Add support for describing prepared statements

Author: akheron

packages/pg/lib/client.js

@@ -332,6 +332,11 @@ Client.prototype._attachListeners = function (con) {
     self.activeQuery.handleDataRow(msg)
   })
 
+  // delegate paramDescription to active query
+  con.on('paramDescription', function (msg) {
+    self.activeQuery.handleParamDescription(msg, con)
+  })
+
   // delegate portalSuspended to active query
   // eslint-disable-next-line no-unused-vars
   con.on('portalSuspended', function (msg) {

packages/pg/lib/connection.js

@@ -403,6 +403,9 @@ Connection.prototype.parseMessage = function (buffer) {
     case 0x73: // s
       return new Message('portalSuspended', length)
 
+    case 0x74: // t
+      return this.parset(buffer, length)
+
     case 0x47: // G
       return this.parseG(buffer, length)
 
@@ -540,6 +543,17 @@ Connection.prototype.parseField = function (buffer) {
   return field
 }
 
+Connection.prototype.parset = function (buffer, length) {
+  var msg = new Message('paramDescription', length)
+  msg.paramCount = this.parseInt16(buffer)
+  var params = []
+  for (var i = 0; i < msg.paramCount; i++) {
+    params.push(this.parseInt32(buffer))
+  }
+  msg.params = params
+  return msg
+}
+
 var DATA_ROW = 'dataRow'
 var DataRowMessage = function (length, fieldCount) {
   this.name = DATA_ROW

packages/pg/lib/query.js

@@ -24,6 +24,7 @@ class Query extends EventEmitter {
     this.types = config.types
     this.name = config.name
     this.binary = config.binary
+    this.describe = config.describe
     // use unique portal name each time
     this.portal = config.portal || ''
     this.callback = config.callback
@@ -45,6 +46,10 @@ class Query extends EventEmitter {
     if (this.name) {
       return true
     }
+    // always prepare if describing a query
+    if (this.describe) {
+      return true
+    }
     // always prepare if there are max number of rows expected per
     // portal execution
     if (this.rows) {
@@ -103,6 +108,11 @@ class Query extends EventEmitter {
     }
   }
 
+  handleParamDescription(msg, con) {
+    this._result.addParams(msg.params)
+    con.sync()
+  }
+
   handleCommandComplete(msg, con) {
     this._checkForMultirow()
     this._result.addCommandComplete(msg)
@@ -202,6 +212,16 @@ class Query extends EventEmitter {
       )
     }
 
+    if (this.describe) {
+      // if describe is set, the query is not executed
+      connection.describe({
+        type: 'S',
+        name: this.name,
+      })
+      connection.flush()
+      return
+    }
+
     if (this.values) {
       try {
         this.values = this.values.map(utils.prepareValue)

packages/pg/lib/result.js

@@ -18,6 +18,7 @@ var Result = function (rowMode, types) {
   this.oid = null
   this.rows = []
   this.fields = []
+  this.params = []
   this._parsers = undefined
   this._types = types
   this.RowCtor = null
@@ -102,4 +103,14 @@ Result.prototype.addFields = function (fieldDescriptions) {
   }
 }
 
+Result.prototype.addParams = function (paramDescriptions) {
+  if (this.params.length) {
+    this.params = []
+  }
+  for (var i = 0; i < paramDescriptions.length; i++) {
+    var desc = paramDescriptions[i]
+    this.params.push(desc)
+  }
+}
+
 module.exports = Result

packages/pg/test/integration/client/prepared-statement-tests.js

@@ -176,3 +176,28 @@ var suite = new helper.Suite()
 
   suite.test('cleanup', () => client.end())
 })()
+
+;(function () {
+  var client = helper.client()
+  client.on('drain', client.end.bind(client))
+
+  suite.test('describe', function (done) {
+    var query = client.query(new Query({
+      text: 'SELECT id, name, age FROM person WHERE age > $1',
+      describe: true
+    }, (err, res) => {
+      assert.deepEqual(res.params, [23])
+      assert.deepEqual(
+        res.fields.map(field => ({ name: field.name, type: field.dataTypeID })),
+        [
+          { name: 'id', type: 23 },
+          { name: 'name', type: 1043 },
+          { name: 'age', type: 23 }
+        ]
+      )
+      done()
+    }))
+  })
+
+  suite.test('cleanup', () => client.end())
+})()

packages/pg/test/unit/client/prepared-statement-tests.js

@@ -155,3 +155,54 @@ test('prepared statement with explicit portal', function () {
     })
   })
 })
+
+var describeClient = helper.client()
+var describeCon = describeClient.connection
+describeCon.parse = function (arg) {
+  process.nextTick(function () {
+    describeCon.emit('parseComplete')
+  })
+}
+var describeDescribeArg = null
+describeCon.describe = function (arg) {
+  describeDescribeArg = arg
+}
+
+var describeFlushCalled = false
+describeCon.flush = function () {
+  describeFlushCalled = true
+  process.nextTick(function () {
+    describeCon.emit('paramDescription', { params: [] })
+    describeCon.emit('rowDescription', { fields: [] })
+  })
+}
+
+var describeSyncCalled = false
+describeCon.sync = function () {
+  process.nextTick(function () {
+    describeSyncCalled = true
+    describeCon.emit('readyForQuery')
+  })
+}
+
+test('describe prepared statement', function () {
+  assert.ok(describeClient.connection.emit('readyForQuery'))
+
+  var query = describeClient.query(new Query({
+    text: 'select * from X where name = $1',
+    describe: true
+  }))
+
+  assert.emits(query, 'end', function () {
+    test('describe argument', function () {
+      assert.equal(describeDescribeArg.type, 'S')
+      assert.equal(describeDescribeArg.name, undefined)
+    })
+    test('flush called', function () {
+      assert.ok(describeFlushCalled)
+    })
+    test('sync called', function () {
+      assert.ok(describeSyncCalled)
+    })
+  })
+})