v5-0006-Control-case-mapping-behavior-with-a-method-table.patch

From eec6c3eb165f85614780374cb83ec98f09d3bd3e Mon Sep 17 00:00:00 2001
From: Jeff Davis <jeff@j-davis.com>
Date: Thu, 26 Sep 2024 12:12:51 -0700
Subject: [PATCH v5 6/8] Control case mapping behavior with a method table.

Previously, case mapping (LOWER(), INITCAP(), UPPER()) behavior
branched based on the provider.

A method table is less error-prone and easier to hook.
---
 src/backend/utils/adt/formatting.c     | 445 ++++---------------------
 src/backend/utils/adt/pg_locale.c      | 102 ++++++
 src/backend/utils/adt/pg_locale_icu.c  | 142 +++++++-
 src/backend/utils/adt/pg_locale_libc.c | 219 ++++++++++++
 src/include/utils/pg_locale.h          |  29 +-
 5 files changed, 539 insertions(+), 398 deletions(-)

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 85a7dd45619..6a0571f93e6 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1570,52 +1570,6 @@ str_numth(char *dest, char *num, int type)
  *			upper/lower/initcap functions
  *****************************************************************************/
 
-#ifdef USE_ICU
-
-typedef int32_t (*ICU_Convert_Func) (UChar *dest, int32_t destCapacity,
-									 const UChar *src, int32_t srcLength,
-									 const char *locale,
-									 UErrorCode *pErrorCode);
-
-static int32_t
-icu_convert_case(ICU_Convert_Func func, pg_locale_t mylocale,
-				 UChar **buff_dest, UChar *buff_source, int32_t len_source)
-{
-	UErrorCode	status;
-	int32_t		len_dest;
-
-	len_dest = len_source;		/* try first with same length */
-	*buff_dest = palloc(len_dest * sizeof(**buff_dest));
-	status = U_ZERO_ERROR;
-	len_dest = func(*buff_dest, len_dest, buff_source, len_source,
-					mylocale->info.icu.locale, &status);
-	if (status == U_BUFFER_OVERFLOW_ERROR)
-	{
-		/* try again with adjusted length */
-		pfree(*buff_dest);
-		*buff_dest = palloc(len_dest * sizeof(**buff_dest));
-		status = U_ZERO_ERROR;
-		len_dest = func(*buff_dest, len_dest, buff_source, len_source,
-						mylocale->info.icu.locale, &status);
-	}
-	if (U_FAILURE(status))
-		ereport(ERROR,
-				(errmsg("case conversion failed: %s", u_errorName(status))));
-	return len_dest;
-}
-
-static int32_t
-u_strToTitle_default_BI(UChar *dest, int32_t destCapacity,
-						const UChar *src, int32_t srcLength,
-						const char *locale,
-						UErrorCode *pErrorCode)
-{
-	return u_strToTitle(dest, destCapacity, src, srcLength,
-						NULL, locale, pErrorCode);
-}
-
-#endif							/* USE_ICU */
-
 /*
  * If the system provides the needed functions for wide-character manipulation
  * (which are all standardized by C99), then we implement upper/lower/initcap
@@ -1663,101 +1617,28 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-#ifdef USE_ICU
-		if (mylocale->provider == COLLPROVIDER_ICU)
+		const char *src = buff;
+		size_t		srclen = nbytes;
+		size_t		dstsize;
+		char	   *dst;
+		size_t		needed;
+
+		/* first try buffer of equal size plus terminating NUL */
+		dstsize = srclen + 1;
+		dst = palloc(dstsize);
+
+		needed = pg_strlower(dst, dstsize, src, srclen, mylocale);
+		if (needed + 1 > dstsize)
 		{
-			int32_t		len_uchar;
-			int32_t		len_conv;
-			UChar	   *buff_uchar;
-			UChar	   *buff_conv;
-
-			len_uchar = icu_to_uchar(&buff_uchar, buff, nbytes);
-			len_conv = icu_convert_case(u_strToLower, mylocale,
-										&buff_conv, buff_uchar, len_uchar);
-			icu_from_uchar(&result, buff_conv, len_conv);
-			pfree(buff_uchar);
-			pfree(buff_conv);
+			/* grow buffer if needed and retry */
+			dstsize = needed + 1;
+			dst = repalloc(dst, dstsize);
+			needed = pg_strlower(dst, dstsize, src, srclen, mylocale);
+			Assert(needed + 1 <= dstsize);
 		}
-		else
-#endif
-		if (mylocale->provider == COLLPROVIDER_BUILTIN)
-		{
-			const char *src = buff;
-			size_t		srclen = nbytes;
-			size_t		dstsize;
-			char	   *dst;
-			size_t		needed;
-
-			Assert(GetDatabaseEncoding() == PG_UTF8);
-
-			/* first try buffer of equal size plus terminating NUL */
-			dstsize = srclen + 1;
-			dst = palloc(dstsize);
-
-			needed = unicode_strlower(dst, dstsize, src, srclen);
-			if (needed + 1 > dstsize)
-			{
-				/* grow buffer if needed and retry */
-				dstsize = needed + 1;
-				dst = repalloc(dst, dstsize);
-				needed = unicode_strlower(dst, dstsize, src, srclen);
-				Assert(needed + 1 == dstsize);
-			}
-
-			Assert(dst[needed] == '\0');
-			result = dst;
-		}
-		else
-		{
-			Assert(mylocale->provider == COLLPROVIDER_LIBC);
-
-			if (pg_database_encoding_max_length() > 1)
-			{
-				wchar_t    *workspace;
-				size_t		curr_char;
-				size_t		result_size;
-
-				/* Overflow paranoia */
-				if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
-					ereport(ERROR,
-							(errcode(ERRCODE_OUT_OF_MEMORY),
-							 errmsg("out of memory")));
-
-				/* Output workspace cannot have more codes than input bytes */
-				workspace = (wchar_t *) palloc((nbytes + 1) * sizeof(wchar_t));
-
-				char2wchar(workspace, nbytes + 1, buff, nbytes, mylocale);
-
-				for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
-					workspace[curr_char] = towlower_l(workspace[curr_char], mylocale->info.lt);
 
