sendgrid/go-gmime

go-gmime's Issues

Return error instead of panic

We should return an error, instead of panic'ing.
Since this is a library, we should let the caller deal with the error.

For example, when calling parse.Recipients() on a message with an empty To list:

(process:24446): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
panic: ZERO pointer

goroutine 25 [running]:
panic(0x42edfa0, 0xc8201b8d10)
        /usr/local/go/src/runtime/panic.go:464 +0x3e6
github.com/sendgrid/go-gmime/gmime.ref(0x0)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/gmime.go:48 +0x75
github.com/sendgrid/go-gmime/gmime.AssignJanitor(0x5e00158, 0xc8201b46a8)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/janitor.go:22 +0x39
github.com/sendgrid/go-gmime/gmime.CastPointer(0x0, 0x41c719f)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/janitor.go:34 +0x81
github.com/sendgrid/go-gmime/gmime.CastInternetAddressList(0x0, 0x44bc748)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/internet_address.go:189 +0x21
github.com/sendgrid/go-gmime/gmime.(*aMessage).AllRecipients(0xc8201b45e8, 0x0)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/message.go:152 +0xc2
github.com/sendgrid/go-gmime/gmime.(*aParse).Recipients(0xc8201b8cd0, 0x0, 0x0)
        /Users/trevorrothaus/go/src/github.com/sendgrid/go-gmime/gmime/parse.go:64 +0x45

Headers() needs to use textproto.Mimeheader.Set() instead of modifying the map directly

https://github.com/sendgrid/go-gmime/blame/5544c54b141c13fa6ac0b4ddc162a65dab1dc8bb/gmime/envelope.go#L64

When Canonical form of the key is different from the actual key, headers().Values() would not return the right value, since the internal map doesn't have the canonical form as the key. Users can get the values by treating Mimeheader as a map as a workaround- but this is confusing and can cause unexpected consequences.