refactor(gcp): harden compute engine request validation

rustcloud/src/gcp/errors.rs

@@ -0,0 +1,67 @@
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub enum GcpApiError {
+    MissingField {
+        field: &'static str,
+    },
+    InvalidFieldType {
+        field: &'static str,
+        expected: &'static str,
+    },
+    InvalidFieldValue {
+        field: &'static str,
+        message: String,
+    },
+    Auth {
+        message: String,
+    },
+    Http {
+        source: reqwest::Error,
+    },
+    Serialization {
+        source: serde_json::Error,
+    },
+}
+
+impl fmt::Display for GcpApiError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            GcpApiError::MissingField { field } => {
+                write!(f, "missing required field: {}", field)
+            }
+            GcpApiError::InvalidFieldType { field, expected } => {
+                write!(f, "invalid field type for '{}', expected {}", field, expected)
+            }
+            GcpApiError::InvalidFieldValue { field, message } => {
+                write!(f, "invalid value for '{}': {}", field, message)
+            }
+            GcpApiError::Auth { message } => write!(f, "gcp auth error: {}", message),
+            GcpApiError::Http { source } => write!(f, "http error: {}", source),
+            GcpApiError::Serialization { source } => write!(f, "serialization error: {}", source),
+        }
+    }
+}
+
+impl Error for GcpApiError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            GcpApiError::Http { source } => Some(source),
+            GcpApiError::Serialization { source } => Some(source),
+            _ => None,
+        }
+    }
+}
+
+impl From<reqwest::Error> for GcpApiError {
+    fn from(source: reqwest::Error) -> Self {
+        GcpApiError::Http { source }
+    }
+}
+
+impl From<serde_json::Error> for GcpApiError {
+    fn from(source: serde_json::Error) -> Self {
+        GcpApiError::Serialization { source }
+    }
+}