Simplify describe message

src/postgres/protocol/describe.rs

@@ -1,63 +1,55 @@
-use super::Encode;
-use std::io;
 
-#[derive(Debug)]
-pub enum DescribeKind {
-    Portal,
-    PreparedStatement,
+/// The Describe message (portal variant) specifies the name of an existing portal
+/// (or an empty string for the unnamed portal). The response is a RowDescription message
+/// describing the rows that will be returned by executing the portal; or a NoData message
+/// if the portal does not contain a query that will return rows; or ErrorResponse if there is no such portal.
+pub fn portal(buf: &mut Vec<u8>, name: &str) {
+    buf.push(b'D');
+
+    let len = 4 + name.len() + 1 + 4;
+    buf.extend_from_slice(&(len as i32).to_be_bytes());
+
+    buf.push(b'P');
+
+    buf.extend_from_slice(name.as_bytes());
+    buf.push(b'\0');
 }
 
-#[derive(Debug)]
-pub struct Describe<'a> {
-    kind: DescribeKind,
-    name: &'a str,
-}
+/// The Describe message (statement variant) specifies the name of an existing prepared statement
+/// (or an empty string for the unnamed prepared statement). The response is a ParameterDescription
+/// message describing the parameters needed by the statement, followed by a RowDescription message
+/// describing the rows that will be returned when the statement is eventually executed
+/// (or a NoData message if the statement will not return rows). ErrorResponse is issued if
+/// there is no such prepared statement. Note that since Bind has not yet been issued,
+/// the formats to be used for returned columns are not yet known to the backend; the
+/// format code fields in the RowDescription message will be zeroes in this case.
+pub fn statement(buf: &mut Vec<u8>, name: &str) {
+    buf.push(b'D');
 
-impl<'a> Describe<'a> {
-    pub fn new(kind: DescribeKind, name: &'a str) -> Self {
-        Self { kind, name }
-    }
-}
+    let len = 4 + name.len() + 1 + 4;
+    buf.extend_from_slice(&(len as i32).to_be_bytes());
 
-impl<'a> Encode for Describe<'a> {
-    fn encode(&self, buf: &mut Vec<u8>) -> io::Result<()> {
-        buf.push(b'D');
+    buf.push(b'S');
 
-        let len = 4 + self.name.len() + 1 + 4;
-        buf.extend_from_slice(&(len as i32).to_be_bytes());
-
-        match &self.kind {
-            DescribeKind::Portal => buf.push(b'P'),
-            DescribeKind::PreparedStatement => buf.push(b'S'),
-        };
-
-        buf.extend_from_slice(self.name.as_bytes());
-        buf.push(b'\0');
-
-        Ok(())
-    }
+    buf.extend_from_slice(name.as_bytes());
+    buf.push(b'\0');
 }
 
 #[cfg(test)]
 mod test {
-    use super::{Describe, DescribeKind, Encode};
-    use std::io;
-
     #[test]
-    fn it_encodes_describe_portal() -> io::Result<()> {
+    fn it_encodes_describe_portal() {
         let mut buf = vec![];
-        Describe::new(DescribeKind::Portal, "ABC123").encode(&mut buf)?;
-        assert_eq!(&buf, b"D\x00\x00\x00\x0fPABC123\x00");
+        super::portal(&mut buf, "ABC123");
 
-        Ok(())
+        assert_eq!(&buf, b"D\x00\x00\x00\x0fPABC123\x00");
     }
 
     #[test]
-    fn it_encodes_describe_statement() -> io::Result<()> {
+    fn it_encodes_describe_statement() {
         let mut buf = vec![];
-        Describe::new(DescribeKind::PreparedStatement, "95 apples").encode(&mut buf)?;
-        assert_eq!(&buf, b"D\x00\x00\x00\x12S95 apples\x00");
+        super::statement(&mut buf, "95 apples");
 
-        Ok(())
+        assert_eq!(&buf, b"D\x00\x00\x00\x12S95 apples\x00");
     }
 }

src/postgres/protocol/mod.rs

@@ -1,11 +1,9 @@
-pub mod bind;
+// Unsorted
 
-mod authentication;
 mod backend_key_data;
 mod command_complete;
 mod data_row;
 mod decode;
-mod describe;
 mod encode;
 mod execute;
 mod message;
@@ -22,13 +20,21 @@ mod startup_message;
 mod sync;
 mod terminate;
 
+// Front-end
+
+pub mod bind;
+pub mod describe;
+
+// Back-end
+
+mod authentication;
+
 pub use self::{
     authentication::Authentication,
     backend_key_data::BackendKeyData,
     command_complete::CommandComplete,
     data_row::DataRow,
     decode::Decode,
-    describe::{Describe, DescribeKind},
     encode::Encode,
     execute::Execute,
     message::Message,