url: optimize path resolution with single-pass algorithm

Author: anonrig

lib/url.js

@@ -23,13 +23,15 @@
 
 const {
   ArrayPrototypeJoin,
+  ArrayPrototypePush,
   Boolean,
   Int8Array,
   ObjectAssign,
   ObjectKeys,
   StringPrototypeAt,
   StringPrototypeCharCodeAt,
   StringPrototypeIndexOf,
+  StringPrototypeLastIndexOf,
   StringPrototypeReplaceAll,
   StringPrototypeSlice,
   decodeURIComponent,
@@ -52,7 +54,6 @@ const {
 
 // This ensures setURLConstructor() is called before the native
 // URL::ToObject() method is used.
-const { spliceOne } = require('internal/util');
 const { isInsideNodeModules } = internalBinding('util');
 
 // WHATWG URL implementation provided by internal/url
@@ -91,6 +92,66 @@ function Url() {
 
 // Reference: RFC 3986, RFC 1808, RFC 2396
 
+/**
+ * Normalize URL path segments by resolving . and .. in a single pass.
+ * This is O(n) compared to the O(n²) spliceOne approach.
+ *
+ * @param {string} path - Combined pathname to normalize
+ * @param {boolean} allowAboveRoot - Whether .. can go above root
+ * @returns {{ segments: string[], up: number, trailingSlash: boolean }}
+ */
+function normalizePathSegments(path, allowAboveRoot) {
+  if (!path) return { segments: [], up: 0, trailingSlash: false };
+
+  const len = path.length;
+  const segments = [];
+  let up = 0;
+  let lastSlash = -1;
+  let segStart = 0;
+  let lastSeg = '';
+  let trailingSlash = false;
+
+  // Iterate through the path, processing segments
+  for (let i = 0; i <= len; i++) {
+    const code = i < len ? StringPrototypeCharCodeAt(path, i) : CHAR_FORWARD_SLASH;
+
+    if (code === CHAR_FORWARD_SLASH) {
+      if (lastSlash === i - 1 || segStart === i) {
+        // Empty segment (// or leading /)
+        // Track that the last segment was empty for trailing slash detection
+        lastSeg = '';
+      } else {
+        const segment = StringPrototypeSlice(path, segStart, i);
+        lastSeg = segment;
+
+        if (segment === '.') {
+          // Current directory - skip
+        } else if (segment === '..') {
+          // Parent directory
+          if (segments.length > 0 && segments[segments.length - 1] !== '..') {
+            segments.pop();
+          } else if (allowAboveRoot) {
+            ArrayPrototypePush(segments, '..');
+          } else {
+            up++;
+          }
+        } else {
+          // Regular segment
+          ArrayPrototypePush(segments, segment);
+        }
+      }
+      lastSlash = i;
+      segStart = i + 1;
+    }
+  }
+
+  // Determine trailing slash based on what the last segment was before normalization
+  // If path ends with /, ., or .., we need a trailing slash
+  trailingSlash = lastSeg === '' || lastSeg === '.' || lastSeg === '..';
+
+  return { segments, up, trailingSlash };
+}
+
 // define these here so at least they only have to be
 // compiled once on the first module load.
 const protocolPattern = /^[a-z0-9.+-]+:/i;
@@ -127,6 +188,7 @@ const {
   CHAR_VERTICAL_LINE,
   CHAR_AT,
   CHAR_COLON,
+  CHAR_DOT,
 } = require('internal/constants');
 
 let urlParseWarned = false;
@@ -824,11 +886,14 @@ Url.prototype.resolveObject = function resolveObject(relative) {
   let mustEndAbs = (isRelAbs || isSourceAbs ||
                     (result.host && relative.pathname));
   const removeAllDots = mustEndAbs;
-  let srcPath = (result.pathname && result.pathname.split('/')) || [];
-  const relPath = (relative.pathname && relative.pathname.split('/')) || [];
   const noLeadingSlashes = result.protocol &&
       !slashedProtocol.has(result.protocol);
 
+  // Build the combined path string for normalization
+  let combinedPath = '';
+  let srcHost = '';  // For noLeadingSlashes protocols
+  let relHost = '';  // For noLeadingSlashes protocols
+
   // If the url is a non-slashed url, then relative
   // links like ../.. should be able
   // to crawl up to the hostname, as well.  This is strange.
@@ -837,22 +902,15 @@ Url.prototype.resolveObject = function resolveObject(relative) {
   if (noLeadingSlashes) {
     result.hostname = '';
     result.port = null;
-    if (result.host) {
-      if (srcPath[0] === '') srcPath[0] = result.host;
-      else srcPath.unshift(result.host);
-    }
+    srcHost = result.host || '';
     result.host = '';
     if (relative.protocol) {
       relative.hostname = null;
       relative.port = null;
       result.auth = null;
-      if (relative.host) {
-        if (relPath[0] === '') relPath[0] = relative.host;
-        else relPath.unshift(relative.host);
-      }
+      relHost = relative.host || '';
       relative.host = null;
     }
-    mustEndAbs &&= (relPath[0] === '' || srcPath[0] === '');
   }
 
