[string] add ParseDigit(), ParseHexDigit(), and other helper func…

…tions (#10282)

This commit adds a set of helper functions to parse a given digit or
hex digit character to its numeric value, or to check if a given
character is a digit, uppercase, or lowercase letter.

src/core/common/string.cpp

@@ -202,13 +202,15 @@ Error StringParseUint8(const char *&aString, uint8_t &aUint8, uint8_t aMaxValue)
     Error       error = kErrorParse;
     const char *cur   = aString;
     uint16_t    value = 0;
+    uint8_t     digit;
 
-    for (; (*cur >= '0') && (*cur <= '9'); cur++)
+    while (ParseDigit(*cur, digit) == kErrorNone)
     {
         value *= 10;
-        value += static_cast<uint8_t>(*cur - '0');
+        value += digit;
         VerifyOrExit(value <= aMaxValue, error = kErrorParse);
         error = kErrorNone;
+        cur++;
     }
 
     aString = cur;
@@ -236,7 +238,7 @@ void StringConvertToUppercase(char *aString)
 
 char ToLowercase(char aChar)
 {
-    if ((aChar >= 'A') && (aChar <= 'Z'))
+    if (IsUppercase(aChar))
     {
         aChar += 'a' - 'A';
     }
@@ -246,14 +248,51 @@ char ToLowercase(char aChar)
 
 char ToUppercase(char aChar)
 {
-    if ((aChar >= 'a') && (aChar <= 'z'))
+    if (IsLowercase(aChar))
     {
         aChar -= 'a' - 'A';
     }
 
     return aChar;
 }
 
+bool IsDigit(char aChar) { return ('0' <= aChar && aChar <= '9'); }
+
+bool IsUppercase(char aChar) { return ('A' <= aChar && aChar <= 'Z'); }
+
+bool IsLowercase(char aChar) { return ('a' <= aChar && aChar <= 'z'); }
+
+Error ParseDigit(char aDigitChar, uint8_t &aValue)
+{
+    Error error = kErrorNone;
+
+    VerifyOrExit(IsDigit(aDigitChar), error = kErrorInvalidArgs);
+    aValue = static_cast<uint8_t>(aDigitChar - '0');
+
+exit:
+    return error;
+}
+
+Error ParseHexDigit(char aHexChar, uint8_t &aValue)
+{
+    Error error = kErrorNone;
+
+    if (('A' <= aHexChar) && (aHexChar <= 'F'))
+    {
+        ExitNow(aValue = static_cast<uint8_t>(aHexChar - 'A' + 10));
+    }
+
+    if (('a' <= aHexChar) && (aHexChar <= 'f'))
+    {
+        ExitNow(aValue = static_cast<uint8_t>(aHexChar - 'a' + 10));
+    }
+
+    error = ParseDigit(aHexChar, aValue);
+
+exit:
+    return error;
+}
+
 const char *ToYesNo(bool aBool)
 {
     static const char *const kYesNoStrings[] = {"no", "yes"};

src/core/common/string.hpp

@@ -282,6 +282,63 @@ char ToLowercase(char aChar);
  */
 char ToUppercase(char aChar);
 
+/**
+ * Checks whether a given character is an uppercase letter ('A'-'Z').
+ *
+ * @param[in] aChar   The character to check.
+ *
+ * @retval TRUE    @p aChar is an uppercase letter.
+ * @retval FALSE   @p aChar is not an uppercase letter.
+ *
+ */
+bool IsUppercase(char aChar);
+
+/**
+ * Checks whether a given character is a lowercase letter ('a'-'z').
+ *
+ * @param[in] aChar   The character to check.
+ *
+ * @retval TRUE    @p aChar is a lowercase letter.
+ * @retval FALSE   @p aChar is not a lowercase letter.
+ *
+ */
+bool IsLowercase(char aChar);
+
+/**
+ * Checks whether a given character is a digit character ('0'-'9').
+ *
+ * @param[in] aChar   The character to check.
+ *
+ * @retval TRUE    @p aChar is a digit character.
+ * @retval FALSE   @p aChar is not a digit character.
+ *
+ */
+bool IsDigit(char aChar);
+
+/**
+ * Parse a given digit character to its numeric value.
+ *
+ * @param[in]  aDigitChar   The digit character to parse.
+ * @param[out] aValue       A reference to return the parsed value on success.
+ *
+ * @retval kErrorNone            Successfully parsed the digit, @p aValue is updated.
+ * @retval kErrorInvalidArgs     @p aDigitChar is not a valid digit character.
+ *
+ */
+Error ParseDigit(char aDigitChar, uint8_t &aValue);
+
+/**
+ * Parse a given hex digit character ('0'-'9', 'A'-'F', or 'a'-'f') to its numeric value.
+ *
+ * @param[in]  aHexChar     The hex digit character to parse.
+ * @param[out] aValue       A reference to return the parsed value on success.
+ *
+ * @retval kErrorNone            Successfully parsed the digit, @p aValue is updated.
+ * @retval kErrorInvalidArgs     @p aHexChar is not a valid hex digit character.
+ *
+ */
+Error ParseHexDigit(char aHexChar, uint8_t &aValue);
+
 /**
  * Coverts a boolean to "yes" or "no" string.
  *

src/core/meshcop/meshcop.cpp

@@ -95,7 +95,7 @@ bool JoinerPskd::IsPskdValid(const char *aPskdString)
     {
         char c = aPskdString[i];
 
