perf: remove skipWhitespace

``skipWhitespace`` had a perverse effect on performance. In general, when
parsing a clean document, it faster to assume there are not extraneous spaces.

CONTRIBUTING.md

@@ -31,6 +31,31 @@ continually check whether it may emit non-error events and this would have a
 measurable cost even when parsing well-formed documents. We decided always emit
 the events anyway and diverge a bit from the XML specifications.
 
+## Optimize for "Clean" XML
+
+This is well-formed XML:
+
+```xml
+<foo a="1" b="2" c="3">something</foo>
+```
+
+This is also well-formed and represents the same document as the previous
+example:
+
+```xml
+              <foo            a                =     "1"
+
+
+b = "2"
+
+c = "3"            >something</foo             >
+
+
+```
+
+We want both documents to be parsed without error by saxes but, when writing
+code, optimize for the former rather than the later.
+
 ## Pay Attention to Performance
 
 The more a PR harms performance,

lib/saxes.js

@@ -656,29 +656,6 @@ class SaxesParser {
     return undefined;
   }
 
-  /**
-   * Skip whitespace characters.
-   *
-   * @private
-   *
-   * @param {ChunkState} chunkState The current chunk state.
-   *
-   * @return {string|undefined} The character that made the test fail, or
-   * ``undefined`` if we hit the end of the chunk.
-   */
-  skipWhitespace(chunkState) {
-    const { limit } = chunkState;
-    while (chunkState.i < limit) {
-      const c = this.getCode(chunkState);
-      if (!isS(c)) {
-        return c;
-      }
-    }
-
-    return undefined;
-  }
-
-
   // STATE HANDLERS
 
   /** @private */
@@ -1084,31 +1061,31 @@ class SaxesParser {
         }
         break;
       case S_XML_DECL_EQ:
-        c = this.skipWhitespace(chunkState);
+        c = this.getCode(chunkState);
         // The question mark character is not valid inside any of the XML
         // declaration name/value pairs.
         if (c === QUESTION) {
           this.state = S_PI_ENDING;
           return;
         }
 
-        if (c) {
+        if (c && !isS(c)) {
           if (c !== EQUAL) {
             this.fail("value required.");
           }
           this.xmlDeclState = S_XML_DECL_VALUE_START;
         }
         break;
       case S_XML_DECL_VALUE_START:
-        c = this.skipWhitespace(chunkState);
+        c = this.getCode(chunkState);
         // The question mark character is not valid inside any of the XML
         // declaration name/value pairs.
         if (c === QUESTION) {
           this.state = S_PI_ENDING;
           return;
         }
 
-        if (c) {
+        if (c && !isS(c)) {
           if (!isQuote(c)) {
             this.fail("value must be quoted.");
             this.q = SPACE;
@@ -1170,11 +1147,11 @@ class SaxesParser {
       }
     }
     else if (this.piBody.length === 0) {
-      c = this.skipWhitespace(chunkState);
+      c = this.getCode(chunkState);
       if (c === QUESTION) {
         this.state = S_PI_ENDING;
       }
-      else if (c) {
+      else if (c && !isS(c)) {
         this.piBody = String.fromCodePoint(c);
       }
     }
@@ -1292,8 +1269,8 @@ class SaxesParser {
 
   /** @private */
   sAttrib(chunkState) {
-    const c = this.skipWhitespace(chunkState);
-    if (!c) {
+    const c = this.getCode(chunkState);
+    if (!c || isS(c)) {
       return;
     }
     if (isNameStartChar(c)) {
@@ -1336,7 +1313,11 @@ class SaxesParser {
 
   /** @private */
   sAttribNameSawWhite(chunkState) {
-    const c = this.skipWhitespace(chunkState);
+    const c = this.getCode(chunkState);
+    if (isS(c)) {
+      return;
+    }
+
     if (c === EQUAL) {
       this.state = S_ATTRIB_VALUE;
     }
@@ -1361,12 +1342,12 @@ class SaxesParser {
 
   /** @private */
   sAttribValue(chunkState) {
-    const c = this.skipWhitespace(chunkState);
+    const c = this.getCode(chunkState);
     if (isQuote(c)) {
       this.q = c;
       this.state = S_ATTRIB_VALUE_QUOTED;
     }
-    else if (c) {
+    else if (c && !isS(c)) {
       this.fail("unquoted attribute value.");
       this.state = S_ATTRIB_VALUE_UNQUOTED;
       this.attribValue = String.fromCodePoint(c);
@@ -1470,11 +1451,11 @@ class SaxesParser {
 
   /** @private */
   sCloseTagSawWhite(chunkState) {
-    const c = this.skipWhitespace(chunkState);
+    const c = this.getCode(chunkState);
     if (c === GREATER) {
       this.closeTag();
     }
-    else if (c) {
+    else if (c && !isS(c)) {
       this.fail("disallowed character in closing tag.");
     }
   }