panic: fix nil pointer dereference when x is a nil pointer by agbaria · Pull Request #253 · uber-go/mock

agbaria · 2025-05-04T13:48:26Z

when expected call fails to find a match, the error log message prints the actual values of the called method args
if one of the args is a nil pointer, function getString will panic on line https://github.com/uber-go/mock/blob/main/gomock/string.go#L16

panic: value method time.Duration.String called using nil *Duration pointer

goroutine 25 [running]:
time.(*Duration).String(0x103ee8b80?)
        <autogenerated>:1 +0x78
go.uber.org/mock/gomock.getString({0x103680500, 0x0})
        /Volumes/Go/pkg/mod/go.uber.org/mock@v0.5.0/gomock/string.go:16 +0x98
go.uber.org/mock/gomock.(*Controller).Call.func1(0x1400049e390, {0x10369d880, 0x140000e8678}, {0x1032d9bec, 0x16}, {0x14000842b10, 0x3, 0x3})
        /Volumes/Go/pkg/mod/go.uber.org/mock@v0.5.0/gomock/controller.go:212 +0x198
go.uber.org/mock/gomock.(*Controller).Call(0x1400049e390, {0x10369d880, 0x140000e8678}, {0x1032d9bec, 0x16}, {0x14000842b10, 0x3, 0x3})
        /Volumes/Go/pkg/mod/go.uber.org/mock@v0.5.0/gomock/controller.go:230 +0x6c

Summary by CodeRabbit

Bug Fixes
- Improved handling of nil pointers to prevent errors when converting them to strings.

CLAassistant · 2025-05-04T13:48:31Z

All committers have signed the CLA.

coderabbitai · 2025-05-04T13:48:33Z

"""

Walkthrough

The getString function in gomock/string.go was updated to add explicit handling for nil pointers. After verifying if the input is a generated mock, the function now checks if the input is a pointer and whether it is nil. If so, it immediately returns the string "nil" without further processing. The rest of the function, including checks for the fmt.Stringer interface and fallback formatting, remains unchanged. No exported or public entity declarations were modified.

Changes

File(s)	Change Summary
gomock/string.go	Enhanced `getString` to explicitly check for and handle nil pointers.

Poem

A pointer may point to nothing at all,
Now getString will heed the call—
If nil it finds, it simply replies,
"nil" is the answer, no need for disguise.
With careful reflection, the bug’s out of sight,
The code now is safer, and all is just right!
🐇✨
"""

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Actionable comments posted: 1

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Reviewing files that changed from the base of the PR and between 871d86b and e1fe370.

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gomock/string.go (1 hunks)

gomock/string.go

ZhangZhuoSJTU · 2025-06-07T02:27:33Z

Hi, I'm trying to reproduce this panic. If possible, could you share your PoC to help trigger the issue?

agbaria · 2025-06-07T08:28:49Z

@ZhangZhuoSJTU reproduced when the EXPECT function fails to match params and has one param of type *time.Duration which was assigned to nil when the actual function was called

benjajaja · 2025-08-01T10:25:49Z

@ZhangZhuoSJTU any nil pointer to a struct that satisfies fmt.Stringer panics. E.g. *uuid.UUID.

fix nil pointer dereference panic when x is a nil pointer

e1fe370

coderabbitai bot reviewed May 4, 2025

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ValueOf instead of TypeOf

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panic: fix nil pointer dereference when x is a nil pointer#253

panic: fix nil pointer dereference when x is a nil pointer#253
agbaria wants to merge 2 commits intouber-go:mainfrom
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