OS Error: Operation not permitted

[MichelDiz]

Describe the bug
Local http communications aren't working.
I've tried gRPC, Dio, HTTP and all of them return the same error.

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: DioError [DioErrorType.DEFAULT]: SocketException: Connection failed (OS Error: Operation not permitted, errno = 1), address = localhost, port = 8080

Doctor Output
Please provide the output of flutter doctor -v:

flutter doctor -v
[✓] Flutter (Channel master, v1.10.1-pre.41, on Mac OS X 10.14.6 18G95, locale pt-BR)
    • Flutter version 1.10.1-pre.41 at /flutter
    • Framework revision 5a3a46ada2 (26 hours ago), 2019-09-07 18:37:41 -0400
    • Engine revision c9ea4dba8d
    • Dart version 2.5.0 (build 2.5.0-dev.4.0 ec7ec4ecf7)

[!] Android toolchain - develop for Android devices
    • Android SDK at /usr/local/Caskroom/android-platform-tools/29.0.2
    • Android NDK location not configured (optional; useful for native profiling support)
    ✗ Unable to locate Android SDK.
      Install Android Studio from: https://developer.android.com/studio/index.html
      On first launch it will assist you in installing the Android SDK components.
      (or visit https://flutter.dev/setup/#android-setup for detailed instructions).
      If the Android SDK has been installed to a custom location, set ANDROID_HOME to that location.
      You may also want to add it to your PATH environment variable.

    • ANDROID_SDK_ROOT = /usr/local/share/android-sdk
    ✗ No valid Android SDK platforms found in /usr/local/Caskroom/android-platform-tools/29.0.2/platforms. Directory was empty.
    • Try re-installing or updating your Android SDK,
      visit https://flutter.dev/setup/#android-setup for detailed instructions.

[✓] Xcode - develop for iOS and macOS (Xcode 10.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 10.3, Build version 10G8
    • CocoaPods version 1.7.5

[!] Android Studio (not installed)
    • Android Studio not found; download from https://developer.android.com/studio/index.html
      (or visit https://flutter.dev/setup/#android-setup for detailed instructions).

[✓] VS Code (version 1.38.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.4.1

[✓] Connected device (1 available)
    • macOS • macOS • darwin-x64 • Mac OS X 10.14.6 18G95

! Doctor found issues in 2 categories.

[stuartmorgan]

As announced, macOS is now sandboxed by default. You need to add the appropriate entitlement (com.apple.security.network.client).

[stuartmorgan]

As it says in the documentation linked from the announcement: "Unless you have a very specific reason, you should always make identical changes to both files."

If you only edited that file, then your Release builds will still have the same error.