size_t j = 0; j < sdslen(s); j++) {
+		s[j] = (char)tolower(s[j]);
+	}
+}
+
+/* Apply toupper() to every character of the sds string 's'. */
+void sdstoupper(sds s) {
+	for (size_t j = 0; j < sdslen(s); j++) {
+		s[j] = (char)toupper(s[j]);
+	}
+}
+
+/* Remove the part of the string from left and from right composed just of
+ * contiguous characters found in 'cset', that is a null terminted C string.
+ *
+ * After the call, the modified sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call.
+ *
+ * Example:
+ *
+ * s = sdsauto("AA...AA.a.aa.aHelloWorld     :::");
+ * s = sdstrim(s, "A. :");
+ * printf("%s\n", s);
+ *
+ * Output will be just "Hello World".
+ */
+void sdstrim(sds s, const char *cset) {
+	struct sdshdr *sh = sdsheader(s);
+	char *start, *end, *sp, *ep;
+	size_t len;
+
+	sp = start = s;
+	ep = end = s + sdslen(s) - 1;
+	while(sp <= end && strchr(cset, *sp)) { sp++; }
+	while(ep > start && strchr(cset, *ep)) { ep--; }
+	len = (size_t)((sp > ep) ? 0 : ((ep - sp) + 1));
+	if (sh->buf != sp) { memmove(sh->buf, sp, len); }
+	sh->buf[len] = '\0';
+	sh->free = sh->free + (sh->len - len);
+	sh->len = len;
+}
+
+/* Set the sds string length to the length as obtained with strlen(), so
+ * considering as content only up to the first null term character.
+ *
+ * This function is useful when the sds string is hacked manually in some
+ * way, like in the following example:
+ *
+ * s = sdsauto("foobar");
+ * s[2] = '\0';
+ * sdsupdatelen(s);
+ * printf("%d\n", sdslen(s));
+ *
+ * The output will be "2", but if we comment out the call to sdsupdatelen()
+ * the output will be "6" as the string was modified but the logical length
+ * remains 6 bytes. */
+void sdsupdatelen(sds s) {
+	struct sdshdr *sh = sdsheader(s);
+	size_t reallen = strlen(s);
+	sh->free += (sh->len - reallen);
+	sh->len = reallen;
+}
+
+/* Split a line into arguments, where every argument can be in the
+ * following programming-language REPL-alike form:
+ *
+ * foo bar "newline are supported\n" and "\xff\x00otherstuff"
+ *
+ * The number of arguments is stored into *argc, and an array
+ * of sds is returned.
+ *
+ * The caller should free the resulting array of sds strings with
+ * sdsfreesplitres().
+ *
+ * Note that sdscatrepr() is able to convert back a string into
+ * a quoted string in the same format sdssplitargs() is able to parse.
+ *
+ * The function returns the allocated tokens on success, even when the
+ * input string is empty, or NULL if the input contains unbalanced
+ * quotes or closed quotes followed by non space characters
+ * as in: "foo"bar or "foo'
+ */
+sds *sdssplitargs(const char *line, int *argc) {
+	const char *p = line;
+	char *current = NULL;
+	char **vector = NULL;
+
+	*argc = 0;
+	while(1) {
+		/* skip blanks */
+		while(*p && isspace(*p)) { p++; }
+		if (*p) {
+			/* get a token */
+			int inq=0;  /* set to 1 if we are in "quotes" */
+			int insq=0; /* set to 1 if we are in 'single quotes' */
+			int done=0;
+
+			if (current == NULL) { current = sdsempty(); }
+			while(!done) {
+				if (inq) {
+					if (*p == '\\' && *(p + 1) == 'x' &&
+					                         is_hex_digit(*(p + 2)) &&
+					                         is_hex_digit(*(p + 3)))
+					{
+						unsigned char byte;
+
+						byte = (unsigned char)((hex_digit_to_int(*(p + 2)) * 16) +
+						                        hex_digit_to_int(*(p + 3)));
+						current = sdscatlen(current, (char*)&byte, 1);
+						p += 3;
+					} else if (*p == '\\' && *(p + 1)) {
+						char c;
+
+						p++;
+						switch(*p) {
+						case 'n': c = '\n'; break;
+						case 'r': c = '\r'; break;
+						case 't': c = '\t'; break;
+						case 'b': c = '\b'; break;
+						case 'a': c = '\a'; break;
+						default: c = *p; break;