-				/*
-				 * Make result large enough; case change might change number
-				 * of bytes
-				 */
-				result_size = curr_char * pg_database_encoding_max_length() + 1;
-				result = palloc(result_size);
-
-				wchar2char(result, workspace, result_size, mylocale);
-				pfree(workspace);
-			}
-			else
-			{
-				char	   *p;
-
-				result = pnstrdup(buff, nbytes);
-
-				/*
-				 * Note: we assume that tolower_l() will not be so broken as
-				 * to need an isupper_l() guard test.  When using the default
-				 * collation, we apply the traditional Postgres behavior that
-				 * forces ASCII-style treatment of I/i, but in non-default
-				 * collations you get exactly what the collation says.
-				 */
-				for (p = result; *p; p++)
-					*p = tolower_l((unsigned char) *p, mylocale->info.lt);
-			}
-		}
+		Assert(dst[needed] == '\0');
+		result = dst;
 	}
 
 	return result;
@@ -1800,147 +1681,33 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-#ifdef USE_ICU
-		if (mylocale->provider == COLLPROVIDER_ICU)
-		{
-			int32_t		len_uchar,
-						len_conv;
-			UChar	   *buff_uchar;
-			UChar	   *buff_conv;
-
-			len_uchar = icu_to_uchar(&buff_uchar, buff, nbytes);
-			len_conv = icu_convert_case(u_strToUpper, mylocale,
-										&buff_conv, buff_uchar, len_uchar);
-			icu_from_uchar(&result, buff_conv, len_conv);
-			pfree(buff_uchar);
-			pfree(buff_conv);
-		}
-		else
-#endif
-		if (mylocale->provider == COLLPROVIDER_BUILTIN)
+		const char *src = buff;
+		size_t		srclen = nbytes;
+		size_t		dstsize;
+		char	   *dst;
+		size_t		needed;
+
+		/* first try buffer of equal size plus terminating NUL */
+		dstsize = srclen + 1;
+		dst = palloc(dstsize);
+
+		needed = pg_strupper(dst, dstsize, src, srclen, mylocale);
+		if (needed + 1 > dstsize)
 		{
-			const char *src = buff;
-			size_t		srclen = nbytes;
-			size_t		dstsize;
-			char	   *dst;
-			size_t		needed;
-
-			Assert(GetDatabaseEncoding() == PG_UTF8);
-
-			/* first try buffer of equal size plus terminating NUL */
-			dstsize = srclen + 1;
-			dst = palloc(dstsize);
-
-			needed = unicode_strupper(dst, dstsize, src, srclen);
-			if (needed + 1 > dstsize)
-			{
-				/* grow buffer if needed and retry */
-				dstsize = needed + 1;
-				dst = repalloc(dst, dstsize);
-				needed = unicode_strupper(dst, dstsize, src, srclen);
-				Assert(needed + 1 == dstsize);
-			}
-
-			Assert(dst[needed] == '\0');
-			result = dst;
+			/* grow buffer if needed and retry */
+			dstsize = needed + 1;
+			dst = repalloc(dst, dstsize);
+			needed = pg_strupper(dst, dstsize, src, srclen, mylocale);
+			Assert(needed + 1 <= dstsize);
 		}
-		else
-		{
-			Assert(mylocale->provider == COLLPROVIDER_LIBC);
-
-			if (pg_database_encoding_max_length() > 1)
-			{
-				wchar_t    *workspace;
-				size_t		curr_char;
-				size_t		result_size;
-
-				/* Overflow paranoia */
-				if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
-					ereport(ERROR,
-							(errcode(ERRCODE_OUT_OF_MEMORY),
-							 errmsg("out of memory")));
-
-				/* Output workspace cannot have more codes than input bytes */
-				workspace = (wchar_t *) palloc((nbytes + 1) * sizeof(wchar_t));
-
-				char2wchar(workspace, nbytes + 1, buff, nbytes, mylocale);
-
-				for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
-					workspace[curr_char] = towupper_l(workspace[curr_char], mylocale->info.lt);
 
