example: Add TCP header modification example

[ThisSeanZhang]

Old PR is: #767

• Replaced tabs with spaces for consistency
• Removed unstable features
• Modified handling of attachment result
• Replaced verbose options and included trigger command in README.md

Thank you for considering a contribution!

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be sure to read and follow the Contributor's Guide. It
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[ThisSeanZhang]

How can I install a plugin in VSCode or check the same rules in CI in some other way? :P

[danielocfb]

How can I install a plugin in VSCode or check the same rules in CI in some other way? :P

You don't need VSCode, you can just do what the workflow does. So in your case check the clippy and/or rustfmt jobs:

libbpf-rs/.github/workflows/test.yml

Lines 185 to 205 in b47f48e

	clippy:
	name: Lint with clippy
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4
	- name: Install deps
	run: sudo apt-get install -y libelf-dev
	- uses: dtolnay/rust-toolchain@stable
	with:
	components: rustfmt
	- uses: Swatinem/rust-cache@v2
	- run: cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths
	rustfmt:
	name: Check code formatting
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4
	- uses: dtolnay/rust-toolchain@nightly
	with:
	components: rustfmt
	- run: cargo fmt -- --check

[danielocfb]

Looks good to me now, thanks! Why did you remove the example from the workspace, though? I think it should stay there.

[danielocfb]

Should we exit here or is there a good reason for continuing as if nothing happened?

[ThisSeanZhang]

Should I use panic or return Err or do you have a better suggestion?

panic!("Failed to Attach BPF, Reason: {:?}", Error::last_os_error());
// or
println!("Failed to Attach BPF, Reason: ");
return Err(Error::last_os_error().into());

[d-e-s-o]

Return is probably best. Thanks!

[ThisSeanZhang]

cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths

I executed cmd and then got this

$ cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths 
   Compiling libbpf-rs v0.23.0 (/home/sean/libbpf-rs/libbpf-rs)
error: transmute used without annotations
   --> libbpf-rs/src/print.rs:127:28
    |
127 |         unsafe { Some(mem::transmute(outer_print_cb as *const ())) };
    |                            ^^^^^^^^^ help: consider adding missing annotations: `transmute::<*const (), unsafe extern "C" fn(u32, *const i8, *mut libbpf_sys::__va_list_tag) -> i32>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_transmute_annotations
    = note: `-D clippy::missing-transmute-annotations` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::missing_transmute_annotations)]`

error: could not compile `libbpf-rs` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `libbpf-rs` (lib) due to 1 previous error
error: could not compile `libbpf-rs` (lib test) due to 1 previous error

did I miss something...

[d-e-s-o]

cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths

I executed cmd and then got this

$ cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths 
   Compiling libbpf-rs v0.23.0 (/home/sean/libbpf-rs/libbpf-rs)
error: transmute used without annotations
   --> libbpf-rs/src/print.rs:127:28
    |
127 |         unsafe { Some(mem::transmute(outer_print_cb as *const ())) };
    |                            ^^^^^^^^^ help: consider adding missing annotations: `transmute::<*const (), unsafe extern "C" fn(u32, *const i8, *mut libbpf_sys::__va_list_tag) -> i32>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_transmute_annotations
    = note: `-D clippy::missing-transmute-annotations` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::missing_transmute_annotations)]`

error: could not compile `libbpf-rs` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `libbpf-rs` (lib) due to 1 previous error
error: could not compile `libbpf-rs` (lib test) due to 1 previous error

did I miss something...

You may be using nightly clippy or a newer version that has added this lint by default. Just allow it for now and move on?

cargo clippy --locked --no-deps --all-targets --tests -- -D warnings -D clippy::absolute_paths -A clippy::missing-transmute-annotations

[danielocfb]

Looks good to me, thanks again!

[ThisSeanZhang]

Thank you very much for your help in this. 🥳