fix: Skip extra header columns in iostat parsing

[InoMurko]

Skip parsing when a stats row has fewer fields than the last Device header row.

It breaks when i >= len(data), i.e. when this data row has fewer whitespace-separated fields than the header has columns (or than we’ve consumed so far).

{
        "@timestamp": "2026-04-25 16:36:53.602",
        "@message": {
            "time": "2026-04-25T16:36:53.602931801Z",
            "stream": "stderr",
            "_p": "F",
            "log": "panic: runtime error: index out of range [7] with length 7",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.635",
        "@message": {
            "time": "2026-04-25T16:36:53.635989261Z",
            "stream": "stderr",
            "_p": "F",
            "log": "",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.636",
        "@message": {
            "time": "2026-04-25T16:36:53.636010651Z",
            "stream": "stderr",
            "_p": "F",
            "log": "goroutine 68 [running]:",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.695",
        "@message": {
            "time": "2026-04-25T16:36:53.695956669Z",
            "stream": "stderr",
            "_p": "F",
            "log": "github.com/offchainlabs/nitro/util/iostat.Run({0x373bce8, 0xc0005595e0}, 0x162e9a5?, 0xc0000a4f50)",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.696",
        "@message": {
            "time": "2026-04-25T16:36:53.696583445Z",
            "stream": "stderr",
            "_p": "F",
            "log": "\t/workspace/util/iostat/iostat.go:91 +0xa06",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.733",
        "@message": {
            "time": "2026-04-25T16:36:53.733730975Z",
            "stream": "stderr",
            "_p": "F",
            "log": "created by github.com/offchainlabs/nitro/util/iostat.RegisterAndPopulateMetrics in goroutine 59",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },
    {
        "@timestamp": "2026-04-25 16:36:53.733",
        "@message": {
            "time": "2026-04-25T16:36:53.733827792Z",
            "stream": "stderr",
            "_p": "F",
            "log": "\t/workspace/util/iostat/iostat.go:23 +0x12c",
            "kubernetes": {
                "pod_name": "sequencer-00-6bb98c996d-9npgf",
                "container_name": "nitro-sequencer-00"
            }
        },
        "kubernetes.pod_name": "sequencer-00-6bb98c996d-9npgf"
    },

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.37%. Comparing base (6dce8d1) to head (c45da41).

❗ There is a different number of reports uploaded between BASE (6dce8d1) and HEAD (c45da41). Click for more details.

HEAD has 29 uploads less than BASE

Flag	BASE (6dce8d1)	HEAD (c45da41)
	36	7

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4676       +/-   ##
===========================================
- Coverage   52.38%   34.37%   -18.02%     
===========================================
  Files         506      506               
  Lines       73739    60420    -13319     
===========================================
- Hits        38630    20767    -17863     
- Misses      29951    35950     +5999     
+ Partials     5158     3703     -1455     

[bragaigor]

Thanks for the contribution! Left a few comments to make it even more robust. Please let me know if you have any questions or need help with any of it. Ah you're also missing a changelog file :)

[bragaigor]

It's looking great! Just a nitpick whitespace suggestion and you're missing a changelog file. You can base that off this one:

nitro/changelog/bragaigor-nit-4678.md

Lines 1 to 2 in 6dce8d1

	### Fixed
	- Re-enable erc20 test

where the bullet point becomes Skip extra header columns in iostat parsing

[InoMurko]

It's looking great! Just a nitpick whitespace suggestion and you're missing a changelog file. You can base that off this one:

nitro/changelog/bragaigor-nit-4678.md

Lines 1 to 2 in 6dce8d1

	### Fixed
	- Re-enable erc20 test

where the bullet point becomes Skip extra header columns in iostat parsing

Thanks @bragaigor. Didn't notice the bad indentation at all! Also, added the changelog file - I don't have a issue ticket so I kept it short in the filename. Hope that's ok.

[bragaigor]

Thanks for the fix and for iterating on the comments, much appreciated. The PR looks great from my side.

Quick heads-up: We recently changed our internal process around merging PRs, so this may take a bit longer than usual to land. Please bear with us, and thanks again for the contribution!