[trac4090] Add support for TokenSubstring

Add support and testing for TokenSubstring.  This token
takes three paramaters (string, start and length) and produces
a new string based on the original string.  It allows negative
values for start and length causing it to count from the end
of the string for start and to get characters before the start
point for length.

src/lib/eval/eval_messages.mes

@@ -18,3 +18,7 @@ $NAMESPACE isc::dhcp
 This debug message indicates that the expression has been evaluated
 to said value. This message is mostly useful during debugging of the
 client classification expressions.
+
+% EVAL_SUBSTRING_BAD_PARAM_CONVERSION starting %1, length %2
+This debug message indicates that the parameter for the starting postion
+or length of the substring couldn't be converted to an integer.

src/lib/eval/tests/token_unittest.cc

@@ -60,6 +60,40 @@ public:
     OptionPtr option_str4_; ///< A string option for DHCPv4
     OptionPtr option_str6_; ///< A string option for DHCPv6
 
+
+    /// @brief Verify that the substring eval works properly
+    ///
+    /// This function takes the parameters and sets up the value
+    /// stack then executes the eval and checks the results.
+    ///
+    /// @param test_string The string to operate on
+    /// @param test_start The postion to start when getting a substring
+    /// @param test_length The length of the substring to get
+    /// @param result_string The expected result of the eval
+    void verifySubstringEval(const std::string& test_string,
+                             const std::string& test_start,
+                             const std::string& test_length,
+                             const std::string& result_string) {
+
+        // create the token
+        ASSERT_NO_THROW(t_.reset(new TokenSubstring()));
+
+        // push values on stack
+        values_.push(test_string);
+        values_.push(test_start);
+        values_.push(test_length);
+
+        // evaluate the token
+        EXPECT_NO_THROW(t_->evaluate(*pkt4_, values_));
+
+        // verify results
+        ASSERT_EQ(1, values_.size());
+        EXPECT_EQ(result_string, values_.top());
+
+        // remove result
+        values_.pop();
+    }
+
     /// @todo: Add more option types here
 };
 
