From 68005592b38027490a08972f13269406b2556a07 Mon Sep 17 00:00:00 2001
From: Changkun Ou <hi@changkun.de>
Date: Thu, 19 May 2022 11:57:50 +0200
Subject: [PATCH] strings, bytes: add CutPrefix and CutSuffix

Fixes #42537

Change-Id: Ie03c2614ffee30ebe707acad6b9f6c28fb134a45
Reviewed-on: https://go-review.googlesource.com/c/go/+/407176
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Changkun Ou <mail@changkun.de>
Reviewed-by: Ian Lance Taylor <iant@google.com>
---
 api/next/42537.txt          |  4 ++++
 src/bytes/bytes.go          | 26 +++++++++++++++++++++++
 src/bytes/bytes_test.go     | 42 +++++++++++++++++++++++++++++++++++++
 src/strings/strings.go      | 22 +++++++++++++++++++
 src/strings/strings_test.go | 42 +++++++++++++++++++++++++++++++++++++
 5 files changed, 136 insertions(+)
 create mode 100644 api/next/42537.txt

diff --git a/api/next/42537.txt b/api/next/42537.txt
new file mode 100644
index 0000000000..4f2446aaf3
--- /dev/null
+++ b/api/next/42537.txt
@@ -0,0 +1,4 @@
+pkg bytes, func CutPrefix([]uint8, []uint8) ([]uint8, bool) #42537
+pkg bytes, func CutSuffix([]uint8, []uint8) ([]uint8, bool) #42537
+pkg strings, func CutPrefix(string, string) (string, bool) #42537
+pkg strings, func CutSuffix(string, string) (string, bool) #42537
\ No newline at end of file
diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
index 27834fc6db..c0cd704180 100644
--- a/src/bytes/bytes.go
+++ b/src/bytes/bytes.go
@@ -1309,3 +1309,29 @@ func Clone(b []byte) []byte {
 	}
 	return append([]byte{}, b...)
 }
+
+// CutPrefix returns s without the provided leading prefix byte slice
+// and reports whether it found the prefix.
+// If s doesn't start with prefix, CutPrefix returns s, false.
+// If prefix is the empty byte slice, CutPrefix returns s, true.
+//
+// CutPrefix returns slices of the original slice s, not copies.
+func CutPrefix(s, prefix []byte) (after []byte, found bool) {
+	if !HasPrefix(s, prefix) {
+		return s, false
+	}
+	return s[len(prefix):], true
+}
+
+// CutSuffix returns s without the provided ending suffix byte slice
+// and reports whether it found the suffix.
+// If s doesn't end with suffix, CutSuffix returns s, false.
+// If suffix is the empty byte slice, CutSuffix returns s, true.
+//
+// CutSuffix returns slices of the original slice s, not copies.
+func CutSuffix(s, suffix []byte) (after []byte, found bool) {
+	if !HasSuffix(s, suffix) {
+		return s, false
+	}
+	return s[:len(s)-len(suffix)], true
+}
diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
index 392657d1fa..05c7ccc50a 100644
--- a/src/bytes/bytes_test.go
+++ b/src/bytes/bytes_test.go
@@ -1700,6 +1700,48 @@ func TestCut(t *testing.T) {
 	}
 }
 
+var cutPrefixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "a", "bc", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutPrefix(t *testing.T) {
+	for _, tt := range cutPrefixTests {
+		if after, found := CutPrefix([]byte(tt.s), []byte(tt.sep)); string(after) != tt.after || found != tt.found {
+			t.Errorf("CutPrefix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
+var cutSuffixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "bc", "a", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutSuffix(t *testing.T) {
+	for _, tt := range cutSuffixTests {
+		if after, found := CutSuffix([]byte(tt.s), []byte(tt.sep)); string(after) != tt.after || found != tt.found {
+			t.Errorf("CutSuffix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
 func TestBufferGrowNegative(t *testing.T) {
 	defer func() {
 		if err := recover(); err == nil {
diff --git a/src/strings/strings.go b/src/strings/strings.go
index 013d718426..4ab78c326b 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -1187,3 +1187,25 @@ func Cut(s, sep string) (before, after string, found bool) {
 	}
 	return s, "", false
 }
+
+// CutPrefix returns s without the provided leading prefix string
+// and reports whether it found the prefix.
+// If s doesn't start with prefix, CutPrefix returns s, false.
+// If prefix is the empty string, CutPrefix returns s, true.
+func CutPrefix(s, prefix string) (after string, found bool) {
+	if !HasPrefix(s, prefix) {
+		return s, false
+	}
+	return s[len(prefix):], true
+}
+
+// CutSuffix returns s without the provided ending suffix string
+// and reports whether it found the suffix.
+// If s doesn't end with suffix, CutSuffix returns s, false.
+// If suffix is the empty string, CutSuffix returns s, true.
+func CutSuffix(s, suffix string) (after string, found bool) {
+	if !HasSuffix(s, suffix) {
+		return s, false
+	}
+	return s[:len(s)-len(suffix)], true
+}
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index a1604c2c47..d6153aa226 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -1611,6 +1611,48 @@ func TestCut(t *testing.T) {
 	}
 }
 
+var cutPrefixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "a", "bc", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutPrefix(t *testing.T) {
+	for _, tt := range cutPrefixTests {
+		if after, found := CutPrefix(tt.s, tt.sep); after != tt.after || found != tt.found {
+			t.Errorf("CutPrefix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
+var cutSuffixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "bc", "a", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutSuffix(t *testing.T) {
+	for _, tt := range cutSuffixTests {
+		if after, found := CutSuffix(tt.s, tt.sep); after != tt.after || found != tt.found {
+			t.Errorf("CutSuffix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
 func makeBenchInputHard() string {
 	tokens := [...]string{
 		"<a>", "<p>", "<b>", "<strong>",