-				/*
-				 * Make result large enough; case change might change number
-				 * of bytes
-				 */
-				result_size = curr_char * pg_database_encoding_max_length() + 1;
-				result = palloc(result_size);
-
-				wchar2char(result, workspace, result_size, mylocale);
-				pfree(workspace);
-			}
-			else
-			{
-				char	   *p;
-
-				result = pnstrdup(buff, nbytes);
-
-				/*
-				 * Note: we assume that toupper_l() will not be so broken as
-				 * to need an islower_l() guard test.  When using the default
-				 * collation, we apply the traditional Postgres behavior that
-				 * forces ASCII-style treatment of I/i, but in non-default
-				 * collations you get exactly what the collation says.
-				 */
-				for (p = result; *p; p++)
-					*p = toupper_l((unsigned char) *p, mylocale->info.lt);
-			}
-		}
+		Assert(dst[needed] == '\0');
+		result = dst;
 	}
 
 	return result;
 }
 
-struct WordBoundaryState
-{
-	const char *str;
-	size_t		len;
-	size_t		offset;
-	bool		init;
-	bool		prev_alnum;
-};
-
-/*
- * Simple word boundary iterator that draws boundaries each time the result of
- * pg_u_isalnum() changes.
- */
-static size_t
-initcap_wbnext(void *state)
-{
-	struct WordBoundaryState *wbstate = (struct WordBoundaryState *) state;
-
-	while (wbstate->offset < wbstate->len &&
-		   wbstate->str[wbstate->offset] != '\0')
-	{
-		pg_wchar	u = utf8_to_unicode((unsigned char *) wbstate->str +
-										wbstate->offset);
-		bool		curr_alnum = pg_u_isalnum(u, true);
-
-		if (!wbstate->init || curr_alnum != wbstate->prev_alnum)
-		{
-			size_t		prev_offset = wbstate->offset;
-
-			wbstate->init = true;
-			wbstate->offset += unicode_utf8len(u);
-			wbstate->prev_alnum = curr_alnum;
-			return prev_offset;
-		}
-
-		wbstate->offset += unicode_utf8len(u);
-	}
-
-	return wbstate->len;
-}
-
 /*
  * collation-aware, wide-character-aware initcap function
  *
@@ -1951,7 +1718,6 @@ char *
 str_initcap(const char *buff, size_t nbytes, Oid collid)
 {
 	char	   *result;
-	int			wasalnum = false;
 	pg_locale_t mylocale;
 
 	if (!buff)
@@ -1979,125 +1745,28 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-#ifdef USE_ICU
-		if (mylocale->provider == COLLPROVIDER_ICU)
+		const char *src = buff;
+		size_t		srclen = nbytes;
+		size_t		dstsize;
+		char	   *dst;
+		size_t		needed;
+
+		/* first try buffer of equal size plus terminating NUL */
+		dstsize = srclen + 1;
+		dst = palloc(dstsize);
+
+		needed = pg_strtitle(dst, dstsize, src, srclen, mylocale);
+		if (needed + 1 > dstsize)
 		{
-			int32_t		len_uchar,
-						len_conv;
-			UChar	   *buff_uchar;
-			UChar	   *buff_conv;
-
-			len_uchar = icu_to_uchar(&buff_uchar, buff, nbytes);
-			len_conv = icu_convert_case(u_strToTitle_default_BI, mylocale,
-										&buff_conv, buff_uchar, len_uchar);
-			icu_from_uchar(&result, buff_conv, len_conv);
-			pfree(buff_uchar);
-			pfree(buff_conv);
+			/* grow buffer if needed and retry */
+			dstsize = needed + 1;
+			dst = repalloc(dst, dstsize);
+			needed = pg_strtitle(dst, dstsize, src, srclen, mylocale);
+			Assert(needed + 1 <= dstsize);
 		}
-		else
-#endif
-		if (mylocale->provider == COLLPROVIDER_BUILTIN)
-		{
-			const char *src = buff;
-			size_t		srclen = nbytes;
-			size_t		dstsize;
-			char	   *dst;
-			size_t		needed;
-			struct WordBoundaryState wbstate = {
-				.str = src,
-				.len = srclen,
-				.offset = 0,
-				.init = false,
-				.prev_alnum = false,
-			};
-
-			Assert(GetDatabaseEncoding() == PG_UTF8);
-
-			/* first try buffer of equal size plus terminating NUL */
-			dstsize = srclen + 1;
-			dst = palloc(dstsize);
-
-			needed = unicode_strtitle(dst, dstsize, src, srclen,
-									  initcap_wbnext, &wbstate);
-			if (needed + 1 > dstsize)
-			{
-				/* reset iterator */
-				wbstate.offset = 0;
-				wbstate.init = false;
-
-				/* grow buffer if needed and retry */
-				dstsize = needed + 1;
-				dst = repalloc(dst, dstsize);
-				needed = unicode_strtitle(dst, dstsize, src, srclen,
-										  initcap_wbnext, &wbstate);
-				Assert(needed + 1 == dstsize);
-			}
-
-			result = dst;
-		}
-		else
-		{
-			Assert(mylocale->provider == COLLPROVIDER_LIBC);
-
-			if (pg_database_encoding_max_length() > 1)
-			{
-				wchar_t    *workspace;
-				size_t		curr_char;
-				size_t		result_size;
-
-				/* Overflow paranoia */
-				if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
-					ereport(ERROR,
-							(errcode(ERRCODE_OUT_OF_MEMORY),
-							 errmsg("out of memory")));
-
-				/* Output workspace cannot have more codes than input bytes */
-				workspace = (wchar_t *) palloc((nbytes + 1) * sizeof(wchar_t));
-
-				char2wchar(workspace, nbytes + 1, buff, nbytes, mylocale);
-
-				for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
-				{
-					if (wasalnum)
-						workspace[curr_char] = towlower_l(workspace[curr_char], mylocale->info.lt);
-					else
-						workspace[curr_char] = towupper_l(workspace[curr_char], mylocale->info.lt);
-					wasalnum = iswalnum_l(workspace[curr_char], mylocale->info.lt);
-				}
-
-				/*
-				 * Make result large enough; case change might change number
-				 * of bytes
-				 */
-				result_size = curr_char * pg_database_encoding_max_length() + 1;
-				result = palloc(result_size);
-
-				wchar2char(result, workspace, result_size, mylocale);
-				pfree(workspace);
-			}
-			else
-			{
-				char	   *p;
 