+						}
+						current = sdscatlen(current, &c, 1);
+					} else if (*p == '"') {
+						/* closing quote must be followed by a space or
+						 * nothing at all. */
+						if (*(p + 1) && !isspace(*(p + 1))) { goto err; }
+						done=1;
+					} else if (!*p) {
+						/* unterminated quotes */
+						goto err;
+					} else {
+						current = sdscatlen(current, p, 1);
+					}
+				} else if (insq) {
+					if (*p == '\\' && *(p + 1) == '\'') {
+						p++;
+						current = sdscatlen(current, "'", 1);
+					} else if (*p == '\'') {
+						/* closing quote must be followed by a space or
+						 * nothing at all. */
+						if (*(p + 1) && !isspace(*(p + 1))) { goto err; }
+						done=1;
+					} else if (!*p) {
+						/* unterminated quotes */
+						goto err;
+					} else {
+						current = sdscatlen(current, p, 1);
+					}
+				} else {
+					switch(*p) {
+					case ' ':
+					case '\n':
+					case '\r':
+					case '\t':
+					case '\0':
+						done=1;
+						break;
+					case '"':
+						inq=1;
+						break;
+					case '\'':
+						insq=1;
+						break;
+					default:
+						current = sdscatlen(current, p, 1);
+						break;
+					}
+				}
+				if (*p) { p++; }
+			}
+			/* add the token to the vector */
+			vector = realloc(vector, (unsigned long)((*argc) + 1) * (sizeof (char *)));
+			vector[*argc] = current;
+			(*argc)++;
+			current = NULL;
+		} else {
+			/* Even on empty input string return something not NULL. */
+			if (vector == NULL) { vector = malloc(sizeof(void*)); }
+			return vector;
+		}
+	}
+
+err:
+	while((*argc)--) {
+		sdsfree(vector[*argc]);
+	}
+	free(vector);
+	if (current) { sdsfree(current); }
+	*argc = 0;
+	return NULL;
+}
+
+/* Split 's' with separator in 'sep'. An array
+ * of sds strings is returned. *count will be set
+ * by reference to the number of tokens returned.
+ *
+ * On out of memory, zero length string, zero length
+ * separator, NULL is returned.
+ *
+ * Note that 'sep' is able to split a string using
+ * a multi-character separator. For example
+ * sdssplit("foo_-_bar", "_-_"); will return two
+ * elements "foo" and "bar".
+ *
+ * This version of the function is binary-safe but
+ * requires length arguments. sdssplit() is just the
+ * same function but for zero-terminated strings.
+ */
+sds *sdssplitlen(const char *s, size_t len, const char *sep, size_t seplen, size_t *count) {
+	size_t elements = 0, slots = 5, start = 0;
+	sds *tokens;
+
+	if (seplen < 1) { return NULL; }
+
+	tokens = malloc(sizeof(sds)*slots);
+	if (tokens == NULL) { return NULL; }
+
+	if (len == 0) {
+		*count = 0;
+		return tokens;
+	}
+	for (size_t j = 0; j < (len - (seplen - 1)); j++) {
+		/* make sure there is room for the next element and the final one */
+		if (slots < elements + 2) {
+			sds *newtokens;
+
+			slots *= 2;
+			newtokens = realloc(tokens, sizeof(sds) * slots);
+			if (newtokens == NULL) { goto cleanup; }
+			tokens = newtokens;
+		}
+		/* search the separator */
+		if ((seplen == 1 && *(s + j) == sep[0]) || (memcmp(s + j, sep, seplen) == 0)) {
+			tokens[elements] = sdsnew(s + start, (size_t)(j - start));
+			if (tokens[elements] == NULL) { goto cleanup; }
+			elements++;
+			start = j + seplen;
+			j = j + seplen - 1; /* skip the separator */
+		}
+	}
+	/* Add the final element. We are sure there is room in the tokens array. */
+	tokens[elements] = sdsnew(s + start, (size_t)(len - start));
+	if (tokens[elements] == NULL) { goto cleanup; }
+	elements++;
+	*count = elements;
+	return tokens;
+
+cleanup:
+	{
+		for (size_t i = 0; i < elements; i++) {
+			sdsfree(tokens[i]);
+		}
+		free(tokens);
+		*count = 0;
+		return NULL;
+	}
+}
+
+// Concatenation
+
+/* Append the specified null termianted C string to the sds string 's'.
