pem-rfc7468: detect PEM headers in decode_vec (#19)

Missed in PR #13

- add test coverage for new cases
- refactor out decoding of encapsulated text
- compromise here on estimating buffer size
  - slightly more overestimation, due to counting whitespace
  - faster due to no two-pass
  - required to ensure that we attempt a base64 decode of the first line
    before chopping the second line

Author: dwhjames

.gitignore

@@ -1,2 +1,2 @@
-/target/
+target/
 **/*.rs.bk

pem-rfc7468/src/decoder.rs

@@ -20,32 +20,42 @@ use crate::{
 use base64ct::{Base64, Encoding};
 use core::{convert::TryFrom, str};
 
-/// Decode a PEM document according to RFC 7468's "Strict" grammar.
-///
-/// On success, writes the decoded document into the provided buffer, returning
-/// the decoded label and the portion of the provided buffer containing the
-/// decoded message.
-pub fn decode<'i, 'o>(pem: &'i [u8], buf: &'o mut [u8]) -> Result<(&'i str, &'o [u8])> {
-    let encapsulation = Encapsulation::try_from(pem)?;
-    let label = encapsulation.label();
-    let mut out_len = 0;
-
+fn decode_encapsulated_text<'i, 'o>(
+    encapsulation: &Encapsulation<'i>,
+    buf: &'o mut [u8],
+    out_len: &mut usize,
+) -> Result<()> {
     for line in encapsulation.encapsulated_text() {
         let line = line?;
-        match Base64::decode(line, &mut buf[out_len..]) {
+
+        match Base64::decode(line, &mut buf[*out_len..]) {
             Err(error) => {
                 // in the case that we are decoding the first line
                 // and we error, then attribute the error to an unsupported header
                 // if a colon char is present in the line
-                if out_len == 0 && line.iter().any(|&b| b == grammar::CHAR_COLON) {
+                if *out_len == 0 && line.iter().any(|&b| b == grammar::CHAR_COLON) {
                     return Err(Error::HeaderDetected);
                 } else {
                     return Err(error.into());
                 }
             }
-            Ok(out) => out_len += out.len(),
+            Ok(out) => *out_len += out.len(),
         }
     }
+    Ok(())
+}
+
+/// Decode a PEM document according to RFC 7468's "Strict" grammar.
+///
+/// On success, writes the decoded document into the provided buffer, returning
+/// the decoded label and the portion of the provided buffer containing the
+/// decoded message.
+pub fn decode<'i, 'o>(pem: &'i [u8], buf: &'o mut [u8]) -> Result<(&'i str, &'o [u8])> {
+    let encapsulation = Encapsulation::try_from(pem)?;
+    let label = encapsulation.label();
+    let mut out_len = 0;
+
+    decode_encapsulated_text(&encapsulation, buf, &mut out_len)?;
 
     Ok((label, &buf[..out_len]))
 }
@@ -57,17 +67,12 @@ pub fn decode<'i, 'o>(pem: &'i [u8], buf: &'o mut [u8]) -> Result<(&'i str, &'o
 pub fn decode_vec(pem: &[u8]) -> Result<(&str, Vec<u8>)> {
     let encapsulation = Encapsulation::try_from(pem)?;
     let label = encapsulation.label();
-    let mut max_len = 0;
-
-    for line in encapsulation.encapsulated_text() {
-        max_len += line?.len() * 3 / 4;
-    }
-
+    // count all chars (gives over-estimation, due to whitespace)
+    let max_len = encapsulation.encapsulated_text.len() * 3 / 4;
     let mut result = vec![0u8; max_len];
     let mut actual_len = 0;
-    for line in encapsulation.encapsulated_text() {
-        actual_len += Base64::decode(line?, &mut result[actual_len..])?.len();
-    }
+
+    decode_encapsulated_text(&encapsulation, &mut result, &mut actual_len)?;
 
     // Actual encoded length can be slightly shorter than estimated
     // TODO(tarcieri): more reliable length estimation

pem-rfc7468/tests/decode.rs

@@ -19,6 +19,16 @@ fn pkcs1_enc_example() {
     }
 }
 
+#[test]
+#[cfg(feature = "alloc")]
+fn pkcs1_enc_example_with_vec() {
+    let pem = include_bytes!("examples/ssh_rsa_pem_password.pem");
+    match pem_rfc7468::decode_vec(pem) {
+        Err(pem_rfc7468::Error::HeaderDetected) => (),
+        _ => panic!("Expected HeaderDetected error"),
+    }
+}
+
 #[test]
 fn header_of_length_64() {
     let pem = include_bytes!("examples/chosen_header.pem");
@@ -29,6 +39,16 @@ fn header_of_length_64() {
     }
 }
 
+#[test]
+#[cfg(feature = "alloc")]
+fn header_of_length_64_with_vec() {
+    let pem = include_bytes!("examples/chosen_header.pem");
+    match pem_rfc7468::decode_vec(pem) {
+        Err(pem_rfc7468::Error::HeaderDetected) => (),
+        res => panic!("Expected HeaderDetected error; Found {:?}", res),
+    }
+}
+
 #[test]
 fn pkcs8_example() {
     let pem = include_bytes!("examples/pkcs8.pem");