test: demomnstrate API contract for metadata TableParquetOptions

datafusion/common/src/config.rs

@@ -1384,6 +1384,20 @@ impl ConfigField for TableParquetOptions {
         // Determine the key if it's a global or column-specific setting
         if key.contains("::") {
             self.column_specific_options.set(key, value)
+        } else if key.eq("metadata") {
+            for maybe_pair in value.split('_') {
+                let (k, v) = match maybe_pair.split(':').collect::<Vec<_>>()[..] {
+                    [k, v] => (k.into(), Some(v.into())),
+                    [k] => (k.into(), None),
+                    _ => {
+                        return Err(DataFusionError::Configuration(format!(
+                            "Invalid metadata provided \"{maybe_pair}\""
+                        )))
+                    }
+                };
+                self.key_value_metadata.insert(k, v);
+            }
+            Ok(())
         } else {
             self.global.set(key, value)
         }

datafusion/sqllogictest/test_files/copy.slt

@@ -283,11 +283,38 @@ OPTIONS (
 'format.statistics_enabled::col2' none,
 'format.max_statistics_size' 123,
 'format.bloom_filter_fpp' 0.001,
-'format.bloom_filter_ndv' 100
+'format.bloom_filter_ndv' 100,
+'format.metadata' 'foo:bar baz'
 )
 ----
 2
 
+# valid vs invalid metadata
+
+statement ok
+COPY source_table
+TO 'test_files/scratch/copy/table_with_metadata/'
+STORED AS PARQUET
+OPTIONS (
+'format.metadata' ''
+)
+
+statement error
+COPY source_table
+TO 'test_files/scratch/copy/table_with_metadata/'
+STORED AS PARQUET
+OPTIONS (
+'format.metadata' 'foo:bar:extra'
+)
+
+statement error
+COPY source_table
+TO 'test_files/scratch/copy/table_with_metadata/'
+STORED AS PARQUET
+OPTIONS (
+'format.wrong-metadata-key' 'foo:bar baz'
+)
+
 # validate multiple parquet file output with all options set
 statement ok
 CREATE EXTERNAL TABLE validate_parquet_with_options STORED AS PARQUET LOCATION 'test_files/scratch/copy/table_with_options/';