patch 9.1.1016: Not possible to convert string2blob and blob2string

Problem:  Not possible to convert string2blob and blob2string
Solution: add support for the blob2str() and str2blob() functions

closes: #16373

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/errors.h b/src/errors.h
index 2811a32..6bab826 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3657,3 +3657,5 @@
 	INIT(= N_("E1513: Cannot switch buffer. 'winfixbuf' is enabled"));
 EXTERN char e_invalid_return_type_from_findfunc[]
 	INIT(= N_("E1514: 'findfunc' did not return a List type"));
+EXTERN char e_str_encoding_failed[]
+	INIT(= N_("E1515: Unable to convert %s '%s' encoding"));
diff --git a/src/evalfunc.c b/src/evalfunc.c
index ef30792..6314252 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1151,6 +1151,7 @@
 static argcheck_T arg2_string_or_list_dict[] = {arg_string_or_list_any, arg_dict_any};
 static argcheck_T arg2_string_or_list_number[] = {arg_string_or_list_any, arg_number};
 static argcheck_T arg2_string_string_or_number[] = {arg_string, arg_string_or_nr};
+static argcheck_T arg2_blob_dict[] = {arg_blob, arg_dict_any};
 static argcheck_T arg3_any_list_dict[] = {arg_any, arg_list_any, arg_dict_any};
 static argcheck_T arg3_buffer_lnum_lnum[] = {arg_buffer, arg_lnum, arg_lnum};
 static argcheck_T arg3_buffer_number_number[] = {arg_buffer, arg_number, arg_number};
@@ -1844,6 +1845,8 @@
 			ret_bool,	    f_bindtextdomain},
     {"blob2list",	1, 1, FEARG_1,	    arg1_blob,
 			ret_list_number,    f_blob2list},
+    {"blob2str",	1, 2, FEARG_1,	    arg2_blob_dict,
+			ret_string,	    f_blob2str},
     {"browse",		4, 4, 0,	    arg4_browse,
 			ret_string,	    f_browse},
     {"browsedir",	2, 2, 0,	    arg2_string,
@@ -2710,6 +2713,8 @@
 			ret_list_number,    f_srand},
     {"state",		0, 1, FEARG_1,	    arg1_string,
 			ret_string,	    f_state},
+    {"str2blob",	1, 2, FEARG_1,	    arg2_string_dict,
+			ret_blob,	    f_str2blob},
     {"str2float",	1, 2, FEARG_1,	    arg2_string_bool,
 			ret_float,	    f_str2float},
     {"str2list",	1, 2, FEARG_1,	    arg2_string_bool,
diff --git a/src/mbyte.c b/src/mbyte.c
index 4a7eada..1570182 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -2107,6 +2107,17 @@
 }
 
 /*
+ * Return length of UTF-8 character, obtained from the first byte.
+ * "b" must be between 0 and 255!
+ * Returns 0 for an invalid first byte value.
+ */
+    int
+utf_byte2len_zero(int b)
+{
+    return utf8len_tab_zero[b];
+}
+
+/*
  * Get the length of UTF-8 byte sequence "p[size]".  Does not include any
  * following composing characters.
  * Returns 1 for "".
diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index bb976e3..7061bab 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -31,6 +31,7 @@
 int utfc_char2bytes(int off, char_u *buf);
 int utf_ptr2len(char_u *p);
 int utf_byte2len(int b);
+int utf_byte2len_zero(int b);
 int utf_ptr2len_len(char_u *p, int size);
 int utfc_ptr2len(char_u *p);
 int utfc_ptr2len_len(char_u *p, int size);
diff --git a/src/proto/strings.pro b/src/proto/strings.pro
index c25555f..ddc53cc 100644
--- a/src/proto/strings.pro
+++ b/src/proto/strings.pro
@@ -31,6 +31,8 @@
 void f_byteidx(typval_T *argvars, typval_T *rettv);
 void f_byteidxcomp(typval_T *argvars, typval_T *rettv);
 void f_charidx(typval_T *argvars, typval_T *rettv);
+void f_blob2str(typval_T *argvars, typval_T *rettv);
+void f_str2blob(typval_T *argvars, typval_T *rettv);
 void f_str2list(typval_T *argvars, typval_T *rettv);
 void f_str2nr(typval_T *argvars, typval_T *rettv);
 void f_strgetchar(typval_T *argvars, typval_T *rettv);
diff --git a/src/strings.c b/src/strings.c
index 54ac178..c26914d 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -1214,6 +1214,146 @@
 }
 
