reverseproxy: avoid panic if failed to parse url

[aca]

1. What does this change do, exactly?

caddy reverse-proxy -from ':30000' -to '127.0.0.1:8384'

this commands panics when failed to parse error as it tries to write to nil pointer.

2. Please link to the relevant issues.

none

4. Checklist

• I have written tests and verified that they fail without my change
• I have squashed any insignificant commits
• This change has comments explaining package types, values, functions, and non-obvious lines of code
• I am willing to help maintain this change if there are issues with it later

[mholt]

Thanks for the PR!

I am going to make sure I can reproduce this first, because I still don't understand what is going on. I am not seeing the error. (See my comment in your issue.)

What is the exact version of Go you are using, please?

[aca]

@mholt oh, this one is not related to issue #2849.
Could you try this command?

caddy reverse-proxy -from ':30000' -to '127.0.0.1:8384' 

I am quite convinced that this will panic regardless of go version.

[aca]

@mholt

 » go version
go version go1.13.2 linux/amd64

[mholt]

Okay, sorry, I thought this was related to #2849.

I can reproduce this one. It's the one in #2849 that I cannot reproduce.

[mholt]

I ask for the Go version because Go made a breaking change (!!) to how URLs are parsed in Go 1.13.1.

[aca]

@mholt oh god.. Didn't know that..

[mholt]

Okay cool, this one was easy to fix (I am pushing a separate commit, if that's alright, with a different fix based on the details I saw in the stack trace, etc).

Thanks for the report!

[mholt]

Pushed the fix in 8ef0a0b -- appreciate your help!