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+/*
+ * The following code is adapted from code originally written by Bjoern
+ * Hoehrmann <bjoern@hoehrmann.de>. See
+ * http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
+ *
+ * The original license:
+ *
+ * Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+*/
+
+#ifndef UTF8_VALIDATOR_HPP
+#define UTF8_VALIDATOR_HPP
+
+#include <websocketpp/common/stdint.hpp>
+
+#include <string>
+
+namespace websocketpp {
+namespace utf8_validator {
+
+/// State that represents a valid utf8 input sequence
+static unsigned int const utf8_accept = 0;
+/// State that represents an invalid utf8 input sequence
+static unsigned int const utf8_reject = 1;
+
+/// Lookup table for the UTF8 decode state machine
+static uint8_t const utf8d[] = {
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 00..1f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 20..3f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 40..5f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 60..7f
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, // 80..9f
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, // a0..bf
+  8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // c0..df
+  0xa,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x4,0x3,0x3, // e0..ef
+  0xb,0x6,0x6,0x6,0x5,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8, // f0..ff
+  0x0,0x1,0x2,0x3,0x5,0x8,0x7,0x1,0x1,0x1,0x4,0x6,0x1,0x1,0x1,0x1, // s0..s0
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,1, // s1..s2
+  1,2,1,1,1,1,1,2,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1, // s3..s4
+  1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,3,1,3,1,1,1,1,1,1, // s5..s6
+  1,3,1,1,1,1,1,3,1,3,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // s7..s8
+};
+
+/// Decode the next byte of a UTF8 sequence
+/**
+ * @param [out] state The decoder state to advance
+ * @param [out] codep The codepoint to fill in
+ * @param [in] byte The byte to input
+ * @return The ending state of the decode operation
+ */
+inline uint32_t decode(uint32_t * state, uint32_t * codep, uint8_t byte) {
+  uint32_t type = utf8d[byte];
+
+  *codep = (*state != utf8_accept) ?
+    (byte & 0x3fu) | (*codep << 6) :
+    (0xff >> type) & (byte);
+
+  *state = utf8d[256 + *state*16 + type];
+  return *state;
+}
+
+/// Provides streaming UTF8 validation functionality
+class validator {
+public:
+    /// Construct and initialize the validator
+    validator() : m_state(utf8_accept),m_codepoint(0) {}
+
+    /// Advance the state of the validator with the next input byte
+    /**
+     * @param byte The byte to advance the validation state with
+     * @return Whether or not the byte resulted in a validation error.
+     */
+    bool consume (uint8_t byte) {
+        if (utf8_validator::decode(&m_state,&m_codepoint,byte) == utf8_reject) {
+            return false;
+        }
+        return true;
+    }
+
+    /// Advance validator state with input from an iterator pair
+    /**
+     * @param begin Input iterator to the start of the input range
+     * @param end Input iterator to the end of the input range
+     * @return Whether or not decoding the bytes resulted in a validation error.
+     */
+    template <typename iterator_type>
+    bool decode (iterator_type begin, iterator_type end) {
+        for (iterator_type it = begin; it != end; ++it) {
+            unsigned int result = utf8_validator::decode(
+                &m_state,
+                &m_codepoint,
+                static_cast<uint8_t>(*it)
+            );
+
+            if (result == utf8_reject) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /// Return whether the input sequence ended on a valid utf8 codepoint
+    /**
+     * @return Whether or not the input sequence ended on a valid codepoint.
+     */
+    bool complete() {
+        return m_state == utf8_accept;
+    }
+
+    /// Reset the validator to decode another message
+    void reset() {
+        m_state = utf8_accept;
+        m_codepoint = 0;
+    }
+private:
+    uint32_t    m_state;
+    uint32_t    m_codepoint;
+};
+
+/// Validate a UTF8 string
+/**
+ * convenience function that creates a validator, validates a complete string
+ * and returns the result.
+ */
+inline bool validate(std::string const & s) {
+    validator v;
+    if (!v.decode(s.begin(),s.end())) {
+        return false;
+    }
+    return v.complete();
+}
+
+} // namespace utf8_validator
+} // namespace websocketpp
+
+#endif // UTF8_VALIDATOR_HPP