[SPARK-17299] TRIM/LTRIM/RTRIM should not strips characters other than spaces

## What changes were proposed in this pull request?
TRIM/LTRIM/RTRIM should not strips characters other than spaces, we were trimming all chars small than ASCII 0x20(space)

## How was this patch tested?
fixed existing tests.

Author: Sandeep Singh <sandeep@techaddict.me>

Closes #14924 from techaddict/SPARK-17299.

common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java

@@ -465,9 +465,9 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
     int s = 0;
     int e = this.numBytes - 1;
     // skip all of the space (0x20) in the left side
-    while (s < this.numBytes && getByte(s) <= 0x20 && getByte(s) >= 0x00) s++;
+    while (s < this.numBytes && getByte(s) == 0x20) s++;
     // skip all of the space (0x20) in the right side
-    while (e >= 0 && getByte(e) <= 0x20 && getByte(e) >= 0x00) e--;
+    while (e >= 0 && getByte(e) == 0x20) e--;
     if (s > e) {
       // empty string
       return EMPTY_UTF8;
@@ -479,7 +479,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   public UTF8String trimLeft() {
     int s = 0;
     // skip all of the space (0x20) in the left side
-    while (s < this.numBytes && getByte(s) <= 0x20 && getByte(s) >= 0x00) s++;
+    while (s < this.numBytes && getByte(s) == 0x20) s++;
     if (s == this.numBytes) {
       // empty string
       return EMPTY_UTF8;
@@ -491,7 +491,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   public UTF8String trimRight() {
     int e = numBytes - 1;
     // skip all of the space (0x20) in the right side
-    while (e >= 0 && getByte(e) <= 0x20 && getByte(e) >= 0x00) e--;
+    while (e >= 0 && getByte(e) == 0x20) e--;
 
     if (e < 0) {
       // empty string

common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java

@@ -232,6 +232,16 @@ public class UTF8StringSuite {
     assertEquals(fromString("数据砖头"), fromString("数据砖头").trim());
     assertEquals(fromString("数据砖头"), fromString("数据砖头").trimLeft());
     assertEquals(fromString("数据砖头"), fromString("数据砖头").trimRight());
+
+    char[] charsLessThan0x20 = new char[10];
+    Arrays.fill(charsLessThan0x20, (char)(' ' - 1));
+    String stringStartingWithSpace =
+      new String(charsLessThan0x20) + "hello" + new String(charsLessThan0x20);
+    assertEquals(fromString(stringStartingWithSpace), fromString(stringStartingWithSpace).trim());
+    assertEquals(fromString(stringStartingWithSpace),
+      fromString(stringStartingWithSpace).trimLeft());
+    assertEquals(fromString(stringStartingWithSpace),
+      fromString(stringStartingWithSpace).trimRight());
   }
 
   @Test

common/unsafe/src/test/scala/org/apache/spark/unsafe/types/UTF8StringPropertyCheckSuite.scala

@@ -98,7 +98,7 @@ class UTF8StringPropertyCheckSuite extends FunSuite with GeneratorDrivenProperty
     }
   }
 
-  val whitespaceChar: Gen[Char] = Gen.choose(0x00, 0x20).map(_.toChar)
+  val whitespaceChar: Gen[Char] = Gen.const(0x20.toChar)
   val whitespaceString: Gen[String] = Gen.listOf(whitespaceChar).map(_.mkString)
   val randomString: Gen[String] = Arbitrary.arbString.arbitrary
 
@@ -107,7 +107,7 @@ class UTF8StringPropertyCheckSuite extends FunSuite with GeneratorDrivenProperty
     def lTrim(s: String): String = {
       var st = 0
       val array: Array[Char] = s.toCharArray
-      while ((st < s.length) && (array(st) <= ' ')) {
+      while ((st < s.length) && (array(st) == ' ')) {
         st += 1
       }
       if (st > 0) s.substring(st, s.length) else s
@@ -115,7 +115,7 @@ class UTF8StringPropertyCheckSuite extends FunSuite with GeneratorDrivenProperty
     def rTrim(s: String): String = {
       var len = s.length
       val array: Array[Char] = s.toCharArray
-      while ((len > 0) && (array(len - 1) <= ' ')) {
+      while ((len > 0) && (array(len - 1) == ' ')) {
         len -= 1
       }
       if (len < s.length) s.substring(0, len) else s
@@ -127,7 +127,7 @@ class UTF8StringPropertyCheckSuite extends FunSuite with GeneratorDrivenProperty
         whitespaceString
     ) { (start: String, middle: String, end: String) =>
       val s = start + middle + end
-      assert(toUTF8(s).trim() === toUTF8(s.trim()))
+      assert(toUTF8(s).trim() === toUTF8(rTrim(lTrim(s))))
       assert(toUTF8(s).trimLeft() === toUTF8(lTrim(s)))
       assert(toUTF8(s).trimRight() === toUTF8(rTrim(s)))
     }