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feat: add CLI for extracting ELF build ID #3

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37 changes: 37 additions & 0 deletions cli.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
#!/usr/bin/env node

import { open } from 'node:fs/promises';
import { DataSource } from './src/data-source.js';
import { ElfFile } from './src/elf.js';

const filePath = process.argv[2];
if (!filePath) {
console.error('Usage: elfy <path-to-elf-file>');
process.exit(1);
}

const fileHandle = await open(filePath, 'r');
try {
Comment on lines +13 to +14
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Copilot AI Apr 9, 2026

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open(filePath, 'r') is outside any error handling, so a missing/unreadable file will throw an unhandled rejection and print a stack trace. Catch the error and print a concise message (e.g., include err.message) with a non-zero exit code.

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const dataSource: DataSource = {
async read(offset: number, length: number): Promise<Uint8Array> {
const buffer = new Uint8Array(length);
const { bytesRead } = await fileHandle.read(buffer, 0, length, offset);
return buffer.slice(0, bytesRead);
},
};

const elf = new ElfFile(dataSource);
const { success, section } = await elf.tryReadSection('.note.gnu.build-id');
if (!success || !section) {
console.error('Could not find .note.gnu.build-id section');
process.exit(1);
}

const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
Comment on lines +30 to +32
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Copilot AI Apr 9, 2026

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The build-id extraction is hard-coded to section.slice(16, 36) (20 bytes). ELF build IDs can have different descriptor sizes, so this can truncate or misread IDs. Parse the note header to determine the descriptor offset/length (or at least derive the end from the note’s descsz) instead of assuming 20 bytes.

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console.log(uuid);
Comment on lines +30 to +34
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The variable name uuid is misleading here: the GNU build-id is not necessarily a UUID (often it’s a SHA-1-like hex string). Consider renaming to something like buildIdHex/buildId to match what is printed.

Suggested change
const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
console.log(uuid);
const buildId = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
console.log(buildId);

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} finally {
await fileHandle.close();
}
Comment on lines +7 to +37
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Avoid calling process.exit(1) inside this try block: it can terminate the process before the finally runs, so the file handle may not be closed. Prefer setting process.exitCode = 1 and returning from a main() function (or otherwise ensuring cleanup happens before exiting).

Suggested change
const filePath = process.argv[2];
if (!filePath) {
console.error('Usage: elfy <path-to-elf-file>');
process.exit(1);
}
const fileHandle = await open(filePath, 'r');
try {
const dataSource: DataSource = {
async read(offset: number, length: number): Promise<Uint8Array> {
const buffer = new Uint8Array(length);
const { bytesRead } = await fileHandle.read(buffer, 0, length, offset);
return buffer.slice(0, bytesRead);
},
};
const elf = new ElfFile(dataSource);
const { success, section } = await elf.tryReadSection('.note.gnu.build-id');
if (!success || !section) {
console.error('Could not find .note.gnu.build-id section');
process.exit(1);
}
const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
console.log(uuid);
} finally {
await fileHandle.close();
}
async function main(): Promise<void> {
const filePath = process.argv[2];
if (!filePath) {
console.error('Usage: elfy <path-to-elf-file>');
process.exitCode = 1;
return;
}
const fileHandle = await open(filePath, 'r');
try {
const dataSource: DataSource = {
async read(offset: number, length: number): Promise<Uint8Array> {
const buffer = new Uint8Array(length);
const { bytesRead } = await fileHandle.read(buffer, 0, length, offset);
return buffer.slice(0, bytesRead);
},
};
const elf = new ElfFile(dataSource);
const { success, section } = await elf.tryReadSection('.note.gnu.build-id');
if (!success || !section) {
console.error('Could not find .note.gnu.build-id section');
process.exitCode = 1;
return;
}
const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
console.log(uuid);
} finally {
await fileHandle.close();
}
}
await main();

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Comment on lines +7 to +37
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This PR introduces a new user-facing CLI entrypoint, but there are no automated tests covering CLI argument handling and output (e.g., missing path, missing section, successful extraction). Consider adding a vitest spec that runs the CLI (or refactors the logic into a testable function) to prevent regressions.

Suggested change
const filePath = process.argv[2];
if (!filePath) {
console.error('Usage: elfy <path-to-elf-file>');
process.exit(1);
}
const fileHandle = await open(filePath, 'r');
try {
const dataSource: DataSource = {
async read(offset: number, length: number): Promise<Uint8Array> {
const buffer = new Uint8Array(length);
const { bytesRead } = await fileHandle.read(buffer, 0, length, offset);
return buffer.slice(0, bytesRead);
},
};
const elf = new ElfFile(dataSource);
const { success, section } = await elf.tryReadSection('.note.gnu.build-id');
if (!success || !section) {
console.error('Could not find .note.gnu.build-id section');
process.exit(1);
}
const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
console.log(uuid);
} finally {
await fileHandle.close();
}
type CliIo = {
stdout?: (message: string) => void;
stderr?: (message: string) => void;
};
export async function runCli(args: string[], io: CliIo = {}): Promise<number> {
const stdout = io.stdout ?? console.log;
const stderr = io.stderr ?? console.error;
const filePath = args[0];
if (!filePath) {
stderr('Usage: elfy <path-to-elf-file>');
return 1;
}
const fileHandle = await open(filePath, 'r');
try {
const dataSource: DataSource = {
async read(offset: number, length: number): Promise<Uint8Array> {
const buffer = new Uint8Array(length);
const { bytesRead } = await fileHandle.read(buffer, 0, length, offset);
return buffer.slice(0, bytesRead);
},
};
const elf = new ElfFile(dataSource);
const { success, section } = await elf.tryReadSection('.note.gnu.build-id');
if (!success || !section) {
stderr('Could not find .note.gnu.build-id section');
return 1;
}
const uuid = Array.from(section.slice(16, 36))
.map(b => b.toString(16).padStart(2, '0'))
.join('');
stdout(uuid);
return 0;
} finally {
await fileHandle.close();
}
}
const exitCode = await runCli(process.argv.slice(2));
if (exitCode !== 0) {
process.exit(exitCode);
}

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3 changes: 3 additions & 0 deletions package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,9 @@
],
"author": "@bobbyg603",
"license": "MIT",
"bin": {
"elfy": "dist/cli.js"
},
"files": [
"dist"
],
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2 changes: 1 addition & 1 deletion tsconfig.json
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,6 @@
"skipLibCheck": true,
"forceConsistentCasingInFileNames": true
},
"include": ["index.ts", "src/**/*.ts"],
"include": ["index.ts", "cli.ts", "src/**/*.ts"],
"exclude": ["node_modules", "dist", "spec"]
}
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