-				result = pnstrdup(buff, nbytes);
-
-				/*
-				 * Note: we assume that toupper_l()/tolower_l() will not be so
-				 * broken as to need guard tests.  When using the default
-				 * collation, we apply the traditional Postgres behavior that
-				 * forces ASCII-style treatment of I/i, but in non-default
-				 * collations you get exactly what the collation says.
-				 */
-				for (p = result; *p; p++)
-				{
-					if (wasalnum)
-						*p = tolower_l((unsigned char) *p, mylocale->info.lt);
-					else
-						*p = toupper_l((unsigned char) *p, mylocale->info.lt);
-					wasalnum = isalnum_l((unsigned char) *p, mylocale->info.lt);
-				}
-			}
-		}
+		Assert(dst[needed] == '\0');
+		result = dst;
 	}
 
 	return result;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index dfb9c3bd952..a106478b119 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -58,6 +58,8 @@
 #include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "common/hashfn.h"
+#include "common/unicode_case.h"
+#include "common/unicode_category.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "utils/builtins.h"
@@ -170,6 +172,83 @@ static pg_locale_t last_collation_cache_locale = NULL;
 static char *IsoLocaleName(const char *);
 #endif
 
+struct WordBoundaryState
+{
+	const char *str;
+	size_t		len;
+	size_t		offset;
+	bool		init;
+	bool		prev_alnum;
+};
+
+/*
+ * Simple word boundary iterator that draws boundaries each time the result of
+ * pg_u_isalnum() changes.
+ */
+static size_t
+initcap_wbnext(void *state)
+{
+	struct WordBoundaryState *wbstate = (struct WordBoundaryState *) state;
+
+	while (wbstate->offset < wbstate->len &&
+		   wbstate->str[wbstate->offset] != '\0')
+	{
+		pg_wchar	u = utf8_to_unicode((unsigned char *) wbstate->str +
+										wbstate->offset);
+		bool		curr_alnum = pg_u_isalnum(u, true);
+
+		if (!wbstate->init || curr_alnum != wbstate->prev_alnum)
+		{
+			size_t		prev_offset = wbstate->offset;
+
+			wbstate->init = true;
+			wbstate->offset += unicode_utf8len(u);
+			wbstate->prev_alnum = curr_alnum;
+			return prev_offset;
+		}
+
+		wbstate->offset += unicode_utf8len(u);
+	}
+
+	return wbstate->len;
+}
+
+static size_t
+strlower_builtin(char *dest, size_t destsize, const char *src, ssize_t srclen,
+				 pg_locale_t locale)
+{
+	return unicode_strlower(dest, destsize, src, srclen);
+}
+
+static size_t
+strtitle_builtin(char *dest, size_t destsize, const char *src, ssize_t srclen,
+				 pg_locale_t locale)
+{
+	struct WordBoundaryState wbstate = {
+		.str = src,
+		.len = srclen,
+		.offset = 0,
+		.init = false,
+		.prev_alnum = false,
+	};
+
+	return unicode_strtitle(dest, destsize, src, srclen,
+							initcap_wbnext, &wbstate);
+}
+
+static size_t
+strupper_builtin(char *dest, size_t destsize, const char *src, ssize_t srclen,
+				 pg_locale_t locale)
+{
+	return unicode_strupper(dest, destsize, src, srclen);
+}
+
+static struct casemap_methods casemap_methods_builtin = {
+	.strlower = strlower_builtin,
+	.strtitle = strtitle_builtin,
+	.strupper = strupper_builtin,
+};
+
 /*
  * POSIX doesn't define _l-variants of these functions, but several systems
  * have them.  We provide our own replacements here.
@@ -1239,6 +1318,7 @@ dat_create_locale_builtin(HeapTuple dattuple)
 	result->deterministic = true;
 	result->collate_is_c = true;
 	result->ctype_is_c = (strcmp(locstr, "C") == 0);
+	result->casemap = &casemap_methods_builtin;
 
 	return result;
 }
@@ -1265,6 +1345,7 @@ coll_create_locale_builtin(HeapTuple colltuple, MemoryContext context)
 	result->deterministic = collform->collisdeterministic;
 	result->collate_is_c = true;
 	result->ctype_is_c = (strcmp(locstr, "C") == 0);
+	result->casemap = &casemap_methods_builtin;
 
 	return result;
 }
@@ -1537,6 +1618,27 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 	return collversion;
 }
 
