fix(headers): avoid double spaces in the headers

[yacir]

it fixes lettre/lettre#949

[paolobarbolini]

LGTM. Thank you for the fix.
Could you add a regression test?

[yacir]

Thanks for the quick answer. Was thinking to add them later to the letter crate here https://github.com/lettre/lettre/blob/master/src/message/header/mod.rs but you're right i ll add it here

[yacir]

@paolobarbolini test added. Let me know if it's okay for you
thanks

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.71%. Comparing base (7c3ca39) to head (d212225).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   98.69%   98.71%   +0.01%     
==========================================
  Files          10       10              
  Lines         537      545       +8     
==========================================
+ Hits          530      538       +8     
  Misses          7        7              

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[paolobarbolini]

Turns out this doesn't work as I'd have originally expected.

new_line_and_space is just a silly micro-optimization that looking back doesn't make sense and I'm thinking of removing. Anyway the way it should work is the same as:

diff --git a/src/headers/writer.rs b/src/headers/writer.rs
index a36e6ab..0e024c5 100644
--- a/src/headers/writer.rs
+++ b/src/headers/writer.rs
@@ -55,11 +55,8 @@ impl<'a> EmailWriter<'a> {
 
     /// Equivalent to calling `new_line()` and `space()` consecutively.
     pub(crate) fn new_line_and_space(&mut self) -> fmt::Result {
-        self.spaces = 0;
-        self.writer.write_str("\r\n ")?;
-        self.line_len = 1;
-        self.optional_breakpoint = false;
-        self.can_go_to_new_line_now = false;
+        self.new_line()?;
+        self.space();
 
         Ok(())
     }

Doing so would break your test, so I'd have to also do:

diff --git a/src/headers/writer.rs b/src/headers/writer.rs
index a36e6ab..a418231 100644
--- a/src/headers/writer.rs
+++ b/src/headers/writer.rs
@@ -45,6 +45,7 @@ impl<'a> EmailWriter<'a> {
 
     /// Go to a new line and reset the `line_len` to `0`.
     pub fn new_line(&mut self) -> fmt::Result {
+        self.spaces = 0;
         self.writer.write_str("\r\n")?;
         self.line_len = 0;
         self.optional_breakpoint = false;

Which breaks many other tests.

[paolobarbolini]

While it produces an ugly output this should now be fixed by c128b46

[yacir]

it's much better now, i ll give a try with my dataset to check if it fixes all the previous failing cases

[yacir]

@paolobarbolini i tested with +3400 real use case.

https://github.com/lettre/email-encoding/releases/tag/v0.2.1	14104c3 or #8
456 encoding errors	6 remaining encoding errors

It's way better, but we still have some corner cases

[paolobarbolini]

Nice. I'm thinking of making a new release and handle any other report separately

[yacir]

I also think it's the best compromise since it fixes ~99% of the errors