AK: Add a basic URL class to help us handle URL's

We're gonna need these as we start to write more networking programs.

AK/URL.cpp

@@ -0,0 +1,130 @@
+#include <AK/StringBuilder.h>
+#include <AK/URL.h>
+
+namespace AK {
+
+static inline bool is_valid_protocol_character(char ch)
+{
+    return ch >= 'a' && ch <= 'z';
+}
+
+static inline bool is_valid_hostname_character(char ch)
+{
+    return ch && ch != '/' && ch != ':';
+}
+
+static inline bool is_digit(char ch)
+{
+    return ch >= '0' && ch <= '9';
+}
+
+bool URL::parse(const StringView& string)
+{
+    enum class State {
+        InProtocol,
+        InHostname,
+        InPort,
+        InPath,
+    };
+
+    Vector<char, 256> buffer;
+    State state { State::InProtocol };
+
+    int index = 0;
+
+    auto peek = [&] {
+        if (index >= string.length())
+            return '\0';
+        return string[index];
+    };
+
+    auto consume = [&] {
+        if (index >= string.length())
+            return '\0';
+        return string[index++];
+    };
+
+    while (index < string.length()) {
+        switch (state) {
+        case State::InProtocol:
+            if (is_valid_protocol_character(peek())) {
+                buffer.append(consume());
+                continue;
+            }
+            if (consume() != ':')
+                return false;
+            if (consume() != '/')
+                return false;
+            if (consume() != '/')
+                return false;
+            if (buffer.is_empty())
+                return false;
+            m_protocol = String::copy(buffer);
+            buffer.clear();
+            state = State::InHostname;
+            continue;
+        case State::InHostname:
+            if (is_valid_hostname_character(peek())) {
+                buffer.append(consume());
+                continue;
+            }
+            if (buffer.is_empty())
+                return false;
+            m_host = String::copy(buffer);
+            buffer.clear();
+            if (peek() == ':') {
+                consume();
+                state = State::InPort;
+                continue;
+            }
+            if (peek() == '/') {
+                state = State::InPath;
+                continue;
+            }
+            return false;
+        case State::InPort:
+            if (is_digit(peek())) {
+                buffer.append(consume());
+                continue;
+            }
+            if (buffer.is_empty())
+                return false;
+            {
+                bool ok;
+                m_port = String::copy(buffer).to_uint(ok);
+                buffer.clear();
+                if (!ok)
+                    return false;
+            }
+            if (peek() == '/') {
+                state = State::InPath;
+                continue;
+            }
+            return false;
+        case State::InPath:
+            buffer.append(consume());
+            continue;
+        }
+    }
+    m_path = String::copy(buffer);
+    return true;
+}
+
+URL::URL(const StringView& string)
+{
+    m_valid = parse(string);
+}
+
+String URL::to_string() const
+{
+    StringBuilder builder;
+    builder.append(m_protocol);
+    builder.append("://");
+    builder.append(m_host);
+    builder.append(':');
+    builder.append(String::number(m_port));
+    builder.append(m_path);
+    return builder.to_string();
+}
+
+}