+size_t
+pg_strlower(char *dst, size_t dstsize, const char *src, ssize_t srclen,
+			pg_locale_t locale)
+{
+	return locale->casemap->strlower(dst, dstsize, src, srclen, locale);
+}
+
+size_t
+pg_strtitle(char *dst, size_t dstsize, const char *src, ssize_t srclen,
+			pg_locale_t locale)
+{
+	return locale->casemap->strtitle(dst, dstsize, src, srclen, locale);
+}
+
+size_t
+pg_strupper(char *dst, size_t dstsize, const char *src, ssize_t srclen,
+			pg_locale_t locale)
+{
+	return locale->casemap->strupper(dst, dstsize, src, srclen, locale);
+}
+
 /*
  * pg_strcoll
  *
diff --git a/src/backend/utils/adt/pg_locale_icu.c b/src/backend/utils/adt/pg_locale_icu.c
index e53bf2d4b33..97e96d5b9fb 100644
--- a/src/backend/utils/adt/pg_locale_icu.c
+++ b/src/backend/utils/adt/pg_locale_icu.c
@@ -51,6 +51,11 @@ static size_t strnxfrm_prefix_icu(char *dest, size_t destsize,
 								  const char *src, ssize_t srclen,
 								  pg_locale_t locale);
 
+typedef int32_t (*ICU_Convert_Func) (UChar *dest, int32_t destCapacity,
+									 const UChar *src, int32_t srcLength,
+									 const char *locale,
+									 UErrorCode *pErrorCode);
+
 /*
  * Converter object for converting between ICU's UChar strings and C strings
  * in database encoding.  Since the database encoding doesn't change, we only
@@ -60,9 +65,20 @@ static UConverter *icu_converter = NULL;
 
 static UCollator *make_icu_collator(const char *iculocstr,
 									const char *icurules);
+
+static size_t strlower_icu(char *dest, size_t destsize,
+						   const char *src, ssize_t srclen,
+						   pg_locale_t locale);
+static size_t strtitle_icu(char *dest, size_t destsize,
+						   const char *src, ssize_t srclen,
+						   pg_locale_t locale);
+static size_t strupper_icu(char *dest, size_t destsize,
+						   const char *src, ssize_t srclen,
+						   pg_locale_t locale);
 static int	strncoll_icu_no_utf8(const char *arg1, ssize_t len1,
 								 const char *arg2, ssize_t len2,
 								 pg_locale_t locale);
+
 static size_t strnxfrm_prefix_icu_no_utf8(char *dest, size_t destsize,
 										  const char *src, ssize_t srclen,
 										  pg_locale_t locale);
@@ -72,8 +88,19 @@ static size_t uchar_length(UConverter *converter,
 static int32_t uchar_convert(UConverter *converter,
 							 UChar *dest, int32_t destlen,
 							 const char *src, int32_t srclen);
+static int32_t icu_to_uchar(UChar **buff_uchar, const char *buff,
+							size_t nbytes);
+static size_t icu_from_uchar(char *dest, size_t destsize,
+							 const UChar *buff_uchar, int32_t len_uchar);
 static void icu_set_collation_attributes(UCollator *collator, const char *loc,
 										 UErrorCode *status);
+static int32_t icu_convert_case(ICU_Convert_Func func, pg_locale_t mylocale,
+								UChar **buff_dest, UChar *buff_source,
+								int32_t len_source);
+static int32_t u_strToTitle_default_BI(UChar *dest, int32_t destCapacity,
+									   const UChar *src, int32_t srcLength,
+									   const char *locale,
+									   UErrorCode *pErrorCode);
 
 static struct collate_methods collate_methods_icu = {
 	.strncoll = strncoll_icu,
@@ -82,6 +109,11 @@ static struct collate_methods collate_methods_icu = {
 	.strxfrm_is_safe = true,
 };
 
+static struct casemap_methods casemap_methods_icu = {
+	.strlower = strlower_icu,
+	.strtitle = strtitle_icu,
+	.strupper = strupper_icu,
+};
 #endif
 
 pg_locale_t
@@ -118,6 +150,7 @@ dat_create_locale_icu(HeapTuple dattuple)
 	result->collate_is_c = false;
 	result->ctype_is_c = false;
 	result->collate = &collate_methods_icu;
+	result->casemap = &casemap_methods_icu;
 
 	return result;
 #else
@@ -163,6 +196,7 @@ coll_create_locale_icu(HeapTuple colltuple, MemoryContext context)
 	result->collate_is_c = false;
 	result->ctype_is_c = false;
 	result->collate = &collate_methods_icu;
+	result->casemap = &casemap_methods_icu;
 
 	return result;
 #else
@@ -336,6 +370,66 @@ make_icu_collator(const char *iculocstr, const char *icurules)
 	}
 }
 