@@ -197,3 +231,176 @@ TEST_F(TokenTest, optionEqualTrue) {
 }
 
 };
+
+// This test checks if an a token representing a substring request
+// throws an excpetion if there aren't enough values on the stack.
+// The stack from the top is: length, start, string.
+// The actual packet is not used.
+TEST_F(TokenTest, substringNotEnoughValues) {
+    ASSERT_NO_THROW(t_.reset(new TokenSubstring()));
+
+    // Subsring requires three values on the stack, try
+    // with 0, 1 and 2 all should thorw an exception
+    EXPECT_THROW(t_->evaluate(*pkt4_, values_), EvalBadStack);
+
+    values_.push("");
+    EXPECT_THROW(t_->evaluate(*pkt4_, values_), EvalBadStack);
+
+    values_.push("0");
+    EXPECT_THROW(t_->evaluate(*pkt4_, values_), EvalBadStack);
+
+    // Three should work
+    values_.push("0");
+    EXPECT_NO_THROW(t_->evaluate(*pkt4_, values_));
+
+    // As we had an empty string to start with we should have an empty
+    // one after the evaluate
+    ASSERT_EQ(1, values_.size());
+    EXPECT_EQ("", values_.top());
+}
+
+// Test getting the whole string in different ways
+TEST_F(TokenTest, substringWholeString) {
+    // Get the whole string
+    verifySubstringEval("foobar", "0", "6", "foobar");
+
+    // Get the whole string with "all"
+    verifySubstringEval("foobar", "0", "all", "foobar");
+
+    // Get the whole string with an extra long number
+    verifySubstringEval("foobar", "0", "123456", "foobar");
+
+    // Get the whole string counting from the back
+    verifySubstringEval("foobar", "-6", "all", "foobar");
+}
+
+// Test getting a suffix, in this case the last 3 characters
+TEST_F(TokenTest, substringTrailer) {
+    verifySubstringEval("foobar", "3", "3", "bar");
+    verifySubstringEval("foobar", "3", "all", "bar");
+    verifySubstringEval("foobar", "-3", "all", "bar");
+    verifySubstringEval("foobar", "-3", "123", "bar");
+}
+
+// Test getting the middle of the string in different ways
+TEST_F(TokenTest, substringMiddle) {
+    verifySubstringEval("foobar", "1", "4", "ooba");
+    verifySubstringEval("foobar", "-5", "4", "ooba");
+    verifySubstringEval("foobar", "-1", "-4", "ooba");
+    verifySubstringEval("foobar", "5", "-4", "ooba");
+}
+
+// Test getting the last letter in different ways
+TEST_F(TokenTest, substringLastLetter) {
+    verifySubstringEval("foobar", "5", "all", "r");
+    verifySubstringEval("foobar", "5", "1", "r");
+    verifySubstringEval("foobar", "5", "5", "r");
+    verifySubstringEval("foobar", "-1", "all", "r");
+    verifySubstringEval("foobar", "-1", "1", "r");
+    verifySubstringEval("foobar", "-1", "5", "r");
+}
+
+// Test we get only what is available if we ask for a longer string
+TEST_F(TokenTest, substringLength) {
+    // Test off the front
+    verifySubstringEval("foobar", "0", "-4", "");
+    verifySubstringEval("foobar", "1", "-4", "f");
+    verifySubstringEval("foobar", "2", "-4", "fo");
+    verifySubstringEval("foobar", "3", "-4", "foo");
+
+    // and the back
+    verifySubstringEval("foobar", "3", "4", "bar");
+    verifySubstringEval("foobar", "4", "4", "ar");
+    verifySubstringEval("foobar", "5", "4", "r");
+    verifySubstringEval("foobar", "6", "4", "");
+}
+
+// Test that we get nothing if the starting postion is out of the string
+TEST_F(TokenTest, substringStartingPosition) {
+    // Off the front
+    verifySubstringEval("foobar", "-7", "1", "");
+    verifySubstringEval("foobar", "-7", "-11", "");
+    verifySubstringEval("foobar", "-7", "all", "");
+
+    // and the back
+    verifySubstringEval("foobar", "6", "1", "");
+    verifySubstringEval("foobar", "6", "-11", "");
+    verifySubstringEval("foobar", "6", "all", "");
+}
+
+// Check what happens if we use strings that aren't numbers for start or length
+// We should return the empty string
+TEST_F(TokenTest, substringBadParams) {
+    verifySubstringEval("foobar", "0ick", "all", "");
+    verifySubstringEval("foobar", "ick0", "all", "");
+    verifySubstringEval("foobar", "ick", "all", "");
+    verifySubstringEval("foobar", "0", "ick", "");
+    verifySubstringEval("foobar", "0", "0ick", "");
+    verifySubstringEval("foobar", "0", "ick0", "");
+    verifySubstringEval("foobar", "0", "allaboard", "");
+}
+
+// lastly check that we don't get anything if the string is empty
+TEST_F(TokenTest, substringStartingEmpty) {
+    verifySubstringEval("", "0", "all", "");
+    verifySubstringEval("foobar", "0", "0", "");
+}
+
+// Check if we can use the substring and equal tokens together
+// We put the result on the stack first then the substring values
+// then evaluate the substring which should leave the original
+// result on the bottom with the substring result on next.
+// Evaulating the equals should produce true for the first
+// and false for the second.
+// throws an excpetion if there aren't enough values on the stack.
+// The stack from the top is: length, start, string.
+// The actual packet is not used.
+TEST_F(TokenTest, substringEquals) {
+    TokenPtr tequal;
+
+    ASSERT_NO_THROW(t_.reset(new TokenSubstring()));
+    ASSERT_NO_THROW(tequal.reset(new TokenEqual()));
+
+    // The final expected value
+    values_.push("ooba");
+
+    // The substring values
+    // Subsring requires three values on the stack, try
+    // with 0, 1 and 2 all should thorw an exception
+    values_.push("foobar");
+    values_.push("1");
+    values_.push("4");
+    EXPECT_NO_THROW(t_->evaluate(*pkt4_, values_));
+
+    // we should have two values on the stack
+    ASSERT_EQ(2, values_.size());
+
+    // next the equals eval
+    EXPECT_NO_THROW(tequal->evaluate(*pkt4_, values_));
+    ASSERT_EQ(1, values_.size());
+    EXPECT_EQ("true", values_.top());
+
+    // get rid of the result
+    values_.pop();
+
+    // and try it again but with a bad final value
+    // The final expected value
+    values_.push("foob");
+
+    // The substring values
+    // Subsring requires three values on the stack, try
+    // with 0, 1 and 2 all should thorw an exception
+    values_.push("foobar");
+    values_.push("1");
+    values_.push("4");
+    EXPECT_NO_THROW(t_->evaluate(*pkt4_, values_));
+
+    // we should have two values on the stack
+    ASSERT_EQ(2, values_.size());
+
+    // next the equals eval
+    EXPECT_NO_THROW(tequal->evaluate(*pkt4_, values_));
+    ASSERT_EQ(1, values_.size());
+    EXPECT_EQ("false", values_.top());
+
+}

src/lib/eval/token.cc

@@ -13,6 +13,7 @@
 // PERFORMANCE OF THIS SOFTWARE.
 
