Add a tagged union for all backend messages.

Move read_message to proto.zig and make it return the tagged union
rather than expecting a message type.

3 files changed, 54 insertions, 2 deletions

diff --git a/src/proto/authentication_request.zig b/src/proto/authentication_request.zig
index 9203482..3ea5cd1 100644
--- a/src/proto/authentication_request.zig
+++ b/src/proto/authentication_request.zig
@@ -30,7 +30,11 @@ pub fn read(_: std.mem.Allocator, b: []const u8) !AuthenticationRequest {
         log.err("invalid message length, expected 4 got {}", .{b.len});
         return ProtocolError.InvalidMessageLength;
     }
-    const inner_type = enum_from_int(InnerAuthRequestType, std.mem.readIntBig(u32, b[0..4])) orelse return ClientError.UnsupportedAuthType;
+    const auth_type_int = std.mem.readIntBig(u32, b[0..4]);
+    const inner_type = enum_from_int(InnerAuthRequestType, auth_type_int) orelse {
+        log.err("Unsupported auth type {}", .{auth_type_int});
+        return ClientError.UnsupportedAuthType;
+    };
     var inner: InnerAuthRequest = switch (inner_type) {
         .AuthRequestTypeOk => .{ .ok = AuthRequestOk{} },
         .AuthRequestTypeCleartextPassword => .{ .cleartext_password = AuthRequestCleartextPassword{} },
diff --git a/src/proto/proto.zig b/src/proto/proto.zig
index df1b717..5e4489d 100644
--- a/src/proto/proto.zig
+++ b/src/proto/proto.zig
@@ -1,3 +1,4 @@
+const std = @import("std");
 pub const StartupMessage = @import("startup_message.zig");
 pub const AuthenticationRequest = @import("authentication_request.zig");
 pub const PasswordMessage = @import("password_message.zig");
@@ -13,6 +14,53 @@ const CopyXResponse = @import("copy_x_response.zig").CopyXResponse;
 pub const CopyInResponse = CopyXResponse('G');
 pub const CopyOutResponse = CopyXResponse('H');
 pub const CopyBothResponse = CopyXResponse('W');
+const enum_from_int = @import("../main.zig").enum_from_int;
+const ProtocolError = @import("../main.zig").ProtocolError;
+
+pub const BackendMessage = union(enum) {
+    AuthenticationRequest: AuthenticationRequest,
+    ErrorResponse: ErrorResponse,
+    ReadyForQuery: ReadyForQuery,
+    ParameterStatus: ParameterStatus,
+    BackendKeyData: BackendKeyData,
+    DataRow: DataRow,
+    RowDescription: RowDescription,
+    CommandComplete: CommandComplete,
+    CopyInResponse: CopyInResponse,
+    CopyOutResponse: CopyOutResponse,
+    CopyBothResponse: CopyBothResponse,
+
+    pub fn deinit(self: *BackendMessage, a: std.mem.Allocator) void {
+        switch (self.*) {
+            inline else => |*sf| {
+                sf.deinit(a);
+            },
+        }
+    }
+};
+
+test {
+    inline for (@typeInfo(BackendMessage).Union.fields) |field| {
+        const msg_type = field.type;
+        if (!@hasDecl(msg_type, "Tag")) @compileError("message type " ++ @typeName(msg_type) ++ " must have a .Tag decl");
+        if (!@hasDecl(msg_type, "read")) @compileError("message type " ++ @typeName(msg_type) ++ " must have a .read decl");
+    }
+}
+
+pub fn read_message(allocator: std.mem.Allocator, stream_reader: anytype) !BackendMessage {
+    const tag = try stream_reader.readByte();
+    const len = try stream_reader.readIntBig(u32);
+    const buf = try allocator.alloc(u8, @as(u32, @intCast(len - 4)));
+    defer allocator.free(buf);
+    try stream_reader.readNoEof(buf);
+    inline for (@typeInfo(BackendMessage).Union.fields) |field| {
+        if (field.type.Tag == tag) {
+            return @unionInit(BackendMessage, field.name, try field.type.read(allocator, buf));
+        }
+    } else {
+        return ProtocolError.InvalidMessageType;
+    }
+}
 
 test {
     _ = AuthenticationRequest;
diff --git a/src/proto/row_description.zig b/src/proto/row_description.zig
index a0e8810..b8105e2 100644
--- a/src/proto/row_description.zig
+++ b/src/proto/row_description.zig
@@ -34,7 +34,7 @@ pub fn read(a: std.mem.Allocator, b: []const u8) !RowDescription {
     for (0..n_fields) |i| {
         const name_start = fbs.pos;
         try reader.skipUntilDelimiterOrEof(0);
-        const name_end = fbs.pos-1;
+        const name_end = fbs.pos - 1;
         const name = res.buf.?[name_start..name_end];
         const field = Field{
             .name = name,