+static size_t
+strlower_icu(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			 pg_locale_t locale)
+{
+	int32_t		len_uchar;
+	int32_t		len_conv;
+	UChar	   *buff_uchar;
+	UChar	   *buff_conv;
+	size_t		result_len;
+
+	len_uchar = icu_to_uchar(&buff_uchar, src, srclen);
+	len_conv = icu_convert_case(u_strToLower, locale,
+								&buff_conv, buff_uchar, len_uchar);
+	result_len = icu_from_uchar(dest, destsize, buff_conv, len_conv);
+	pfree(buff_uchar);
+	pfree(buff_conv);
+
+	return result_len;
+}
+
+static size_t
+strtitle_icu(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			 pg_locale_t locale)
+{
+	int32_t		len_uchar;
+	int32_t		len_conv;
+	UChar	   *buff_uchar;
+	UChar	   *buff_conv;
+	size_t		result_len;
+
+	len_uchar = icu_to_uchar(&buff_uchar, src, srclen);
+	len_conv = icu_convert_case(u_strToTitle_default_BI, locale,
+								&buff_conv, buff_uchar, len_uchar);
+	result_len = icu_from_uchar(dest, destsize, buff_conv, len_conv);
+	pfree(buff_uchar);
+	pfree(buff_conv);
+
+	return result_len;
+}
+
+static size_t
+strupper_icu(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			 pg_locale_t locale)
+{
+	int32_t		len_uchar;
+	int32_t		len_conv;
+	UChar	   *buff_uchar;
+	UChar	   *buff_conv;
+	size_t		result_len;
+
+	len_uchar = icu_to_uchar(&buff_uchar, src, srclen);
+	len_conv = icu_convert_case(u_strToUpper, locale,
+								&buff_conv, buff_uchar, len_uchar);
+	result_len = icu_from_uchar(dest, destsize, buff_conv, len_conv);
+	pfree(buff_uchar);
+	pfree(buff_conv);
+
+	return result_len;
+}
+
 /*
  * strncoll_icu
  *
@@ -470,7 +564,7 @@ strnxfrm_prefix_icu(char *dest, size_t destsize,
  * The result string is nul-terminated, though most callers rely on the
  * result length instead.
  */
-int32_t
+static int32_t
 icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes)
 {
 	int32_t		len_uchar;
@@ -497,8 +591,8 @@ icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes)
  *
  * The result string is nul-terminated.
  */
-int32_t
-icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar)
+static size_t
+icu_from_uchar(char *dest, size_t destsize, const UChar *buff_uchar, int32_t len_uchar)
 {
 	UErrorCode	status;
 	int32_t		len_result;
@@ -513,10 +607,11 @@ icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar)
 				(errmsg("%s failed: %s", "ucnv_fromUChars",
 						u_errorName(status))));
 
-	*result = palloc(len_result + 1);
+	if (len_result + 1 > destsize)
+		return len_result;
 
 	status = U_ZERO_ERROR;
-	len_result = ucnv_fromUChars(icu_converter, *result, len_result + 1,
+	len_result = ucnv_fromUChars(icu_converter, dest, len_result + 1,
 								 buff_uchar, len_uchar, &status);
 	if (U_FAILURE(status) ||
 		status == U_STRING_NOT_TERMINATED_WARNING)
@@ -527,6 +622,43 @@ icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar)
 	return len_result;
 }
 
+static int32_t
+icu_convert_case(ICU_Convert_Func func, pg_locale_t mylocale,
+				 UChar **buff_dest, UChar *buff_source, int32_t len_source)
+{
+	UErrorCode	status;
+	int32_t		len_dest;
+
+	len_dest = len_source;		/* try first with same length */
+	*buff_dest = palloc(len_dest * sizeof(**buff_dest));
+	status = U_ZERO_ERROR;
+	len_dest = func(*buff_dest, len_dest, buff_source, len_source,
+					mylocale->info.icu.locale, &status);
+	if (status == U_BUFFER_OVERFLOW_ERROR)
+	{
+		/* try again with adjusted length */
+		pfree(*buff_dest);
+		*buff_dest = palloc(len_dest * sizeof(**buff_dest));
+		status = U_ZERO_ERROR;
+		len_dest = func(*buff_dest, len_dest, buff_source, len_source,
+						mylocale->info.icu.locale, &status);
+	}
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("case conversion failed: %s", u_errorName(status))));
+	return len_dest;
+}
+
+static int32_t
+u_strToTitle_default_BI(UChar *dest, int32_t destCapacity,
+						const UChar *src, int32_t srcLength,
+						const char *locale,
+						UErrorCode *pErrorCode)
+{
+	return u_strToTitle(dest, destCapacity, src, srcLength,
+						NULL, locale, pErrorCode);
+}
+
 /*
  * strncoll_icu_no_utf8
  *
diff --git a/src/backend/utils/adt/pg_locale_libc.c b/src/backend/utils/adt/pg_locale_libc.c
index b8ccd24715d..79828ab3524 100644
--- a/src/backend/utils/adt/pg_locale_libc.c
+++ b/src/backend/utils/adt/pg_locale_libc.c
@@ -11,6 +11,9 @@
 
 #include "postgres.h"
 
+#include <limits.h>
+#include <wctype.h>
+
 #include "access/htup_details.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_collation.h"
@@ -48,6 +51,16 @@ static int	strncoll_libc_win32_utf8(const char *arg1, ssize_t len1,
 									 pg_locale_t locale);
 #endif
 
