Check encoded string is not too long

Currently it is possible to encode a string that is more than 90
characters long, this is in violation of BIP-173. We recently added a
function `crate::encoded_length` that does the length check,
call it when encoding in all the encode and encode to fmt functions.

Author: tcharding

src/lib.rs

@@ -142,7 +142,6 @@ pub mod segwit;
 use alloc::{string::String, vec::Vec};
 use core::fmt;
 
-#[cfg(feature = "alloc")]
 use crate::error::write_err;
 #[cfg(doc)]
 use crate::primitives::decode::CheckedHrpstring;
@@ -220,7 +219,7 @@ pub fn decode(s: &str) -> Result<(Hrp, Vec<u8>), DecodeError> {
 /// `Ck` algorithm (`NoChecksum` to exclude checksum all together).
 #[cfg(feature = "alloc")]
 #[inline]
-pub fn encode<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, fmt::Error> {
+pub fn encode<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, EncodeError> {
     encode_lower::<Ck>(hrp, data)
 }
 
@@ -230,7 +229,9 @@ pub fn encode<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, fmt::Error>
 /// `Ck` algorithm (`NoChecksum` to exclude checksum all together).
 #[cfg(feature = "alloc")]
 #[inline]
-pub fn encode_lower<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, fmt::Error> {
+pub fn encode_lower<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, EncodeError> {
+    let _ = encoded_length::<Ck>(&hrp, data)?;
+
     let mut buf = String::new();
     encode_lower_to_fmt::<Ck, String>(&mut buf, hrp, data)?;
     Ok(buf)
@@ -242,7 +243,9 @@ pub fn encode_lower<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, fmt::
 /// `Ck` algorithm (`NoChecksum` to exclude checksum all together).
 #[cfg(feature = "alloc")]
 #[inline]
-pub fn encode_upper<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, fmt::Error> {
+pub fn encode_upper<Ck: Checksum>(hrp: Hrp, data: &[u8]) -> Result<String, EncodeError> {
+    let _ = encoded_length::<Ck>(&hrp, data)?;
+
     let mut buf = String::new();
     encode_upper_to_fmt::<Ck, String>(&mut buf, hrp, data)?;
     Ok(buf)
@@ -257,7 +260,7 @@ pub fn encode_to_fmt<Ck: Checksum, W: fmt::Write>(
     fmt: &mut W,
     hrp: Hrp,
     data: &[u8],
-) -> Result<(), fmt::Error> {
+) -> Result<(), EncodeError> {
     encode_lower_to_fmt::<Ck, W>(fmt, hrp, data)
 }
 
@@ -270,7 +273,9 @@ pub fn encode_lower_to_fmt<Ck: Checksum, W: fmt::Write>(
     fmt: &mut W,
     hrp: Hrp,
     data: &[u8],
-) -> Result<(), fmt::Error> {
+) -> Result<(), EncodeError> {
+    let _ = encoded_length::<Ck>(&hrp, data)?;
+
     let iter = data.iter().copied().bytes_to_fes();
     let chars = iter.with_checksum::<Ck>(&hrp).chars();
     for c in chars {
@@ -288,7 +293,9 @@ pub fn encode_upper_to_fmt<Ck: Checksum, W: fmt::Write>(
     fmt: &mut W,
     hrp: Hrp,
     data: &[u8],
-) -> Result<(), fmt::Error> {
+) -> Result<(), EncodeError> {
+    let _ = encoded_length::<Ck>(&hrp, data)?;
+
     let iter = data.iter().copied().bytes_to_fes();
     let chars = iter.with_checksum::<Ck>(&hrp).chars();
     for c in chars {
@@ -456,6 +463,49 @@ impl From<DecodeError> for DecodeFromReaderError {
     fn from(e: DecodeError) -> Self { Self::Decode(e) }
 }
 
+/// An error while encoding an address.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub enum EncodeError {
+    /// Encoding HRP and data into a bech32 string exceeds the spec limit of 90 characters.
+    TooLong(EncodedLengthError),
+    /// Error writing to the formatter.
+    Fmt(fmt::Error),
+}
+
+impl fmt::Display for EncodeError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use EncodeError::*;
+
+        match *self {
+            TooLong(ref e) => write_err!(f, "encoded string too long"; e),
+            Fmt(ref e) => write_err!(f, "write to formatter failed"; e),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for EncodeError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        use EncodeError::*;
+
+        match *self {
+            TooLong(ref e) => Some(e),
+            Fmt(ref e) => Some(e),
+        }
+    }
+}
+
+impl From<EncodedLengthError> for EncodeError {
+    #[inline]
+    fn from(e: EncodedLengthError) -> Self { Self::TooLong(e) }
+}
+
+impl From<fmt::Error> for EncodeError {
+    #[inline]
+    fn from(e: fmt::Error) -> Self { Self::Fmt(e) }
+}
+
 /// Encoding bech32 string exceeds the spec limit of 90 characters.
 #[derive(Debug, Clone, PartialEq, Eq)]
 #[non_exhaustive]