From 367cb48096b50ab66bced24633808f0e1dd43ed7 Mon Sep 17 00:00:00 2001
From: Krishnan Parthasarathi <krisis@users.noreply.github.com>
Date: Tue, 16 Nov 2021 15:26:48 -0800
Subject: [PATCH] reduceErrs to handle context.Canceled errors (#13670)

With this change, reduceErrs will group all errors due to
context cancelation as the same.

e.g, Following are errors due to context cancelation seen
from 3 remote disks. Their error values are different but
they are all caused due to the same context cancelation.

['Post
"http://minio2:9000/minio/storage/data1/v37/statvol?disk-id=101cbc99-f5d2-4a9d-b18b-97e872b3e4a7&volume=mybucket":
context canceled',
 'Post
 "http://minio3:9000/minio/storage/data1/v37/statvol?disk-id=7a84474b-a4fd-4b80-8aab-d308a587c280&volume=mybucket":
 context canceled',
 'Post
 "http://minio4:9000/minio/storage/data1/v37/statvol?disk-id=d60d571a-83c8-487d-9e14-beebc94682d2&volume=mybucket":
 context canceled']
---
 cmd/erasure-metadata-utils.go      | 5 +++++
 cmd/erasure-metadata-utils_test.go | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/cmd/erasure-metadata-utils.go b/cmd/erasure-metadata-utils.go
index 16ae8118b..ef28834ef 100644
--- a/cmd/erasure-metadata-utils.go
+++ b/cmd/erasure-metadata-utils.go
@@ -39,6 +39,11 @@ func reduceErrs(errs []error, ignoredErrs []error) (maxCount int, maxErr error)
 		if IsErrIgnored(err, ignoredErrs...) {
 			continue
 		}
+		// Errors due to context cancelation may be wrapped - group them by context.Canceled.
+		if errors.Is(err, context.Canceled) {
+			errorCounts[context.Canceled]++
+			continue
+		}
 		errorCounts[err]++
 	}
 
diff --git a/cmd/erasure-metadata-utils_test.go b/cmd/erasure-metadata-utils_test.go
index 4d24b0673..a64976481 100644
--- a/cmd/erasure-metadata-utils_test.go
+++ b/cmd/erasure-metadata-utils_test.go
@@ -54,6 +54,10 @@ func TestDiskCount(t *testing.T) {
 // Test for reduceErrs, reduceErr reduces collection
 // of errors into a single maximal error with in the list.
 func TestReduceErrs(t *testing.T) {
+	canceledErrs := make([]error, 0, 5)
+	for i := 0; i < 5; i++ {
+		canceledErrs = append(canceledErrs, fmt.Errorf("error %d: %w", i, context.Canceled))
+	}
 	// List all of all test cases to validate various cases of reduce errors.
 	testCases := []struct {
 		errs        []error
@@ -86,6 +90,8 @@ func TestReduceErrs(t *testing.T) {
 		{[]error{errFileNotFound, errFileNotFound, errFileNotFound,
 			errFileNotFound, errFileNotFound, nil, nil, nil, nil, nil},
 			nil, nil},
+		// Checks if wrapped context cancelation errors are grouped as one.
+		{canceledErrs, nil, context.Canceled},
 	}
 	// Validates list of all the testcases for returning valid errors.
 	for i, testCase := range testCases {