+static size_t strlower_libc(char *dest, size_t destsize,
+							const char *src, ssize_t srclen,
+							pg_locale_t locale);
+static size_t strtitle_libc(char *dest, size_t destsize,
+							const char *src, ssize_t srclen,
+							pg_locale_t locale);
+static size_t strupper_libc(char *dest, size_t destsize,
+							const char *src, ssize_t srclen,
+							pg_locale_t locale);
+
 static struct collate_methods collate_methods_libc = {
 	.strncoll = strncoll_libc,
 	.strnxfrm = strnxfrm_libc,
@@ -69,6 +82,208 @@ static struct collate_methods collate_methods_libc = {
 #endif
 };
 
+static struct casemap_methods casemap_methods_libc = {
+	.strlower = strlower_libc,
+	.strtitle = strtitle_libc,
+	.strupper = strupper_libc,
+};
+
+static size_t
+strlower_libc(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			  pg_locale_t locale)
+{
+	locale_t	loc = locale->info.lt;
+	size_t		result_size;
+
+	if (pg_database_encoding_max_length() > 1)
+	{
+		wchar_t    *workspace;
+		size_t		curr_char;
+
+		/* Overflow paranoia */
+		if ((srclen + 1) > (INT_MAX / sizeof(wchar_t)))
+			ereport(ERROR,
+					(errcode(ERRCODE_OUT_OF_MEMORY),
+					 errmsg("out of memory")));
+
+		/* Output workspace cannot have more codes than input bytes */
+		workspace = (wchar_t *) palloc((srclen + 1) * sizeof(wchar_t));
+
+		char2wchar(workspace, srclen + 1, src, srclen, locale);
+
+		for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
+			workspace[curr_char] = towlower_l(workspace[curr_char], loc);
+
+		/*
+		 * Make result large enough; case change might change number of bytes
+		 */
+		result_size = curr_char * pg_database_encoding_max_length();
+		if (result_size + 1 > destsize)
+			return result_size;
+
+		wchar2char(dest, workspace, result_size + 1, locale);
+		pfree(workspace);
+	}
+	else
+	{
+		char	   *p;
+
+		result_size = srclen;
+		if (result_size + 1 > destsize)
+			return result_size;
+
+		strlcpy(dest, src, result_size + 1);
+
+		/*
+		 * Note: we assume that tolower_l() will not be so broken as to need
+		 * an isupper_l() guard test.  When using the default collation, we
+		 * apply the traditional Postgres behavior that forces ASCII-style
+		 * treatment of I/i, but in non-default collations you get exactly
+		 * what the collation says.
+		 */
+		for (p = dest; *p; p++)
+			*p = tolower_l((unsigned char) *p, loc);
+	}
+
+	result_size = strlen(dest);
+	return result_size;
+}
+
+static size_t
+strtitle_libc(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			  pg_locale_t locale)
+{
+	locale_t	loc = locale->info.lt;
+	int			wasalnum = false;
+	size_t		result_size;
+
+	if (pg_database_encoding_max_length() > 1)
+	{
+		wchar_t    *workspace;
+		size_t		curr_char;
+
+		/* Overflow paranoia */
+		if ((srclen + 1) > (INT_MAX / sizeof(wchar_t)))
+			ereport(ERROR,
+					(errcode(ERRCODE_OUT_OF_MEMORY),
+					 errmsg("out of memory")));
+
+		/* Output workspace cannot have more codes than input bytes */
+		workspace = (wchar_t *) palloc((srclen + 1) * sizeof(wchar_t));
+
+		char2wchar(workspace, srclen + 1, src, srclen, locale);
+
+		for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
+		{
+			if (wasalnum)
+				workspace[curr_char] = towlower_l(workspace[curr_char], loc);
+			else
+				workspace[curr_char] = towupper_l(workspace[curr_char], loc);
+			wasalnum = iswalnum_l(workspace[curr_char], loc);
+		}
+
+		/*
+		 * Make result large enough; case change might change number of bytes
+		 */
+		result_size = curr_char * pg_database_encoding_max_length();
+
+		if (result_size + 1 > destsize)
+			return result_size;
+
+		wchar2char(dest, workspace, result_size + 1, locale);
+		pfree(workspace);
+	}
+	else
+	{
+		char	   *p;
+
+		if (srclen + 1 > destsize)
+			return srclen;
+
+		strlcpy(dest, src, srclen + 1);
+
+		/*
+		 * Note: we assume that toupper_l()/tolower_l() will not be so broken
+		 * as to need guard tests.  When using the default collation, we apply
+		 * the traditional Postgres behavior that forces ASCII-style treatment
+		 * of I/i, but in non-default collations you get exactly what the
+		 * collation says.
+		 */
+		for (p = dest; *p; p++)
+		{
+			if (wasalnum)
+				*p = tolower_l((unsigned char) *p, loc);
+			else
+				*p = toupper_l((unsigned char) *p, loc);
+			wasalnum = isalnum_l((unsigned char) *p, loc);
+		}
+	}
+
+	result_size = strlen(dest);
+	return result_size;
+}
+
+static size_t
+strupper_libc(char *dest, size_t destsize, const char *src, ssize_t srclen,
+			  pg_locale_t locale)
+{
+	locale_t	loc = locale->info.lt;
+	size_t		result_size;
+
+	if (pg_database_encoding_max_length() > 1)
+	{
+		wchar_t    *workspace;
+		size_t		curr_char;
+
+		/* Overflow paranoia */
+		if ((srclen + 1) > (INT_MAX / sizeof(wchar_t)))
+			ereport(ERROR,
+					(errcode(ERRCODE_OUT_OF_MEMORY),
+					 errmsg("out of memory")));
+
+		/* Output workspace cannot have more codes than input bytes */
+		workspace = (wchar_t *) palloc((srclen + 1) * sizeof(wchar_t));
+
+		char2wchar(workspace, srclen + 1, src, srclen, locale);
+
+		for (curr_char = 0; workspace[curr_char] != 0; curr_char++)
+			workspace[curr_char] = towupper_l(workspace[curr_char], loc);
+
+		/*
+		 * Make result large enough; case change might change number of bytes
+		 */
+		result_size = curr_char * pg_database_encoding_max_length();
+		if (result_size + 1 > destsize)
+			return result_size;
+
+		wchar2char(dest, workspace, result_size + 1, locale);
+		pfree(workspace);
+	}
+	else
+	{
+		char	   *p;
+
+		result_size = srclen;
+		if (result_size + 1 > destsize)
+			return result_size;
+
+		strlcpy(dest, src, srclen + 1);
+
+		/*
+		 * Note: we assume that toupper_l() will not be so broken as to need
+		 * an islower_l() guard test.  When using the default collation, we
+		 * apply the traditional Postgres behavior that forces ASCII-style
+		 * treatment of I/i, but in non-default collations you get exactly
+		 * what the collation says.
+		 */
+		for (p = dest; *p; p++)
+			*p = toupper_l((unsigned char) *p, loc);
+	}
+
+	result_size = strlen(dest);
+	return result_size;
+}
+
 pg_locale_t
 dat_create_locale_libc(HeapTuple dattuple)
 {
@@ -102,6 +317,8 @@ dat_create_locale_libc(HeapTuple dattuple)
 	result->info.lt = loc;
 	if (!result->collate_is_c)
 		result->collate = &collate_methods_libc;
+	if (!result->ctype_is_c)
+		result->casemap = &casemap_methods_libc;
 
