Improve HTTP headers logic (#1584)

* Relax forbidden headers constraints
  - remove restriction on browser-related headers
- allow any glob pattern (no need to end with `/` or `*`, because glob
patterns already require users to explicitly declare prefix matches if
that's the intention)
* Replace `List<Pair<, ...>>`; use `Map<String, ...>` instead
* Use glob pattern strings as an API throughout, instead of `Pattern`
(e.g. in `HttpClientBuilder`)
* Add HTTP headers to message passing API
* Add HTTP headers to executor API (introduces `ExecutorSpiOptions4`)
* Add tests for Gradle, CLI, and pkl-executor invocations
* Improve documentation
* Add `isGlobPattern` API to class `String` for in-language validation
of http headers
* Behavior change: make sure explicitly configured `User-Agent` in
`HttpClientBuilder` can be shadowed by headers (allows users to set
`--http-header "**=User-Agent: My User Agent"` and for this to be the
only user agent).

CC @kyokuping

pkl-cli/src/test/kotlin/org/pkl/cli/CliEvaluatorTest.kt

@@ -1614,6 +1614,24 @@ result = someLib.x
     assertThat(output).isEqualTo("result = 1\n")
   }
 
+  @Test
+  fun `eval configured http headers`(wwRuntimeInfo: WireMockRuntimeInfo) {
+    stubFor(get(anyUrl()).willReturn(ok("result = 1")))
+    val file = URI("${wwRuntimeInfo.httpBaseUrl}/foo.pkl")
+    val output =
+      evalToConsole(
+        CliEvaluatorOptions(
+          CliBaseOptions(
+            sourceModules = listOf(file),
+            httpHeaders = mapOf("**" to mapOf("X-Foo" to listOf("Foo"))),
+            allowedModules =
+              listOf(Pattern.compile("http:"), Pattern.compile("file:"), Pattern.compile("pkl:")),
+          )
+        )
+      )
+    verify(getRequestedFor(urlEqualTo("/foo.pkl")).withHeader("X-Foo", equalTo("Foo")))
+  }
+
   @Test
   fun `eval file with non-ASCII name`() {
     val tempDirUri = tempDir.toUri()

pkl-cli/src/test/kotlin/org/pkl/cli/CliMainTest.kt

@@ -169,4 +169,60 @@ class CliMainTest {
     link.createSymbolicLinkPointingTo(dir)
     return link
   }
+
+  @Test
+  fun `invalid http header glob pattern`() {
+    val ex =
+      assertThrows<BadParameterValue> {
+        rootCmd.parse(arrayOf("eval", "--http-header", "foo{{}}=bar:baz", "myModule.pkl"))
+      }
+    assertThat(ex.message)
+      .contains("Sub-patterns cannot be nested. To fix, remove or escape the inner `{` character.")
+  }
+
+  @Test
+  fun `forbidden http header name`() {
+    val ex =
+      assertThrows<BadParameterValue> {
+        rootCmd.parse(arrayOf("eval", "--http-header", "**=Connection: baz", "myModule.pkl"))
+      }
+    assertThat(ex.message).contains("HTTP header `Connection` is a reserved header")
+  }
+
+  @Test
+  fun `bad http header value`() {
+    val ex =
+      assertThrows<BadParameterValue> {
+        rootCmd.parse(arrayOf("eval", "--http-header", "**=X-Foo:🙃", "myModule.pkl"))
+      }
+    assertThat(ex.message).contains("HTTP header value `🙃` has invalid syntax")
+  }
+
+  @Test
+  fun `multiple headers`() {
+    val cmd = RootCommand()
+    cmd.parse(
+      arrayOf(
+        "eval",
+        "--http-header",
+        "**=X-Foo:Foo",
+        "--http-header",
+        "**=X-Foo:Foo2",
+        "--http-header",
+        "**=X-Bar:Bar",
+        "--http-header",
+        "https://example.com/**=X-Qux:Qux",
+        "pkl:base",
+      )
+    )
+
+    val evalCmd = cmd.registeredSubcommands().filterIsInstance<EvalCommand>().first()
+    assertThat(evalCmd.baseOptions.httpHeaders)
+      .isEqualTo(
+        mapOf(
+          "**" to mapOf("X-Foo" to listOf("Foo", "Foo2"), "X-Bar" to listOf("Bar")),
+          "https://example.com/**" to mapOf("X-Qux" to listOf("Qux")),
+        )
+      )
+  }
 }