Encode Describe messages

sqlx-postgres-protocol/src/describe.rs

@@ -0,0 +1,64 @@
+use crate::Encode;
+use std::io;
+
+#[derive(Debug)]
+pub enum DescribeKind {
+    Portal,
+    PreparedStatement,
+}
+
+#[derive(Debug)]
+pub struct Describe<'a> {
+    kind: DescribeKind,
+    name: &'a str,
+}
+
+impl<'a> Describe<'a> {
+    pub fn new(kind: DescribeKind, name: &'a str) -> Self {
+        Self { kind, name }
+    }
+}
+
+impl<'a> Encode for Describe<'a> {
+    fn encode(&self, buf: &mut Vec<u8>) -> io::Result<()> {
+        buf.push(b'D');
+
+        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(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::{Describe, DescribeKind};
+    use crate::Encode;
+    use std::io;
+
+    #[test]
+    fn it_encodes_describe_portal() -> io::Result<()> {
+        let mut buf = vec![];
+        Describe::new(DescribeKind::Portal, "ABC123").encode(&mut buf)?;
+        assert_eq!(&buf, b"D\x00\x00\x00\x0fPABC123\x00");
+
+        Ok(())
+    }
+
+    #[test]
+    fn it_encodes_describe_statement() -> io::Result<()> {
+        let mut buf = vec![];
+        Describe::new(DescribeKind::PreparedStatement, "95 apples").encode(&mut buf)?;
+        assert_eq!(&buf, b"D\x00\x00\x00\x12S95 apples\x00");
+
+        Ok(())
+    }
+}

sqlx-postgres-protocol/src/lib.rs

@@ -6,6 +6,7 @@ pub mod bind;
 mod command_complete;
 mod data_row;
 mod decode;
+mod describe;
 mod encode;
 mod execute;
 mod message;
@@ -28,6 +29,7 @@ pub use self::{
     command_complete::CommandComplete,
     data_row::DataRow,
     decode::Decode,
+    describe::{Describe, DescribeKind},
     encode::Encode,
     execute::Execute,
     message::Message,