folly: adding folly::ltrimWhitespace / folly::rtrimWhitespace

Summary:
folly: adding folly::trimWhitespace

extending the idea of folly::skipWhitespace.
the reason for adding it, we want to be able to do:

auto s = skipWhitespace(trimWhitespace(" aaaa "))

very similar to python's strip()

Test Plan:
adding unit tests:

# make ; _bin/folly/test/string_test --gtest_filter="String.whitespace"
# fbmake --ccache off --distcc off dbg -j 16
fbmake dbg -j 16
Fbmake run id: G62i4cDP42U
Note: Google Test filter = String.whitespace
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from String
[ RUN      ] String.whitespace
[       OK ] String.whitespace (0 ms)
[----------] 1 test from String (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (0 ms total)
[  PASSED  ] 1 test.

Reviewed By: ldbrandy@fb.com

Subscribers: ldbrandy, folly-diffs@, yfeldblum, chalfant, azhavnerchik

FB internal diff: D2109364

Signature: t1:2109364:1433192444:862e237bba1928fcb94be1f95c57a68d457939e9

folly/String.h

@@ -554,7 +554,30 @@ std::string join(const Delim& delimiter, Iterator begin, Iterator end) {
  * Returns a subpiece with all whitespace removed from the front of @sp.
  * Whitespace means any of [' ', '\n', '\r', '\t'].
  */
-StringPiece skipWhitespace(StringPiece sp);
+StringPiece ltrimWhitespace(StringPiece sp);
+
+/**
+ * Returns a subpiece with all whitespace removed from the back of @sp.
+ * Whitespace means any of [' ', '\n', '\r', '\t'].
+ */
+StringPiece rtrimWhitespace(StringPiece sp);
+
+/**
+ * Returns a subpiece with all whitespace removed from the back and front of @sp.
+ * Whitespace means any of [' ', '\n', '\r', '\t'].
+ */
+inline StringPiece trimWhitespace(StringPiece sp) {
+  return ltrimWhitespace(rtrimWhitespace(sp));
+}
+
+/**
+ * Returns a subpiece with all whitespace removed from the front of @sp.
+ * Whitespace means any of [' ', '\n', '\r', '\t'].
+ * DEPRECATED: @see ltrimWhitespace @see rtrimWhitespace
+ */
+inline StringPiece skipWhitespace(StringPiece sp) {
+  return ltrimWhitespace(sp);
+}
 
 /**
  * Fast, in-place lowercasing of ASCII alphabetic characters in strings.

folly/StringBase.cpp

@@ -18,18 +18,19 @@
 
 namespace folly {
 
-StringPiece skipWhitespace(StringPiece sp) {
+static inline bool is_oddspace(char c) {
+  return c == '\n' || c == '\t' || c == '\r';
+}
+
+StringPiece ltrimWhitespace(StringPiece sp) {
   // Spaces other than ' ' characters are less common but should be
   // checked.  This configuration where we loop on the ' '
   // separately from oddspaces was empirically fastest.
-  auto oddspace = [] (char c) {
-    return c == '\n' || c == '\t' || c == '\r';
-  };
 
 loop:
   for (; !sp.empty() && sp.front() == ' '; sp.pop_front()) {
   }
-  if (!sp.empty() && oddspace(sp.front())) {
+  if (!sp.empty() && is_oddspace(sp.front())) {
     sp.pop_front();
     goto loop;
   }
@@ -37,4 +38,20 @@ loop:
   return sp;
 }
 
+StringPiece rtrimWhitespace(StringPiece sp) {
+  // Spaces other than ' ' characters are less common but should be
+  // checked.  This configuration where we loop on the ' '
+  // separately from oddspaces was empirically fastest.
+
+loop:
+  for (; !sp.empty() && sp.back() == ' '; sp.pop_back()) {
+  }
+  if (!sp.empty() && is_oddspace(sp.back())) {
+    sp.pop_back();
+    goto loop;
+  }
+
+  return sp;
+}
+
 }

folly/test/StringTest.cpp

@@ -1290,6 +1290,53 @@ BENCHMARK(joinInt, iters) {
   }
 }
 
+TEST(String, whitespace) {
+  // trimWhitespace:
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("kavabanga"));
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("kavabanga \t \n  "));
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("   \t \r \n \n kavabanga"));
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("\t \r \n   kavabanga \t \n  "));
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("   \t \r \n \n kavabanga"));
+  EXPECT_EQ("kavabanga",
+        trimWhitespace("\t \r \n   kavabanga \t \n  "));
+  EXPECT_EQ(
+    ltrimWhitespace(rtrimWhitespace("kavabanga")),
+    rtrimWhitespace(ltrimWhitespace("kavabanga")));
+  EXPECT_EQ(
+    ltrimWhitespace(rtrimWhitespace("kavabanga  \r\t\n")),
+    rtrimWhitespace(ltrimWhitespace("kavabanga  \r\t\n")));
+  EXPECT_EQ("", trimWhitespace("\t \r \n   \t \n  "));
+  EXPECT_EQ("", trimWhitespace(""));
+  EXPECT_EQ("", trimWhitespace("\t"));
+  EXPECT_EQ("", trimWhitespace("\r"));
+  EXPECT_EQ("", trimWhitespace("\n"));
+  EXPECT_EQ("", trimWhitespace("\t "));
+  EXPECT_EQ("", trimWhitespace("\r  "));
+  EXPECT_EQ("", trimWhitespace("\n   "));
+  EXPECT_EQ("", trimWhitespace("    \t"));
+  EXPECT_EQ("", trimWhitespace("    \r"));
+  EXPECT_EQ("", trimWhitespace("    \n"));
+
+  // ltrimWhitespace:
+  EXPECT_EQ("kavabanga", ltrimWhitespace("\t kavabanga"));
+  EXPECT_EQ("kavabanga \r\n", ltrimWhitespace("\t kavabanga \r\n"));
+  EXPECT_EQ("", ltrimWhitespace("\r "));
+  EXPECT_EQ("", ltrimWhitespace("\n   "));
+  EXPECT_EQ("", ltrimWhitespace("\r   "));
+
+  // rtrimWhitespace:
+  EXPECT_EQ("\t kavabanga", rtrimWhitespace("\t kavabanga"));
+  EXPECT_EQ("\t kavabanga", rtrimWhitespace("\t kavabanga \r\n"));
+  EXPECT_EQ("", rtrimWhitespace("\r "));
+  EXPECT_EQ("", rtrimWhitespace("\n   "));
+  EXPECT_EQ("", rtrimWhitespace("\r   "));
+}
+
 int main(int argc, char *argv[]) {
   testing::InitGoogleTest(&argc, argv);
   gflags::ParseCommandLineFlags(&argc, &argv, true);