Fix Reader.Limited end of stream conditions

Author: whatisaphone

lib/std/Io/Reader/Limited.zig

@@ -27,6 +27,7 @@ pub fn init(reader: *Reader, limit: Limit, buffer: []u8) Limited {
 
 fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
     const l: *Limited = @fieldParentPtr("interface", r);
+    if (l.remaining == .nothing) return error.EndOfStream;
     const combined_limit = limit.min(l.remaining);
     const n = try l.unlimited.stream(w, combined_limit);
     l.remaining = l.remaining.subtract(n).?;
@@ -51,8 +52,51 @@ test stream {
 
 fn discard(r: *Reader, limit: Limit) Reader.Error!usize {
     const l: *Limited = @fieldParentPtr("interface", r);
+    if (l.remaining == .nothing) return error.EndOfStream;
     const combined_limit = limit.min(l.remaining);
     const n = try l.unlimited.discard(combined_limit);
     l.remaining = l.remaining.subtract(n).?;
     return n;
 }
+
+test "end of stream, read, hit limit exactly" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(4), &.{});
+    const r = &l.interface;
+
+    var buf: [2]u8 = undefined;
+    try r.readSliceAll(&buf);
+    try r.readSliceAll(&buf);
+    try std.testing.expectError(error.EndOfStream, l.interface.readSliceAll(&buf));
+}
+
+test "end of stream, read, hit limit after partial read" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(5), &.{});
+    const r = &l.interface;
+
+    var buf: [2]u8 = undefined;
+    try r.readSliceAll(&buf);
+    try r.readSliceAll(&buf);
+    try std.testing.expectError(error.EndOfStream, l.interface.readSliceAll(&buf));
+}
+
+test "end of stream, discard, hit limit exactly" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(4), &.{});
+    const r = &l.interface;
+
+    try r.discardAll(2);
+    try r.discardAll(2);
+    try std.testing.expectError(error.EndOfStream, l.interface.discardAll(2));
+}
+
+test "end of stream, discard, hit limit after partial read" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(5), &.{});
+    const r = &l.interface;
+
+    try r.discardAll(2);
+    try r.discardAll(2);
+    try std.testing.expectError(error.EndOfStream, l.interface.discardAll(2));
+}