Improve print parsed

[stelfrag]

Summary

• Improve print_parsed_as_constant (use existing print_netdata_double)
  Prevent possible crash

#7 vsnprintfz [0x5C348B40F483] (/src/libnetdata/libnetdata.c:68)
#8 snprintfz [0x5C348B40F483] (/src/libnetdata/libnetdata.c:81)
#9 print_parsed_as_constant [0x5C348B413A2E] (/src/libnetdata/eval/eval-utils.c:97)
#10 eval_variable [0x5C348B40799A] (/src/libnetdata/eval/eval-evaluate.c:22)
#11 eval_value [0x5C348B40799A] (/src/libnetdata/eval/eval-evaluate.c:46)
#12 eval_nop [0x5C348B40799A] (/src/libnetdata/eval/eval-evaluate.c:207)
#13 eval_node [0x5C348B404A32] (/src/libnetdata/eval/eval-evaluate.c:292)
#14 eval_value [0x5C348B404A32] (/src/libnetdata/eval/eval-evaluate.c:38)
#15 eval_less [0x5C348B404A32] (/src/libnetdata/eval/eval-evaluate.c:112)
#16 eval_node [0x5C348B402226] (/src/libnetdata/eval/eval-evaluate.c:292)
#17 eval_value [0x5C348B402226] (/src/libnetdata/eval/eval-evaluate.c:38)
#18 eval_and [0x5C348B402226] (/src/libnetdata/eval/eval-evaluate.c:72)
#19 eval_node [0x5C348AD66CCB] (/src/libnetdata/eval/eval-evaluate.c:292)
#20 expression_evaluate [0x5C348AD66CCB] (/src/libnetdata/eval/eval-evaluate.c:305)

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Summary by cubic

Fixes a potential crash during expression evaluation by using the shared double formatter and adding safety checks in vsnprintfz. Also simplifies number formatting for consistency.

• Bug Fixes
  • Use print_netdata_double in print_parsed_as_constant with DOUBLE_MAX_LENGTH to avoid manual trimming and buffer risks.
  • Add null checks for dst and fmt in vsnprintfz; zero-terminate dst when fmt is null.

^{Written for commit 1fe5c57. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 2 files

Confidence score: 4/5

• This PR looks safe to merge overall, with only a minor edge-case risk noted.
• In src/libnetdata/libnetdata.c, if fmt is NULL the guard returns without null-terminating dst, which could leave callers reading stale/unterminated data after a failure.
• Pay close attention to src/libnetdata/libnetdata.c - ensure dst is set to an empty string when fmt is NULL.

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/libnetdata/libnetdata.c">

<violation number="1" location="src/libnetdata/libnetdata.c:66">
P2: Guarding against NULL fmt returns without null-terminating dst, so callers may read stale/unterminated data after a failure. Ensure dst is set to an empty string when fmt is NULL.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant Eval as Expression Evaluator
    participant Utils as Eval Utils
    participant Lib as libnetdata
    participant Buf as Buffer

    Note over Eval,Buf: Expression Evaluation Flow (e.g., eval_variable)

    Eval->>Utils: print_parsed_as_constant(out, value)
    
    rect rgb(23, 37, 84)
    Note right of Utils: NEW: Use standard double formatter
    Utils->>Lib: print_netdata_double(b, value)
    
    Lib->>Lib: vsnprintfz(dst, n, fmt, args)
    alt NEW: Input Validation
        Note right of Lib: Check if dst, fmt, or n is NULL/zero
        Lib-->>Lib: Return 0 early if invalid
    else Valid Inputs
        Lib->>Lib: vsnprintf(dst, n, fmt, args)
        Lib-->>Lib: Force null-termination: dst[n-1] = '\0'
    end
    
    Lib-->>Utils: Formatted string in stack buffer 'b'
    end

    Utils->>Buf: buffer_strcat(out, b)
    Buf-->>Utils: String appended
    Utils-->>Eval: Completion

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[Copilot]

Pull request overview

This PR prevents a potential crash in expression evaluation by improving the robustness of numeric formatting functions.

Changes:

• Added null pointer checks in vsnprintfz() to prevent crashes when called with invalid arguments
• Refactored print_parsed_as_constant() to use the shared print_netdata_double() function with a larger buffer (DOUBLE_MAX_LENGTH = 512 bytes) instead of custom formatting with a 101-byte buffer

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libnetdata/libnetdata.c	Added null checks for dst, fmt, and n parameters in vsnprintfz() to prevent crashes
src/libnetdata/eval/eval-utils.c	Replaced custom double formatting logic with print_netdata_double(), using DOUBLE_MAX_LENGTH buffer to handle very large numbers safely

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[thiagoftsm]

PR is working as expected locally. LGTM!