 #include <eval/token.h>
+#include <boost/lexical_cast.hpp>
 #include <string>
 
 using namespace isc::dhcp;
@@ -53,3 +54,77 @@ TokenEqual::evaluate(const Pkt& /*pkt*/, ValueStack& values) {
     else
         values.push("false");
 }
+
+void
+TokenSubstring::evaluate(const Pkt& /*pkt*/, ValueStack& values) {
+
+    if (values.size() < 3) {
+        isc_throw(EvalBadStack, "Incorrect stack order. Expected at least "
+                  "3 values for substring operator, got " << values.size());
+    }
+
+    string len_str = values.top();
+    values.pop();
+    string start_str = values.top();
+    values.pop();
+    string string_str = values.top();
+    values.pop();
+
+    // If we have no string to start with we push an empty string and leave
+    if (string_str.empty()) {
+        values.push("");
+        return;
+    }
+
+    // Convert the starting position and legnth from strings to numbers
+    // the length may also be "all" in which case simply make it the
+    // legnth of the string.
+    // If we have a problem push an empty string and leave
+    int start_pos, length;
+    try {
+        start_pos = boost::lexical_cast<int>(start_str);
+        if ("all" == len_str) {
+            length = string_str.length();
+        } else {
+            length = boost::lexical_cast<int>(len_str);
+        }
+    } catch (const boost::bad_lexical_cast&) {
+#if 0
+        // Logging not yet built
+        LOG_DEBUG(eval_logger, EVAL_DBG_TRACE,
+                  EVAL_SUBSTRING_BAD_PARAM_CONVERSION)
+            .arg(start_str)
+            .arg(len_str);
+#endif
+        values.push("");
+        return;
+    }
+
+    // If the starting postion is outside of the string push an
+    // empty string and leave
+    if (((start_pos >= 0) && (start_pos >= string_str.length())) |
+        ((start_pos < 0) && (-start_pos > string_str.length()))) {
+        values.push("");
+        return;
+    }
+
+    // Adjust the values to be something for substr.  We first figure out
+    // the staring postion, then update it and the length to get the
+    // characters before or after it depnding on the sign of length
+    if (start_pos < 0) {
+        start_pos = string_str.length() + start_pos;
+    }
+
+    if (length < 0) {
+        length = -length;
+        if (length <=  start_pos){
+            start_pos -= length;
+        } else {
+            length = start_pos;
+            start_pos = 0;
+        }
+    }
+
+    // and finally get the substring
+    values.push(string_str.substr(start_pos, length));
+}

src/lib/eval/token.h

@@ -56,7 +56,7 @@ public:
 /// - option[123] (a token that extracts value of option 123)
 /// - == (an operator that compares two other tokens)
 /// - substring(a,b,c) (an operator that takes three arguments: a string,
-///   first and last character)
+///   first character and length)
 class Token {
 public:
 
@@ -158,6 +158,52 @@ public:
     void evaluate(const Pkt& pkt, ValueStack& values);
 };
 
+/// @brief Token that represents the substring operator (returns a portion
+/// of the supplied string)
+///
+/// This token represents substring(str, start, len)  An operator that takes three
+/// arguments: a string, the first character and the length.
+class TokenSubstring : public Token {
+public:
+    /// @brief Constructor (does nothing)
+    TokenSubstring() {}
+
+    /// @brief Extract a substring from a string
+    ///
+    /// Evaluation does not use packet information, but rather consumes the last
+    /// three parameters and requires at least three parameters to be present on
+    /// stack.  From the top it expects the values on the stack as:
+    ///  len
+    ///  start
+    ///  str
+    ///
+    /// str is the string to extract a substring from.  If it is empty an empty
+    /// string is pushed onto the value stack.
+    ///
+    /// start is the postion from which the code starts extracting the substring.
+    /// 0 is before the first character and a negative number starts from the end,
+    /// with -1 being before the last character.  If the starting point is
+    /// outside of the original string an empty string is pushed onto the value
+    /// stack.
+    ///
+    /// length is the number of characters from the string to extract.
+    /// "all" means all remaining characters from start to the end of string.
+    /// A negative number means to go from start towards the beginning of
+    /// string, but doesn't include start.
+    /// If length is longer than the remaining portion of string
+    /// then the entire remaining portion is placed on the value stack.
+    /// Note: a negative value of length only indicates which characters to
+    /// extract, it does NOT indicate any attempt to reverse the string.
+    /// For example substring("foobar", 4, -2) will result in "ob".
+    ///
+    /// @throw EvalBadStack if there's less than 3 values on stack
+    ///
+    /// @brief pkt (unused)
+    /// @brief values - stack of values (3 arguments will be poped, 1 result
+    ///        will be pushed)
+    void evaluate(const Pkt& pkt, ValueStack& values);
+};
+
 }; // end of isc::dhcp namespace
 }; // end of isc namespace