 /*
+ * Convert the string "str", from encoding "from" to encoding "to".
+ */
+    static char_u *
+convert_string(char_u *str, char_u *from, char_u *to)
+{
+    vimconv_T	vimconv;
+
+    vimconv.vc_type = CONV_NONE;
+    if (convert_setup(&vimconv, from, to) == FAIL)
+	return NULL;
+    vimconv.vc_fail = TRUE;
+    if (vimconv.vc_type == CONV_NONE)
+	str = vim_strsave(str);
+    else
+	str = string_convert(&vimconv, str, NULL);
+    convert_setup(&vimconv, NULL, NULL);
+
+    return str;
+}
+
+/*
+ * "blob2str()" function
+ * Converts a blob to a string, ensuring valid UTF-8 encoding.
+ */
+    void
+f_blob2str(typval_T *argvars, typval_T *rettv)
+{
+    blob_T  *blob;
+    char_u  *str;
+    char_u  *p;
+    int	    blen;
+
+    if (check_for_blob_arg(argvars, 0) == FAIL
+	    || check_for_opt_dict_arg(argvars, 1) == FAIL)
+	return;
+
+    blob = argvars->vval.v_blob;
+    blen = blob_len(blob);
+
+    rettv->v_type = VAR_STRING;
+
+    str = alloc(blen + 1);
+    if (str == NULL)
+	return;
+
+    for (int i = 0; i < blen; i++)
+	str[i] = (char_u)blob_get(blob, i);
+    str[blen] = NUL;
+
+    p = str;
+    if (argvars[1].v_type != VAR_UNKNOWN)
+    {
+	dict_T *d = argvars[1].vval.v_dict;
+	if (d != NULL)
+	{
+	    char_u *enc = dict_get_string(d, "encoding", FALSE);
+	    if (enc != NULL)
+	    {
+		char_u *from = enc_canonize(enc_skip(enc));
+		p = convert_string(str, from, p_enc);
+		vim_free(str);
+		if (p == NULL)
+		{
+		    semsg(_(e_str_encoding_failed), "from", from);
+		    vim_free(from);
+		    return;
+		}
+		vim_free(from);
+	    }
+	}
+    }
+
+    if (STRCMP(p_enc, "utf-8") == 0 || STRCMP(p_enc, "utf8") == 0)
+    {
+	if (!utf_valid_string(p, NULL))
+	{
+	    semsg(_(e_str_encoding_failed), "from", p_enc);
+	    vim_free(p);
+	    return;
+	}
+    }
+
+    rettv->vval.v_string = p;
+}
+
+/*
+ * "str2blob()" function
+ */
+    void
+f_str2blob(typval_T *argvars, typval_T *rettv)
+{
+    blob_T	*blob;
+    char_u	*p;
+    size_t	len;
+
+    if (check_for_string_arg(argvars, 0) == FAIL
+	    || check_for_opt_dict_arg(argvars, 1) == FAIL)
+	return;
+
+    if (rettv_blob_alloc(rettv) == FAIL)
+	return;
+
+    blob = rettv->vval.v_blob;
+
+    p = tv_get_string_chk(&argvars[0]);
+    if (p == NULL)
+	return;
+
+    int free_str = FALSE;
+    if (argvars[1].v_type != VAR_UNKNOWN)
+    {
+	dict_T *d = argvars[1].vval.v_dict;
+	if (d != NULL)
+	{
+	    char_u *enc = dict_get_string(d, "encoding", FALSE);
+	    if (enc != NULL)
+	    {
+		char_u *to = enc_canonize(enc_skip(enc));
+		p = convert_string(p, p_enc, to);
+		if (p == NULL)
+		{
+		    semsg(_(e_str_encoding_failed), "to", to);
+		    vim_free(to);
+		    return;
+		}
+		vim_free(to);
+		free_str = TRUE;
+	    }
+	}
+    }
+
+    len = STRLEN(p);
+    for (size_t i = 0; i < len; i++)
+	ga_append(&blob->bv_ga, (int)p[i]);
+
+    if (free_str)
+	vim_free(p);
+}
+
+/*
  * "str2list()" function
  */
     void
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index f80754f..8b0af91 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -4257,4 +4257,73 @@
   call v9.CheckLegacyAndVim9Success(lines)
 endfunc
 
