runtime: add byte count parser for GOMEMLIMIT

This change adds a parser for the GOMEMLIMIT environment variable's
input. This environment variable accepts a number followed by an
optional prefix expressing the unit. Acceptable units include
B, KiB, MiB, GiB, TiB, where *iB is a power-of-two byte unit.

For #48409.

Change-Id: I6a3b4c02b175bfcf9c4debee6118cf5dda93bb6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/393400
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>

1 files changed, 123 insertions, 0 deletions

diff --git a/src/runtime/string_test.go b/src/runtime/string_test.go
index 4eda12c35d..1ea7f5e481 100644
--- a/src/runtime/string_test.go
+++ b/src/runtime/string_test.go
@@ -454,3 +454,126 @@ func TestAtoi32(t *testing.T) {
 		}
 	}
 }
+
+func TestParseByteCount(t *testing.T) {
+	for _, test := range []struct {
+		in  string
+		out int64
+		ok  bool
+	}{
+		// Good numeric inputs.
+		{"1", 1, true},
+		{"12345", 12345, true},
+		{"012345", 12345, true},
+		{"98765432100", 98765432100, true},
+		{"9223372036854775807", 1<<63 - 1, true},
+
+		// Good trivial suffix inputs.
+		{"1B", 1, true},
+		{"12345B", 12345, true},
+		{"012345B", 12345, true},
+		{"98765432100B", 98765432100, true},
+		{"9223372036854775807B", 1<<63 - 1, true},
+
+		// Good binary suffix inputs.
+		{"1KiB", 1 << 10, true},
+		{"05KiB", 5 << 10, true},
+		{"1MiB", 1 << 20, true},
+		{"10MiB", 10 << 20, true},
+		{"1GiB", 1 << 30, true},
+		{"100GiB", 100 << 30, true},
+		{"1TiB", 1 << 40, true},
+		{"99TiB", 99 << 40, true},
+
+		// Good zero inputs.
+		//
+		// -0 is an edge case, but no harm in supporting it.
+		{"-0", 0, true},
+		{"0", 0, true},
+		{"0B", 0, true},
+		{"0KiB", 0, true},
+		{"0MiB", 0, true},
+		{"0GiB", 0, true},
+		{"0TiB", 0, true},
+
+		// Bad inputs.
+		{"", 0, false},
+		{"-1", 0, false},
+		{"a12345", 0, false},
+		{"a12345B", 0, false},
+		{"12345x", 0, false},
+		{"0x12345", 0, false},
+
+		// Bad numeric inputs.
+		{"9223372036854775808", 0, false},
+		{"9223372036854775809", 0, false},
+		{"18446744073709551615", 0, false},
+		{"20496382327982653440", 0, false},
+		{"18446744073709551616", 0, false},
+		{"18446744073709551617", 0, false},
+		{"9999999999999999999999", 0, false},
+
+		// Bad trivial suffix inputs.
+		{"9223372036854775808B", 0, false},
+		{"9223372036854775809B", 0, false},
+		{"18446744073709551615B", 0, false},
+		{"20496382327982653440B", 0, false},
+		{"18446744073709551616B", 0, false},
+		{"18446744073709551617B", 0, false},
+		{"9999999999999999999999B", 0, false},
+
+		// Bad binary suffix inputs.
+		{"1Ki", 0, false},
+		{"05Ki", 0, false},
+		{"10Mi", 0, false},
+		{"100Gi", 0, false},
+		{"99Ti", 0, false},
+		{"22iB", 0, false},
+		{"B", 0, false},
+		{"iB", 0, false},
+		{"KiB", 0, false},
+		{"MiB", 0, false},
+		{"GiB", 0, false},
+		{"TiB", 0, false},
+		{"-120KiB", 0, false},
+		{"-891MiB", 0, false},
+		{"-704GiB", 0, false},
+		{"-42TiB", 0, false},
+		{"99999999999999999999KiB", 0, false},
+		{"99999999999999999MiB", 0, false},
+		{"99999999999999GiB", 0, false},
+		{"99999999999TiB", 0, false},
+		{"555EiB", 0, false},
+
+		// Mistaken SI suffix inputs.
+		{"0KB", 0, false},
+		{"0MB", 0, false},
+		{"0GB", 0, false},
+		{"0TB", 0, false},
+		{"1KB", 0, false},
+		{"05KB", 0, false},
+		{"1MB", 0, false},
+		{"10MB", 0, false},
+		{"1GB", 0, false},
+		{"100GB", 0, false},
+		{"1TB", 0, false},
+		{"99TB", 0, false},
+		{"1K", 0, false},
+		{"05K", 0, false},
+		{"10M", 0, false},
+		{"100G", 0, false},
+		{"99T", 0, false},
+		{"99999999999999999999KB", 0, false},
+		{"99999999999999999MB", 0, false},
+		{"99999999999999GB", 0, false},
+		{"99999999999TB", 0, false},
+		{"99999999999TiB", 0, false},
+		{"555EB", 0, false},
+	} {
+		out, ok := runtime.ParseByteCount(test.in)
+		if test.out != out || test.ok != ok {
+			t.Errorf("parseByteCount(%q) = (%v, %v) want (%v, %v)",
+				test.in, out, ok, test.out, test.ok)
+		}
+	}
+}