fix(http): preserve all headers from Headers object (angular#57802)

when initialized from a `Headers` object containing multiple values for the same header, `HttpHeaders` now contains all the header values instead of only having one of them.

Fixes angular#57798

PR Close angular#57802

Author: jnizet

packages/common/http/src/headers.ts

@@ -56,21 +56,15 @@ export class HttpHeaders {
           const index = line.indexOf(':');
           if (index > 0) {
             const name = line.slice(0, index);
-            const key = name.toLowerCase();
             const value = line.slice(index + 1).trim();
-            this.maybeSetNormalizedName(name, key);
-            if (this.headers.has(key)) {
-              this.headers.get(key)!.push(value);
-            } else {
-              this.headers.set(key, [value]);
-            }
+            this.addHeaderEntry(name, value);
           }
         });
       };
     } else if (typeof Headers !== 'undefined' && headers instanceof Headers) {
       this.headers = new Map<string, string[]>();
-      headers.forEach((values: string, name: string) => {
-        this.setHeaderEntries(name, values);
+      headers.forEach((value: string, name: string) => {
+        this.addHeaderEntry(name, value);
       });
     } else {
       this.lazyInit = () => {
@@ -249,6 +243,16 @@ export class HttpHeaders {
     }
   }
 
+  private addHeaderEntry(name: string, value: string) {
+    const key = name.toLowerCase();
+    this.maybeSetNormalizedName(name, key);
+    if (this.headers.has(key)) {
+      this.headers.get(key)!.push(value);
+    } else {
+      this.headers.set(key, [value]);
+    }
+  }
+
   private setHeaderEntries(name: string, values: any) {
     const headerValues = (Array.isArray(values) ? values : [values]).map((value) =>
       value.toString(),

packages/common/http/test/headers_spec.ts

@@ -46,6 +46,16 @@ describe('HttpHeaders', () => {
       expect(headers.getAll('foo')).toEqual(['second']);
     });
 
+    it('should keep all values when initialized from a Headers object with duplicate headers', () => {
+      const standardHeaders = new Headers([
+        ['Set-Cookie', 'cookie1=foo'],
+        ['Set-Cookie', 'cookie2=bar'],
+      ]);
+      const headers = new HttpHeaders(standardHeaders);
+
+      expect(headers.getAll('Set-Cookie')).toEqual(['cookie1=foo', 'cookie2=bar']);
+    });
+
     it('should throw an error when null is passed as header', () => {
       // Note: the `strictNullChecks` set to `false` in TS config would make `null`
       // valid value within the headers object, thus this test verifies this scenario.