+" Tests for the str2blob() function
+func Test_str2blob()
+  let lines =<< trim END
+    call assert_equal(0z, str2blob(""))
+    call assert_fails("call str2blob([])", 'E1174: String required for argument 1')
+    call assert_equal(0z6162, str2blob("ab"))
+    call assert_equal(0zC2ABC2BB, str2blob("«»"))
+    call assert_equal(0zC59DC59F, str2blob("ŝş"))
+    call assert_equal(0zE0AE85E0.AE87, str2blob("அஇ"))
+    call assert_equal(0zF09F81B0.F09F81B3, str2blob("🁰🁳"))
+    call assert_equal(0z616263, str2blob('abc', {}))
+    call assert_equal(0zABBB, str2blob('«»', {'encoding': 'latin1'}))
+    call assert_equal(0zC2ABC2BB, str2blob('«»', {'encoding': 'utf8'}))
+
+    call assert_fails("call str2blob('abc', [])", 'E1206: Dictionary required for argument 2')
+    call assert_fails("call str2blob('abc', {'encoding': []})", 'E730: Using a List as a String')
+    call assert_fails("call str2blob('abc', {'encoding': 'ab12xy'})", 'E1515: Unable to convert to ''ab12xy'' encoding')
+    call assert_fails("call str2blob('ŝş', {'encoding': 'latin1'})", 'E1515: Unable to convert to ''latin1'' encoding')
+    call assert_fails("call str2blob('அஇ', {'encoding': 'latin1'})", 'E1515: Unable to convert to ''latin1'' encoding')
+    call assert_fails("call str2blob('🁰🁳', {'encoding': 'latin1'})", 'E1515: Unable to convert to ''latin1'' encoding')
+  END
+  call v9.CheckLegacyAndVim9Success(lines)
+endfunc
+
+" Tests for the blob2str() function
+func Test_blob2str()
+  let lines =<< trim END
+    call assert_equal("", blob2str(0z))
+    call assert_fails("call blob2str([])", 'E1238: Blob required for argument 1')
+    call assert_equal("ab", blob2str(0z6162))
+    call assert_equal("«»", blob2str(0zC2ABC2BB))
+    call assert_equal("ŝş", blob2str(0zC59DC59F))
+    call assert_equal("அஇ", blob2str(0zE0AE85E0.AE87))
+    call assert_equal("🁰🁳", blob2str(0zF09F81B0.F09F81B3))
+    call assert_equal('«»', blob2str(0zABBB, {'encoding': 'latin1'}))
+    call assert_equal('«»', blob2str(0zC2ABC2BB, {'encoding': 'utf8'}))
+
+    #" Invalid encoding
+    call assert_fails("call blob2str(0z80)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zC0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zE0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zF0)", "E1515: Unable to convert from 'utf-8' encoding")
+
+    call assert_fails("call blob2str(0z6180)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61C0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61E0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61F0)", "E1515: Unable to convert from 'utf-8' encoding")
+
+    call assert_fails("call blob2str(0zC0C0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61C0C0)", "E1515: Unable to convert from 'utf-8' encoding")
+
+    call assert_fails("call blob2str(0zE0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zE080)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zE080C0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61E080C0)", "E1515: Unable to convert from 'utf-8' encoding")
+
+    call assert_fails("call blob2str(0zF08080C0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0z61F08080C0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zF0)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zF080)", "E1515: Unable to convert from 'utf-8' encoding")
+    call assert_fails("call blob2str(0zF08080)", "E1515: Unable to convert from 'utf-8' encoding")
+
+    call assert_fails("call blob2str(0z6162, [])", 'E1206: Dictionary required for argument 2')
+    call assert_fails("call blob2str(0z6162, {'encoding': []})", 'E730: Using a List as a String')
+    call assert_fails("call blob2str(0z6162, {'encoding': 'ab12xy'})", 'E1515: Unable to convert from ''ab12xy'' encoding')
+  END
+  call v9.CheckLegacyAndVim9Success(lines)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 96a51da..13ffc5d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1016,
+/**/
     1015,
 /**/
     1014,