+ *
+ * After the call, the passed sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdscat(sds s, const char *t) {
+	return sdscatlen(s, t, strlen(t));
+}
+
+/* Append the specified sds 't' to the existing sds 's'.
+ *
+ * After the call, the modified sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdscatsds(sds s, const sds t) {
+	return sdscatlen(s, t, sdslen(t));
+}
+
+/* Append the specified binary-safe string pointed by 't' of 'len' bytes to the
+ * end of the specified sds string 's'.
+ *
+ * After the call, the passed sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdscatlen(sds s, const void *t, size_t len) {
+	struct sdshdr *sh;
+	size_t curlen = sdslen(s);
+
+	s = sdsMakeRoomFor(s, len);
+	if (s == NULL) { return NULL; }
+	sh = sdsheader(s);
+	memcpy(s + curlen, t, len);
+	sh->len = curlen + len;
+	sh->free = sh->free - len;
+	s[curlen + len] = '\0';
+	return s;
+}
+
+/* Append to the sds string "s" an escaped string representation where
+ * all the non-printable characters (tested with isprint()) are turned into
+ * escapes in the form "\n\r\a...." or "\x<hex-number>".
+ *
+ * After the call, the modified sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdscatrepr(sds s, const char *p, size_t len) {
+	s = sdscatlen(s, "\"", 1);
+	while(len--) {
+		switch(*p) {
+		case '\\':
+		case '"':
+			s = sdscatprintf(s, "\\%c", *p);
+			break;
+		case '\n': s = sdscatlen(s, "\\n", 2); break;
+		case '\r': s = sdscatlen(s, "\\r", 2); break;
+		case '\t': s = sdscatlen(s, "\\t", 2); break;
+		case '\a': s = sdscatlen(s, "\\a", 2); break;
+		case '\b': s = sdscatlen(s, "\\b", 2); break;
+		default:
+			if (isprint(*p)) {
+				s = sdscatprintf(s, "%c", *p);
+			} else {
+				s = sdscatprintf(s, "\\x%02x", (unsigned char)*p);
+				break;
+			}
+		}
+		p++;
+	}
+	return sdscatlen(s, "\"", 1);
+}
+
+/* Like sdscatpritf() but gets va_list instead of being variadic. */
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+sds sdscatvprintf(sds s, const char *fmt, va_list ap) {
+	va_list cpy;
+	char *buf, *t;
+	size_t buflen = 16;
+
+	while(1) {
+		buf = malloc(buflen);
+		if (buf == NULL) { return NULL; }
+		buf[buflen - 2] = '\0';
+		va_copy(cpy, ap);
+		vsnprintf(buf, buflen, fmt, cpy);
+		if (buf[buflen - 2] != '\0') {
+			free(buf);
+			buflen *= 2;
+			continue;
+		}
+		break;
+	}
+	t = sdscat(s, buf);
+	free(buf);
+	return t;
+}
+#pragma GCC diagnostic warning "-Wformat-nonliteral"
+
+/* Append to the sds string 's' a string obtained using printf-alike format
+ * specifier.
+ *
+ * After the call, the modified sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call.
+ *
+ * Example:
+ *
+ * s = sdsempty("Sum is: ");
+ * s = sdscatprintf(s, "%d + %d = %d", a, b, a + b).
+ *
+ * Often you need to create a string from scratch with the printf-alike
+ * format. When this is the need, just use sdsempty() as the target string:
+ *
+ * s = sdscatprintf(sdsempty(), "... your format ...", args);
+ */
+sds sdscatprintf(sds s, const char *fmt, ...) {
+	va_list ap;
+	char *t;
+	va_start(ap, fmt);
+	t = sdscatvprintf(s, fmt, ap);
+	va_end(ap);
+	return t;
+}
+
+
+/// Freeing
+
+/* Free an sds string. No operation is performed if 's' is NULL. */
+void sdsfree(sds s) {
+	if (s == NULL) { return; }
+	free(sdsheader(s));
+}
+
+/* Free the result returned by sdssplitlen(), or do nothing if 'tokens' is NULL. */
+void sdsfreesplitres(sds *tokens, size_t count) {
+	if (!tokens) { return; }
+	while(count--) {
+		sdsfree(tokens[count]);
+	}
+	free(tokens);
+}
+
+
+// Low-level functions
+
+/* Return the total size of the allocation of the specifed sds string,
+ * including:
+ * 1) The sds header before the pointer.
