util: New buffered infinite chan primitive

I'm sure there are better implementations, but this feels clean enough
for now. Let's see if this is useful or not.

util/infinitechan.go

@@ -0,0 +1,84 @@
+// Mgmt
+// Copyright (C) James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package util
+
+// InfiniteChan is a buffered channel that has a theoretical infinite size. Of
+// could you can run out of memory though. This is the same idea as a
+// `make(chan T, $size)` but where $size grows to however big you need it to be.
+type InfiniteChan[T any] struct {
+	In  chan<- T
+	Out <-chan T
+}
+
+// NewInfiniteChan builds a new InfiniteChat of the correct type.
+func NewInfiniteChan[T any]() *InfiniteChan[T] {
+	in := make(chan T)
+	out := make(chan T)
+
+	go func() {
+		defer close(out)
+
+		buffer := make([]T, 0) // "infinite"
+		closed := false
+
+		for {
+			if closed && len(buffer) == 0 {
+				// Clean shutdown: all data sent, now close and exit
+				return
+			}
+
+			var next T    // next value to send
+			var ch chan T // blocks unless "enabled" below
+
+			// We have at least one value, so "enable" the send chan.
+			if len(buffer) > 0 {
+				next = buffer[0]
+				ch = out
+			}
+
+			select {
+			case val, ok := <-in: // recv
+				if !ok {
+					closed = true
+					continue
+				}
+				buffer = append(buffer, val)
+
+			case ch <- next: // send
+				buffer = buffer[1:]
+			}
+		}
+	}()
+
+	return &InfiniteChan[T]{
+		In:  in,
+		Out: out,
+	}
+}

util/infinitechan_test.go

@@ -0,0 +1,69 @@
+// Mgmt
+// Copyright (C) James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+//go:build !root
+
+package util
+
+import (
+	"testing"
+)
+
+func TestInfiniteChan(t *testing.T) {
+	ch := NewInfiniteChan[string]()
+
+	expected := []string{"one", "two", "three", "four", "five"}
+
+	// producer
+	go func() {
+		for _, val := range expected {
+			ch.In <- val
+		}
+		close(ch.In)
+	}()
+
+	// consumer
+	var result []string
+	for val := range ch.Out {
+		result = append(result, val)
+	}
+
+	// check length
+	if len(result) != len(expected) {
+		t.Errorf("expected: %d items, actual: %d", len(expected), len(result))
+		return
+	}
+
+	// check ordering and values
+	for i := range expected {
+		if result[i] != expected[i] {
+			t.Errorf("expected(%d): %v, actual: %v", i, expected[i], result[i])
+		}
+	}
+}