   if (isRelAbs) {
@@ -868,30 +926,65 @@ Url.prototype.resolveObject = function resolveObject(relative) {
     }
     result.search = relative.search;
     result.query = relative.query;
-    srcPath = relPath;
-    // Fall through to the dot-handling below.
-  } else if (relPath.length) {
+    // Use relative path directly
+    if (noLeadingSlashes && relHost) {
+      combinedPath = (relative.pathname && relative.pathname.charAt(0) === '/' ?
+        relHost + relative.pathname : relHost + '/' + (relative.pathname || ''));
+    } else {
+      combinedPath = relative.pathname || '';
+    }
+  } else if (relative.pathname) {
     // it's relative
     // throw away the existing file, and take the new path instead.
-    srcPath ||= [];
-    srcPath.pop();
-    srcPath = srcPath.concat(relPath);
     result.search = relative.search;
     result.query = relative.query;
+
+    // Build combined path: source path (minus last segment) + relative path
+    let srcPathname = result.pathname || '';
+    if (noLeadingSlashes && srcHost) {
+      srcPathname = (srcPathname && srcPathname.charAt(0) === '/' ?
+        srcHost + srcPathname : srcHost + '/' + srcPathname);
+    }
+
+    // Remove the last segment from source (the "file" part)
+    const lastSlashIndex = StringPrototypeLastIndexOf(srcPathname, '/');
+    if (lastSlashIndex >= 0) {
+      srcPathname = StringPrototypeSlice(srcPathname, 0, lastSlashIndex + 1);
+    } else {
+      srcPathname = '';
+    }
+
+    // Append relative pathname
+    let relPathname = relative.pathname;
+    if (noLeadingSlashes && relHost) {
+      relPathname = (relPathname && relPathname.charAt(0) === '/' ?
+        relHost + relPathname : relHost + '/' + relPathname);
+    }
+    combinedPath = srcPathname + relPathname;
   } else if (relative.search !== null && relative.search !== undefined) {
     // Just pull out the search.
     // like href='?foo'.
     // Put this after the other two cases because it simplifies the booleans
     if (noLeadingSlashes) {
-      result.hostname = result.host = srcPath.shift();
+      // Extract host from first segment of source path
+      const srcPathname = result.pathname || '';
+      const firstSlashIdx = StringPrototypeIndexOf(srcPathname, '/');
+      if (firstSlashIdx > 0) {
+        result.hostname = result.host = StringPrototypeSlice(srcPathname, 0, firstSlashIdx);
+      } else if (firstSlashIdx === -1 && srcPathname) {
+        result.hostname = result.host = srcPathname;
+      } else if (srcHost) {
+        result.hostname = result.host = srcHost;
+      } else {
+        result.hostname = result.host = '';
+      }
       // Occasionally the auth can get stuck only in host.
-      // This especially happens in cases like
-      // url.resolveObject('mailto:local1@domain1', 'local2@domain2')
       const authInHost =
-        result.host && result.host.indexOf('@') > 0 && result.host.split('@');
+        result.host && StringPrototypeIndexOf(result.host, '@') > 0;
       if (authInHost) {
-        result.auth = authInHost.shift();
-        result.host = result.hostname = authInHost.shift();
+        const atIdx = StringPrototypeIndexOf(result.host, '@');
+        result.auth = StringPrototypeSlice(result.host, 0, atIdx);
+        result.host = result.hostname = StringPrototypeSlice(result.host, atIdx + 1);
       }
     }
     result.search = relative.search;
@@ -903,9 +996,24 @@ Url.prototype.resolveObject = function resolveObject(relative) {
     }
     result.href = result.format();
     return result;
+  } else {
+    // No relative path at all, use source path
+    if (noLeadingSlashes && srcHost) {
+      const srcPathname = result.pathname || '';
+      combinedPath = (srcPathname && srcPathname.charAt(0) === '/' ?
+        srcHost + srcPathname : srcHost + '/' + srcPathname);
+    } else {
+      combinedPath = result.pathname || '';
+    }
   }
 
-  if (!srcPath.length) {
+  // Check if we need to handle noLeadingSlashes mustEndAbs
+  if (noLeadingSlashes) {
+    const startsWithSlash = combinedPath && combinedPath.charAt(0) === '/';
+    mustEndAbs &&= startsWithSlash;
+  }
+
+  if (!combinedPath) {
     // No path at all. All other things were already handled above.
     result.pathname = null;
     // To support http.request
@@ -918,75 +1026,78 @@ Url.prototype.resolveObject = function resolveObject(relative) {
     return result;
   }
 
