fix(zipkin): avoid getting a nil value in log phase(#10590)

[junhao69535]

Description

An error(attempt to index local 'opentracing' (a nil value)) occurs in the following situations:

• failed to parse b3 header and return 400.
• plugins with higher priority return or throw exceptions.

All of the above result in a not being assigned value to ctx.opentracing. so got a error in log phase. this pr will fix it.

Fixes #10590

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[Vacant2333]

u can insert a new line at here to help the ci works

[junhao69535]

ok, thk

[junhao69535]

@Vacant2333
my new test cast as following:

=== TEST 23: no error in log phase while b3 header invalid
--- request
GET /echo
--- more_headers
b3: 80f198ee56343ba864fe8b2a57d3eff7
--- response_headers
x-b3-sampled:
--- error_code: 400
--- grep_error_log eval
qr/attempt to index local 'opentracing' \(a nil value\)
--- grep_error_log_out

i want to assert that there is no corresponding error in the log, what should I do?

[Vacant2333]

u may need to try this https://apisix.apache.org/docs/apisix/internal/testing-framework/#executing-shell-commands, im not sure if it will works🤣, i didnt find some testcase need to do like u want

[luoluoyuyu]

i want to assert that there is no corresponding error in the log, what should I do?

You can use no_error_log https://github.com/apache/apisix/blob/master/docs/en/latest/plugin-develop.md?plain=1#L549

[junhao69535]

i want to assert that there is no corresponding error in the log, what should I do?

You can use no_error_log https://github.com/apache/apisix/blob/master/docs/en/latest/plugin-develop.md?plain=1#L549

there is a error in rewrite phase, but no error in log phase.