README: display clear errors in the example

[nim65s]

Description

Hi,

Building the example in the README raise the following warning:

warning: unused import: `Query`
 --> src/main.rs:1:24
  |
1 | use influxdb::{Client, Query, Timestamp, ReadQuery};
  |                        ^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

And running it for me shows:

thread 'main' panicked at src/main.rs:35:5:
Write result was not okay

which is not super helpful.

With the proposed changes, I get:

Error writing result: authorization error. User not authorized

which is more clear :)

Checklist

• [x] Formatted code using cargo fmt --all
• [ ] Linted code using clippy
  • [ ] with reqwest feature: cargo clippy --manifest-path influxdb/Cargo.toml --all-targets --no-default-features --features use-serde,derive,reqwest-client -- -D warnings
  • [ ] with surf feature: cargo clippy --manifest-path influxdb/Cargo.toml --all-targets --no-default-features --features use-serde,derive,hyper-client -- -D warnings
• [x] Updated README.md using cargo doc2readme -p influxdb --expand-macros
• [x] Reviewed the diff. Did you leave any print statements or unnecessary comments?
• [x] Any unfinished work that warrants a separate issue captured in an issue with a TODO code comment

[nim65s]

done, thanks for the review

[nim65s]

@msrd0 : The point of this PR is to display a more precise error message to the end user, so we need to display {e} or something similar.

ie. to go from something like "Write result was not okay" to something like "Write result was not okay, because your user is not authorized". I don't think we can do this with .expect().

[nim65s]

Alternatively, we could have main() returning a Result<(), influxdb::Error>, and use ? in read and write.

[msrd0]

Is the difference between display and debug this big? I just looked it up, and expect("msg") is the same as unwrap_or_else(|e| panic!("msg: {e:?}")). I think given that this code is an example and has no intention to have "perfect" error handling, I'd go with either expect or unwrap and panic.

While your code outputs a nice error message to the terminal and exits, I think it is a bit more verbose than necessary for an example, and it needs a bit longer for a human to detect it as error-handling code. But I believe examples should be as concise as possible.

[msrd0]

Using ? is also a good idea

[nim65s]

Now I get Error: AuthorizationError, which is good enough for me to understand that I need to setup auth :)

[nim65s]

Ok, I was wrong about the use of msg in expect(), thanks for the clarification. I'm open to use that too, as you prefer.