-        VerifyOrExit(isdigit(c) || isupper(c));
+        VerifyOrExit(IsDigit(c) || IsUppercase(c));
         VerifyOrExit(c != 'I' && c != 'O' && c != 'Q' && c != 'Z');
     }
 

src/core/net/ip6_address.cpp

@@ -586,22 +586,9 @@ Error Address::ParseFrom(const char *aString, char aTerminatorChar)
 
         while (true)
         {
-            char    c = *aString;
             uint8_t digit;
 
-            if (('A' <= c) && (c <= 'F'))
-            {
-                digit = static_cast<uint8_t>(c - 'A' + 10);
-            }
-            else if (('a' <= c) && (c <= 'f'))
-            {
-                digit = static_cast<uint8_t>(c - 'a' + 10);
-            }
-            else if (('0' <= c) && (c <= '9'))
-            {
-                digit = static_cast<uint8_t>(c - '0');
-            }
-            else
+            if (ParseHexDigit(*aString, digit) != kErrorNone)
             {
                 break;
             }

src/core/utils/parse_cmdline.cpp

@@ -48,37 +48,6 @@ static bool IsSeparator(char aChar) { return (aChar == ' ') || (aChar == '\t') |
 
 static bool IsEscapable(char aChar) { return IsSeparator(aChar) || (aChar == '\\'); }
 
-static Error ParseDigit(char aDigitChar, uint8_t &aValue)
-{
-    Error error = kErrorNone;
-
-    VerifyOrExit(('0' <= aDigitChar) && (aDigitChar <= '9'), error = kErrorInvalidArgs);
-    aValue = static_cast<uint8_t>(aDigitChar - '0');
-
-exit:
-    return error;
-}
-
-static Error ParseHexDigit(char aHexChar, uint8_t &aValue)
-{
-    Error error = kErrorNone;
-
-    if (('A' <= aHexChar) && (aHexChar <= 'F'))
-    {
-        ExitNow(aValue = static_cast<uint8_t>(aHexChar - 'A' + 10));
-    }
-
-    if (('a' <= aHexChar) && (aHexChar <= 'f'))
-    {
-        ExitNow(aValue = static_cast<uint8_t>(aHexChar - 'a' + 10));
-    }
-
-    error = ParseDigit(aHexChar, aValue);
-
-exit:
-    return error;
-}
-
 Error ParseCmd(char *aCommandString, Arg aArgs[], uint8_t aArgsMaxLength)
 {
     Error   error = kErrorNone;

tests/unit/test_string.cpp

@@ -337,6 +337,8 @@ void TestStringParseUint8(void)
         {"0256", kErrorParse}, // Larger than max `uint8_t`
     };
 
+    uint8_t digit;
+
     printf("\nTest 11: TestStringParseUint8() function\n");
 
     for (const TestCase &testCase : kTestCases)
@@ -363,6 +365,64 @@ void TestStringParseUint8(void)
         }
     }
 
+    for (char c = '0'; c <= '9'; c++)
+    {
+        VerifyOrQuit(IsDigit(c));
+        VerifyOrQuit(!IsUppercase(c));
+        VerifyOrQuit(!IsLowercase(c));
+
+        SuccessOrQuit(ParseDigit(c, digit));
+        VerifyOrQuit(digit == (c - '0'));
+
+        SuccessOrQuit(ParseHexDigit(c, digit));
+        VerifyOrQuit(digit == (c - '0'));
+    }
+
+    for (char c = 'A'; c <= 'Z'; c++)
+    {
+        VerifyOrQuit(!IsDigit(c));
+        VerifyOrQuit(IsUppercase(c));
+        VerifyOrQuit(!IsLowercase(c));
+        VerifyOrQuit(ParseDigit(c, digit) != kErrorNone);
+
+        if (c <= 'F')
+        {
+            SuccessOrQuit(ParseHexDigit(c, digit));
+            VerifyOrQuit(digit == (c - 'A' + 10));
+        }
+        else
+        {
+            VerifyOrQuit(ParseHexDigit(c, digit) != kErrorNone);
+        }
+    }
+
+    for (char c = 'a'; c <= 'z'; c++)
+    {
+        VerifyOrQuit(!IsDigit(c));
+        VerifyOrQuit(!IsUppercase(c));
+        VerifyOrQuit(IsLowercase(c));
+        VerifyOrQuit(ParseDigit(c, digit) != kErrorNone);
+
+        if (c <= 'f')
+        {
+            SuccessOrQuit(ParseHexDigit(c, digit));
+            VerifyOrQuit(digit == (c - 'a' + 10));
+        }
+        else
+        {
+            VerifyOrQuit(ParseHexDigit(c, digit) != kErrorNone);
+        }
+    }
+
+    VerifyOrQuit(!IsDigit(static_cast<char>('0' - 1)));
+    VerifyOrQuit(!IsDigit(static_cast<char>('9' + 1)));
+
+    VerifyOrQuit(!IsUppercase(static_cast<char>('A' - 1)));
+    VerifyOrQuit(!IsUppercase(static_cast<char>('Z' + 1)));
+
+    VerifyOrQuit(!IsLowercase(static_cast<char>('a' - 1)));
+    VerifyOrQuit(!IsLowercase(static_cast<char>('z' + 1)));
+
     printf("\n\n -- PASS\n");
 }