+ * 2) The string.
+ * 3) The free buffer at the end if any.
+ * 4) The implicit null term.
+ */
+size_t sdsAllocSize(sds s) {
+	struct sdshdr *sh = sdsheader(s);
+
+	return sizeof(*sh) + sh->len + sh->free + 1;
+}
+
+/* Increment the sds length and decrements the left free space at the
+ * end of the string according to 'incr'. Also set the null term
+ * in the new end of the string.
+ *
+ * This function is used in order to fix the string length after the
+ * user calls sdsMakeRoomFor(), writes something after the end of
+ * the current string, and finally needs to set the new length.
+ *
+ * Usage example:
+ *
+ * Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the
+ * following schema, to cat bytes coming from the kernel to the end of an
+ * sds string without copying into an intermediate buffer:
+ *
+ * oldlen = sdslen(s);
+ * s = sdsMakeRoomFor(s, BUFFER_SIZE);
+ * nread = read(fd, s + oldlen, BUFFER_SIZE);
+ * ... check for nread <= 0 and handle it ...
+ * sdsIncrLen(s, nread);
+ */
+void sdsIncrLen(sds s, size_t incr) {
+	struct sdshdr *sh = sdsheader(s);
+
+	assert(sh->free >= incr);
+	sh->len += incr;
+	sh->free -= incr;
+	s[sh->len] = '\0';
+}
+
+/* Enlarge the free space at the end of the sds string so that the caller
+ * is sure that after calling this function can overwrite up to addlen
+ * bytes after the end of the string, plus one more byte for nul term.
+ *
+ * Note: this does not change the *length* of the sds string as returned
+ * by sdslen(), but only the free buffer space we have. */
+sds sdsMakeRoomFor(sds s, size_t addlen) {
+	struct sdshdr *sh, *newsh;
+	size_t free = sdsavail(s);
+	size_t len, newlen;
+
+	if (free >= addlen) { return s; }
+	len = sdslen(s);
+	sh = sdsheader(s);
+	newlen = (len + addlen);
+	if (newlen < SDS_MAX_PREALLOC) {
+		newlen *= 2;
+	} else {
+		newlen += SDS_MAX_PREALLOC;
+	}
+	newsh = realloc(sh, sizeof(struct sdshdr) + newlen + 1);
+	if (newsh == NULL) { return NULL; }
+
+	newsh->free = newlen - len;
+	return newsh->buf;
+}
+
+/* Reallocate the sds string so that it has no free space at the end. The
+ * contained string remains not altered, but next concatenation operations
+ * will require a reallocation.
+ *
+ * After the call, the passed sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdsRemoveFreeSpace(sds s) {
+	struct sdshdr *sh;
+
+	sh = sdsheader(s);
+	sh = realloc(sh, sizeof(struct sdshdr) + sh->len + 1);
+	sh->free = 0;
+	return sh->buf;
+}
+
+
+/// Low-level helper functions
+
+/* Helper function for sdssplitargs() that returns non zero if 'c'
+ * is a valid hex digit. */
+int is_hex_digit(char c) {
+	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') ||
+	       (c >= 'A' && c <= 'F');
+}
+
+/* Helper function for sdssplitargs() that converts a hex digit into an
+ * integer from 0 to 15 */
+int hex_digit_to_int(char c) {
+	switch(c) {
+	case '0': return 0;
+	case '1': return 1;
+	case '2': return 2;
+	case '3': return 3;
+	case '4': return 4;
+	case '5': return 5;
+	case '6': return 6;
+	case '7': return 7;
+	case '8': return 8;
+	case '9': return 9;
+	case 'a': case 'A': return 10;
+	case 'b': case 'B': return 11;
+	case 'c': case 'C': return 12;
+	case 'd': case 'D': return 13;
+	case 'e': case 'E': return 14;
+	case 'f': case 'F': return 15;
+	default: return 0;
+	}
+}
+