From 4c9f3277d11fe95a365e84cd12bede6f8c4e5f56 Mon Sep 17 00:00:00 2001
From: Joel Alvarez <jeresoft@gmail.com>
Date: Mon, 27 Jul 2026 13:42:58 -0700
Subject: [PATCH] feat: model API security boundaries

---
 src/lib.rs               |   1 +
 src/security_boundary.rs | 118 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)
 create mode 100644 src/security_boundary.rs

diff --git a/src/lib.rs b/src/lib.rs
index c3e7dfd..74c87b4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,4 +10,5 @@ pub mod executable_contract;
 pub mod http;
 pub mod identity_access;
 pub mod operation_policy;
+pub mod security_boundary;
 pub mod style_selection;
diff --git a/src/security_boundary.rs b/src/security_boundary.rs
new file mode 100644
index 0000000..a95ced2
--- /dev/null
+++ b/src/security_boundary.rs
@@ -0,0 +1,118 @@
+//! Modelo mínimo de una frontera de seguridad observable en una API.
+
+use std::fmt;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DataSensitivity {
+    Public,
+    Sensitive,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ErrorExposure {
+    SafeMessage,
+    InternalDetail,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SecurityBoundary {
+    input_name: String,
+    sensitivity: DataSensitivity,
+    error_exposure: ErrorExposure,
+}
+
+impl SecurityBoundary {
+    pub fn new(
+        input_name: impl Into<String>,
+        sensitivity: DataSensitivity,
+        error_exposure: ErrorExposure,
+    ) -> Result<Self, SecurityError> {
+        let input_name = required_text(input_name.into(), "entrada")?;
+        if sensitivity == DataSensitivity::Sensitive
+            && error_exposure == ErrorExposure::InternalDetail
+        {
+            return Err(SecurityError::SensitiveDataCannotExposeInternalDetail);
+        }
+        Ok(Self {
+            input_name,
+            sensitivity,
+            error_exposure,
+        })
+    }
+
+    pub fn rejects(&self, value: &str) -> bool {
+        value.trim().is_empty() || value.len() > 128
+    }
+
+    pub fn error_exposure(&self) -> ErrorExposure {
+        self.error_exposure
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SecurityError {
+    EmptyText { subject: &'static str },
+    SensitiveDataCannotExposeInternalDetail,
+}
+
+impl fmt::Display for SecurityError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::EmptyText { subject } => write!(f, "La {subject} no puede estar vacía."),
+            Self::SensitiveDataCannotExposeInternalDetail => write!(
+                f,
+                "Los datos sensibles no pueden exponer detalles internos."
+            ),
+        }
+    }
+}
+impl std::error::Error for SecurityError {}
+
+fn required_text(value: String, subject: &'static str) -> Result<String, SecurityError> {
+    let value = value.trim().to_owned();
+    if value.is_empty() {
+        return Err(SecurityError::EmptyText { subject });
+    }
+    Ok(value)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{DataSensitivity, ErrorExposure, SecurityBoundary, SecurityError};
+
+    #[test]
+    fn accepts_a_safe_boundary_for_sensitive_input() {
+        let boundary = SecurityBoundary::new(
+            "importe",
+            DataSensitivity::Sensitive,
+            ErrorExposure::SafeMessage,
+        )
+        .unwrap();
+        assert!(boundary.rejects(""));
+    }
+
+    #[test]
+    fn rejects_internal_details_for_sensitive_input() {
+        let error = SecurityBoundary::new(
+            "importe",
+            DataSensitivity::Sensitive,
+            ErrorExposure::InternalDetail,
+        )
+        .unwrap_err();
+        assert_eq!(
+            error,
+            SecurityError::SensitiveDataCannotExposeInternalDetail
+        );
+    }
+
+    #[test]
+    fn rejects_overlong_untrusted_input() {
+        let boundary = SecurityBoundary::new(
+            "consulta",
+            DataSensitivity::Public,
+            ErrorExposure::SafeMessage,
+        )
+        .unwrap();
+        assert!(boundary.rejects(&"x".repeat(129)));
+    }
+}