feat: add support for describe statement (#125)

* feat: add support for describe statement

Adds support for DescribeStatement by transforming sql statements into a
select statement that queries the (types of) the parameters in the
original query. This can be used to temporarily support prepared
statements until a DescribeStatement endpoint is available in the
backend.

* test: add metadata results

* test: fix pgx tests

* perf: first describe portal

* feat: execute actual select first

* deps: use client lib SNAPSHOT

* fix: remove local absolute path

* fix: test failures

* fix: JDBC metadata test

* fix: address review comments

* fix: remove parameterized offset clause

Spangres does not (yet) support offset clauses that are not an integer literal.

* fix: ignore test for unsupported backend feature

src/main/java/com/google/cloud/spanner/pgadapter/parsers/Parser.java

@@ -25,6 +25,7 @@
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import org.postgresql.core.Oid;
+import org.postgresql.util.PGbytea;
 
 /**
  * Parser is the parsing superclass, used to take wire format data types and convert them
@@ -52,13 +53,9 @@ public static FormatCode of(short code) {
   protected T item;
 
   /**
-   * Untyped parameters are allowed in PostgreSQL, and some drivers use this deliberately to work
-   * around side effects regarding dates and timestamps with and without timezones. See for example
-   * https://github.com/pgjdbc/pgjdbc/blob/3af3b32cc5b77db3e7af1cbc217d6288fd0cf9b9/pgjdbc/src/main/java/org/postgresql/jdbc/PgPreparedStatement.java#L1322
+   * TODO: Remove when we have full support for DescribeStatement.
    *
-   * <p>TODO: This method currently only checks whether the value could be a timestamp with
-   * timezone. Date and timestamp without timezone are also known to be sent with type code {@link
-   * Oid#UNSPECIFIED} by the JDBC driver, and must be implemented once Spanner supports these types.
+   * <p>Guess the type of a parameter with unspecified type.
    *
    * @param item The value to guess the type for
    * @param formatCode The encoding that is used for the value
@@ -69,6 +66,17 @@ private static int guessType(byte[] item, FormatCode formatCode) {
     // TODO: Put 'guessType' behind a command line flag so it is only enabled when wanted.
     if (formatCode == FormatCode.TEXT && item != null) {
       String value = new String(item, StandardCharsets.UTF_8);
+      if (value.equals("t") || value.equals("f")) {
+        return Oid.BOOL;
+      }
+      if (value.length() >= 2 && value.charAt(0) == '\\' && value.charAt(1) == 'x') {
+        try {
+          PGbytea.toBytes(item);
+          return Oid.BYTEA;
+        } catch (Exception e) {
+          // ignore and fall through
+        }
+      }
       if (TimestampParser.isTimestamp(value)) {
         return Oid.TIMESTAMPTZ;
       }

src/main/java/com/google/cloud/spanner/pgadapter/parsers/UnspecifiedParser.java

@@ -26,7 +26,13 @@
 class UnspecifiedParser extends Parser<Value> {
 
   UnspecifiedParser(byte[] item, FormatCode formatCode) {
-    this.item = item == null ? null : Value.string(new String(item, UTF8));
+    this.item =
+        item == null
+            ? null
+            : Value.untyped(
+                com.google.protobuf.Value.newBuilder()
+                    .setStringValue(new String(item, StandardCharsets.UTF_8))
+                    .build());
   }
 
   @Override

src/main/java/com/google/cloud/spanner/pgadapter/statements/IntermediatePortalStatement.java

@@ -42,8 +42,9 @@ public class IntermediatePortalStatement extends IntermediatePreparedStatement {
   public IntermediatePortalStatement(
       ConnectionHandler connectionHandler,
       OptionsMetadata options,
+      String name,
       ParsedStatement parsedStatement) {
-    super(connectionHandler, options, parsedStatement);
+    super(connectionHandler, options, name, parsedStatement);
     this.statement = Statement.of(parsedStatement.getSqlWithoutComments());
     this.parameterFormatCodes = new ArrayList<>();
     this.resultFormatCodes = new ArrayList<>();