 	return result;
 }
@@ -137,6 +354,8 @@ coll_create_locale_libc(HeapTuple colltuple, MemoryContext context)
 	result->info.lt = loc;
 	if (!result->collate_is_c)
 		result->collate = &collate_methods_libc;
+	if (!result->ctype_is_c)
+		result->casemap = &casemap_methods_libc;
 
 	return result;
 }
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 6c2a0456f22..4bd9e6de7a3 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -93,6 +93,20 @@ struct collate_methods
 	bool		strxfrm_is_safe;
 };
 
+/* methods that define string case mapping behavior */
+struct casemap_methods
+{
+	size_t		(*strlower) (char *dest, size_t destsize,
+							 const char *src, ssize_t srclen,
+							 pg_locale_t locale);
+	size_t		(*strtitle) (char *dest, size_t destsize,
+							 const char *src, ssize_t srclen,
+							 pg_locale_t locale);
+	size_t		(*strupper) (char *dest, size_t destsize,
+							 const char *src, ssize_t srclen,
+							 pg_locale_t locale);
+};
+
 /*
  * We use a discriminated union to hold either a locale_t or an ICU collator.
  * pg_locale_t is occasionally checked for truth, so make it a pointer.
@@ -117,6 +131,7 @@ struct pg_locale_struct
 	bool		ctype_is_c;
 
 	struct collate_methods *collate;	/* NULL if collate_is_c */
+	struct casemap_methods *casemap;	/* NULL if ctype_is_c */
 
 	union
 	{
@@ -141,6 +156,15 @@ extern void init_database_collation(void);
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
+extern size_t pg_strlower(char *dest, size_t destsize,
+						  const char *src, ssize_t srclen,
+						  pg_locale_t locale);
+extern size_t pg_strtitle(char *dest, size_t destsize,
+						  const char *src, ssize_t srclen,
+						  pg_locale_t locale);
+extern size_t pg_strupper(char *dest, size_t destsize,
+						  const char *src, ssize_t srclen,
+						  pg_locale_t locale);
 extern int	pg_strcoll(const char *arg1, const char *arg2, pg_locale_t locale);
 extern int	pg_strncoll(const char *arg1, ssize_t len1,
 						const char *arg2, ssize_t len2, pg_locale_t locale);
@@ -160,11 +184,6 @@ extern const char *builtin_validate_locale(int encoding, const char *locale);
 extern void icu_validate_locale(const char *loc_str);
 extern char *icu_language_tag(const char *loc_str, int elevel);
 
-#ifdef USE_ICU
-extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
-extern int32_t icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar);
-#endif
-
 /* These functions convert from/to libc's wchar_t, *not* pg_wchar_t */
 extern size_t wchar2char(char *to, const wchar_t *from, size_t tolen,
 						 pg_locale_t locale);
-- 
2.34.1