feat: add extract_extension function

Author: hatamiarash7

src/functions/extract_extension.cpp

@@ -0,0 +1,75 @@
+#include "extract_extension.hpp"
+
+#include <regex>
+
+namespace duckdb
+{
+    // Function to extract the extension from a URL
+    void ExtractExtensionFunction (DataChunk &args, ExpressionState &state, Vector &result)
+    {
+        // Extract the input from the arguments
+        auto &input_vector = args.data[0];
+        auto result_data   = FlatVector::GetData<string_t> (result);
+
+        for (idx_t i = 0; i < args.size (); i++)
+        {
+            auto input = input_vector.GetValue (i).ToString ();
+            std::transform (input.begin (), input.end (), input.begin (), ::tolower);
+
+            try
+            {
+                // Extract the extension using the utility function
+                auto ext       = netquack::ExtractExtension (input);
+                result_data[i] = StringVector::AddString (result, ext);
+            }
+            catch (const std::exception &e)
+            {
+                result_data[i] = "Error extracting extension: " + std::string (e.what ());
+            }
+        };
+    }
+
+    namespace netquack
+    {
+        std::string ExtractExtension (const std::string &input)
+        {
+            // Regex to extract valid file extensions from paths/URLs
+            // Explanation:
+            // (?<!\.)                - Negative lookbehind ensures no preceding dot (avoids "..ext")
+            // \.                     - Literal dot (extension separator)
+            // ([a-zA-Z0-9]{1,10})    - Capturing group for extension:
+            //                         - 1-10 alphanumeric chars (prevents long garbage matches)
+            // (?=[?#]|$)             - Positive lookahead for:
+            //                         - Query separator (?)
+            //                         - Fragment (#)
+            //                         - Or end of string ($)
+            //
+            // Examples matched:
+            //   /path/image.jpg      -> jpg
+            //   /doc.v12.pdf         -> pdf
+            //   /archive.tar.gz      -> gz
+            //   https://site.com/page.html?param=1 -> html
+            //
+            // Rejected cases:
+            //   /path..jpg           -> no match (double dot)
+            //   /path.               -> no match (no extension after dot)
+            //   /.hidden_file        -> no match (no alnum after dot)
+            //   /path.with.dots/file -> no match (not at end)
+            std::regex ext_regex (R"(^(?!.*\.\.)(?:.*\/)?[^\/?#]+\.([a-zA-Z0-9]{1,10})(?=[?#]|$))");
+            std::smatch ext_match;
+
+            // Use regex_search to find the extension component in the input string
+            if (std::regex_search (input, ext_match, ext_regex))
+            {
+                // Check if the extension group was matched and is not empty
+                if (ext_match.size () > 1 && ext_match[1].matched)
+                {
+                    return ext_match[1].str ();
+                }
+            }
+
+            // If no extension is found, return an empty string
+            return "";
+        }
+    } // namespace netquack
+} // namespace duckdb

src/functions/extract_extension.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "duckdb.hpp"
+
+namespace duckdb
+{
+    // Function to extract the extension from a URL
+    void ExtractExtensionFunction (DataChunk &args, ExpressionState &state, Vector &result);
+
+    namespace netquack
+    {
+        // Function to extract the extension from a URL or host
+        std::string ExtractExtension (const std::string &input);
+    } // namespace netquack
+} // namespace duckdb

src/netquack_extension.cpp

@@ -9,6 +9,7 @@
 #include "duckdb/main/extension_util.hpp"
 #include "duckdb/parser/parsed_data/create_scalar_function_info.hpp"
 #include "functions/extract_domain.hpp"
+#include "functions/extract_extension.hpp"
 #include "functions/extract_host.hpp"
 #include "functions/extract_path.hpp"
 #include "functions/extract_port.hpp"
@@ -94,6 +95,13 @@ namespace duckdb
             ExtractPortFunction);
         ExtensionUtil::RegisterFunction (instance, netquack_extract_port_function);
 
+        auto netquack_extract_extension_function = ScalarFunction (
+            "extract_extension",
+            { LogicalType::VARCHAR },
+            LogicalType::VARCHAR,
+            ExtractExtensionFunction);
+        ExtensionUtil::RegisterFunction (instance, netquack_extract_extension_function);
+
         auto netquack_update_tranco_function = ScalarFunction (
             "update_tranco",
             { LogicalType::BOOLEAN },