Enable REGEXP by connecting Crystal's stdlib Regex (#62)

spec/db_spec.cr

@@ -128,4 +128,9 @@ DB::DriverSpecs(DB::Any).run do
   it "handles multi-step pragma statements" do |db|
     db.exec %(PRAGMA journal_mode = memory)
   end
+
+  it "handles REGEXP operator" do |db|
+    (db.scalar "select 'unmatching text' REGEXP '^m'").should eq 0
+    (db.scalar "select 'matching text' REGEXP '^m'").should eq 1
+  end
 end

src/sqlite3.cr

@@ -6,4 +6,13 @@ module SQLite3
 
   # :nodoc:
   TIME_ZONE = Time::Location::UTC
+
+  # :nodoc:
+  REGEXP_FN = ->(context : LibSQLite3::SQLite3Context, argc : Int32, argv : LibSQLite3::SQLite3Value*) do
+    argv = Slice.new(argv, sizeof(Void*))
+    pattern = LibSQLite3.value_text(argv[0])
+    text = LibSQLite3.value_text(argv[1])
+    LibSQLite3.result_int(context, Regex.new(String.new(pattern)).matches?(String.new(text)).to_unsafe)
+    nil
+  end
 end

src/sqlite3/connection.cr

@@ -4,6 +4,8 @@ class SQLite3::Connection < DB::Connection
     filename = self.class.filename(database.uri)
     # TODO maybe enable Flag::URI to parse query string in the uri as additional flags
     check LibSQLite3.open_v2(filename, out @db, (Flag::READWRITE | Flag::CREATE), nil)
+    # 2 means 2 arguments; 1 is the code for UTF-8
+    check LibSQLite3.create_function(@db, "regexp", 2, 1, nil, SQLite3::REGEXP_FN, nil, nil)
   rescue
     raise DB::ConnectionRefused.new
   end

src/sqlite3/lib_sqlite3.cr

@@ -5,6 +5,8 @@ lib LibSQLite3
   type SQLite3 = Void*
   type Statement = Void*
   type SQLite3Backup = Void*
+  type SQLite3Context = Void*
+  type SQLite3Value = Void*
 
   enum Code
     # Successful result
@@ -72,6 +74,7 @@ lib LibSQLite3
   end
 
   alias Callback = (Void*, Int32, UInt8**, UInt8**) -> Int32
+  alias FuncCallback = (SQLite3Context, Int32, SQLite3Value*) -> Void
 
   fun open_v2 = sqlite3_open_v2(filename : UInt8*, db : SQLite3*, flags : ::SQLite3::Flag, zVfs : UInt8*) : Int32
 
@@ -108,4 +111,8 @@ lib LibSQLite3
   fun finalize = sqlite3_finalize(stmt : Statement) : Int32
   fun close_v2 = sqlite3_close_v2(SQLite3) : Int32
   fun close = sqlite3_close(SQLite3) : Int32
+
+  fun create_function = sqlite3_create_function(SQLite3, funcName : UInt8*, nArg : Int32, eTextRep : Int32, pApp : Void*, xFunc : FuncCallback, xStep : Void*, xFinal : Void*) : Int32
+  fun value_text = sqlite3_value_text(SQLite3Value) : UInt8*
+  fun result_int = sqlite3_result_int(SQLite3Context, Int32) : Nil
 end