Move Error type into crate root

src/custom_service_account.rs

@@ -16,9 +16,8 @@ use tokio::sync::RwLock;
 use tracing::{instrument, Level};
 use url::form_urlencoded;
 
-use crate::error::Error;
 use crate::types::{HttpClient, Signer, Token};
-use crate::TokenProvider;
+use crate::{TokenProvider, Error};
 
 /// A custom service account containing credentials
 ///

src/default_authorized_user.rs

@@ -9,9 +9,8 @@ use serde::{Deserialize, Serialize};
 use tokio::sync::RwLock;
 use tracing::{instrument, Level};
 
-use crate::error::Error;
 use crate::types::{HttpClient, Token};
-use crate::TokenProvider;
+use crate::{Error, TokenProvider};
 
 #[derive(Debug)]
 pub(crate) struct ConfigDefaultCredentials {

src/default_service_account.rs

@@ -7,9 +7,8 @@ use hyper::{Method, Request};
 use tokio::sync::RwLock;
 use tracing::{instrument, Level};
 
-use crate::TokenProvider;
-use crate::error::Error;
 use crate::types::{HttpClient, Token};
+use crate::{Error, TokenProvider};
 
 #[derive(Debug)]
 pub(crate) struct MetadataServiceAccount {

src/gcloud_authorized_user.rs

@@ -7,10 +7,9 @@ use async_trait::async_trait;
 use tokio::sync::RwLock;
 use which::which;
 
-use crate::error::Error;
-use crate::error::Error::{GCloudError, GCloudNotFound, GCloudParseError};
 use crate::types::Token;
-use crate::TokenProvider;
+use crate::Error::{GCloudError, GCloudNotFound, GCloudParseError};
+use crate::{Error, TokenProvider};
 
 #[derive(Debug)]
 pub(crate) struct GCloudAuthorizedUser {

src/lib.rs

@@ -91,6 +91,7 @@
 use std::sync::Arc;
 
 use async_trait::async_trait;
+use thiserror::Error;
 use tracing::{instrument, Level};
 
 mod custom_service_account;
@@ -102,9 +103,6 @@ use default_authorized_user::ConfigDefaultCredentials;
 mod default_service_account;
 use default_service_account::MetadataServiceAccount;
 
-mod error;
-pub use error::Error;
-
 mod gcloud_authorized_user;
 use gcloud_authorized_user::GCloudAuthorizedUser;
 
@@ -175,3 +173,105 @@ pub trait TokenProvider: Send + Sync {
     /// Get the project ID for the authentication context
     async fn project_id(&self) -> Result<Arc<str>, Error>;
 }
+
+/// Enumerates all possible errors returned by this library.
+#[derive(Error, Debug)]
+pub enum Error {
+    /// No available authentication method was discovered
+    ///
+    /// Application can authenticate against GCP using:
+    ///
+    /// - Default service account - available inside GCP platform using GCP Instance Metadata server
+    /// - GCloud authorized user - retrieved using `gcloud auth` command
+    ///
+    /// All authentication methods have been tested and none succeeded.
+    /// Service account file can be downloaded from GCP in json format.
+    #[error("No available authentication method was discovered")]
+    NoAuthMethod(Box<Error>, Box<Error>, Box<Error>),
+
+    /// Error in underlying RustTLS library.
+    /// Might signal problem with establishing secure connection using trusted certificates
+    #[error("TLS error")]
+    TlsError(#[source] rustls::Error),
+
+    /// Error when establishing connection to OAuth server
+    #[error("Could not establish connection with OAuth server")]
+    OAuthConnectionError(#[source] hyper::Error),
+
+    /// Wrong path to custom service account credentials provided
+    ///
+    /// By default, the custom service account credentials are parsed from the path pointed to by the
+    /// `GOOGLE_APPLICATION_CREDENTIALS` environment variable.
+    #[error("Invalid path to custom service account")]
+    CustomServiceAccountPath(#[source] std::io::Error),
+
+    /// Failed to parse the application credentials provided
+    ///
+    /// By default, the custom service account credentials are parsed from the path pointed to by the
+    /// `GOOGLE_APPLICATION_CREDENTIALS` environment variable.
+    #[error("Unable to parse custom service account credentials")]
+    CustomServiceAccountCredentials(#[source] serde_json::error::Error),
+
+    /// Default user profile not found
+    ///
+    /// User can authenticate locally during development using `gcloud auth login` which results in creating
+    /// `~/.config/gcloud/application_default_credentials.json` which couldn't be find on the machine
+    #[error("User authentication profile not found")]
+    UserProfilePath(#[source] std::io::Error),
+
+    /// Wrong format of user profile
+    #[error("User profile was not parsable")]
+    UserProfileFormat(#[source] serde_json::error::Error),
+
+    /// Could not connect to  server
+    #[error("Could not establish connection with server")]
+    ConnectionError(#[from] hyper::Error),
+
+    /// Could not parse response from server
+    #[error("Could not parse server response")]
+    ParsingError(#[source] serde_json::error::Error),
+
+    /// Could not connect to server
+    #[error("Server unavailable: {0}")]
+    ServerUnavailable(String),
+
+    /// Could not sign requested message
+    #[error("Could not sign")]
+    SignerFailed,
+
+    /// Could not initialize signer
+    #[error("Couldn't initialize signer")]
+    SignerInit,
+
+    /// Could not find Home directory in the environment
+    #[error("Home directory not found")]
+    NoHomeDir,
+
+    /// Project ID not supported for current authentication method
+    #[error("Project ID not supported for current authentication method")]
+    NoProjectId,
+
+    /// Project ID not found through current authentication method
+    #[error("Project ID not found through current authentication method")]
+    ProjectIdNotFound,
+
+    /// Project ID is invalid UTF-8
+    #[error("Project ID is invalid UTF-8")]
+    ProjectIdNonUtf8,
+
+    /// GCloud executable not found
+    #[error("GCloud executable not found in $PATH")]
+    GCloudNotFound,
+
+    /// GCloud returned an error status
+    #[error("GCloud returned a non OK status")]
+    GCloudError,
+
+    /// GCloud output couldn't be parsed
+    #[error("Failed to parse output of GCloud")]
+    GCloudParseError,
+
+    /// Represents all other cases of `std::io::Error`.
+    #[error(transparent)]
+    IOError(#[from] std::io::Error),
+}