Move the tools' arguments and the host rules to proto

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/proto/src/hosts.rs

@@ -0,0 +1,61 @@
+//! Host names and patterns, shared by `brokerd` and the egress proxy so both check hosts with the
+//! same rules.
+
+/// A host label is 1 to 63 bytes of `a-z`, `0-9` or `-`, and neither starts nor ends with `-`.
+fn valid_label(label: &str) -> bool {
+    if !(1..=63).contains(&label.len()) {
+        return false;
+    }
+    let bytes = label.as_bytes();
+    if bytes.iter().next() == Some(&b'-') || bytes.iter().last() == Some(&b'-') {
+        return false;
+    }
+    bytes
+        .iter()
+        .all(|&byte| matches!(byte, b'a'..=b'z' | b'0'..=b'9' | b'-'))
+}
+
+/// A host is 1 to 253 bytes of dot-separated labels, each a whole non-dot name, and the last label
+/// starts with a letter. That last rule keeps out every spelling of an IPv4 address.
+pub fn valid_host(host: &str) -> bool {
+    if !(1..=253).contains(&host.len()) {
+        return false;
+    }
+    let labels: Vec<&str> = host.split('.').collect();
+    if labels.len() < 2 {
+        return false;
+    }
+    for label in &labels {
+        if !valid_label(label) {
+            return false;
+        }
+    }
+    match labels.iter().last() {
+        Some(last) => matches!(last.bytes().next(), Some(byte) if byte.is_ascii_lowercase()),
+        None => false,
+    }
+}
+
+/// A host, or `*.` followed by a host. Nothing else.
+pub fn valid_host_pattern(pattern: &str) -> bool {
+    match pattern.strip_prefix("*.") {
+        Some(base) => valid_host(base),
+        None => valid_host(pattern),
+    }
+}
+
+/// Does `pattern` match `host`? Without `*.` the strings must be equal; with `*.base` the host must
+/// end in `.base` with something before the dot.
+pub fn host_matches(pattern: &str, host: &str) -> bool {
+    let base = match pattern.strip_prefix("*.") {
+        Some(base) => base,
+        None => return pattern == host,
+    };
+    match host.strip_suffix(base) {
+        Some(before) => match before.strip_suffix('.') {
+            Some(prefix) => !prefix.is_empty(),
+            None => false,
+        },
+        None => false,
+    }
+}