1 files changed, 96 insertions, 0 deletions
diff --git a/src/validate_ipv4_address.rs b/src/validate_ipv4_address.rs
new file mode 100644
index 0000000..1b9f7b2
--- /dev/null
+++ b/src/validate_ipv4_address.rs
@@ -0,0 +1,96 @@
+#![warn(clippy::pedantic)]
+
+use super::character_classes::{
+    DIGIT,
+};
+use super::context::Context;
+use super::error::Error;
+
+struct Shared {
+    num_groups: usize,
+    octet_buffer: String,
+}
+
+enum State {
+    NotInOctet(Shared),
+    ExpectDigitOrDot(Shared),
+}
+
+impl State {
+    fn finalize(self) -> Result<(), Error> {
+        match self {
+            Self::NotInOctet(_) => Err(Error::TruncatedHost),
+            Self::ExpectDigitOrDot(state) => Self::finalize_expect_digit_or_dot(state),
+        }
+    }
+
+    fn finalize_expect_digit_or_dot(state: Shared) -> Result<(), Error> {
+        let mut state = state;
+        if !state.octet_buffer.is_empty() {
+            state.num_groups += 1;
+            if state.octet_buffer.parse::<u8>().is_err() {
+                return Err(Error::InvalidDecimalOctet);
+            }
+        }
+        match state.num_groups {
+            4 => Ok(()),
+            n if n < 4 => Err(Error::TooFewAddressParts),
+            _ => Err(Error::TooManyAddressParts),
+        }
+    }
+
+    fn new() -> Self {
+        Self::NotInOctet(Shared{
+            num_groups: 0,
+            octet_buffer: String::new(),
+        })
+    }
+
+    fn next(self, c: char) -> Result<Self, Error> {
+        match self {
+            Self::NotInOctet(state) => Self::next_not_in_octet(state, c),
+            Self::ExpectDigitOrDot(state) => Self::next_expect_digit_or_dot(state, c),
+        }
+    }
+
+    fn next_not_in_octet(state: Shared, c: char) -> Result<Self, Error> {
+        let mut state = state;
+        if DIGIT.contains(&c) {
+            state.octet_buffer.push(c);
+            Ok(Self::ExpectDigitOrDot(state))
+        } else {
+            Err(Error::IllegalCharacter(Context::Ipv4Address))
+        }
+    }
+
+    fn next_expect_digit_or_dot(state: Shared, c: char)-> Result<Self, Error> {
+        let mut state = state;
+        if c == '.' {
+            state.num_groups += 1;
+            if state.num_groups > 4 {
+                return Err(Error::TooManyAddressParts);
+            }
+            if state.octet_buffer.parse::<u8>().is_err() {
+                return Err(Error::InvalidDecimalOctet);
+            }
+            state.octet_buffer.clear();
+            Ok(Self::NotInOctet(state))
+        } else if DIGIT.contains(&c) {
+            state.octet_buffer.push(c);
+            Ok(Self::ExpectDigitOrDot(state))
+        } else {
+            Err(Error::IllegalCharacter(Context::Ipv4Address))
+        }
+    }
+}
+
+pub fn validate_ipv4_address<T>(address: T) -> Result<(), Error>
+    where T: AsRef<str>
+{
+    address.as_ref()
+        .chars()
+        .try_fold(State::new(), |machine, c| {
+            machine.next(c)
+        })?
+        .finalize()
+}