From d90ca5c0d7df85874e92e9931850ec1077830043 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20B=C3=BChler?= <source@stbuehler.de>
Date: Mon, 24 Jun 2024 14:16:21 +0200
Subject: [PATCH] add inet_addr-like IPv4Addr parser

---
 src/lib.rs              |   1 +
 src/parsers/inetaddr.rs | 117 ++++++++++++++++++++++++++++++++++++++++
 src/parsers/mod.rs      |  10 ++++
 3 files changed, 128 insertions(+)
 create mode 100644 src/parsers/inetaddr.rs
 create mode 100644 src/parsers/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index 20e89ca..06655dd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -80,6 +80,7 @@ pub use self::{
 };
 
 pub mod errors;
+pub mod parsers;
 
 mod serde_common;
 
diff --git a/src/parsers/inetaddr.rs b/src/parsers/inetaddr.rs
new file mode 100644
index 0000000..c050d6f
--- /dev/null
+++ b/src/parsers/inetaddr.rs
@@ -0,0 +1,117 @@
+use std::net::{AddrParseError, IpAddr, Ipv4Addr};
+
+/// Parse "loose" IPv4 address similar to POSIX `inet_addr`
+///
+/// This also accepts inputs that are not 4 decimal represented octects separated by dots.
+///
+/// * Allows less than 4 numbers separated by dots; the last number is
+///   interpreted as an 32-bit (no dot), 24-bit (1 dot), 16-bit (2 dots) number.
+///   Other numbers still must be octets (i.e. 8 bit)
+/// * Allows hexadecimal ("0x" or "0X" prefix) and octal ("0" prefix) numbers
+///   in all places.
+///
+/// See <https://pubs.opengroup.org/onlinepubs/9699919799/functions/inet_addr.html>
+pub fn inet_addr(s: &str) -> Option<Ipv4Addr> {
+	let mut slots = [0u32; 4];
+	let mut last_slot = 0;
+	for (ndx, part) in s.split('.').enumerate() {
+		if ndx >= 4 {
+			// too many '.'
+			return None;
+		}
+		let slot = if part.starts_with("0x") || part.starts_with("0X") {
+			let part = &part[2..];
+			if part.starts_with("+") {
+				// we don't want to support "0x+..."
+				return None;
+			}
+			u32::from_str_radix(part, 16)
+		} else if part.starts_with("0") {
+			u32::from_str_radix(part, 8)
+		} else {
+			part.parse::<u32>()
+		};
+		slots[ndx] = slot.ok()?;
+		last_slot = ndx;
+	}
+	debug_assert!(last_slot <= 3, "can't have more than 4");
+
+	let num = if last_slot == 0 {
+		slots[0]
+	} else {
+		let mut base: u32 = 0;
+		for ndx in 0..last_slot {
+			if slots[ndx] >= 256 {
+				// leading parts must be octects
+				return None;
+			}
+			// shift by 24, 16 or 8
+			base = base | (slots[ndx] << (3 - ndx) * 8);
+		}
+		// last 3 => have 4 => 1 byte, last 2 => have 3 => 2 bytes, last 1 => have 2 => 3 bytes
+		let last_slot_bit_limit = (4 - last_slot) * 8;
+		if slots[last_slot] >= 1 << last_slot_bit_limit {
+			// last part too big
+			return None;
+		}
+		// never shift last slot
+		base | slots[last_slot]
+	};
+
+	Some(Ipv4Addr::from(num))
+}
+
+/// Parse IPv4 address; fall back to `inet_addr` if normal parser fails
+pub fn parse_loose_ipv4(s: &str) -> Result<Ipv4Addr, AddrParseError> {
+	match s.parse() {
+		Ok(a) => Ok(a),
+		Err(e) => {
+			if let Some(a) = inet_addr(s) {
+				Ok(a)
+			} else {
+				Err(e)
+			}
+		}
+	}
+}
+
+/// Parse IP address; fall back to `inet_addr` if normal parser fails
+pub fn parse_loose_ip(s: &str) -> Result<IpAddr, AddrParseError> {
+	match s.parse() {
+		Ok(a) => Ok(a),
+		Err(e) => {
+			if let Some(a) = inet_addr(s) {
+				Ok(IpAddr::V4(a))
+			} else {
+				Err(e)
+			}
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use std::net::{AddrParseError, IpAddr, Ipv4Addr};
+
+	fn run(s: &str, expect: Ipv4Addr) {
+		assert_eq!(super::inet_addr(s), Some(expect));
+		assert_eq!(super::parse_loose_ipv4(s), Ok::<_, AddrParseError>(expect));
+		assert_eq!(super::parse_loose_ip(s), Ok::<_, AddrParseError>(IpAddr::V4(expect)));
+	}
+
+	#[test]
+	fn test_loose_ipv4() {
+		run("10.0.1.2", Ipv4Addr::from([10, 0, 1, 2]));
+		run("10.0.258", Ipv4Addr::from([10, 0, 1, 2]));
+		run("0xA000102", Ipv4Addr::from([10, 0, 1, 2]));
+		run("0XA000102", Ipv4Addr::from([10, 0, 1, 2]));
+		run("012.0x102", Ipv4Addr::from([10, 0, 1, 2]));
+
+		run("127.0.0.1", Ipv4Addr::from([127, 0, 0, 1]));
+		run("127.0.1", Ipv4Addr::from([127, 0, 0, 1]));
+		run("127.1", Ipv4Addr::from([127, 0, 0, 1]));
+
+		run("0", Ipv4Addr::from([0, 0, 0, 0]));
+		run("1", Ipv4Addr::from([0, 0, 0, 1]));
+	}
+}
diff --git a/src/parsers/mod.rs b/src/parsers/mod.rs
new file mode 100644
index 0000000..63f2341
--- /dev/null
+++ b/src/parsers/mod.rs
@@ -0,0 +1,10 @@
+//! Extra parsers
+//!
+//! The `FromStr` implementations in this crate are rather strict
+//! about the allowed input.  Depending on the data format that needs
+//! to be handled the functions here might help implementing custom
+//! parsers.
+
+mod inetaddr;
+
+pub use self::inetaddr::{inet_addr, parse_loose_ip, parse_loose_ipv4};