Add unhex(X) scalar function

This commit adds `unhex(X)` scalar function. Function with `unhex(X,Y)`
two arguments is not implemented yet.

Relates to issue #144

COMPAT.md

@@ -112,7 +112,7 @@ This document describes the SQLite compatibility status of Limbo:
 | trim(X)                      | Yes    |         |
 | trim(X,Y)                    | Yes    |         |
 | typeof(X)                    | Yes    |         |
-| unhex(X)                     | No     |         |
+| unhex(X)                     | Yes    |         |
 | unhex(X,Y)                   | No     |         |
 | unicode(X)                   | Yes    |         |
 | unlikely(X)                  | No     |         |

core/function.rs

@@ -77,6 +77,7 @@ pub enum ScalarFunc {
     SqliteVersion,
     UnixEpoch,
     Hex,
+    Unhex,
 }
 
 impl Display for ScalarFunc {
@@ -112,6 +113,7 @@ impl Display for ScalarFunc {
             ScalarFunc::SqliteVersion => "sqlite_version".to_string(),
             ScalarFunc::UnixEpoch => "unixepoch".to_string(),
             ScalarFunc::Hex => "hex".to_string(),
+            ScalarFunc::Unhex => "unhex".to_string(),
         };
         write!(f, "{}", str)
     }
@@ -182,6 +184,7 @@ impl Func {
             "json" => Ok(Func::Json(JsonFunc::Json)),
             "unixepoch" => Ok(Func::Scalar(ScalarFunc::UnixEpoch)),
             "hex" => Ok(Func::Scalar(ScalarFunc::Hex)),
+            "unhex" => Ok(Func::Scalar(ScalarFunc::Unhex)),
             _ => Err(()),
         }
     }

core/translate/expr.rs

@@ -1215,7 +1215,8 @@ pub fn translate_expr(
                         ScalarFunc::Trim
                         | ScalarFunc::LTrim
                         | ScalarFunc::RTrim
-                        | ScalarFunc::Round => {
+                        | ScalarFunc::Round
+                        | ScalarFunc::Unhex => {
                             let args = if let Some(args) = args {
                                 if args.len() > 2 {
                                     crate::bail_parse_error!(

core/vdbe/mod.rs

@@ -1551,6 +1551,12 @@ impl Program {
                                 let result = exec_hex(reg_value);
                                 state.registers[*dest] = result;
                             }
+                            ScalarFunc::Unhex => {
+                                let reg_value = state.registers[*start_reg].clone();
+                                let ignored_chars = state.registers.get(*start_reg + 1);
+                                let result = exec_unhex(&reg_value, ignored_chars);
+                                state.registers[*dest] = result;
+                            }
                             ScalarFunc::Random => {
                                 state.registers[*dest] = exec_random();
                             }
@@ -2171,6 +2177,20 @@ fn exec_hex(reg: &OwnedValue) -> OwnedValue {
     }
 }
 
+fn exec_unhex(reg: &OwnedValue, ignored_chars: Option<&OwnedValue>) -> OwnedValue {
+    if ignored_chars.is_some() {
+        unimplemented!("unhex(X,Y) is not implemented");
+    }
+
+    match reg {
+        OwnedValue::Null => OwnedValue::Null,
+        _ => match hex::decode(reg.to_string()) {
+            Ok(bytes) => OwnedValue::Blob(Rc::new(bytes)),
+            Err(_) => OwnedValue::Null,
+        },
+    }
+}
+
 fn exec_unicode(reg: &OwnedValue) -> OwnedValue {
     match reg {
         OwnedValue::Text(_)
@@ -2292,7 +2312,7 @@ mod tests {
     use super::{
         exec_abs, exec_char, exec_hex, exec_if, exec_length, exec_like, exec_lower, exec_ltrim,
         exec_max, exec_min, exec_nullif, exec_quote, exec_random, exec_round, exec_rtrim,
-        exec_sign, exec_substring, exec_trim, exec_typeof, exec_unicode, exec_upper,
+        exec_sign, exec_substring, exec_trim, exec_typeof, exec_unhex, exec_unicode, exec_upper,
         execute_sqlite_version, get_new_rowid, AggContext, Cursor, CursorResult, LimboError,
         OwnedRecord, OwnedValue, Result,
     };
@@ -2644,6 +2664,33 @@ mod tests {
         assert_eq!(exec_hex(&input_float), expected_val);
     }
 
+    #[test]
+    fn test_unhex() {
+        let input = OwnedValue::Text(Rc::new(String::from("6F")));
+        let expected = OwnedValue::Blob(Rc::new(vec![0x6f]));
+        assert_eq!(exec_unhex(&input, None), expected);
+
+        let input = OwnedValue::Text(Rc::new(String::from("6f")));
+        let expected = OwnedValue::Blob(Rc::new(vec![0x6f]));
+        assert_eq!(exec_unhex(&input, None), expected);
+
+        let input = OwnedValue::Text(Rc::new(String::from("611")));
+        let expected = OwnedValue::Null;
+        assert_eq!(exec_unhex(&input, None), expected);
+
+        let input = OwnedValue::Text(Rc::new(String::from("")));
+        let expected = OwnedValue::Blob(Rc::new(vec![]));
+        assert_eq!(exec_unhex(&input, None), expected);
+
+        let input = OwnedValue::Text(Rc::new(String::from("61x")));
+        let expected = OwnedValue::Null;
+        assert_eq!(exec_unhex(&input, None), expected);
+
+        let input = OwnedValue::Null;
+        let expected = OwnedValue::Null;
+        assert_eq!(exec_unhex(&input, None), expected);
+    }
+
     #[test]
     fn test_abs() {
         let int_positive_reg = OwnedValue::Integer(10);

testing/scalar-functions.test

@@ -119,6 +119,30 @@ do_execsql_test hex-null {
   select hex(null)
 } {}
 
+do_execsql_test unhex-str-ab {
+  SELECT unhex('6162');
+} {ab}
+
+do_execsql_test unhex-int-ab {
+  SELECT unhex(6162);
+} {ab}
+
+do_execsql_test unhex-dot-uppercase {
+  SELECT unhex('2E');
+} {.}
+
+do_execsql_test unhex-dot-lowercase {
+  SELECT unhex('2e');
+} {.}
+
+do_execsql_test unhex-no-hex {
+  SELECT unhex('x');
+} {}
+
+do_execsql_test unhex-null {
+  SELECT unhex(NULL);
+} {}
+
 do_execsql_test trim {
   SELECT trim('   Limbo    ');
 } {Limbo}