common: New function replace_substr.

* common/stringhelp.c (replace_substr): New.
* common/t-stringhelp.c (test_replace_substr): New test.

3 files changed, 151 insertions, 1 deletions

diff --git a/common/stringhelp.c b/common/stringhelp.c
index 9347c3551..8bbc68ab1 100644
--- a/common/stringhelp.c
+++ b/common/stringhelp.c
@@ -2,7 +2,7 @@
  * Copyright (C) 1998, 1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007,
  *               2008, 2009, 2010  Free Software Foundation, Inc.
  * Copyright (C) 2014 Werner Koch
- * Copyright (C) 2015, 2021  g10 Code GmbH
+ * Copyright (C) 2015, 2021, 2025  g10 Code GmbH
  *
  * This file is part of GnuPG.
  *
@@ -1721,6 +1721,37 @@ format_text (const char *text_in, int target_cols, int max_cols)
 }
 
 
+/* In STRING replace the first occurance of SUBSTR by the string
+ * REPLACE.  Return a new malloced string or set ERRNO and set NULL on
+ * error.  If SUBSTR is not found a verbatim copy of STRING is
+ * returned.  */
+char *
+replace_substr (const char *string, const char *substr, const char *replace)
+{
+  size_t stringlen, substrlen, replacelen, n;
+  const char *s;
+  char *buffer;
+
+  stringlen = strlen (string);
+  substrlen = strlen (substr);
+  replacelen = strlen (replace);
+
+  if (stringlen < substrlen || !(s = strstr (string, substr)))
+    return xtrystrdup (string);
+
+  stringlen -= substrlen;  /* Found thus sryinglen >= substrlen */
+  buffer = xtrymalloc (stringlen + replacelen +1);
+  if (!buffer)
+    return NULL;
+  memcpy (buffer, string, n=(s-string));
+  memcpy (buffer+n, replace, replacelen);
+  strcpy (buffer+n+replacelen, s+substrlen);
+
+
+  return buffer;
+}
+
+
 /* Substitute variables in STRING and return a new string.  GETVAL is
  * a function which maps NAME to its value; that value is a string
  * which may not change during the execution time of this function.
diff --git a/common/stringhelp.h b/common/stringhelp.h
index d93373ec5..037ee8139 100644
--- a/common/stringhelp.h
+++ b/common/stringhelp.h
@@ -170,6 +170,13 @@ int compare_version_strings (const char *my_version, const char *req_version);
 /* Format a string so that it fits within about TARGET_COLS columns.  */
 char *format_text (const char *text, int target_cols, int max_cols);
 
+
+/* Return a new malloced string with the first occurance of SUBSTR in
+ * STRING replaced by REPLACE.  Returns NULL on memory error.  */
+char *replace_substr (const char *string,
+                      const char *substr, const char *replace);
+
+
 /* Substitute variables in STRING.  */
 char *substitute_vars (const char *string,
                        const char *(*getval)(void *cookie, const char *name),
diff --git a/common/t-stringhelp.c b/common/t-stringhelp.c
index b43bb7932..3bd9ba928 100644
--- a/common/t-stringhelp.c
+++ b/common/t-stringhelp.c
@@ -1202,6 +1202,117 @@ test_compare_version_strings (void)
 
 
 static void
+test_replace_substr (void)
+{
+  struct {
+    const char *string;
+    const char *substr;
+    const char *replace;
+    const char *result;
+  } t[] = {
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      "view ",
+      "Look afar and view the end from the beginning."
+    },
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      "xxx ",
+      "Look afar and xxx the end from the beginning."
+    },
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      "xx ",
+      "Look afar and xx the end from the beginning."
+    },
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      "x ",
+      "Look afar and x the end from the beginning."
+    },
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      " ",
+      "Look afar and  the end from the beginning."
+    },
+    { "Look afar and see the end from the beginning.",
+      "see ",
+      "",
+      "Look afar and the end from the beginning."
+    },
+    { "Be different: conform.",
+      "",
+      "xxx",
+      "xxxBe different: conform."
+    },
+    { "Be different: conform.",
+      "foo",
+      "bar",
+      "Be different: conform."
+    },
+    { "Be different: conform.",
+      "different",
+      "unlike",
+      "Be unlike: conform."
+    },
+    { "Be different: conform.",
+      "B",
+      "Bee",
+      "Beee different: conform."
+    },
+    { "Be different: conform.",
+      ".",
+      "",
+      "Be different: conform"
+    },
+    { "Be different: conform.",
+      ".",
+      "!",
+      "Be different: conform!"
+    },
+    { "Be different: conform.",
+      ".",
+      "...",
+      "Be different: conform..."
+    },
+    { "Be different: conform.",
+      ":",
+      " - this is a very long replacement string - ",
+      "Be different - this is a very long replacement string -  conform."
+    },
+    { "",
+      "",
+      "",
+      ""
+    }
+  };
+  int idx;
+  char *res;
+
+  for (idx=0; idx < DIM(t); idx++)
+    {
+      res = replace_substr (t[idx].string, t[idx].substr, t[idx].replace);
+      if (!res)
+        {
+          fprintf (stderr,"error replacing in '%s' (test %d): %s\n",
+                   t[idx].string, idx, strerror (errno));
+          exit (2);
+        }
+      if (strcmp (res, t[idx].result))
+        {
+          fprintf (stderr, "string is '%s'\n", t[idx].string);
+          fprintf (stderr, "   substr '%s'\n", t[idx].substr);
+          fprintf (stderr, "  replace '%s'\n", t[idx].replace);
+          fprintf (stderr, " expected '%s'\n", t[idx].result);
+          fprintf (stderr, "      got '%s'\n", res);
+          fail (idx);
+        }
+      xfree (res);
+    }
+}
+
+
+static void
 test_substitute_envvars (void)
 {
   struct {
@@ -1317,6 +1428,7 @@ main (int argc, char **argv)
   test_split_fields_colon ();
   test_compare_version_strings ();
   test_format_text ();
+  test_replace_substr ();
   test_substitute_envvars ();
 
   xfree (home_buffer);