-  // If a url ENDs in . or .., then it must get a trailing slash.
-  // however, if it ends in anything else non-slashy,
-  // then it must NOT get a trailing slash.
-  let last = srcPath[srcPath.length - 1];
-  const hasTrailingSlash = (
-    ((result.host || relative.host || srcPath.length > 1) &&
-    (last === '.' || last === '..')) || last === '');
-
-  // Strip single dots, resolve double dots to parent dir
-  // if the path tries to go above the root, `up` ends up > 0
-  let up = 0;
-  for (let i = srcPath.length - 1; i >= 0; i--) {
-    last = srcPath[i];
-    if (last === '.') {
-      spliceOne(srcPath, i);
-    } else if (last === '..') {
-      spliceOne(srcPath, i);
-      up++;
-    } else if (up) {
-      spliceOne(srcPath, i);
-      up--;
+  // Use optimized single-pass normalization (O(n) instead of O(n²))
+  const allowAboveRoot = !mustEndAbs && !removeAllDots;
+  const { segments, up, trailingSlash } = normalizePathSegments(combinedPath, allowAboveRoot);
+
+  const pathHadMultipleSegments = combinedPath && StringPrototypeIndexOf(combinedPath, '/') !== -1;
+  const hasTrailingSlash = trailingSlash &&
+    (result.host || relative.host || pathHadMultipleSegments);
+
+  // Handle remaining 'up' count - add leading .. if allowed
+  let srcPath = segments;
+  if (up > 0 && allowAboveRoot) {
+    // Prepend '..' segments for remaining up count
+    const newPath = [];
+    for (let i = 0; i < up; i++) {
+      ArrayPrototypePush(newPath, '..');
     }
-  }
-
-  // If the path is allowed to go above the root, restore leading ..s
-  if (!mustEndAbs && !removeAllDots) {
-    while (up--) {
-      srcPath.unshift('..');
+    for (let i = 0; i < srcPath.length; i++) {
+      ArrayPrototypePush(newPath, srcPath[i]);
     }
+    srcPath = newPath;
   }
 
-  if (mustEndAbs && srcPath[0] !== '' &&
-      (!srcPath[0] || srcPath[0].charAt(0) !== '/')) {
-    srcPath.unshift('');
+  // Handle mustEndAbs - ensure path starts with /
+  let isAbsolute = srcPath.length > 0 && srcPath[0] === '';
+  if (!isAbsolute && srcPath.length > 0 && srcPath[0] &&
+      srcPath[0].charAt(0) === '/') {
+    isAbsolute = true;
   }
 
-  if (hasTrailingSlash && StringPrototypeAt(ArrayPrototypeJoin(srcPath, '/'), -1) !== '/') {
-    srcPath.push('');
-  }
-
-  const isAbsolute = srcPath[0] === '' ||
-      (srcPath[0] && srcPath[0].charAt(0) === '/');
-
-  // put the host back
+  // put the host back for noLeadingSlashes protocols
   if (noLeadingSlashes) {
     result.hostname =
-      result.host = isAbsolute ? '' : srcPath.length ? srcPath.shift() : '';
+      result.host = isAbsolute ? '' : srcPath.length ? srcPath[0] : '';
+    if (result.host) {
+      // Remove the host from srcPath (first element)
+      srcPath = srcPath.length > 1 ?
+        ArrayPrototypeJoin(srcPath, '/').slice(result.host.length + 1).split('/') :
+        [];
+      if (srcPath.length === 1 && srcPath[0] === '') srcPath = [];
+    }
     // Occasionally the auth can get stuck only in host.
-    // This especially happens in cases like
-    // url.resolveObject('mailto:local1@domain1', 'local2@domain2')
-    const authInHost = result.host && result.host.indexOf('@') > 0 ?
-      result.host.split('@') : false;
+    const authInHost = result.host && StringPrototypeIndexOf(result.host, '@') > 0;
     if (authInHost) {
-      result.auth = authInHost.shift();
-      result.host = result.hostname = authInHost.shift();
+      const atIdx = StringPrototypeIndexOf(result.host, '@');
+      result.auth = StringPrototypeSlice(result.host, 0, atIdx);
+      result.host = result.hostname = StringPrototypeSlice(result.host, atIdx + 1);
     }
   }
 
   mustEndAbs ||= (result.host && srcPath.length);
 
   if (mustEndAbs && !isAbsolute) {
-    srcPath.unshift('');
+    // Need to add leading empty string for absolute path
+    const newPath = [''];
+    for (let i = 0; i < srcPath.length; i++) {
+      ArrayPrototypePush(newPath, srcPath[i]);
+    }
+    srcPath = newPath;
+    isAbsolute = true;
+  }
+
+  if (hasTrailingSlash &&
+      (srcPath.length === 0 ||
+       StringPrototypeAt(ArrayPrototypeJoin(srcPath, '/'), -1) !== '/')) {
+    ArrayPrototypePush(srcPath, '');
   }
 
   if (!srcPath.length) {
     result.pathname = null;
     result.path = null;
   } else {
-    result.pathname = srcPath.join('/');
+    result.pathname = ArrayPrototypeJoin(srcPath, '/');
   }
 
   // To support request.http